SMOG MONITOR

Abstract: It has been found that the amount of smog formed in air and the smog concentration in air can be determined by the consumption of a single species, namely nitric oxide, and more particularly the oxidation of NO. A key step leading to smog formation is the dissociation of oxygen molecules by various smog forming reactions. For each oxygen molecule thus dissociated it can be taken that an approximately equivalent amount of nitric oxide is caused to be consumed. Measurement of the total amount of nitric oxide consumed thus provides a quantitative measure of the amount of smog produced. The rate of smog formation can be determined by the amount of smog produced, as indicated by nitric oxide consumption (and thus oxygen dissociation) in the presence of excess nitric oxide, during a selected period under selected conditions of illumination and temperature. Alternatively, for the measurement of smog formation rate the total amount of nitric oxide consumed during the selected reaction period can be determined by addition of excess ozone to the air prior to the selected period in which circumstances the gross consumption of nitric oxide is measured as increase in ozone concentration, there being an equivalence between the nitric oxide consumed and the ozone produced under the selected conditions.

Description: SMOG MONITOR TECHNICAL FIELD This invention relates to methods and systems for analysing the formation of smog in air, and more particularly for determining: ( a ) rate coefficient of smog formation in air; ( b ) rate of smog formation in air under selected temperature and illumination conditions; ( c ) time required for maximum smog formation in air under selected temperature and illumination conditions; ( d ) time period during which smog formation in air has occurred; ( e ) location of a source of Reactive Organic Compounds ( ROC ) present in air; ( f ) time required for production of a given amount of smog in air; ( g) concentration of smog in air; ( h ) amount of prior smog formation in air; ( i ) maximum potential smog formation in air; ( j ) current extent of smog formation in air; ( ) ozone concentration in air; ( 1 ) nitric oxide, NO and/or ozone concentrations in air; (i n ) Reactive Organic Compounds (ROC) concentration of air; and/or ( n ) total concentration of ROC previously introduced into air. The following parameters can also be determined from the methods and systems of the invention : total concentration of nitric oxide previously introduced into air, total concentrations of N0 χ and N0 y previously introduced into air, N0/N0 χ concentration ratio of N0 χ previously i ntroduced into air, R0C/N0 χ concentration ratio of the total ROC and NO previously introduced into air and average time of prior Λ t introductions of ROC into air. BACKGROUND ART Photochemical smog, which is commonly characterized by ozone concentrations in the order of 0.1 pp or greater in air, is an air quality problem in many urban areas, particularly those with high levels of sunlight. Photochemical smog formation passes through three sequential phases: ( 1 ) oxidation of NO to N0 2 , (2) production of 0 3 . and ( 3 ) a final phase when O3 is maintained at, or near, its maximum amount. Chemical processes occurring during each phase are intimately related and interactions between various competing and consecutive chemical reactions make analysis of smog formation difficult. Also because the atmosphere is in a state of dynamic flux since, as well as changing dispersion variables, there are changing emissions and changing meteorological conditions, e.g. sunlight, rain and temperature. In the atmosphere smog formation does not always reach completion because reactants are often dispersed before the final phase. As a consequence of the above difficulties there is presently, despite considerable prior research efforts, a need for systems and methods which can provide reliable measures of smog formation in the atmosphere. The commonly employed measure of smog concentration, ozone concentration, gives only a partial indication of the amount of smog formation. This problem arises because many chemical species, in addition to ozone, are products of the smog forming reactions and also because ozone is not a stable compound and is readily consumed, especially by reaction with nitric oxide. Thus at any given time the observed concentration of ozone in air s dependent upon the amount of prior emissions of nitric oxide into the air. Considerable efforts by the inventor have thus been directed towards developing a robust method for determining the amount of photochemical smog formation in air and a laboratory size smog chamber which provides reproducible and accurate estimates of the photochemical reactivity potential of air being tested therein. However, it has been found that prior art smog chambers are prone to give irreproducible and inaccurate results which are thought to be due to different contributions from many variables, e.g. nature of the chamber walls and surface reactions therewith, shaded zones in the chamber, mixing rates, outgassing, chamber pretreatment, chamber deposits, impurities in reactants, non-uniform temperatures, etc. and smog reaction rates that are dependent on the extent of reaction. There is also a need for a method for predicting smog formation from Reactive Organic Compounds (ROC)/air mixtures. Such a method could be used for screening solvents and fuels and assessing the photoreactivities of hydrocarbon wastes. suesτιτu TsH£Ϊτ ~ Photoche ical smog formation from reactive organic compounds (ROO/nitric oxide/air mixtures occurs as follows: Present methods for measuring the essential reactant, ROC, which is essential for smog formation in the atmosphere are inadequate since they are either not sufficiently sensitive, are very cumbersome and labour- intensive or do not take account of the widely differing smog forming reactivities of the individual organic species which taken together comprise ROC. Frequently, the atmospheric concentrations of the individual ROC species, while sufficient to produce significant quantities of photochemical smog, are too small to be detected by the currently available sensors. Air can be analysed for ROC by high resolution gas chromatography using flame ionisation or photoionization detectors but these techniques require cumbersome sample preconcentration procedures, are labour-intensive and give data on only a subset of the photochemically active species present. Furthermore, knowledge of the concentrations of the components of the ROC mixture does not allow the photochemical reactivity of the air to be quantitatively estimated because the role of many of the individual ROC species, and their reaction products, in the chemistry of smog formation, is uncertain. An approach sometimes adopted for ROC analysis is to measure the total non-methanic hydrocarbon concentration of the air as a single peak, backflushed from a chromatographic column after methane has been eluted, or alternatively as the difference in signal from air and air scrubbed of ROC species but without methane removal. For some purposes this arrangement provides adequate sensitivity but the method is subject to errors in the measured concentrations because no account can be taken of the differing sensitivities of the detector to the various individual ROC species. In other words, these techniques typically do not provide a measure of the reactivity of the total ROC in air since they do not provide their ROC compositions and this is important since in the atmosphere 250 or more ROC species have been identified of which there can be 60 major species or more and the rate of smog formation can be greatly affected by the nature and the relative proportions of the ROC species which are present. Photochemical smog formation is a complex process wherein a multitude of reactant species are simultaneously consumed to give a wide variety of chemical product species. It is possible to measure the concentrations of many of these reactants and products and in the past such measurements have been utilized in various ways as indicators of the extent of photochemical smog production. For example, some measures that have been used to evaluate extent of reaction are: ozone concentration, peroxyacetyl nitrate concentration; nitrogen dioxide concentration; time to reach a maximum ozone concentration; time taken for the concentrations of NO and NO- to be equal, ozone concentration attained after illumination for a fixed period and intensity; time for NO concentration ' to reach one half of its initial value. Such data, however, gives only a limited indication of the progress of reaction and are complex and difficult to interpret in terms of the overall rate and extent of the smog-forming reactions. Additionally the rates at which these individual reactants and products are consumed and produced vary as smog formation progresses. OBJECTS OF INVENTION Objects of this invention are to provide methods and systems for analysing the formation of smog in air, and more particularly for determining: (a) rate coefficient of smog formation in air; (b) rate of smog formation in air under selected temperature and illumination conditions; (c) time required for maximum smog formation in air under selected temperature and illumination conditions; (d) time period during which smog formation in air has occurred; (e) location of a source of Reactive Organic Compounds (ROC) present in air; (f) time required for production of a given amount of smog in air; SUBSTITUTE SHEET (g) concentration of smog in air; (h) amount of prior smog formation in air; (i) maximum potential smog formation in air; (j) current extent of smog formation in air; (k) ozone concentration in air; (1) nitric oxide, NO and/or ozone concentrations in air; ( ) ROC concentration of air; and/or (n) total concentration of prior ROC emissions into air. DEFINITIONS Air Atmospheric air, including pristine air and pristine air into which smog-forming substances (including ROC and NO Λ have been introduced at some times (including up to some days) previously. Air may have undergone various transport and dispersion processes including mixing with air of other compositions and dilution by pristine air; a R0C Activity coefficient for smog formation by ROC at time t; (units: moles smog/mole ROC/unit illumination/unit f(T) or moles smog/mole ROC carbon/ unit illumination/unit f(T)) a ROC ( i ) Activity coefficient for smog formation from species R0C(i); V Volume at time t; G A parameter determined according to equation (58); H Coefficient of expression (70) and formulae derived from (70); L Coefficient of expression (70) and formulae derived from (70); E the extent of smog formation in air at time t, extent being the proportion of amount of smog produced by SUBSTITUTE SHEET ti me t compared to the maxi mum potenti al amount of smog formation ; NO. NO + NO. NO. "Total gaseous oxidized nitrogen" is the sum of N0,N0 2 , peroxynitric acid, (H0 2 N0 2 ); nitric acid ( HN0 3 ) ; peroxyacetyl nitrate, (PAN); nitrous acid ( HN0 2 >, dinitrogen pentoxide ( -O e ), nitrate radical ( NOj ) and other gaseous organic nitrates. Other nitrogen species at lower oxidation states, e.g. N 2 0, N 2> NH 3> HCN, CH 3 CN are not components of NO ; Smog Concentration The sum of the concentrations of ozone and NO less the concentration of NO; Amount of The gross amount of nitric oxide oxidized in the air Smog Formation by smog chemistry, i.e. the moles of NO consumed by the reaction: R0 2 + NO —> Products; Hydroxyl alkoxy and peroxy free radical species; Reactive organic compounds including carbonyl , alkane, alkene, aromatic, carbon monoxide and other types of gasphase carbonaceous species which when present in illuminated air undergo reaction wherein oxygen molecules are consumed and nitric oxide is oxidized; ROC(i) A specified individual ROC compound or a specified mixture of ROC compounds. T,I Q t y smog Rate of smog formation in air at time (t) with temperature ( T ) and illumination intensity (I); Xsmog The mole fraction of smog in air at time t; SUBSTITUTE SHcET Xι The mole fraction of species i in the mixture after the first selected period; II. The mole fraction of species i in the mixture after the second selected period; III. The mole fraction of species i in the mixture after the third selected period; The mole fraction of species i in air at time t (mole fraction) ; n i Number of Moles, n, of species i in air of volume V at time t (moles) ; ■ V The vol ume of a defi ned parcel of ai r ( ) at ti me t ; f t Amount of previous smog formation in air of volume smog V at time t (moles) ; Denotes emissions of number of moles, n, of species i into air; °"ϊ Cumulative emissions of species i into air of volume V during time period t = 0 to t = t, in moles; n n* + n ' t NOχ NO N0 2; O F The fraction of NO in NOv emissions (°n /°n ); NO * NO N0 X The notional concentration of smog formed in air in Λ smog the absence of NO removal processes (mole fraction); ° χ ? The cumulative emissions of species i into air expressed as a fraction of the moles of species i emitted to the moles of air (mole fraction); I iϊ^rϋirπϊS: extra t Concentration of smog to be produced at *smog some future time (mole fraction); added n i Number of moles, n, of species i added to the air in the course of analysis (moles); 'NO Number of moles, n, of NO present after first selected period (moles); -t Rate coefficient of reaction j at time t; Rate of reaction j at time t; *. Ratio of rate of reaction j to rate of reaction k P j,k = R j /R k ; fmax. Maximum potential moles of smog formation in air; smog Tmax. Maximum potential moles of smog that can be present smog in air, being total of contributions from both smog formation processes and emissions of N0~; select. X A selected concentration of smog in air (mole smog fraction); fmax t Maximum potential concentration of smog formed in ^ • smog air (mole fraction); T ax t Maximum potential concentration of smog that can x smog be present in air, being total of contributions from both smog formation processes and emissions of N0 2 into air (mole fraction); Rate coefficient for smog formation at time t; smog Gas constant; SUB J r t I i u « i —- i ._____. t___, Pressure at time t; Temperature at time t; Concentration of species i in reference air: Volume injected .by device n in a specified time; Flowrate; Illumination intensity (in units of rate coefficient for N0 2 photolysis, min~ ). Υ Coefficient of equation (39) β A coefficient of smog formation. "reference Can be simply known temperature and illumi.nation temperature and conditions or can be conditions determined with i llumination reference to a reference gas under the same or conditions" known temperature and illumination conditions. DISCLOSURE OF INVENTION The present inventor has found that the amount of smog formed in air and the smog concentration in air can be determined by the consumption of a single species, namely nitric oxide, and more particularly the oxidation of NO. A key step leading to smog formation is the dissociation of oxygen molecules by various smog forming reactions. The present inventor has found that for each oxygen molecule thus dissociated it can be taken that an approximately equivalent amount of nitric oxide is caused to be consumed. Measurement of the total amount of nitric oxide consumed thus provides a quantitative measure of the amount of smog produced. The rate of smog formation can be determined by the amount of smog produced, as indicated by nitric oxide consumption (and thus oxygen dissociation ) in the presence of excess nitric oxide, during a selected period under selected conditions of illumination and temperature. Alternatively, for the measurement of smog formation rate the total amount of nitric oxide consumed during the selected reaction period can be determined by addition SUBSTITUTE SHEET of excess ozone to the air prior to the selected period in which circumstances the gross consumption of nitric oxide is measured as increase in ozone concentration, there being an equivalence between the nitric oxide consumed and the ozone produced under the selected conditions. Brief summaries of the techniques used to determine various parameters are given below: 1A. Determination of the amount of smog formed in air This can be achieved by firstly sampling the air, secondly adding NO so that it is present in excess and, thirdly, measuring the difference between the total amount of nitric oxide which has been present in the air (i.e. the- NO emissions into the air prior to sampling plus that added during analysis) and the concentration of residual NO present after the added NO has been allowed to react with and be consumed by any ozone that may have been present in the air. IB. Determination of smog concentration in air Concentration of smog in air is determined by addition of excess nitric oxide to the air and after reaction with substantially all ozone present determining the concentration of smog as the difference between the total concentration of the oxidised nitrogen species (i.e. NO, N0 2 , peroxyacetyl nitrate, gaseous nitric acid etc) in the mixture and the nitric oxide concentration of the mixture. A second function of the nitric oxide addition is that by removing ozone it stabilises the air in the dark, minimising the production of nitric acid within the apparatus. This is beneficial because nitric acid is readily absorbed on surfaces and can thus be lost from the gas phase within the apparatus and before being measured at the detector. 2A. Determination of rate coefficient for smog formation Rate coefficient for smog formation is determined by subjecting air containing excess NO to photochemical reaction under controlled conditions of temperature and illumination and by measuring the rate at which excess nitric oxide is consumed. A second function of the addition of excess nitric oxide to the air is that when excess nitric oxide is present the rate of nitric oxide consumption is, to a good approximation, independent of the extent of smog formation. Addition of excess nitric oxide makes the measured rate of smog formation independent of the original nitric oxide concentration of the air. A further function of the excess nitric oxide is that it minimises the concentration of ozone in the system, thus minimising the ozone induced j -SUBSTITUTE S side reactions such as formation of nitric acid in the unilluminated parts of the system. Ozone can also undergo unwanted reactions in the dark with alkenes. 2B. Determination of rate coefficient for smog formation in air Rate coefficient for smog formation in air is determined by subjecting air containing excess ozone to photochemical reaction under controlled conditions of temperature and illumination and by measuring the rate at which further amounts of ozone are produced. In the presence of excess ozone, nitric oxide is consumed by the smog-forming reactions to produce nitrogen dioxide. Nitrogen dioxide undergoes photochemical reaction to produce ozone and regenerate nitric oxide. A small, steady state, nitric oxide concentration is thus maintained. The net amount of ozone produced under these conditions is a measure of the amount of nitric oxide consumed by smog formation and is thus a measure of the amount of oxygen molecules consumed by smog formation. 3. Prediction of extent of maximum potential smog formation in air Prediction of the extent of maximum potential smog formation in air can be ascertained by determination of rate coefficient of smog formation, smog concentration and the total oxidised nitrogen concentration of the air (NO ) and the application of computational formulae as described herein. 4. Prediction of rate and extent of smog formation in air under selected conditions Prediction of the rate and extent of smog formation that would apply to sampled air when subjected to a wide range of selected atmospheric conditions can be ascertained from the above determined properties of the air and application of the computational formulae described herein. 5. Determination of time required for formation of selected amounts of smog in air under selected conditions Determination of the time required for formation of selected amounts of smog in air under a wide range of selected conditions can be ascertained from the above determined properties of the air and application of the computational formulae described herein. 6. Determination of ROC concentration of air ROC concentration is determined by subjecting air containing excess NO to photochemical reaction under controlled conditions of temperature and illumination for a selected period and by measuring the concentration of excess nitric oxide consumed. The nitric oxide consumption is proportional to the ROC concentration of the air and is thus a measure of the ROC J S ^τTsHi^ concentration of the air. A second function of the addition of excess nitric oxide to the air is that when excess nitric oxide is present nitric oxide consumption is, to a good approximation, independent of the extent of previous photochemical reaction involving the ROC. Addition of excess nitric oxide makes smog formation independent of the original nitric oxide concentration of the air. A further function of the excess nitric oxide is that it minimises the concentration of ozone in the system, thus minimising ozone induced side reactions such as formation of nitric acid in the unilluminated parts of the system. Ozone can also undergo unwanted reactions in the dark with alkenes. TABLE SUMMARISING EMBODIMENTS Number of Embodi ent Brief Description of Embodiments 1 Method for determining rate coefficient of smog formation in air; (via NO excess); Method for determining rate coefficient of smog formation in air; (via 0 3 excess); 3 Method for determining concentration of smog in air; 4 Method for determining amount of prior smog formation in air; 5 Method for determining maximum potential and optionally the current extent of smog formation in air; Method for determining rate of smog formation in air under selected temperature and illumination (via excess NO); Method for determining rate of smog formation in air under selected temperature and illumination (via excess 0~); Method for determining time required for maximum smog formation in air under selected conditions of illumination and temperature; Method for determining time period during which smog formation in air has occurred; 10 Method for determining time required for production of a given amount of smog in air under selected temperature and illumination conditions; 11 Method of determining ozone concentration in air (via determined NO and smog concentrations); 12 Method for determining nitric oxide and NO or ozone or both concentrations in air (via determined sunlight, SUBSTITUTE SHEET temperature, NO and smog concentrations); 13 System for determining rate coefficient of smog formation in air (corresponding to method 1, via NO); 14 System for determining rate coefficient of smog formation in air (corresponding to method 2, via 0.,); 15 System for determining concentration of smog in air (corresponding to method 3); 16 System for determining amount of prior smog formation in air (corresponding to method 4); 17 System for determining maximum potential and optionally the current extent of smog formation in air (Corresponding to method 5); 18 System for determining rate of smog formation in air under selected temperature and illumination conditions (corresponding to method 6, NO excess); 19 System for determining rate of smog formation in air under selected temperature and illumination conditions (corresponding to method 7, 0 3 excess); 20 System for determining time required for maximum smog formation in air under selected conditions of illumination and temperature (corresponding to method 8); 21 System for determining time period during which smog formation in air has occurred (corresponding to method 9); 22 System for determining time required for production of a selected amount of smog in air under selected temperature and illumination conditions (corresponding to method 10); 23 System for determining ozone concentration of air (corresponding to method 11, via determined NO and smog concentrations); 24 System for determining nitric oxide and NO or ozone or both concentrations in air (corresponding to method 12); 25 Method for determining ROC concentration of air and/or total concentration of prior ROC emissions into air; and 26 System for determining ROC concentration of air and/or total concentration of prior ROC emissions into air (corresponding to method 25 ) . According to a first embodiment of this invention there is provided a method for determining rate coefficient of smog formation in air, the SUBSTITUTE SHEET method comprising: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (b) permitting the mixture to react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) determining a first nitric oxide concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under reference temperature and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; (f) determining a second nitric oxide concentration of the mixture after the third selected period; and (g) determining the rate coefficient of smog formation from the first and second nitric oxide concentrations, the reference temperature and illumination conditions and the duration of the second selected period. According to a second embodiment of this invention there is provided a method for determining rate coefficient of smog formation in air, the method comprising: (a) adding excess ozone to the air to provide an excess ozone/air mi ture; (b) permitting the mixture to react for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (c) determining a first ozone concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under reference temperature and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess ozone in the mixture reacts with any nitric oxide present in the mixture; (f) determining a second ozone concentration of the mixture after the third selected period; and (g) determining the rate coefficient from the first and second ozone SUBSTITUTE SHEET concentrations, the reference temperature and illumination conditions and the duration of the second selected period. Optionally the method of the second embodiment further includes the step of (a)(i) adding a quantity of nitrogen oxides to the mixture prior to step (b). This optional step is recommended for those occasions when the nitrogen oxides concentration of the air is small and limiting on the rate of reaction during step (d). According to a third embodiment of this invention there is provided a method for determining concentration of smog in air, which method comprises: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (b) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; (c) determining the nitric oxide concentration of the mixture after the selected period; (d) determining the total oxidized nitrogen (NO ) concentration of the mixture after the selected period; and (e) determining the concentration of smog in the air from the nitric oxide concentration of (c) and the NO concentration of (d). Optionally the method of the third embodiment further includes the step of (c)(i) converting NO in the mixture to nitric oxide prior to step (d). When step(c)(i) is included the NO concentration in step d) can be determined by simply determining the nitric oxide concentration of the mixture. According to a fourth embodiment of this invention there is provided a method for determining the amount of prior smog formation in air, which method comprises: (A) determining NO concentration of air; (B) determining the concentration of smog in air by the method of the third embodiment; (C) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (D) determining the amount of prior smog formation in air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (C) and the concentration of smog in the air as determined in (B). Optionally the method of the fourth embodiment further includes the SUBSTITUTE SKJΞΞT steps of (A)(i), converting NO in the air to nitric oxide prior to step (A). When step (A)(i) is included the concentration in step (A) can be determined by simply determining the nitric oxide concentration of the air. According to a fifth embodiment of this invention there is provided a method for determining maximum potential smog formation in air, which method comprises: (α) determining the amount of prior smog formation in air by the method of the fourth embodiment; (β) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (γ) determining the maximum potential smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air. According to a sixth embodiment of this invention there is provided a method for determining rate of smog formation in air under selected temperature and illumination conditions, which method comprises: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (b) permitting the mixture to react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) determining a first nitric oxide concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under selected temperature and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; (f) determining a second nitric oxide concentration of the mixture after the third selected period; and (g) determining the rate from the first and second nitric oxide concentrations and the duration of the second selected period. According to a seventh embodiment of this invention there is provided a method for determining rate of smog formation in air under selected temperature and illumination conditions, which method comprises: (a) adding excess ozone to the air to provide an excess ozone/air I SUBSTITUTE SHEET -17- mixture; . f a f1rs t selected period oxide in the mixture ; concentrat i on o f t h e mixture after t h e ( c ) d etermining a first u* unβ f i rst selected period; after the f1rst comprising: ^offiri ent of smog f ormation in the air According to a ninth embodiment of this invention there i provided a method for determining time period during which smog formation in air has occurred, the time period being substantially the same as or within a predetermined period for which the illumination and temperature conditions are Known, wherein the end of the predetermined period coincides with the end of the time period, the method comprising: (A) determining temperatures of the air for the predetermined period; (B) determining sunlight intensities for the predetermined period; (C) determining the rate coefficient of smog formation in the air according to the method of the first or second embodiments; or (C)(i) determining rates of smog formation in the air according to the methods of the sixth or seventh embodiments under temperatures and light intensities corresponding to the determined temperatures and sunlight intensities; (D) determining the amount of prior smog formation in the air at the end of the time period according to the method of the fourth embodiment; and (E) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation, the rate coefficient, the determined temperatures and sunlight intensities, or (EXi) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation and the rates of smog formation. Optionally the location of the source of ROC present in air may be determined on the basis of the time period of smog formation and separately determined speed of movement and trajectory of the air during the time period. According to a tenth embodiment of this invention there is provided a method for determining time required for production of a selected amount of smog in air under selected temperature and illumination conditions and with selected initial amount of smog in the air, the method comprising: (A) determining rate coefficient of smog formation in air according to the method of the first or second embodiments; or (A)(i) determining rates of smog formation in the air under the selected temperature and illumination conditions according to the method of the sixth or seventh embodiments; (B) determining NO concentration of the air; (C) determining the amount of NO previously emitted into the air from the NO concentration of (B) and the selected initial amount of smog SUBSTITUTE * -H 4 ____J in the air; and (D) determining the time required for production of selected amount of smog in the air for the selected conditions of temperature and illumination from the rate coefficient and the amount of NO ; or (D)(i) determining the time required for production of the selected amount of smog in the air for the selected conditions of temperature and illumination from the rate and the amount of NO previously emitted into the air. Optionally the method of the tenth embodiment further includes the steps of(AKii), converting NO in the air to nitric oxide prior to step (B). When step (A)(ii) is included the concentration in step (B) can be determined by simply determining the nitric oxide concentration of the air. According to an eleventh embodiment of this invention there is provided a method for determining ozone concentration in air, which method comprises: (A) determining nitric oxide concentration of the air; (B) determining NO concentration of the air; (C) determining concentration of smog in the air according to the method of the third embodiment; and (D) calculating the ozone concentration of the air from the measured nitric oxide concentration, NO concentration and the concentration of smog in the air. According to a twelfth embodiment of this invention there is provided a method for determining nitric oxide and/or ozone concentrations in air, which method comprises: (A) determining the sunlight intensity of the air; (B) determining the temperature of the air; (C) determining the NO concentration of the air; (D) determining the smog concentration of the air according to the method of the third embodiment; and (E) determining the concentrations of nitric oxide and/or ozone in air from the NO and smog concentrations, the sunlight intensity and the temperature. Optionally the method of the twelfth embodiment further includes step(BKi); converting NO in the air to nitric oxide prior to step (C). When step (B)(i) is included the concentration in step (C) can be determined by simply determining the nitric oxide concentration of the air. According to a thirteenth embodiment of this invention there is j SUBSTITUTE SH £T provided a system for determining rate coefficient of smog formation in air, which system comprises: (a) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a) in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under known temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (f) a nitric oxide analyser operatively associated with the first reactor, to determine a first nitric oxide concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second nitric oxide concentration of the mixture after the third selected period; (g) a temperature sensor operatively associated with the photoreactor to determine the temperature of the mixture; (h) an illumination sensor operatively associated with the illumination source to determine the amount of illumination of the illuminated mixture; and (i) calculating means operatively associated with the temperature and illumination sensors and the nitric oxide analyser to calculate the rate coefficient from the first and second nitric oxide concentrations, the known temperature and illumination conditions and the duration of the second selected period. According to a fourteenth embodiment of this invention there is provided a system for determining rate coefficient of smog formation in air, which system comprises: (a) a first combiner for combining excess ozone with the air to provide an excess ozone/air mixture; SUBSTITUTE SH££T (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a) in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under known temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (f) an ozone analyser operatively associated with the first reactor to determine a first ozone concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second ozone concentration of the mixture after the third selected period; (g) a temperature sensor operatively associated with the photoreactor to determine the temperature of the mixture; (h) an illumination sensor operatively associated with the illumination source to determine the amount of illumination of the illuminated mixture; and (i) calculating means operatively associated with the temperature and illumination sensors and the ozone analyser to calculate the rate coefficient from the first and second ozone concentrations, the known temperature and illumination conditions and the duration of the second selected period. Optionally the system of the fourteenth embodiment further includes a second combiner operatively associated with the first combiner for combining a quantity of nitrogen oxides with the air. According to a fifteenth embodiment of this invention there is provided a system for determining concentration of smog in air, which system comprises: (a) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (b) a reactor operatively associated with the combiner wherein the ! SVBST. ' TIJT mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; (d) a NO analyser operatively associated with the reactor to determine the NO concentration of the mixture; and (e) calculating means operatively associated with the nitric oxide analyser and the NO analyser to calculate the concentration of smog from the NO and nitric oxide concentrations. Preferably the NOy,, analy Jser of (d) includes a NOy,, converter to convert all NO in the mixture to nitric oxide, the converter being operatively associated with the nitric oxide analyser of (c). In this preferred arrangement the NO analyser consists of the NO converter and the nitric oxide analyser of (c). According to a sixteenth embodiment of this invention there is provided a system for determining amount of prior smog formation in air, which system comprises: (a) a first NO analyser to determine the NO concentration of the air; (b) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (c) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (d) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; (e) a second NO analyser operatively associated with the reactor to determine the NO concentration of the mi ture; and (f) calculating means operatively associated with the nitric oxide analyser and the first and second NO analysers to calculate the amount of prior smog formation in air from the NO concentration of the air and the NO and NO concentrations of the excess nitric oxide/air mixture. Preferably the NO analyser of (a) is the same NO analyser employed in (e) operatively associated to the combiner of (b) so as to SUBSTITUTE SKSET | determine the NO concentration of air before excess nitric oxide is combined with air. Also preferably the NO analyser of (a) and (d) includes a NO converter to convert all NO in the mixture to nitric oxide, the converter being operatively associated with the nitric oxide analyser of (d). In this preferred arrangement the NO analyser consists of the NO converter and the nitric oxide analyser of (d). According to a seventeenth embodiment of this invention there is provided a system for determining maximum potential and optionally the current extent of smog formation in air, which system comprises: (a) a first NO,, analyser for determining the NO,, concentration y J y of the air; (b) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (c) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (d) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; (e) a second NO analyser operatively associated with the reactor to determine the NO concentration of the mixture; and (f) calculating means operatively associated and coupled with the nitric oxide analyser and the first and second NO analysers to calculate the maximum potential and optionally the current extent of smog formation in air from the NO concentration of the air and the NO and NO concentrations of the excess nitric oxide/air mixture. Preferably the NO analyser of (a) is the same NO analyser employed in (e) coupled to and operatively associated to the combiner of (b) so as to determine the NO concentration of air before excess nitric oxide is combined with air. Also preferably the NO analyser of (a) and (e) includes a NO converter to convert all NO in the mixture to nitric oxide, the converter being operatively associated with the nitric oxide analyser of (d). In this preferred arrangement the NO analyser consists of the NO converter and the nitric oxide analyser of (d). According to an eighteenth embodiment of this invention there is j SUBSTITUTE SHEET provided a system for determining rate of smog formation in air under selected temperature and illumination conditions, which system comprises: (a) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period * wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a), in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under selected temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can in the second reactor react for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (f) a nitric oxide analyser operatively associated with the first reactor to determine a first nitric oxide concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second nitric oxide concentration of the mixture after the third selected period; and (g) calculating means operatively associated with the nitric oxide analyser to calculate the rate from the first and second nitric oxide concentrations and the duration of the second selected period. According to a nineteenth embodiment of this invention there is provided a system for determining rate of smog formation in air under selected temperature and illumination conditions, which system comprises: (a) a first combiner for combining excess ozone is combined with the air to provide an excess ozone/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the reactor for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the SUBSTITUTE SH£ET photoreactor to illuminate the mixture of (a), in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under selected temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (f) an ozone analyser operatively associated with the first reactor to determine a first ozone concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second ozone concentration of the mixture after the third selected period; and (g) calculating means operatively associated with the ozone analyser to calculate the rate from the first and second ozone concentrations and the duration of the second selected period. In preferred embodiments of the thirteenth, fourteenth, eighteenth and nineteenth embodiments the first and second reactors and the photoreactor are the same reactor. In other preferred embodiments the first reactor and the photoreactor are the same reactor and in yet other embodiments the second reactor and the photoreactor are the same reactor. In still other preferred embodiments the first reactor and photoreactor are two separate vessels through which the mixture can continuously flow in separate streams and the second reactor is a separate vessel through which the mixture from the photoreactor can continuously flow. In such embodiments, the first reactor provides a first residence time for the mixture when continuously flowing therethrough and the photoreactor and the second reactor in combination provide a second residence time for the mixture when continuously flowing therethrough, the first and second residence times being substantially the same. Optionally the system of the nineteenth embodiment further includes a second combiner operatively associated with the combiner of ozone in which second combiner a quantity of N0 V is added to air. This is recommended when the nitric oxide concentration of air is small and limiting on the rate of reaction in the photolytic reactor. According to a twentieth embodiment of this invention there is provided a system for determining time required for maximum smog formation in air under selected conditions of illumination and temperature wherein SUBSTITUTE SH£ET the system includes: (A) a NO analyser to determine the NO concentration of the air; (B) the system of the thirteenth or fourteenth embodiments to determine the rate coefficient of smog formation in the air; or (BXi) the system of the eighteenth or nineteenth embodiments to determine the rates of the smog formation in air under the selected conditions; (C) the system of the seventeenth embodiment to determine the maximum potential smog formation in the air; and (D) calculating means operatively associated with the analyser of (A) and the systems of (B) and (C) to calculate the maximum time for smog formation, under the selected temperature and illumination conditions from the NO concentration, the extent of smog formation and the rate coefficient; or (D)(i) calculating means operatively associated with the analyser of (A) and the systems of (BXi) and (C) to calculate the maximum time for smog formation, under the selected temperature and illumination conditions from the NO concentration, the extent of smog formation and the rates. Preferably the NO analyser of (A) includes a NO converter to convert all the NO in the air to nitric oxide and a nitric oxide analyser to determine the total nitric oxide. In this preferred arrangement the NO analyser consists of the NO converter and the nitric oxide analyser and the NO analysers of the systems of ( A ) , ( B ) or (BXi) and (C) are the same analyser. According to a twenty-first embodiment of this invention there is provided a system for determining time period during which smog formation in air has occurred, the time period being substantially the same as or within a selected period for which the illumination and temperature conditions are known, wherein the end of the selected period coincides with the end of the time period the system includes: (A) the system of the thirteenth or fourteenth embodiments for determining the rate coefficient of smog formation in the air; or (AXi) the system of the eighteenth or nineteenth embodiments for determining the rates of smog formation in the air; (B) the system of the fifteenth embodiment for determining concentration of smog in the air; (C) an NO analyser for determining the NO concentration of air; (D) a temperature sensor to determine the temperature of the air for SUBSTITUTE SH£ET the duration of the selected period; (E) a light sensor to determine the sunlight illumination during the selected period; and (F) calculating means operatively associated with the temperature sensor, the light sensor, the NO analyser and the systems for determining the rate coefficient of smog formation and smog concentration, to calculate the time period during which smog formation in air has occurred under the measured sunlight and temperature conditions; or (FXi) calculating means operatively associated with the temperature sensor, the light sensor, the NO analyser and the systems of a(i) and (b) to calculate the time period during which smog formation has occurred under the measured sunlight and temperature conditions. Preferably the NO,, analyser of (C) includes a NO,, converter to y y convert all NO in the mixture to nitric oxide, the converter being operatively associated with a nitric oxide analyser. In this preferred arrangement the NO,, analyser consists of the NO,, converter and the - y y nitric oxide analyser and the NO analysers of the systems of (A) and (B) and the NO analyser of (C) are the same analyser. Optionally the system of the twenty-first embodiment further includes means of determining the speed and trajectory of the air during the selected period and calculating means to determine the location of the emission sources of ROC present in air on the basis of the time period of smog formation, the air speed and trajectory. According to a twenty-second embodiment of this invention there is provided a system for determining time required for production of a selected amount of smog in air under selected temperature and illumination conditions the ' system comprising (A) the system of the thirteenth or fourteenth embodiments for determining rate coefficient of smog formation in the air; or (AXi) the system of the eighteenth or nineteenth embodiments for determining the rates of smog formation in the air; (B) the system of the fifteenth embodiment for determining concentration of smog in the air; (C) an NO,, analyser for determining the NO,, concentration of the y J 3 y air; and (D) calculating means operatively associated with the systems for determining: the rate coefficient, smog concentration and the NO analyser, to calculate the time required for the production of a selected j SUBSTITUTE •xr ' l ' ϊϋ Si i B amount of smog in the air under selected temperature and illumination conditions; or (DXi) calculating means operatively associated with the systems of (A)(i) and (B) and the NO analyser, to calculate the time required for the production of a selected amount of smog in air under selected temperature and illumination conditions. Preferably the to convert substantially converter being opera ser of (B). In this preferred arrangement the NO analyser consists of the NO converter and the nitric oxide analyser of (B). According to a twenty-third embodiment of this invention there is provided a system for determining ozone concentration in air which system comprises: (A) a nitric oxide analyser to determine the nitric oxide concentration of the air; (B) a NO analyser to determine the NO concentration of the air; (C) the system of the fifteenth embodiment for determining the concentration of smog in the air; and (D) calculating means operatively associated with the nitric oxide analyser of (A) the NO analyser of (B) and the system of (C) to calculate the ozone concentration from the nitric oxide concentration, NO concentration and smog concentration of the air. Preferably the nitric oxide analyser of ( A) and the NO analyser of (B) are the same nitric oxide and NO analysers of the system of (C). According to a twenty-fourth embodiment of this invention there is provided a system for determining nitric oxide and NO or ozone or both concentrations in air which system comprises: (A) a light sensor to determine the sunlight intensity of the air; (B) a temperature sensor to determine the temperature of the air; (C) an NO analyser to determine the NO concentration of the (D) the system of the fifteenth embodiment to determine the smog concentration of the air; and (E) calculating means operatively associated with the light and temperature sensors and the NO analyser and smog concentration measurement systems the calculating means to calculate the nitric oxide and ozone concentrations of the air from the sunlight intensity, air SUBSTITUTE SHEET temperature and the NO and smog concentrations. Preferably the NO analyser of (C) is the same NO analyser of the system (D). According to a twenty-fifth embodiment of this invention there is provided a method for determining ROC concentration of air and/or a method for determining total concentration of prior ROC emissions into air, which method comprises: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; ( b ) permitting the mixture to react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c ) determining a first nitric oxide concentration of the mixture after the first selected period; _ (d ) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under known temperature and illumination conditions; ( e ) permitting the mixture, after illumination, to react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; (f ) determining a second nitric oxide concentration of the mixture after the third selected period; and ( g ) determining the ROC concentration of air, and/or determining the total concentration of prior ROC emissions into the air, from the first and second nitric oxide concentrations According to a twenty-sixth embodiment of this-invention there is provided a system for determining ROC concentration of air and/or total concentration of prior ROC emissions into air, which system comprises: (a ) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; ( b ) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; ( c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a), in the photoreactor, or the SUBSTITUTE SHEET (ID(iv) determining the total oxidized nitrogen (NO ) concentration of the mixture after the selected period; and (II)(v) determining the concentration of smog formation from the nitric oxide concentration of (ID(iii) and the NO concentration of (ID(iv). (III) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (IV) determining the amount of prior smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (III) and the concentration of smog in the air as determined in (II); and (E) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation, the rate coefficient, and the determined temperatures and sunlight intensities; and (β) determining speed of movement and trajectory in the air during the time period; and (γ) locating said source of ROC from said time period and said speed and trajectory in the air over said time period. According to a still further embodiment of this invention there is provided a method for determining the current extent of smog formation in air, which method comprises the steps of: (I) determining maximum potential smog formation in air by the method of the fifth embodiment; and (II) calculating the extent of smog formation in air as the ratio of the concentration of smog in air to the maximum potential concentration of smog in air. The temperature of the mixture can be kept constant during illumination, can be allowed to vary and optionally monitored or the temperature of the mixture can be varied according to a preselected or selected temperature profile. Thus, it is preferred that a temperature controller/programmer is operatively associated with the photoreactors of the thirteenth, fourteenth, eighteenth, nineteenth and twenty-sixth embodiments. The illumination can be kept constant or can be varied according to a preselected or selected illumination profile. It is therefore preferred that an illuminator controller/programmer is operatively associated with and coupled with the illumination sources of the thirteen, fourteenth, eighteenth, nineteenth and twenty-sixth embodiments. Preferred illumination sources provide an actinic flux of similar intensity and spectral distribution to sunlight at about noon on a clear day. It may be adequate for the purpose, however, to approximate the solar spectrum by only the "UVA" part of the total wavelength band. Illumination may be provided by a single type of lamp or various lamp type and filter combinations. For example, actinic UV fluorescent tubes are suitable as is a high pressure xenon arc and pyrex glass filter combination. The preferred illumination intensity is that which yields a rate coefficient for the photodissociation of nitrogen dioxide (N0 2 + hv →* NO + 0) of ~ 0.4 min " . However intensities which depart markedly from this value are viable. Times preferred for the first and third reaction periods are of the order of a few minutes, which is sufficient for the reaction of nitric oxide with ozone to be substantially complete. The preferred time for the second selected period is about 10 minutes or so long as is required to produce measurable consumption of nitric oxide in air containing significant quantity of ROC. The systems of the thirteenth, fourteenth, fifteenth, sixteenth, seventeenth, eighteenth, nineteenth and twenty-sixth embodiments optionally include first metered delivery means to deliver metered doses of air to the combiner and includes second metered delivery means to deliver metered doses of nitric oxide to the combiner. The fourteenth and nineteenth embodiments optionally include third metered delivery means to deliver metered doses of ozone to the combiner and ozone filter to filter ozone prior to injection into the combiner. Optionally the systems of the thirteenth, fourteenth, fifteenth, sixteenth, seventeenth, eighteenth, nineteenth and twenty-sixth embodiments include an air filter to filter air prior to injection into the combiner and a nitric oxide filter to filter nitric oxide prior to injection into the combiner. It is preferred that the photoreactor is constructed from material that is transparent to illumination and is chemically unreactive. FEP teflon film is an example of material which is suitable for this purpose. FEP teflon film has the advantages that it is chemically unreactive and is transparent to ultraviolet light and is available in thin but robust film form. The concentration of nitric oxide excess in the nitric oxide/air ! SUBSTITUTE SHEET j -33- mixture or ozone excess in the ozone/air mixture is typically in the range about 0.05 to about 1 ppm (mole fraction) but the upper range lim i t should not be of a concentration which induces reactions to occur in the m i xture which result in a significant change in the nature of the chemistry of the mi χture. For example, a large excess of nitric oxide can cause a reduct i on in the hydroxyl radical concentration of the photoreactor, result i ng i n a reduction in the rate of nitric oxide consumption in the photoreactor. The l0 wer range limit should be sufficient to provide for complete react i on of the ozone or nitric oxide of the air with the excess nitric oxide or ozone respectively. More typically the range is about 0.05 to about 0.3 ppm and even more typically about 0.05 to about 0.15 ppm. Preferably the concentration is about 0.1 ppm. GENERAL DESCRIPTION OF THE METHOD OF CALCULATION Whilst photochemical smog formation is the result of some several hundred or more elementary reaction steps in the light of the present inventor's finding that the amount of smog formed in air and the smog concentration in air can be determined by the oxidation of NO, the overall reactions of smog formation can be described by the follow i ng representative expressions: +O2 1 > ROC + hv - nR02 + ROC (2) RO2 + NO N0 2 +02 (3) NO2 + hv -* NO + O3 (4) NO + O3 - O2 (5) RO2 + O2 ■ * R0C N0 y + RO -» stable gas phase nitrogen 6> containing products N0 y + RO? →- stable non gaseous nitrogen < 7) containing products where R0÷ denotes hydroxyl, alkoxy and peroxy free radical species, ROC and ROC are "reactive organic compounds" including carbonyl , alkane, alkene, aromatic, carbon monoxide and other types of gas phase carbonaceous species which when present and illuminated in air undergo reactions whereby oxygen is consumed and NO is oxidized, N0 χ denotes NO and N0 2 and n i s a proportionality coefficient. SUBSTITUTE SHEET Providing there is sufficient illumination, reactions (2), (3) and (4) continue until the NO concentration is reduced to such a level that there is insufficient NO available to freely maintain reaction (2) and smog formation is curtailed. In addition to ROj reaction with NO, free radicals produced by reaction (1) may aTso undergo radical-radical recombination via reaction (5). During smog formation ROC molecules may cycle through reaction (1) several times. Although the constituent species of ROC are changed by participation in the reactions, to a good approximation for air of ROC composition as usually found in urban regions, the rate coefficient for reaction (1) remains surprisingly constant, independently of the extent of reaction and at least for illumination intensities and durations equivalent to the sunlight of an unclouded summer's day. Nitric oxide undergoes reaction with free radical species via reactions (2), (6) and (7). However in general the rate of NO reaction via (2) is much greater than the rate of NO reaction via (6) and (7). For many purposes NO reaction by (6) and (7) can be neglected. Reaction of NO in accordance with reactions (2), (6) and (7) is a measure of smog formation. The rate of NO consumption by these reactions is.a measure of the rate of smog formation while the concentration of NO so consumed is a measure of the smog concentration. In illuminated air NO consumed by reaction (2) can be regenerated by reaction (3), producing moles of 0 3 equivalent to the NO regenerated. By the addition of excess NO to air, 0, is reacted according to reaction (4) with the consumption of equivalent NO. f t The moles of smog formed in air up to time t, ( n smoα -* > that is the number of moles of NO consumed by reaction (2), is determined as being equal to the total number of moles of NO emitted into the air (°n • J Mn o') up to time t plus moles of excess nitric oxide added during aHHoH analysis ( n NQ ) less the moles of nitric oxide remaining after completion of reaction (4) in the analysis system ( n NQ ) : f ,,t oΛ added n I , 0% n smog " n N0 + n N0 " n N0 <8) While there are many nitrogenous species known to be present in air and constituting NO it is usual for NO to be emitted into the air in only two forms, namely NO and NO. and these emissions together are commonly denoted as NO Λ: SUBSTITUTE SHEET N0 = NO + N0 2 . < 9 ) Furthermore, the bulk of all anthropogenic N0 χ emissions are in the form of NO. The fraction of NO in N0 χ emissions ( °F NQ ) can vary with the specific type of N0 χ emission source ( e.g. the burnt gases from furnaces, motor vehicles, domestic heating) but commonly falls within the range 0.6 to 1.0. For urban atmospheres the value of F NQ is frequently in the range of 0.7 to 0.95. However, °F N0 can be determined explicitly by measurement of the NO/NO χ composition of the NO emissions at their source. Thus the NO emitted into the air can be determined as a function of the emission of NO into the air, since for emissions: On* (10) n NO. n NO. hence O t Or o t (11) n N0 " NO π NO and to a fair approximation 0 F NQ has the value of 0.9. NOTE: For some purposes it is sufficiently accurate to employ the value 1 for °F N0 , in which case: o n t „ o_t (12) n N0 ~ π N0 During smog formation some N0 y is lost from the air by reaction ( 7 ) , some NO being incorporated into nongaseous nitrogenous species, thus the NO content of the air at time t, <njj 0y > after significant smog forming reaction has taken place, may be less than the amount of N0 y emitted into the air (°n NQ ) . The rate y of NO loss from the air is slow compared to the rate of smog formation and so for many purposes the NO loss is relatively small and can be neglected, i.e.: SUBSTITUTE SHEET -35- In daylight and for air with compositions as commonly found in urban regions, reaction (7) proceeds at a rate (R and which is a function of the rate of reaction (2), (R 2 ): R 7 = f ( R 2 ) (14) To a good approximation the form of the function f(R«) is one of direct proportion: R 7 = P 7 2 R 2 (15) where Py 2 is the proportionality coefficient. A typical value for P 7 is determined by the inventor to be 0.125. Thus optionally (15) and t the measured value of n^ Q may be used to obtain a more accurate estimate of °n. in place of (13). The concentration of smog in air is a function of: the rate of smog formation, the pre-existing smog concentration, the dispersion and dilution of the air by meteorological processes and the loss of smog from the air by the deposition of ozone and NO species, incorporation of NO into particulate materials and other loss processes. Defining smog concentration to be the sum of the concentrations of the gaseous oxidized nitrogen species, plus the ozone concentration, less the concentration of nitric oxide, the smog concentration of air at time t, X. is determined by the method of the third embodiment and by means of the system of the fifteenth embodiment, namely from the NO concentration of the mixture after the selected period of the third embodiment, step (c) ( χ NQ ) and the total oxidized nitrogen concentration of the mixture at step (d), ( X N0 ), by the equation: X smog = X N0 " X N0 (16) Defining the amount of smog formation in volume V of air at time t, ( n smoα -*» to be the number of moles of NO previously consumed by reaction (2), f t n is given by equation (17): - n NO (17) and from (10) and (11) (18) and from (15), correcting the NO content of air for loss of NO from the air by reaction (7): ° y " y * P 7,2 fn smog 19) Substituting (19) for °nj 0 in (18) Substituting (20) in (17) and rearranging (21) fn smog " ( ° F N0 n N0 + n 0 " n N0 } ' (1 " ° F N0 P 7,2 } ' y 3 -a rr ar Now in the presence of excess added NO ( n*, Q ) and after reaction in darkness for a selected period such that reaction (4) is complete ° F N0 n N0y., + n 0 J ~ n N0 (22) O p t added I t = ' " NO π N0 + π N0 " π N0 * now the amount of NO present after the selected period ( n NQ ) and addition of excess NO is given by: - 1 - n n t added n ,.-. n N0 y = π N0 y + n N0 23) h ι_e n „ncre * °cF NQ n„ N t Q + addedn-, NQ ,(2_4..) I n °F ,n- ~ π N0 " ~ NO NO substituting (24) into (22): SUBSTITUTE SHEET -38- (25) ° F N0 n N0„ + n 0~ " n N0 y - 3 = n N0 - ( 1-°F N0 ) n NQ - n NO and substituting (25) into ( 21 ~ ' F N0 P 7,2 ] Now Dal ton's Law states for ideal gases, concentration ( mole fraction) of species i at time t (χf ) is given by: where R is the gas constant and T*. P* and * are the temperature, pressure and volume of the gas respectively at time t. Multiplying throughout (26) by substituting ( 27 ) : - Λ Nn0 ' " - θF N0 )X N0 y ]/ o, Cl - °F ' ' N il O ft P r 7,,2 ,3 for: fχ smog < fmaXχ smog 28) where fxt smog denotes the concentration of smog that would be present in the absence of NO loss from the air by reaction (7). *y f t Equation (28) is valid for values of X_ mr . n less than the fmax t smog maximum potential smog formation ( X sm0Q - ) but ^ er the smog maximum has been reached NO loss processes continue and new smog is not formed. In this circumstance P-, 2 can no longer be approximated by a value of 0.125. Now: x smog = X N0 " X N0 (16) Substituting (16) into (28): fχ smog = C smog " (1 " ° F N0> }, ]/ (29) fr: f X*smog < fmaX xsm o o n g Optionally, the approximations: and 7 2 ~ 0 can be made, then (29) yields: Summarizing, the smog concentration in air (X^ m ^ is determined by the system of the fifteenth embodiment and the method of the third embodiment and calculated from equation (16), i.e. t I I x smog = X N0 " X N0 (16) The NO concentration of the air may also be measured as per the fourth and sixteenth embodiments and the smog formation expressed as the notional concentration of smog formed in air in the absence of smog removal p es (fχt r rocess s,_mog), as calculated by equation (29): Γ S-UBSTITUTE SHEET V ^smog = CX Λ *smog (1 " ° F N0 ^ ]/ (29) ( 1 F P ) r N0 γ ι,r for- V Λ smog < fmax χ Λt smog where for most ci rcumstances °F NQ = 0.9 and P 7 £ = 0- 125 The maximum potential smog formation in air is controlled by the rate of reaction (2) relative to the combined rates of reactions (6) and (7). When reactions (6) and (7) have consumed 0 2 such that reaction (3) cannot regenerate NO in sufficient concentration to maintain reaction (2) smog formation is curtailed and new smog production eventually ceases. Thus to a fair approximation the maximum potential smog formation in air ( ,fmax-X,t rmΛ ,„n. fmaxnt ■ . __ι., nn κ „. o„ > sm g a r s m mog) is given by: fmax t _ β o t (3]) x smog " l3 λ N0 lJ f axn. mΛn = n βo„n M t n ,- * . smog NO (32) where the function β is dependent on the rate of reaction (2) relative to the combined rates of reactions (6) and (7) and for air of compositions commonly found in urban areas can be approximated by the value β = 4. Substituting expressions (19) and (27) into equation (31) and rearranging yields expression for maximum potential concentration of smog formed in air in terms of the observables χ NQ and X smoα where y 9 fXt smog is given by equation (29): f " og ■ B< } * P 7,2 f og' <33 > when < χtsmog < fιnax X*smo Jg The total maximum p r otential concentration of smog 3 ( max χsmog) in air is defined as the sum of the concentrations of smog formed in air by smog SUBSTITUTE ^-K- -r formation processes plus the concentration of smog emitted into air as N0~: Tmax t _ fmax t o t x smog " x smog + X N0 £ l where °χ N0 is the concentration of N0 2 emissions into air. Now from equations (9), (10), (11) and (27) ° 2 = 1 -° F N0 Oχ N0 y < 116 > substituting (116) into (115) Tmax t fmax t x smog smog (1-°F r N0)°x λ N t 0y (117) and substituting (31) into (117) gives Tmax t _ o t (β+1 _° F } x smog - X N0 y U3+l (118) By equations (19) a d (27) equation (118) can be expressed as Tmax.,t x smog " <β+1 -° F N0 )(χ N0 y + P 7,2 f smog } (119) , w lh he. n n / (f v χt„ sm m o Λ „g where fxt smog is g -iven by J eq ιuation (29). The extent of smog formation at time t, (E smoα , is given by: F t _ ,f t ,fmax t j smog smog smog (34) and r _ ,f γ t / fmax t j smog ^smog Λ smog (35) Rate of smog formation at selected temperature (T) and illumination intensity (I), ( ' smog) in the p r resence of excess NO is g -iven by: T,I og " <! *N0 - " '"* <36 > where IIIχ N0 and Iχ NQ are the concentrations of NO after the third and first selected periods and t is the duration of the second selected p r eriod of embodiments six and eighteen. The rate ' Q„sm„og SUBSTITUTE SH££7 corresponds to the rate of NO consumption by reactions (2) and (6). The N0 2 produced by reaction (2) can react further via reaction (3) and smog formation is then exhibited as ozone production. When excess ozone is present the steady state NO concentration maintained by reactions (3) and (4) is small and then to a good approximation the increase in ozone concentration resulting from smog formation is quantitatively equal to the NO consumed by reaction (2) less the NO Λ. consumed by reactions (6) and (7). In this circumstance the rate of smog formation is given by: T,I Q mna = (∑ X - HI X ) / H t {1-1/β} ) ( 37 ) 9 °3 °3 where ~-- and W are the concentrations of ozone after the 03 0 3 π third and first selected period and t is the duration of the second period of embodiments seven and nineteen and β is a term to account for the NO consumed by reactions (6) and (7). Typically a suitable value for β is β=4. Rate coefficient for smog 3 formation Rs„ m m Λ og„ is g -iven by J : smo Π g = T,I *smog ltf(τt) • (38 where I and T are the illumination intensity and temperature during the second selected period of embodiments one or two or thirteen or fourteen. f(T ) is a function of temperature and ' Q„smo„g is obtained by the method of the first or second embodiments and the system of the thirteenth or fourteenth embodiments and equations (36) or (37) rreessppeeccttiivveellyy,, aaind the function f(T ) can be adequately approximated by the expression: f (T t) = e-lOOOγd/^-l/Slδ) ( 39 ) where γ has the value of 4.7 and T is temperature in degrees Kelvin. T 'iQ depe of air and: SUBSTITUTE SHEET -43- t n t (40 ) R smog = f =1 R0C( i ) x R0C ( i ) and R smog ° n R0C ( i ) <41> where Dnr( - . s an activity coefficient for smog formation by ROC ( ι ) and wherSn ROC ( i) can be an individual ROC or a mixture of various ROC's , Smog formation is described by the equations: f t (42) smog = (PVRT* ) / TΪIQ *smog-' t where where < X smog β X N0 } T ' I Q vt smog = 0 < f X*smog * β ° S « o u } Time required for selected amount of smog formation, for example: time for maχ imum smog formation, embodiments 8 and 20; time period dur i ng which smog formation has occurred, embodiments 9 and 21; or time required for production of a given amount of smog in air embodiments 10 and 22, may be calculated for selected or measured I* and T* via equations ( 39 ), ( 4 2) and (43). The ozone concentration of air is given by: t t t v t ( 44 ) x 0 3 = x smog + X N0 " x N0 y where smog concentration x^ and nitric oxide concentration are determined by the method of the eleventh embodiment and the system of the twenty third embodiment. r SUBSTITUTE SHEET When air is illuminated the concentrations of ozone and nitric oxide in the air are interrelated and dependent on the intensity of light. According to reactions (3) and (4): 0 J 2, N N00 22 ++ hv NO (3) and NO + 0 3 →- N0 2 (4) when air is illuminated there is rapid exchange of oxygen atoms between NO- and 0,. In sunlight the rates of reactions (3) and (4) are much faster than the rates of reactions (2) (6) and (7). Thus the rates of reactions (3) and (4) are approximately equal, i.e.: k 3 X N0 = k 4 X X 0 ( 64) where k, and k« are the rate coefficients at time t for reactions (3) and (4) respectively and k, incorporates the illumination intensity. For ambient air, the sunlight intensity is usually sufficiently steady for equation (64) to be valid. From equation (64) and by definition of NO Λ (equation (9)) Substituting (124) into equation (44) an rearranging gives ( X* ) - ( X* - X* - if/k 1) £ (124) NO N0 y smog 34 NO - k fc χ t /k l = 0 (125) 3- N0 X 4 By an analogous argument an expression for χt can also be derived: 0 3 SUBSTITUTE SHEBT k (χ t ) 2 + ( k t _ k t χ t + k t χ t } χ t 4 03 3 4 smog 4 NOy 03 ( 1 26) + k (χ t - x - £ ) = 0 3 NOy smog N0 X Experimental observation of smog formation under natural sunlight conditions and concentrations simulating ambient air shows that when f X* falls outside the range: Λ smog <V X N0 - H °x λt N0 ) < V Λ smog (70) < < ( ' °γ m t ++ Λ L * NQ ) ) y where appropriate values for coefficients H and L are H = L = 1 /2 then the terms involving k, of equations ( 125 ) and ( 126 ) t t have only a small influence on the values of χ NQ and χ Q 3 as is also the case in darkness ( i.e. 3 = 0 ) . In these cases equation 125 simplifies to .t .t _ t X N0 ^NOy " ssmmoogg <x ssmmoogg < NNC0 y (gg) and equation 126 simplifies to X* = 0 ( X t ≤ X* > 0 3 smog NOy (gg) 0r X o 3 = X smog " NOy smog N0 y When f * ' falls within the domain given by ( 70 ) and , smog kξ≠O then experimental study of smog formation under conditions pertinent to ambient air demonstrates that SUBSTITUTE SHEET -46- Y * ~ c* (when V s i n the (71 ) X N0 ~ NO Λ smog . .--* * I U y x (domai n gi ven by expression ( 70 ) ) . - t Then substi tution of X N0 for χ N0 y * in equations ( 125) and (126) is appropriate and. taking the value of k 4 from the literature, enables the values of χ NQ and χ Q to be 3 evaluated. Thus from measurements according to the method of embodiment twelve and the system of embodiment twenty-four and equations ( 68 ) , ( 69 ) , ( 71 ) , ( 125 ) and ( 126 ) the ozone and nitric oxide concentrations of the a i r are determined. BRIEF DESCRIPTION OF DRAWINGS Preferred embodiments of the systems and methods of this invention are described below with reference to the following drawings in which:- Fig. 1 is a block diagram of a system for determining rate coefficient of smog formation in air; Fig. 2 is a block diagram of a system for determining concentrat i on of smog in air; Fig. 3 is a block diagram of a system for determining rate of smog formation in air and also for determining ROC concentration of air and total concentration of prior ROC emissions into air; Fig. 4 is a block diagram of an alternative system for determin i ng rate coefficient of smog formation in air; smog concentration, amount of prior smog formation, maximum potential smog concentration, extent of smog formation, rate of smog formation under selected temperature and illumination conditions, NO 0 3 and nitric oxide concentrat i ons of air time period required for maximum smog formation, ROC content of a i r, total concentrations of ROC, N0 y and NO previously introduced into air, NO/NO concentration ratio of the N0 χ previously introduced into a i r, ROC/NO concentration ratio of total previous introductions into a i r, time period during which smog formation has occurred, average t i me of previous introductions of ROC into air, and time period required for production of selected amount of smog in air; Fig. 5 is a block diagram of a further alternative system for determining rate coefficient of smog formation in air; SUBSTITUTE SHEET Fig. 6 is a block diagram of an alternative system for determining rate of smog formation in air; Fig. 7 is a block diagram of a system for determining maximum potential extent of smog formation in air and determining current extent of smog formation in air. Fig. 8 is a schematic diagram of a preferred photoreactor for use in a system of the invention; and Fig. 9 is a schematic cross-section of the edge of the photoreactor of Fig. 8. Fig. 10 is a block diagram of a preferred nitric oxide analyser. Fig. 11 is partially sectional plan view of the sample selection valve which together with the radial flow chemi luminescent reactor are two components preferrably used in the nitric oxide analyser of Fig. 10 as well as a section view along A-A of the plan view. Fig. 12 is a block diagram of a system similar to the system depicted in Fig. 4 and which was used in an Example run. Fig. 13 is a plot of CI χ* 0 - CII x(j 0 vs te "k 90 t which was used to calibrate the illumination source of the system depicted in Fig. 12. BEST MODE AND OTHER MODES FOR CARRYING OUT THE INVENTION Referring to Fig. 1 a system 10 for determining rate coefficient of smog formation in air includes an air filter 11 which filters incoming air and a metered delivery injector 12 which delivers a metered dose of the filtered air to combiner 13. A metered dosage of excess nitric oxide is combined with the filtered air in combiner 13 after passing through nitric oxide filter 14 and being injected therein by metered delivery injector 15. As a result an excess nitric oxide/air mixture is formed in combiner 13 and dispensed via two separate streams. The concentration of nitric oxide at injector 15 is typically a high concentration so that the volume of mixture produced by combiner 13 is close to the volume of air from which it is generated, i.e. so that the volume of nitric oxide required to produce the excess nitric oxide/air mixture is small compared to the volume of air to which it is added and thus the volume of nitric oxide added can be neglected for computational purposes. Reactor 16 in. hich the mixture can react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture is operatively coupled to combiner 13. j SUBSTITUTE SHfET 1 -48- Photoreactor 17 is also operatively coupled to combiner 13. Illumination source 18 is operatively disposed about photoreactor 17 to illuminate the mixture in photoreactor 17 for a second selected per i od under known temperature and illumination conditions. Illumination from source 18 can be kept constant or can be varied according to a preselected or selected illumination profile. Illumination controller/programmer 19 is operatively coupled to source 18 and an illumination sensor consisting of photodiode 20 and photometer 21 for this latter purpose. Temperature sensor 22 is operatively coupled to photoreactor 17 and temperature controller/programmer 23 to determine the temperature of the mixture in photoreactor 17. The temperature of the mixture in photoreactor 17 can be kept constant during illumination or can be allowed to vary and monitored or can be varied according to a preselected or selected temperature profile by temperature controller/programmer 23 which is operatively coupled to photoreactor 17 via lines 24 and 25. A reactor 29 in which during a third selected period excess nitric oxide of the mixture reacts with substantially all ozone is operatively coupled to photoreactor 17. Nitric oxide analyser 26 is operatively coupled to reactor 16 to determine a ' first nitric oxide concentration of the mixture after the first selected period at point CI and operatively coupled to reactor 29 to determine a second nitric oxide concentration of the mixture after the third selected period at point CII. The mixture is vented from the system via analyser 26 and vent 27. Computer 28 is operatively coupled to temperature sensor 22, photometer 21 and analyser 26 to calculate the rate coefficient from the first and second nitric oxide concentrations, the known temperature and illumination conditions and the duration of the second selected period. Typically reactor 16 is of similar form and volume as the combination of the reaction vessels of photoreactor 17 and reactor 29 and the residence time for the mixture to pass from combiner 13 to CI is the same as the time required to pass from combiner 13 to CII. By this means the mixtures available at CI and CII have a common origin at combiner 13. Thus, when the composition of air entering filter 11 has components of rapidly varying concentration the mixtures at CI and CII have a common origin from air of identical compositions. SUBSTITUTE SHEET The rate coefficient of smog formation in air can be determined in the following manner. A metered amount of air is delivered to combiner 13, after passing through filter 11 and injector 12. Excess nitric oxide is added to the air in combiner 13, after passing through filter 14, and injector 15 to provide an excess nitric oxide/air mixture in combiner 13. The mixture is transferred to reactor 16 and photoreactor 17. The mixture is permitted to react in reactor 16 for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture. A first nitric oxide concentration of the mixture is then measured by analyser 26 at point CI. The mixture is illuminated in photoreactor 17 for a second selected period under selected and known temperature and illumination conditions. After illumination the mixture is permitted to react for a third selected period in reactor 29. A second nitric oxide concentration of the mixture is measured after the third selected period at point CII by analyser 26. Preferably the duration of the first period is equal to the total duration of the second and third periods. The rate coefficient is then calculated by computer 28 from the first and second nitric oxide concentrations, χ N0 and χ N0 respectively, the known temperature (T) and illumination conditions (I) and the duration of the second selected period ( t) and where the rate of smog formation is defined as the consumption of nitric oxide per unit time by reaction (2): R0 £ + NO ** N0 2 (2) where N0 2 denotes predominantly nitrogen dioxide but also organic nitrates and other trace nitrogenous products. Firstly the rate of smog formation ( ' Q smoα ) in photoreactor 17 is calculated according to equation (36)and corrected for dilution of air by mixing with added nitric oxide by the expression: ( v 12+ v 15 )/v, 2 ] where , 2 and v, 5 are the volumes of gas injected during specified time by injectors 12 and 15 respectively and when v , 2 >>v ι5 * πe erm (v, 2 + v, 5 )/v, 2 can be approximated by the value 1 and where for a SUBSTITUTE SHEET continuously flowing system and continuously well mixed photoreactor 17, residence time in the photoreactor 17 ( t) is given by H t = v 1? /f 17 (51) where v ]7 is the volume of photoreactor 17 and f, 7 is the volumetric flowrate of mixture through photoreactor 17. The rate coefficient R„s m mo Λ „g is then calculated from the known illumination and temperature conditions of photoreactor 17 and the value of ' Q smoα b application of equation (38): R smog, = T,IQ smo ™ g ltf(τt> ( 38 ) and equation (39): fcΛ = e - 100θΥ(1/τt - 1/316) (39) where γ has a value of 4.7 and T, the temperature of photoreactor 17, is in degrees Kelvin and I is the illumination intensity within photoreactor 17. Referring to Fig. 2 a system 50 for determining concentration of smog in air includes an air filter 51 which filters incoming air and a metered delivery injector 52 which delivers a metered dose of the filtered air to combiner 53. A metered dosage of excess nitric oxide is combined with the filtered air in combiner 53 via nitric oxide filter 54 and metered delivery injector 55. As a result an excess nitric oxide/air mixture is formed in combiner 53. The concentration of nitric oxide at injector 55 is typically high so that the volume of nitric oxide required to produce an excess nitric oxide/air mixture is small compared to the volume of the air with which it is combined, thus optionally enabling the volume of the nitric oxide added to be neglected for computational purposes. Reactor 56 in which the mixture can react for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture is operatively coupled to combiner 53. Nitric oxide analyser 57 is operatively coupled to reactor 56 to determine the nitric oxide concentration of the mixture at point BI. Analyser 57 is also operatively coupled to reactor 56 via converter 58 which converts all the NO in the SUBSTITUTE S EET smog is then calculated by computer 59 from the NO y of og is the gross concentration of nitric oxide consumed via reaction ( 2 ) : R0 2 + NO NO, (2) some πitrie oxide thus consumed can he regenerate d by reaction <3>: NO. + hv °* 2 NO ♦ O3 <3 ) react . ons ^ s r; ; ::;; r s r ;ι; H -- reV , oUs , y reenerated b <3> is consumed by reaction ( 4 ) : NO + 0, -■> NO, (4) The concent __.ra -t,i-on f s - m m na (γX t >> Is calculate^d by^eq & u y at m io fχ n jng ^ ( 52 ) which is equation (16 ) , correc t eα added nitric oxide: (5 t r,I v -- )(V r -n + V r r) /VςO -1 Xsmog " C ( X N0 V " N0 52 55 SUBSTITUTE SH£FT where χ N0 is the concentration of nitric oxide at BII and N0 is the concentration of nitric oxide at BI and v 52 and v 55 are the volumes of gas injected in specified time by injectors 52 and 55 respectively. Referring to Fig. 3 a system 70 for determining rate of smog formation in air under selected temperature and illumination conditions and ROC concentration of air and total concentration of prior ROC emissions into air includes an air filter 71 which filters incoming air and a metered delivery injector 72 which delivers a metered dose of the filtered air to combiner 73. A metered dosage of excess nitric oxide is combined with the filtered air in combiner 73 after passing through nitric oxide filter 74 and being injected into combiner 73 by metered delivery injector 75. The mixture is then dispensed via two separate streams. The concentration of nitric oxide at injector 75 is typically high so that the volume of nitric oxide required to produce an excess nitric oxide/air mixture is small compared to the volume of the air with which it is combined, thus enabling the volume of the nitric oxide added to be neglected for computational purposes. Reactor 76 in which the mixture can react for a first selected period wherein excess nitric oxide in the mixture reacts substantially all ozone in the mixture is operatively coupled to combiner 73. Photoreactor 77 is also operatively coupled to combiner 73. Illumination source 78 is operatively disposed about photoreactor 77 to illuminate the mixture in photoreactor 77 for a second selected period under selected temperature and illumination conditions. Illumination from source 78 can be kept constant or can be varied according to a preselected or selected illumination profile. Illumination controller/programmer 79 is operatively coupled to source 78 and an illumination sensor consisting of photodiode 81 and photometer 80 for this latter purpose. Temperature sensor 82 is operatively coupled to photoreactor 77 and temperature controller/programmer 83 to determine the temperature of the mixture in photoreactor 77. The temperature of the mixture in photoreactor 77 can be kept constant during illumination or can be allowed to vary and monitored or can be varied according to a preselected or selected temperature profile by temperature controller/programmer 83 which is operatively coupled to photoreactor 77 via lines 84 and 85. Reactor 89 in which during the third selected period excess nitric oxide of the mixture reacts with substantially all ozone is operatively coupled to photoreactor 77. Nitric oxide analyser 86 is operatively coupled to reactor 76 to determine a first nitric oxide concentration of the mixture after the first selected period at point CI and operatively coupled to reactor 89 to determine a second nitric oxide concentration of the mixture after the third selected period at point CII. The mixture is vented from the system via analyser 86 and vent 87. Preferably reactor 76 is of the same form and volume as the combination of the reaction vessels of photoreactor 77 and reactor 89 and the residence time for the mixture to pass from combiner 73 to CI is the same as that for the other part of the mixture to pass from combiner 73 to CII. Computer 88 is operatively coupled to analyser 86 to calculate the rate from the " first and second nitric oxide concentrations and the duration of the second selected period and the ROC concentration of air and total concentration of prior ROC emissions into air from the first and second nitric oxide concentration. The rate of smog formation in air can be determined in the following manner. A metered amount of air is delivered to combiner 73 after passing through filter 71, and injector 72. Excess nitric oxide is added to the air in combiner 73 after passing through filter 74, and injector 75 to provide an excess nitric oxide/air mixture in combiner 73. The mixture is transferred to reactor 76 and photoreactor 77. The mixture is permitted to react in reactor 76 for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture. A first nitric oxide concentration of the mixture is then measured by analyser 86 at point CI. The mixture is illuminated in photoreactor 77 for a second selected period under selected temperature and illumination conditions and further allowed to react for a third selected period in reactor 89. A second nitric oxide concentration of the mixture is measured after the third selected period at point CII by analyser 86. Preferably the duration of the first period is equal to the total duration of the second and third periods. TH . af T 'V under selected temperature and illumination then ϊlϊu ed by computer 88 from the first and second conditions is then calculate d o H resDe ctively ) nitric oxide concentrations ( 0 and X N0 respect i and the duration of the second selected peno ( ) . ^ The rate of smog formation is measured as the by the expression: (v ?2 + v 75 )/v 72 l photoreactor 77 residence time in photoreactor 77 ,s g i ve '" o , e e d to combiner 73 after passing through filter amount of a, i llv oχ , de „ added to the air in combiner 71, and injector 72. txces Dr0 vide an excess 73 after passing through filter 74, an • " ^ referred to -tnc oxide/air mixture in combiner e i ^ ^ ^ ^ reactor „ and pho oreac - ^^ ^ ^ ^ ,„ the reactor 76 for a first se i ecreu μ m γt .ιre A first ,xture reacts with substantially all .one ,n e i xture.^ ^ ^ SUBSTITUTE SK££T and further allowed to react for a third selected period in reactor 89. A second nitric oxide concentration of the mixture is measured after the third selected period at point CII by analyser 86. Preferably the duration of the first period is equal to the total duration of the second and third periods. A metered amount of reference air of known ROC concentration and ROC composition representative of that of the air for analysis is delivered to combiner 73 after passing through filter 71, and injector 72. Excess nitric oxide is added to the reference air in combiner 73 after passing through filter 74, and injector 75 to provide an excess nitric oxide reference air mixture in combiner 73. The reference mixture is transferred to reactor 76 and photoreactor 77. The reference mixture is permitted to react in reactor 76 for a first selected period wherein excess nitric oxide in the reference mixture reacts with substantially all ozone in the reference mixture. A first nitric oxide concentration of the reference mixture is then measured by analyser 86 at point CI. The reference mixture is illuminated in photoreactor 77 for a second selected period under selected temperature and illumination conditions and further allowed to react for a third selected period in reactor 89. A second nitric oxide concentration of the reference mixture is measured after the third selected period at point CII by analyser 86. The duration of the first, second and third periods and selected temperature and illumination conditions of photoreactor 77 are maintained the same during passage of both the air and the reference air through system 70. The ROC concentration of the air ( X RO ) and the total concentration of prior ROC emissions 0 X D O C > In o the air is calculated by computer 88 from the first and second nitric oxide concentrations of the air mixture ( * , Q and χ NQ respectively) and the first and second nitric oxide concentrations of the I r III r reference air mixture ( χ NQ and χ NQ respectively) and the ROC concentration of the reference air (X nnC\ In the presence of excess nitric oxide, nitric oxide is consumed in photoreactor 77 in proportion to the ROC concentration of the air within the reactor. The ROC concentration of air is calculated from the nitric oxide consumed by the air compared to the nitric oxide consumed under the same conditions by reference air of known ROC concentration by equation SUBSTITUTE SH£fT ( 128) χ t _ χ r ( I χ _ πl v ) / ( I v 1" . X R0C " R0C^ X N0 T / X N0 ιπ x r N0) (128) The products of reaction by ROC species are also ROC species and for ROC compositions representative of urban air product ROC have similar photochemical reactivity to the reactant ROC, at least to a good approximation for the extent of reaction as can occur in the atmosphere on a sunny day. As the reactivity of prior ROC emissions is conserved the total concentration of prior ROC emissions is given by of smog formation, smog concentration, amount of prior smog formation, maximum potential smog concentration, extent of smog formation in air, rate of smog formation under selected temperature and illumination conditions, NO ozone and nitric oxide concentrations of air, time period required for maximum smog formation in air under selected conditions of temperature and illumination, ROC content of air, total concentration of ROC previously introduced into air, total concentration of NO previously introduced into air, total concentration of nitric oxide previously introduced into air, NO/NO concentration ratio of the NO Λ previously introduced into air, ROC/NOΛ concentration ratio of total ROC and total NO previously introduced into air, time period during which smog formation has occurred, average time of previous introductions of ROC into the air and time period required for production of selected amount of smog in air under selected conditions of temperature and illumination, includes an air filter 101 which filters incoming air and a metered delivery injector 102 whicn delivers a metered dose of the f ltered air to combiner 103 and a second metered dose to Al and NO converter 120. A metered dosage of excess nitric oxide is combined with the filtered air in combiner 103 after passing through nitric oxide filter 104 and being injected therein by metered delivery injector 105. As a result an excess nitric oxide/air mixture is formed in combiner 103 and dispensed therefrom via three separate streams. Reactor 106 in which the mixture can react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture, is operatively coupled to combiner 103 and reactor 106A. Photoreactor 107 is also operatively coupled to combiner 103. Illumination source 108 is operatively disposed about photoreactor 107 to illuminate the mixture in photoreactor 107 for SUBSTITUTE SH£ET a second selected period under known temperature and illumination conditions. Illumination from source 108 can be kept constant or can be varied according to a preselected or selected illumination profile. Illumination controller/programmer 110 is operatively coupled to source 108 and an illumination sensor consisting of photodiode 111 and photometer 109 for this latter purpose. The illumination intensity can be determined via absolute measurement of the illumination intensity by sensor 111 and photometer 109 or alternatively by calibration. Calibration of the illumination intensity may be achieved by providing a supply of air of known rate coefficient of smog formation to filter 101, the residence time of the known air/nitric oxide mixture in photoreactor 107, the temperature of photoreactor and the nitric oxide concentrations at CI and CII. Temperature sensor 112 is operatively coupled to photoreactor 107 and temperature controller/programmer 113 to determine the temperature of the mixture in photoreactor 107. The temperature of the mixture in photoreactor 107 can be kept constant during illumination or can be allowed to vary and monitored or can be varied according to a preselected or selected temperature profile by temperature controller/programmer 1T * 3 which is operatively coupled to photoreactor 107 via lines 114 and 115. Reactor 116 in which during a third selected period excess nitric oxide reacts with substantially all ozone in the mixture is operatively coupled to photoreactor 107. Nitric oxide analyser 117 is operatively coupled to reactor 106A to determine a first nitric oxide concentration of the mixture after the first selected period at point CI and operatively coupled to reactor 116 to determine a second nitric oxide concentration of the mixture after the third selected period at point CII. Reactors 106 and 106A have form and configuration similar to the combined assembly of photoreactor 107 and reactor 116, respectively, by which means the mixing processes and the residence time of that part of the mixture passing from combiner 103 to point CI is approximately the same as that part of the mixture passing from combiner 103 to point CII, thus ensuring that the mixture composition at any moment at CI and at CII pertain to air which initially formed part of a common mixture in combiner 103. This feature is particularly useful when the composition of air passing through filter 101 is variable. SUBSTITUTE SHEET Reactor 118 in which mixture can react for a fourth selected period wherein excess nitric oxide of the mixture reacts with substantially all ozone in the mixture is operatively coupled to combiner 103. Analyser 117 is operatively coupled to reactor 118 to determine nitric oxide concentration of the mixture at point BI. Analyser 117 is also operatively coupled to reactor 118 via NO converter 119 to determine a NO concentration of the mixture at point BII. Analyser 117 is also operatively coupled to injector 102 to determine the nitric oxide concentration of the air at point Al. Analyser 117 is also operatively coupled to injector 102 via NO converter 120 to determine the NO concentration of the air at point All. The mixture and air are vented from the system via analyser 117 and vent 121. Computer 122 is operatively coupled to temperature sensor 112, photometer 109, analyser 117. Computer 122 is also operatively coupled to temperature sensor 123 and illumination sensor 124. Temperature sensor 123 is disposed to determine the temperature of the ambient air prior to analysis by system 100 and illumination sensor 124 is disposed to determine the sunlight flux in the ambient air. Optionally, a nitric acid scrubber 125 is coupled to the inlet at converter 120 and a nitric acid scrubber 126 is coupled to the inlet of converter 119 to remove nitric acid vapour from the air and mixture respectively prior to entering the converters 119 and 120. Computer 122 processes signals from operatively coupled to sensors and analyser to calculate: the rate coefficient of smog formation in air from the nitric oxide concentrations at CI and CII, the known temperature and illumination conditions of photoreactor 107 and the duration of the second selected period; the concentration of smog in air from the nitric oxide concentrations at BI and BII; the amount of prior smog formation from concentrations of nitric oxide at All, BI and BII; the maximum potential smog concentration of air from the nitric oxide concentrations measured at All, BI and BII; extent of smog formation in air from the concentrations of nitric oxide measured at All, BI and BII; the rate of smog formation under the selected conditions of temperature and illumination from the nitric oxide concentrations measured at CI and CII and the duration of the second selected period; the NO concentration of air from the nitric oxide concentration measured at All; the ozone concentration of air from the nitric oxide concentrations measured at Al, BI and BII and the nitric oxide concentration of air from the nitric SUBSTITUTE SHEET oxide concentration measured at Al and (or alternatively ) the ozone and nitric oxide concentrations of air from the measured nitric oxide concentrations at All, BI and BII and the temperature of air as measured, at sensor 123 and illumination intensity of sunlight at sensor 124; the time period required for maximum smog formation in air under selected conditions of illumination and temperature from the measured nitric oxide concentrations at All, BI, BII,. CI and CII, and the duration of the second selected period; time period during which smog formation in air has occurred, the time period being substantially the same as or within a selected period for which the illumination and temperature conditions are known, wherein the end of the selected period coincides with the end of the time period from the measured nitric oxide concentrations at All, BI, BII, CI, CII, the duration of the second selected period, the temperature measured at sensor 112 and illumination intensity measured at sensor 111 and the temperature and illumination of air monitored by sensors 123 and 124 respectively throughout the duration of the selected period during which smog formation in air has occurred; time period required for production of selected amount of smog in air under selected conditions of temperature and illumination from the nitric oxide concentrations measured at All, BI, BII, CI and CII, the duration of the second selected period, the temperature measured at sensor 112 and the illumination intensity measured at sensor 111 and the selected conditions of temperature and illumination of the air and the selected amount of smog; the ROC content of air from the nitric oxide concentrations at CI and CII, the temperature measured at sensor 112 and illumination intensity measured at sensor 111 and the duration of the second selected period; the total concentration of ROC previously introduced into air from the ROC content of air determined as above; the NO concentration of air from the nitric oxide concentration measured at All; the total concentrations of NO and NO previously introduced into air from the nitric oxide concentrations measured at Al, All, BI and BII or alternatively from the measured nitric oxide concentrations measured at All, BI and BII, the temperature of the air measured at sensor 123 and illumination intensity of sunlight measured at sensor 124; the total concentration of nitric oxide previously introduced into air from the nitric oxide concentrations measured at Al, All, BI and BII or alternatively from the nitric oxide concentrations measured at All, BI and BII, the temperature of the air measured at sensor 123 and r SUBSTITUTE SHEET 111umϊnatlon intensity of sunlight measured at sensor 124; the N0/N0 χ concentration ratio of the N0 χ introduced into air 0 F NQ ) from the NO concentrations measured at Al, All, BI and BII, the temperature of the air measured at sensor 123 and the illumination intensity of sunlight measured at sensor 124; the R0C/N0 χ concentration ratio of the total ROC and total NO previously introduced into air from the nitric oxide concentrations measured at All, BI, BII, CI and CII, the temperature measured at sensor 112 and illumination intensity measured at sensor 111, the duration of the second selected period and also the NO concentration measured at Al or alternatively the temperature of the air measured at temperature sensor 123 and illumination intensity of sunlight measured at sensor 124; average time of prior introductions of ROC into air from the concentrations of nitric oxide at All, BI, BII, CI and CII, the temperature-time profile of the air measured at temperature sensor 123, the illumination intensity-time profile of the air measured at sunlight illumination sensor 124 and also the NO concentration measured at Al or alternatively the air temperature measured at sensor 123 at the time of sampling the air and the illumination intensity measured at sensor 124 at the time of sampling the air. The rate coefficient of smog formation in air can be determined in the following manner: A metered amount of air is delivered to combiner 103 after passing through filter 101 and injector 102. Excess nitric oxide is added to the air in combiner 103 after passing through filter 104 and injector 105 to provide an excess nitric oxide/air mixture in combiner 103. Metered amounts of the mixture are transferred to reactor 106 and 106A and photoreactor 107. The mixture is permitted to react in reactor 106 and 106A for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture. A first nitric oxide concentration of the mixture is then measured by analyser 117 at point CI. The mixture is illuminated in photoreactor 107 for a second selected period under known temperature and illumination conditions and then transferred to reactor 116. The mixture is permitted to react in reactor 116 for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone. SUBSTITUTE SH£ A second nitric oxide concentration of the mixture is measured after the third selected period at point CII by analyser 117. The rate coefficient is then calculated by computer 122 from the first and second nitric oxide concentrations, the known temperature and illumination conditions of photoreactor 107 and the duration of the second selected period. In system 100 optionally reactors 106 and 106A and reactor 118 are the same reactor and then points BI and CI become the same point, however there is an advantage in employing separate reactors of differing volumes as reactors 106 and 106A and reactor 118. This is because preferably the residence time of the mixture in reactors 106 and 106A is the same as the combined residence times of mixture in reactors 107 and 116, and the residence time in photoreactor 107 is preferred to be in the order of ten minutes, the longer the residence time in photoreactor 107 the greater being the sensitivity of system 100 for determining rate of smog formation and rate coefficient of smog formation. The residence time preferred for the mixture in reactor 118 is shorter than the preferred residence time in photoreactor 107 and is of the order of one minute and it is preferred that the residence time of the mixture in reactor 118 is as short as is consistent with the reaction of ozone with excess nitric oxide going substantially to completion in reactor 118. This is desirable especially when the composition of air at filter 101 is rapidly varying for then the air delivered from filter 101 to analyser 117 via points Al and All will be close to having the same composition as air delivered from filter 101 to analyser 117 via points BI and BII. This in turn minimizes the possibility of transitory spurious values for ozone concentrations being determined by system 100 due to the mixture measured at points A and B having as origins air of different compositions. The rate coefficient for smog formation in air is determined by measurement of nitric oxide consumed by reaction (2): in photoreactor 107. Some nitrogen dioxide produced by reaction (2) undergoes further reaction in photoreactor 107, producing ozone and regenerating nitric oxide by reaction (3): SUBSTITUTE SHJΞΞ °2 N0 2 + hv -> NO + 0 3 ( 3 ) Nitric oxide regenerated by reaction (3) further reacts with excess nitric oxide by reaction (4): NO + 0 3 →- N0 2 (4) either within photoreactor 107 or subsequently in reactor 116. The nitric oxide consumed by photoreaction of ROC species in photoreactor 107 is the difference in nitric oxide concentrations of the mixture at points CII and CI. The rate of smog - formation ( ' Q„s„m,„o„g) in photoreactor 107 is calculated by equation (36), corrected for dilution of air by mixing with added nitric oxide, by the expression: T g - < [ I * NO - "V"" < 5) ""lOZ + V 105 ) * 102 ] Ϊ where χ NQ is the concentration of nitric oxide measured at CII and χ NQ is the nitric oxide concentration measured at CI by analyser 117 and where v, Q2 and v, Q5 are the volumes of gas injected during specified time into combiner 103, by injectors 102 and 105 respectively. Optionally where 1Q2 » V, 05 the term ( v, Q2 + V *I Q C- ) - /V ] 02 can *-* e approximated by the value 1 and where for a continual flowthrough system 100 and continuously well mixed photoreactor 107, residence time in the photoreactor 107 ( t) is given by: I∑t - v 107 / f 107 (55) where v, Q7 is the volume of photoreactor 107, and f, Q7 is the volumetric flowrate of mixture supplied by combiner 103 and passing through photoreactor 107. The rate coefficient Rs„mog is calculated from the known illumination and temperature conditions of photoreactor 107 and the value of ' Q smoα by application of equation (38): *smog = T ' I Qsmo n g/I t f(T t ) (38) SUBSTITUTE SHEET and equation (39): where γ has a value of 4.7 and the temperature of photoreactor 107 (Λ is in degrees Kelvin and I *1s the illumination intensity within photoreactor 107. The concentration of smog in air can be determined in the following manner. A metered volume of air is delivered to combiner 103 after passing through filter 101 and injector 102. Metered volume of excess nitr i c oxide is added to the air in combiner 103 after passing through filter 104 and injector 105 to provide an excess nitric oxide/air mixture in combiner 103. The mixture is transferred to reactor 118. The mixture is permitted to react in reactor 118 for a fourth selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture. A third nitric oxide concentration of the mixture is then measured by analyser 117 at point BI. Mixture from reactor 118 is delivered to nitric oxide converter 119 wherein the N0 y in the mixture- is converted to nitric oxide. The mixture is delivered from converter 119 to point BII and a fourth nitric oxide concentration measured by analyser 117. The concentration of smog in air is then calculated by computer 122 from the third and fourth nitric oxide concentrations. As already indicated, smog concentration of air is the sum of the concentrations of ozone and N0^ less the concentration of NO, and y* is the concentration of smog in air at time t. It follows smoo that v* is eαuivalent to the concentration of nitrogen dioxide Λ smog , , , and other gas phase nitrogen containing species in air produced by reaction of nitrogen dioxide, that is, the nitrogenous products of reactions (3) and (6 ) : °2 N0 2 + hv -» NO + 0 3 (3) NO + RO: →* Stable gas phase nitrogen (6 ) containing products SUBSTITUTE SH W hen excess nitric oxide is added to air, nitrogen dioxide consumed b y reaction (3) is regenerated from the ozone produced by reaction ( 3 ) b y reaction (4): NO t 0 3 →* N0 £ C 4) enabling the smog concentration of air ( Xs mog > to be calculated from the difference in nitric oxide concentrations at points BII and BI, by equation (57): t _ r( BII _ BI } (57) X -smog X N0 W (v 102 + 105 )7 V 102 ] where BII χ N0 an d BI χ NQ are the concentrations of nitric oxide at points BII and BI respectively and measured by analyser 117 and v 1Q2 and v 1Λr are the volumes of gas injected during specified time into 105 combiner 103 by injectors 102 and 105 respectively. The rate of smog formation in air under selected temperature and illumination conditions can be determined in the following manner: A metered amount of air is delivered to combiner 103 after passing through filter 10 1 and injector 102. Excess nitric oxide is added to the air in combiner 103 after passing through filter 104 and injector 105 to provide an excess nitric oxide/air mixture in combiner 103. Metered amounts of the mixture are transferred to reactors 106 and 106A and photoreactor 107. The mixture is permitted to react in reactors 106 and 106A for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture. A first nitric oxide concentration of the mixture is then measured by analyser 11 7 at point CI. The mixture is illuminated in photoreactor 107 for a second selected period under the selected temperature and illumination conditions and then transferred to reactor 116. The mixture is permitted to react in reactor 116 for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone. The rate of smog formation in air under the selected temperature and illumination conditions of photoreactor 107 is the rate of reaction (2): SUBSTITUTE SH£ otherwise: ° ; χt 0 3 7 (1 + β - 2 ° F Nrf E ^og = l > (60) Equation ( 60 ) arises from the following considerations: t t When E s = 1 then the value of χjj Q is small and approaching zero, thus for the purpose of these calculations nitric oxide concentration can be assigned the value ■ ° (E - ■ > A,s0 " hen og - * the " f * - fm " ~ _ and by equation (31) x smog = β χ N0 (E smog = 1) < 12 0> y The concentration of smog in air has a component in addition to that formed via reaction (2), that is the smog emitted directly into the air as the N0 ■ ? ■- present in emissions of NOX (ie °χI U ) 2 From equations (9), (10), (11) and (27) ° X N0 = (1 " ° F N0 } ° X N0 Ϊ2D 2 y The maximum potential smog concentration of air is Tmax x t Λ smog which, on the basis of equations (120) and (121), is given by equation (118) Tmax ^ t o„t , Ω , o r . x smog = X N0 <β + ] " W (118) y Now for the case E* mog = 1 (and χJ Q = 0) it follows from equations ( 17 ) , ( 18 ) and ( 27 ) that the ozone concentration of air is given by γ t Tmax v t o c o v t fC t .. X 0 - x smog " F N0 X N0 <E smog =1) <122 ) 3 y Substitution of (118) into (122) gives °χ in terms of χ* Xj - % 0 <β + 1 - 2°F N0 ) <E* -l 3 (123) and ( 123 3) can be*rearranged to make oX j tJ 0 the dependent variable, yielding equation (60). - 1 The amount of prior smog formation in air is calculated according to equations (29), (31), (57), (58) and (62) by equation (61): SUBSTITUTE SH£ET -66- Λ smog π °F p ) > G^l <61 > ( 1 " N0 V l ,Z determined coefficients which for most circumstances pertinent to air of composition as commonly found in urban regions can be assigned the values: β = 4 ° F N0 = °- 9 P ? 2 = 0.125. The value of P ? 2 is a function of the relative rates of reactions ( 7 ) and ( 2 ) . However! the rate of reaction ( 7 ) can be variable as the product distribution of the reaction of N0 £ with R0 2 can vary. In some circumstances nitric acid, one of the reaction products, can rema i n in the gas phase or alternatively a variable proportion of the nitric ac i d formed can be incorporated, possibly by adsorption, into non-gaseous species. The effect of this variability of product distribution on the value of P ? 2 may optionally be minimized by incorporation of nitric acid scrubbers 125 and 126 into the system. When scrubbers 125 and 126 are included then nitric acid is excluded from the defin i tion of N0 y . A suitable nitric acid scrubber is a porous nylon membrane or nylon tube through which the sample and mixture are passed. Nylon surfaces remove nitric acid from air. When nitric acid is thus removed prior to converters 120 and 121 then the relative rates of reactions ( 7 ) and ( 2 ) are made less variable but the rate of reaction ( 7 ) is increased. When nitric acid scrubbers are incorporated into system 100 a value of about p = 0.25 is suitable for most determinations of prior smog formation in air. Trnax t The maximum potential smog concentration in air ( X- sm0 g ) can be calculated from the determined value of °χ N0 in air accordingto equation ( 31 ) : Tm x χ t . o t (β+1 . o F j ( 118 ) λ smog NO ϋ y ] SUBSTITUTE SHcET The extent of smog formation in air at time t (E* ) b ein α ., ,. ^ smog ' y the proportion of smog produced by time t compared to the maximum potential amount of smog formation can be determined from f x t ._,, max t ,. . ^ . ^smog X smog accordιng to equations ( 61 ) and (31) respectively according to equation (35): £ - _ ( f y / fmax t . smog Λ smog λ smog ( 35) System 100 provides other methods for determination of the nitric oxide and ozone concentrations of air, which are as follows: The illumination i ntens i ty of air is measured by sensor 124 and the temperature o f air is measured by sensor 123. The nitric oxide and ozone concentrations are determined by first calculating the rate coefficient of reaction (3), kjj, from the known coefficients for 0 2 photolysis, the illumination intensity measured by sensor 124 and the temperature measured by sensor 12 3 . I f * is zero then the nitric oxide and ozone concentrations are calculated by equations ( 68 ) and ( 69 ) respectively and the values of χ* and v* • ^smog Λ N0 ' obtained as described previously. If k 3 is non zero then the values of 0 χJ Q , ° j t f t x smog and x smog are o t ained as described previously and the domain of f χ ~ determined according to expression (70). If the value of f * falls . .. ^ Λ smog outs i de the range of expression (70) then the nitric oxide and ozone concentrations are calculated according to equations ( 68 ) and (6 9 ) respectively. When f χ^ mog falls within the range specified by expression ( 70 ) then the rate coefficient for reaction (4) is calculated from the known rate parameters and the temperature measured by sensor 123. The nitric oxide and ozone concentration of air are calculated from the values of k*. kj, χ^ og and χJ Q y according to equations ( 125 ) and (126) respectively and equation (71) by equations ( 73) and (74) respectively. SUBSTITUTE SHEET -68- x x N0 - - ( ιx 1 NO - X smog /k I +C(X N0 -X Λ *smog -k* 3/k* 4> + k| 3χ* NU /kJ "■ l T /2 } 2 y \ I Δ) CValΫd domain for (73) and (74) is when f χJ mog is in the range v y The time period required for maximum smog formation in air subsequent to the period of the actual smog formation under selected conditions of temperature and illumination can be determined in the following manner: The values of °χj 0 and f γ smg are determined as *y above described and the maximum potential smog concentration of a i r calculated according to equation ( 31 ) : fmax ^ t o„t (31) "srm m og - ■ - *N0 ■ J ,extra c t •> J._ The amount of further smog formation required ( , X srπog t0 produce maximum smog concentration is calculated according to equation (79): extra v t fmax t f χ t (79) λ smog ~ λ smog Λ smog The time period t^), where t ] is the commencement and t £ is the completion time to form the amount of smog equivalent to extract is determ i ne from the rate coefficient for smog formationdetermined as described above and is calculated for the selected temperature and illumination conditions according to equations ( 39 ) , ( 42 ) and (43) by the solution of equation ( 80 ) for ( t ∑ - t } ) : extra t _ r t2 R t - ,t -1000 Υ (1/T t -l/316 ) dt = Q (80) λ smog ti smog and where a suitable value for γ is 4.7. , SUBSTITUTE SHEET -69- The time period during which smog formation in air has occurred ( t -t ) the time period being substantially the same as or within a selecϊed period wherein the end of the selected period coincides with the end of the formation period, can be determined in the following manner. For the duration of selected period the illumination intensity of the " a i r is measured by sensor 124 and the temperature of the air is measured by sensor 123. At the end of selected period <t t > the rate coefficient for smog formation in air, R^ og( and the amount of smog formation in air V , and the amount of prior emissions of N0 y into the air' ° Sm ° 9 'are determined as described above. The time period Λ 11 » NO ' ( -t ) is calculated from these values according to equations ( 27 ) , ( 39 ) ,° ( 42 ) and (43) by solution of equation ( 81 ) for t t -t 0 >: V _ j .t-t T,I t dt = 0 ( 81 ) λ smog t=o v smog where f - -rQ_ s - mog -- R κ * smo g I lt f(T t ) when X smog < β X NOy T Q smog=° fχ < β ° X N0 y and f<T*> - e- 1000 ^ 1/Tt " 1/316> The time period determined by equation ( 81 ) is contingent on the premise that all the ROC of the air is present at the commencement of the time period. When this is not the case the determined commencement time t is some average of the times during which ROC was introduced into the a?r. When condition f χ* mog - β°X^ Is met during the time period then maximum potential smog formation is reached and the time period determined is a minimum period because the maximum extent of smog formation may have existed for an indeterminate time prior to the end of the selected period. Optionally if the trajectory and speed of movement of the air during the selected period is known, then the time period during which smog formation has occurred can be used in conjunction with this further SUBSTITUTE SH£ET information to estimate the location of the source of the ROC emissions, which corresponds to the location of the air at time t = t Q . The time period (t, to t ) required for production sele t of selected amount of smog in air (a Xsmog } under seTected conditions of temperature and illumination can be determined in the following manner. The values of X smog X-smog and R* are determined as above described. The selected amount of smog smog is tested according to expression (82) to determine if the smog amount selected is within the range of possible smog amounts: select ≤ ( max t _ f χ t } (82 > λ smog - Λ smog Λ smog If expression (82) is false then the time required for production of selected amount of smog is indefinite because the selected amount is more than the amount that can be produced from the air. When expression (82) is true then time period ( t to t m > is calculated by solution of equation (83) for t--.: , ^ , . , -1000γ ( I /! - 1/316) select _ j-tm R t ∑ t dt = 0 Λ smog J t smog y t (83 ) where t, is the time at commencement of smog formation and t m is the time when production of selected amount of smog in air is attained and a suitable value for the coefficient γ is 4.7. The ROC content of air (χ^ oc ) can be determined in the followinq manner. The rate coefficient for smog formation in air 3 _!__. R - is determined as described above and the value of χ Rnr smog ■Λυι ~ calculated according to equation ( 105 ) Y = R* / a* C105 ) x R0C smog ROC where for ROC emissions of compositions as commonly found in urban regions a suitable value for a RQC is a r = 0.0067 moles smog/mole ROC carbon/unit illumination intensity where illumination intensity has units of rate coefficient for N0 2 photolysis integrated with respect to time. Alternatively the value of a RQC can be separately determined. The value of χ r thus determined has units of concentration in air ROC of carbon present as ROC. SUBSTITUTE SHEET I The total concentration of ROC previously introduced into air (°χ R0C ) can be determined in the following manner. The ROC content of air is determined as described above. As to a good approximation the value of the smog forming reactivity of air (R ) ■ ^ smog is independent of the amount of illumination to which the ROC/air mixture o,,t has been exposed on the day of measurement. The value of x ROC can be calculated according to equation (106) o t t (106) X R0C " X R0C The total concentration of NO., previously introduced into air (°X t ) can be determined in the following manner. The values of N0 t t t are determined for the air as X N0 ' X N0 and X 0 described above and the value of G calculated according to equation (58), when G has a value of G <1 the value of °χ is calculated from the determined values of χ N according to equation (59) and where suitable values for the coefficients P 7 2 and °F N0 are 0.125 and 0.9 respectively or otherwise, when G 1 , from the determined values of χ Q according to 3 equation (60) and where a suitable value for the coefficient β is 4. The total concentration of nitric oxide previously introduced into air (°χ ) can be determined in the following manner. The value of χ N0 for the air is determined as described above. Following equation (11) expressed in terms of concentrations the value of °X " MΛ O S cal where in most circumstances pertaining to urban air a suitable value for the coefficient °F Q is 0.9 or alternatively the value of °F N0 can be independently determined by measurement of the NO emissions at their Λ source. The NO/NO concentration ratio of the NO introduced into air x x ( F Mn ) can be determined in the following manner. The concentrations t t t t X smoq , X 0 , X N0 and χ N0 of the air are determined 3 y from the nitric oxide concentrations measured at Al, All, BI and BII and SUBSTITUTE SHEET -72- calculated as described above according to equations ( 57 ) , ( 62 ) , ( 3 ) an ( 89 ) respectively. The temperature of the air at the time of sampl i ng the air is determined by temperature sensor 123 and the sunlight illum i nat i on intensity at the time of sampling the air is determined by sensor 124. The value of n is determined from these values by solut i on for °F of the set of equations (29), (58), ( 59 ) , ( 60 ) , ( 109 ) and ( 68 ) or ( 69? or ( 73 ) or ( 74 ) and where suitable values for the coefficients of these equations are P = 0.125, 3=4 and H=L=1/2 The R0C/N0 χ concentration ratio of the total ROC and total N 0> previously introduced into air 0 ROC / ) > can be o.t determined in the following manner. The values of X R0C and are determined for the air as described above and follow i ng equations ( 10 ) and (106) the R0C/N0 χ concentration ratio can be calculated from the determined concentrations according to equat i on ( 108 ) delivery injector 135. The nitric oxide/air mixture thus formed is delivered to second combiner 136. A metered dosage of excess ozone is combined w i th the mixture in combiner 136 after passing through ozone filter 137 and be i ng injected therein by metered delivery injector 138. SUBSTITUTE SK£ET this latter purpose. operati . e , y cou p,e d to photoreactor 140 and SUBSTITUTE SK£ET delivered to combiner 136. Excess ozone is added to the mixture in combiner 136, after passing through filter 137 by injector 138 to provide a nitric oxide/excess ozone/air mixture in combiner 136. The mixture is spl t into two streams, one stream being transferred to reactor 139 and the other to photoreactor 140. The mixture is permitted to react in reactor 139 for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture. A first ozone concentration of the mixture is then measured by analyser 150 at point CI. The mixture is illuminated in photoreactor 140 for a second selected period under selected and known temperature and illumination conditions. After illumination the mixture is permitted to react for a third selected period in reactor 149. A second ozone concentration of the mixture is measured after the third selected period at point CII by analyser 150. Preferably the duration of the first period is equal to the total duration of the second and third period. The rate coefficient is then calculated by computer 152 from the first and second ozone concentrations, the known temperature and illumination conditions and the duration of th-e second selected period. Addition of nitric oxide to air combiner 133 ensures that there is sufficient but small concentration of nitric oxide available in photoreactor 140 to enable reaction (2) not to be limited by insufficient nitric oxide. Smog production is thus to a good approximation equivalent to nitric oxide consumed by reaction (2): R0^ + NO NO, (2) The nitrogen dioxide produced quantitatively by reaction (2) subsequently reacts to produce approximately equivalent ozone by reaction (3) N0 £ + hv NO + 0- (3) Thus smog formation in photoreactor 140 can be measured according to the increase in ozone concentration produced by reaction in the photoreactor. On this basis the rate coefficient is calculated by equations (38) and (84). SUBSTITUTE S EΈT ( 38) smog smog where l OOOγd /T 1 - 1 /31 6) f(T L ) - e ( 39) and γ *■ = 4 .7 and T . I Q t smog { [ ( CI x cπ x ■ o n )/ π t] (84) ' • . < * , 32 + v , 35 + v , 38> ' v 132> where C i I. n and c X π J" X. n are the ozone concentrati ons at poi nts u 3 ^ CI and CII respectively, πt, is the duration of the second selected period and , 3 „, v, 35 and v, 3g are the volumes injected in a specified time by injectors 132, 135 and 138 respectively and I is the illumination intensity and T is the temperature in degrees Kelvin of photoreactor 140. Referring to Fig. 6 a system 160 for determining rate of smog formation in air under selected temperature and illumination conditions includes an air filter 161 which filters incoming air and a metered delivery injector 162 which delivers a metered dose of the filtered air to a first combiner 163. A metered dosage of nitric oxide is combined with the filtered air in combiner 163 after passing through nitric oxide filter 164 and being injected into combiner 163 by metered delivery injector 165. First combiner 163 delivers the mixture to second combiner 166. A metered dosage of excess ozone is combined with the mixture in second combiner 166 after passing through ozone filter 167 and being injected into combiner 166 by metered injector 168. A reactor 169 in which the mixture can react for a first selected period wherein excess ozone in the mixture reacts substantially all nitric oxide in the mixture is operatively coupled to combiner 166. Photoreactor 170 is also operatively coupled to combiner 166. Illumination source 171 is operatively disposed about photoreactor 170 to illuminate the mixture in photoreactor 170 for a second selected period under selected temperature and illumination conditions. Illumination from source 171 can be kept constant or can be varied according to a SUBSTITUTE S ' 5r-' u"? I preselected or selected illumination profile. Illumination controller/programmer 172 is operatively coupled to source 171 and an illumination sensor consisting of photodiode 173 and photometer 174 for this latter purpose. A temperature sensor 175 is operatively coupled to photoreactor 170 and temperature controller/programmer 176 to determine the temperature of the mixture in photoreactor 170. The temperature of the mixture in photoreactor 170 can be kept constant during illumination or can be allowed to vary and monitored or can be varied according to a preselected or selected temperature profile by temperature controller/programmer 176 which is operatively coupled to photoreactor 170 via lines 177 and 178. Reactor 179 in which during a third selected period excess ozone of the mixture reacts with substantially all nitric oxide is operatively coupled to photoreactor 170. Ozone analyser 180 is operatively coupled to reactor 169 to determine a first ozone concentration of the mixture after the- first selected period at point CI and operatively coupled to reactor 179 to determine a second ozone concentration of the mixture after the third selected period at point CII. The mixture is vented from the system via analyser 180 and vent 181. Computer 182 is operatively coupled to analyser 180 to calculate the rate from the first and second ozone concentrations and the duration of the second selected period. The rate of smog formation in air can be determined in the following manner. A metered amount of air is delivered to combiner 163 after passing through filter 161, and injector 162. Optionally nitric oxide is added to the air in combiner 163 after passing through filter 164, by injector 165 to provide a nitric oxide/air mixture in combiner 163. The mi ture is transferred to a second combiner, combiner 166. Excess ozone is added to the mixture in combiner 166 after passing through filter 167, by injector 168 to provide a nitric oxide/excess ozone/air mixture in combiner 166. The mixture is split into two streams one stream being transferred to reactor 169 and the other to photoreactor 170. The mixture is permitted to react in reactor 169 for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture. A first ozone concentration of the mixture is then measured by analyser 180 at point CI. The mixture is illuminated in photoreactor 170 for a second selected period under selected temperature SUBSTITUTE SH£ET I and illumination conditions and further allowed to react for a third selected period in reactor 179 where excess ozone reacts with nitric oxide. A second ozone concentration of the mixture is measured after the third selected period at point CII by analyser 180. Preferably the duration of the first period is equal to the total duration of the second and third periods.. The rate under selected temperature and illumination conditions is then calculated by " computer 182 from the first and second ozone concentrations and the duration of the second selected period. Addition of nitric oxide to air at combiner 163 ensures that there is sufficient but small concentration of nitric oxide available in photoreactor 170 to enable the rate of reaction (2) not to be limited by insufficient nitric oxide. Smog production as measured by ozone formation in photoreactor 170 is thus to a good approximation equivalent to nitric oxide consumed by reaction (2): The nitrogen dioxide produced quantitatively by reaction (2) subsequently reacts to produce approximately equivalent ozone by reaction (3): . °2 N0 2 + hv →- NO + 0 3 (3) Thus smog formation in photoreactor 170 can be measured according to the increase in ozone concentration produced by reaction in photoreactor 170. On this basis the rate of smog - formations ' Q„s„m,og) in air under the selected temperature and illumination conditions of photoreactor 170 is calculated according to equation (85): C(v 162 + V 165 + V 168 )/V 162 ] > where CIχ n and IIχ n are the ozone concentrations at points u 3 ^3 CI and CII respectively, t is the duration of the second period and v 1 6 2 ' 1 6 5 anc ' v lf i 8 are ^ ne vo ^ u es injected in specified time by injectors 162, 165 and 168 respectively. SUBSTITUTE SHEET -78- Referring to Fig. 7 a system 200 for determining extent and maximum potential smog formation in air includes an air filter 201 which filters incoming air and a metered delivery injector 202 which delivers a metered dose of the filtered air to combiner 203 and a separate dose of the filtered air to NO converter 209. A metered dosage of excess nitric oxide is combined with the filtered air in combiner 203 via nitric oxide filter 204 and metered delivery injector 205. As a result an excess nitric oxide/air mixture is formed in combiner 203. Reactor 206 in which the mixture can react for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture is operatively coupled to combiner 203. Nitric oxide analyser 207 is operatively coupled to reactor 206 to determine the nitric oxide concentration of the mixture at point BI. Analyser 207 is operatively coupled to reactor 206 via converter 208 which converts all the NO in the mixture to nitric oxide so that the W y concentration of the Y mixture can be determined as nitric oxide at point BII by analyser 207. The mixture is vented from the system via analyser 207 and vent 211. Converter 209 is operatively coupled to analyser 207 via point All so that the total NO concentration of the air can be determined as nitric oxide at point All. The air is vented from the system via analyser 207 and vent 211. Computer 210 is operatively coupled to analyser 207 to calculate the maximum potential and extent of smog formation from the determined NO and nitric oxide concentrations of the mixture and the NO y concentration of the air. The extent and maximum potential smog formation in air can be determined in the following manner. A metered amount of air is delivered to combiner 203 after passing through filter 201 by injector 202. Excess nitric oxide is added to the air in combiner 203 after passing through filter 204, by injector 205 to provide an excess nitric oxide/air mixture in combiner 203. The mixture is transferred to reactor 206 where it is permitted to react for a selected period wherein excess nitric oxide in the mixture reacts with substantially aTl ozone in the mixture. The nitric oxide concentration of the mixture is then measured by analyser 207 at point BI. The NO concentration of the mixture is measured as nitric oxide after passing through converter 208 at point BII. j SUBSTITUTE SB££T A metered amount of air is also delivered to nitric oxide analyser 207 via converter 209. The NO concentration of the air is determined at point All as nitric oxide after passing through converter 209. The extent (E ) and maximum potential smog formation fma t Smog ( χsmog Λ ) is then calculated by J comp f uter 210 from the NOy., concentration of air and the mixture and the nitric oxide concentration of the mixture according to equation (33) and equations (86), (87) and (88): fmax t t x smog - β( AII xNO + P 7,2 x smog } (86) and Λ smog - {CX (1 " ° F N0 P 7,2» and x smog = [( X N0 " X N0 > (88) (V 202 + V 205 )/V 202 ] where A χ NQ , B χ NQ , BII X N0 are the nitric oxide concentrations measured at All, BI and BII respectively and v 2Q2 is the volume of air injected by injector 202 into combiner 203 and v 2Q5 is the volume of gas injected by combiner 205 in a specified time and where the values of β, P 7 „ and °F NQ are approximated by β -= 4, P 7 2 = 0.125 and °F N0 = 0.9 and the extent of smog formation in air (E ), that is the proportion of smog produced to the maximum potential amount of smog produced is calculated from equation (35): E l smog = (35) Figs 8 and 9 depict a preferred photoreactor for use in a system of the invention and a schematic cross-section of the edge of this photoreactor respectively. When designing a photoreactor for use in a system of the invention it is desirable to:- (a) minimise the extent to which chemical reactions occur on the surface of the photoreactor; SUBSTITUTE SHEE (b) provide for the transmission of both UV and visible light through the walls of the photoreactor; (c) ensure that the sample within the photoreactor is well mixed; and (d) purge the housing containing the photoreactor with purified air so as to minimize the possibility of contamination of the photoreactor by the ambient or room air and the possible diffusion through the walls and into the photoreactor of reactive species which may be present in the air surrounding the reactor. Referring to Fig. 8 reactor 300 has walls 301 consisting of two sheets of thin FEP teflon film, supported by and sealed at frame 302. Frame 302 is held by bracing pieces 303. An excess nitric oxide or ozone/air mixture is directed into photoreactor 300 via inlet tube 304 and leaves photoreactor 300 via teflon feed-through tube 305 which penetrates walls 301 at point 306. The excess nitric oxide or ozone/air mixture passes as a jet stream into photoreactor 300 from inlet end 307 and thus stirs the mixture in photoreactor 300. The excess nitric oxide or ozone/air mixture leaves photoreactor 300 via exit end 308. At least a portion of inlet tube 304 fits inside outlet tube 305. This arrangement is particularly satisfactory since only one feed-through port is required in walls 301. Frame 302 retains two gaskets forming a seal and is described in detail below with reference to Fig. 9. Fig. 9 shows a sectional view of frame 302 which includes two pieces of shaped aluminium D-section rod. Two sheets of FEP teflon film which form reactor walls 301 are held with the inside faces of frame 302 by two gaskets 309 to provide a gas tight seal between reactor film walls 301. The gaskets 309 are formed from sheet elasto eric material, Viton ( trade mark) rubber being suitable. The assembly of frame 302, gaskets 309 and reactor walls 301 are secured together by screw fasteners 310 and 311. The advantage of using FEP teflon film for walls 301 is that it is unreactive. Contact between FEP teflon film walls 301 and other materials, e.g. metal of frame 302 is minimized in photoreactor 300 thus reducing the extent to which active species can diffuse through walls 301 and contact frame 302 or gaskets 309, undergo reactions and rediffuse back into reactor 300. Further, in photoreactor 300, frame 302 and bracing pieces 303, are minimized in area so as to minimize absorption of radiant energy by frame 302 and pieces 303 thus minimizing heat SUBSTITUTE SHEET transferred to the mixture in photoreactor 300. The mixture within reactor 300 is kept well stirred by the jet-like action of the incoming mixture from inlet end 307. The use of only two sheets of FEP teflon film for walls 301 (thickness approximately 0.025mm) and a single continuous joint minimizes sealing problems that can occur at corner joints. The configuration of photoreactor 300 enables all the mixture in the photoreactor to be simultaneously illuminated thus avoiding dark reactions which could occur if there were shadows cast by frame 302 on the mixture in photoreactor 300. The configuration of photoreactor 300 enables the volume of the photoreactor to be varied after assembly, by adjustment of the length of bracing pieces 303. Figure 10 depicts a preferred nitric oxide analyser for use in a system of the invention. Figure 11 depicts a sample selection valve which together with the radial flow chemi luminescent reactor are two preferred components of the nitric oxide analyser of figure 10. When designing a nitric oxide analyser for use in the system of the invention it is desirable to achieve an analyser that is highly sensitive to nitric oxide and to: (a) Provide for the rapid switching between samples. (b) Minimise the time required to purge the analyser between samples. (c) Provide the ability to measure small differences in the nitric oxide concentrations of two sample streams. (d) Provide the ability to complete rapidly the analysis of six separate streams (i.e. Streams Al, All, BI, BII CI , CII). (e) Provide means to rapidly zero and calibrate the response of the analyser. Referring to figure 10 the nitric oxide analyser sample stream selection valve 400 has eight inlet ports. The sample and mixture streams of the smog monitor at Al, All, BI, BII, CI and CII are fed to the corresponding labelled inlet ports 401 of valve 400 as shown in figure 10. Nitric oxide-free air is supplied to inlet port DI and a mixture of known nitric oxide concentration is supplied to port DII. Valve 400 has a common outlet port 402 and eight vent ports 403 which are individually connected to their corresponding inlet ports 401. Gas flow from each inlet port is switched to either the outlet port 402 or the corresponding vent ports 403 by means of eight gas switching solenoid valves. The unselected streams freely vent to waste at vents 403 and a SUBSTITUTE SHEET single selected steam is delivered from outlet 402 to flow divider 404. Flow metering orifice 405 is connected to flow divider 404 and dispenses a metered flow rate of the selected stream into chemi luminescent reactor inlet 408. Flow in excess of that required by metering orifice 405 is supplied to divider 404 and the excess is freely vented to atmosphere at vent 407. A suitable flow at orifice 405 is 750 scc/min. At the inlet 408 to radial-flow chemi luminescent reactor cell 406 the selected and metered stream is mixed with a metered supply of ozonised air which is provided by ozoniser 409 and delivered at a constant flow rate by metering orifice 410 to the reactor inlet 408. The mixture from inlet 408 flows with radial flow pattern through the disc shaped chemiluminescent reaction cell 406, passing between mirrored back plate 420 and optical filter 413. The mixture passes around the edge of the circular mirror plate 420 and is exhausted via activated carbon ozone scrubber 411 by vacuum pump 412 and vented to waste. Light produced in the radial flow chemiluminescent reaction cell 406 by reaction of ozone with nitric oxide passes through optical filter element 413 and is detected by photomultiplier 414. Signal output from photo ultipl ier 414 is fed to signal processor 415 via line 416. Controller 417 switches stream selection valve 400 via line 419 and the selection is communicated to signal processor 415 via line 418. An advantage of the disc shaped radial flow chemiluminescent reaction cell is that for a given cell volume the system has the minimum gas mixture residence time and provides rapid purge out of the cell when a new sample stream is selected at valve 400. This arrangement also provides good optical coupling with the photocathode of the photomultiplier. Utilization of mirror backed glass disc back plate 420 in the reaction cell 406 further enhances the intensity of light collected at the photocathode of photomultiplier 414. A suitable dimension for the reaction cell 406 is 6mm by 55mm diameter and typically the cell is operated at a pressure of 1/10 atmosphere or less and which s maintained by vacuum pump 412. Figure 11 shows a schematic representation of a preferred sample stream selection valve 400, a component part of the nitric oxide analyser. Valve 400 has a stainless steel body 423 and eight inlet ports 401 disposed symmetrically about a centrally located common outlet port 402. Each inlet port 401 is connected with an associated vent port 403 and also to the outlet port 402 via outlet manifold 426. Flow from inlet SUBSTITUTE SHf -83- ports 401 is directed either to manifold 426 via valve seats 425 when 425 is open or to vent ports 403 when valve seat 425 is closed. The valve plunger 428 is activated by solenoid 430 and can take up two positions: (1) normally closed; valve seat 425 is closed and valve seat 429 is open to allow flow from inlet port 401 to vent freely to atmosphere via the corresponding vent 403; and (2) open; solenoid 430 is energised, plunger 428 is withdrawn against return spring 431 to close valve seat 429 to open seat 425, directing flow from inlet 401 via drilling 427 to manifold 426 and out of the valve body 423 via common outlet port 402. The volume of manifold 426 is small as also is the volume of the valve seat to manifold drillings 427. The drillings 427 are short to minimize dead volume and to ensure rapid purging of the manifold assembly when flow streams are switched by the action of the solenoids 430. In operation each stream flows through its respective inlet port 401 into valve body 423. Only one solenoid 430 is energised at any time. The stream with the energised solenoid passes out of the valve via valve seat 425, drilling ' 427 manifold 426 and outlet port 402. The stream of the unenergised solenoids flow freely through their respective solenoid valves passing plungers 428 and valve seat 429 to vent at vent 403. Inlet ports 401 are disposed close to their corresponding valve seats 425 thus ensuring that when unenergised each solenoid valve is continuously well purged with the gas stream. An advantage of this design of valve 400 is that it enables several streams to be independently and rapidly switched into a common manifold. Because the volume of manifold 426 is small and drillings 427 are short the dead volume of the system between valve seats 425 and outlet port 402 is small. Thus the gas of any selected stream is rapidly displaced from manifold 426 by the next selected stream when the solenoid selection is changed. Bleed of the previous sample from drillings 427 into the newly selected stream is minimised by making drillings 427 short. Thus stream selection valve 400 requires only a very short time period to completely purge out with each newly selected stream. The outlet port 402 is connected to chemiluminescent reaction cell 406 via stream divider 404 by short lengths of tubing of small volume. SUBSTITUTE SHEE The advantage of using a radial flow chemiluminescent reaction cell coupled with small dead volume stream selection valve 400 is that it enables the nitric oxide analyser of figure 10 to be rapidly switched from sample stream to stream with minimum time required between measurements for purge out of the previous sample stream from the analyser before commencment of measurement of the newly selected stream. The advantage of rapidly switching between streams is that when the nitric oxide concentration difference between streams is to be determined and the composition of the air sampled by the smog monitor is variable the error in the concentration difference measurement is minimised when the time difference between the measurement of each stream is minimised. The nitric oxide analyser is operated in the following manner. Stream selection is controlled by controller 417 which selects streams according to the following routine, activating the selected solenoids of valve 400 via communication line 419. Controller 417 operates two kinds of cycles, X and Y. Cycle X provides analysis of streams Al through to CII. The time taken for analysis of each stream is composed of the time required to purge the previous stream from the analysis system (time period ) and a second period when the uncontaminated stream is analysed for a time period equal to an integral multiple of time period n. Cycle X has the sequence: AKm.n), AIKm.n), BI(m,n), BIKm.n), CI(m,n), CII(m,2n), CI(m,n) where AI(m,n) denotes stream Al selected and for period m + n. During time period m the nitric oxide analyser is purged by the newly selected Al stream without data processor 415 recording the output from the photomultiplier 414. Following completion of period M controller 417 activates data acquisition by data processor 415 of output signal from photomultiplier 414 for a period n. On completion of the n time period controller 417 stops acquisition of data by 415 and immediately deselects port Al and selects port All valve 4Q0 and similarly through the rest of the cycle, except that for CII measurement data is acquired for a period of duration 2n. Cycle Y contains the same sequence as cycle X but in addition includes selection of either port DI or DII. SUBSTITUTE SHEET Cycle Y has the sequence: AKm.n), AIKm.n), BKm.n), BII(m,n), CI(m,n), CII(m,2n), CI(m,n), DEI or II](m,n) A suitable time for completion of either cycle X or Y is 45 seconds and a suitable value for m is 0.714 seconds. The duration of period n is different from cycles X and Y. For cycle X, m = 5.0 seconds and for cycle Y, m = • 4.36 seconds. Typically the smog monitor operates with controller 417 directing completion of three X cycles followed by a Y cycle every fourth cycle, with stream DI being activated during the Y cycle, thus providing a zero NO concentration reference point for the nitric oxide analyser. From time to time the nitric oxide analyser is calibrated, typically once per day, by substitution of one of the X cycles every fourth cycle by a Y cycle wherein stream DII is selected. Port DII of valve 400 is provided with a calibration gas mixture of known nitric oxide concentration during the period of the calibration which is typical ly 15 minutes. The advantages of this arrangement are: The nitric oxide analyser can be zeroed and calibrated without interruption to the analysis of streams Al to CII. Analysis of all the required streams is rapidly completed in the space of 45 seconds. Rapid completion of the measurement cycle minimises the likelihood that the composition of the air being sampled and analysed will vary significantly during the course of a single cycle, thus minimising the error in the values determined for the nitric oxide concentration difference between streams. It is desirable to determine the nitric oxide concentration difference between streams CI and CII to higher accuracy than is required for the Al, All and BI, BII concentration differences. The analyser provides very accurate measurement of small nitric oxide concentration differences between stream CI and CII by devoting proportionally greater time to measurement of these streams and by measuring the CI stream both immediately before and immediately following the CII measurement. SUBSTITUTE SHEET AN EXAMPLE OF THE INVENTION AND APPLICATION TO PHOTOCHEMICAL SMOG MONITORING An example of system 100 was fabricated substantially in accordance with that described with reference to figure 4 and as shown in figure 12. Reactor 107 was fabricated from FEP (Trade Mark) Teflon film (registered Trade Mark) with an internal volume of 17 litres. Reactors 116 and 118 were of identical construction, which consisted of a PTFE Teflon pipe of internal diameter 40mm and length 1000mm (Volume 1.26 litres), with end closures of PTFE teflon and with mixture inlet and outlet at opposing ends. Reactors 106 and 106A were a combination of reactors identical with the configuration of reactors 107 and 116 respectively. Illumination source 108 was a combination of several fluorescent UV lights with light output rich in the UVA region of the spectrum together with white light fluorescent lamps. Illumination intensity was kept constant when the system was in operation. Source 108 had a total power consumption of 440 watts. Twenty two fluorescent lamps 108 were disposed about photoreactor 107. The lamps are separated from photoreactor 107 by an airtight FEP Teflon film window 500. Photoreactor 107 is located centrally within airtight chamber 501 formed by window 500. Reactor 106 is surrounded by an opaque airtight housing 502 forming chamber 503 about reactor 106 and housing 502 is connected to chamber 501 by two ventilation lines 504 and 505. Line 504 included blower 506 to circulate purified air between chambers 501 and 503. Heat exchanger 509 is mounted in the circulating purified air flow. The temperature within chambers 500 and 502 is sensed by temperature sensor 507 and the temperature of the purified air controlled to a selected temperature by controller 508 and heat exchanger 509. Temperature sensor 507 is linked to controller 508 by line 510 and temperature controller 508 to heat exchanger 506 by line 511. The temperature was selected on the basis of being as warm as was compatible with smog formation under the ambient conditions to be measured, so as to cause the rate of reactions in photoreactor 107 to be sufficiently fast, the sensitivity of measurement of rate of smog SUBSTITUTE SHEE formation being greater the higher the temperature ( and light intens i ty) of photoreactor 107. The maximum temperature desirable is limited by the onset of reactions which do not take place in the atmosphere. On these grounds the selected temperature was 40°C. Maintaining the temperature of reactors 106 and 107 warmer than that of the air to be measured minimizes the likelyhood of condensation of water or reaction products onto the walls of reactors 106 or 107. A supply of purified air was provided by air purifier 512 (AADCO 737 series, AADCO, Inc., 2257 Lewis Avenue, Rockville, MD. 20851, U.S.A.) and supplied to housing 503 via line 510 and excess air freely exhausted from chamber 503 and vent 514. By purging chambers 503 and 501 with purified air, photoreactor 107 is maintained in an environment with minimal ROC and NO concentrations, thus reducing the likelihood of contamination of reactor 106 and photoreactor 107 by air of the room within which system 100 was located, including diffusion of reactive contaminants through the FEP Teflon film walls. The materials of fabrication of all components were chosen on the basis that there would be minimum outgassing therefrom. For example, materials with plasticizers were not employed. Teflon insulated wires were used to link the sensors in system 100 and Teflon tubes were used to link the components with the reactors of system 100. Reactors 106 and 107 were maintained at a common constant temperature of 40°C by temperature controller 508. Nitric oxide gas was supplied to filter 104 as a mixture of about 800ppm nitric oxide in nitrogen and was injected by metered delivery injector 105 at a constant rate of 1.8 ml per minute. The flowrate of mixture through reactor 118 was maintained at 0.38 litres/min and through reactors 106 and 106A, and photoreactor 107 and reactor 116 at 1.47 litres/min. Analyser 117 was capable of determining nitric oxide concentration of two gas streams simultaneously and computer 122 calculated the concentration and concentration difference of each pair of streams Al and All, BI and BII or CI and CII. Analyser 117 was configured to determine nitric oxide concentration at points Al and All for approximately 5 minutes, then at BI and BII for five minutes and then at CI and CII for a further five minutes and then continue by repeating the cycle indefinitely. SUBSTITUTE SUEF -88- The residence time of mixture flowing in plug flow through reactor 118 was approximately 3.3 minutes and the residence time of m i xture i n well stirred photoreactor 107 was 11.6 minutes and residence t i me i n reactor 116 under conditions of plug flow, 0.86 minutes. The residence time of mixture in reactors 106 and 106A was equal to the sum of the residence times of reactors 107 and 116, namely 12.6 minutes. Thus because of the differing residence time for streams emerging at Al, All, BI BII CI and CII to pass through system 100 via the various flow paths from filter 101 to analyser 117 and the sequential analysis of a i r and mixture passing points Al, All, BI. BII. CI and CII, the air and mixture measured at points Al. All. BI. BII, CI and CII within any one analyser cycle represented separate sub samples of air which passed as a s i ngle sample through filter 101. Thus to a fair approximation, analyses made at po i nts Al, All, i, BII CI and CII within the one nitric oxide analyser measurement cycle represent separate analyses of the same air. This is advantageous when the composition of air entering filter 101 is variable, as is frequently the case when ambient air is monitored. In this example of the operation of system 100 it was located i n the rural outskirts of a major city, approximately 16 km from the central business district " and some kilometers from any known strong source of ROC or nitrogen oxides emissions. The topography of the region was generally flat, with no significant mountains or hills. The locality is known to be subject periodically to episodes of photochemical smog. The atmosphere at the location was sampled directly into filter 101. The illumination intensity in photoreactor 107 provided by source 108 was determined by calibration of the system in the following manner. Pure air free of ROC and nitrogen oxides, was supplied throughout the calibration procedure to filter 101. The system was operated as described for smog monitoring until steady and equal nitric ox i de concentrations were measured by analyser 117 at points CI and CII. Cycling of analyser 117 was then reprogrammed so that points CI and CII were measured frequently for the remaining duration of the calibrat i on procedure. A known small amount of ROC ( O n R0C (std) ) of known Sm ° g forming activity <a R0C(std) > was then rapidly introduced into the purified air entering filter 101. The nitric oxide concentration at CI and CII was analysed by analyser 117 for a period of an hour after introduction of the ROC mixture. SUBSTITUTE SHEET -89- The ROC mixture employed as the calibration standard and introduced at filter 101 consisted of a mixture of gaseous alkane, alkene and alkyne hydrocarbons and had an activity coefficient for smog formation value of a = 0.016 moles smog/mole ROC/unit i 1 lumination/umt f(T) whe?e illumination is expressed in units of J^.dt, k 3 being the rate coefficient for N0 £ photolysis. The mean molecular weight of the ROC(std) mixture was: MWROC(std) = 31 <8g An amount of 1.53 x 10 "4 g of the ROC calibration standard was introduced into system 100 at filter 101 giving an initial amount of ROC in photoreactor 107 of 7.00 x 10 "5 g ( 2.20 x 10 " moles ) which was then subject to continuous dilution by the flow of ROC-free mixture through photoreactor 107 and to photoreaction by illumination provided by source 108. These processes can be described by the mechanism: dilution ROC - * -* * ilos4t- RnOrC (90) dilution SMOG -> lost Smog where the rate coefficients for dilution of ROC (k gQ ) and dilution of smog (k g2 ) are equal, i.e.: k - k thus the°smog concentration in photoreactor 107 after introduction of the calibration standard at time t=0, is described by t γ t (94) dχ smog = k 91 X R0C " K 92 x smog dt (95) and - dx k tx ROC 90 ROC dt Integrati on of ( 95) equati on yi el ds X R0C = X R0C e ( 96 ) Substitution of expression (96) for X R0C in equation (94) and kg Q for k g2 and integrating gives: t t-o "k90t x smog " κ 91 x R0C te (97) Now the rate coefficient for exponential dilution, (k.-*,) is given by: k dn = f/V (98) where f is the flowrate and V the volume of the vessel. Therefore for photoreactor 107 under the conditions of the calibration: k go = k g2 = 1.47/17 = 8.52 x 10 "2 min -1 Now by design and under the specified operating conditions of system 100 the smog concentration produced by photoreaction in photoreactor 107 is equivalent to the difference in nitric oxide concentrations between the corresponding mixture from reactor 106A when measured at CI and the mixture from reactor 116 measured at point CII: t _ CI t _ CII t smog " X N0 λ N0 ^ yy Substitution of the expression (99) into equation (97) yields, for the calibration: _k 90^ CI y t - CII y t - k y t= ° te (100) N0 X N0 ~ 91 x R0C υu Thus for calibration the value of CI t CII t x NO ~ X N0 i nt *icated by computer 122 is proportional to the value of te- 90 and the plot of (CIχ N Q ~ CIχ Jj versus te ~ ^° thas g^dient of kg, XO *. where in the present case k gfl has the value 8.52 x 10 " min ~ and t is the time duration after introduction of the ROC calibration mixture into photoreactor 107. For the case of this example the values obtained for these quantities at various elapsed times are listed in Table 1 and are plotted in Fig. 13, which also shows the line of best fit, which has a gradient of 0.0139 and intercept of 0.0029. SUBSTIT UTϊ SHE To a fair approximation and to the precision of analyser 117 the data of Table 1 fall on a straight line. This indicates that: (1) Rate of smog formation is independent of the duration of the reactions involving ROC. (2) Rate of smog formation is proportional to the amount of ROC present in air. (3) Processes occurring at the walls of the reactors 106, 106A and 116 and photoreactor 107 do not contribute significantly to the chemical dynamics of the system. The line of best fit passes close to but not through the origin, this intercept is attributable to small errors in the estimation of the initial time and the initial inhomogeneity of ROC distribution in photoreactor 107 immediately on introduction of the ROC calibration mixture. Thus by equation (100) and the gradient of the graph of Fig. 13 k g] χ^° = 0.0139 x 10 "6 mole fraction min _1 (101) An alternative to determination of k gQ by measurement of photoreactor 107 volume and flowrates is available by application of data from Table 1. k go = (In t(2)-ln t(l ))/(t(2)-t(l )) (102) where t(l) and t(2) are any two times (t(2)>t(D) when the respective smog concentrations of photoreactor 107 are equal. An advantage of calibration by introduction of ROC into system 100 as described is that the system performance over a wide range of ROC concentrations can be evaluated. In the case of this example the quantity of ROC initially present in photoreactor 107 was, in terms of concentration, 7.70 ppmC (where pp C denotes mole carbon X 10 /mole mixture). After 59 minutes, dilution reduces this concentration in photoreactor 107 to 0.050 ppmC. Now by definition the rate of smog formation in photoreactor 107 (T ' lQ smog ) is 9 iven b ^ : where T and I are the temperature and i l l umi nati on i ntens i ty respecti vely SUBSTITUTE SHEET of photoreactor 107. From (101) and (103 ) therefore, ' Q =0.0139ppm.min for the conditions of the calibration, smog Now also for the conditions of photoreactor 107 and by equations (38), (39) and (41 ) T,I Qs mog is also given by: T,lQj mo RT^lte-1000γ(l/T-l/316) n ∑ (a RO c(i)° ^ R0C(i )> p y i=1 (104) Substitution of the calibration value for ' Q s " into equation (104) and from the known values of the other terms and where i=R0C calibration mixture the illumination intensity I is determined. -4700 (1/313-1/316) 0.0139 x 10 "6 x 1 x 17 x e It = 0.08206 x 313 x 0.016 x 2.20 x 10 ~6 = 0.227 min -1 That is the value of k for photoreactor 107 and illumination source -1 108 assembly is determined to be 0.227 min . The calibration procedure as described is also suitable for determining the value of the activity coefficient for smog formation (a Rnr ) of particular ROC or ROC mixtures. This is accomplished by first determining the value of I for the photoreactor 107 then introducing a known quantity of the R0C/R0C mixture to be evaluated as for the ROC calibration mixture during calibration. The value of a Ror is then determined from the measurements by evaluation of equation (104) using the known value of I . System 100 was installed at the described location and operated to monitor throughout a day smog in the atmosphere, analysing air continuously sampled over the period 0958 to 1654 hours. The temperature of the atmosphere and the sunlight intensity was measured by sensors 123 and 124 respectively for the same day for the selected period of 0622 to 1826 hr, these times corresponding approximately with dawn and dusk. The values for the temperature and sunlight intensities at selected times throughout the day are given in Table 2. The nitric oxide concentrations measured by analyser 117 at points Al, All, BI, BII, CI and CII and the corresponding time of sampling the air ( t ) are listed in Table 3. The rate of smog formation ( ' Q smoα -* ^or air within photoreactor 107 SUBSTP * UTE SHct was calculated according to equations (55) and (56) and where Iχ. Mn TTT T 4- PTT +• and χ N0 of equation (55) correspond to χ NQ and x . of Table 3 and T and I are the temperature and illumination conditions within p ^hotoreactor 107. Values of T,I Q " sm Λ o Λ g determined for each measurement time are listed in row 8 of Table 3. Instrument transients can g -ive rise to spurious values for ' Q„smog as is i1lustrated by the negative value obtained in Table 3 for time 1044. The rate coefficient for smog - formation Rsmog is calculated from the known temperature and illumination conditions of photoreactor 107 and the value of T ' I Q '!s ' mog by equations (38) and (39). The results are expressed as Rsmog xlO and for each example measurement are listed in row 9 of Table 3 where the units of R ςmoα are ppm smog/unit of incident light/unit f(T) where the incident light intensity is expressed as the rate coefficient for O- photolysis (k-) τ The concen.t.r.a. ^ tio_n o_ Λ f smog ,i_n a_,i_r. Aχ . .....,.1 DT equation (57). Values of χ * , Q and BII smog is calculated by X N0 are 1isted in Table 3, rows 4 and 5, and, for system 100 as employed, v, Q2 = 1.47+1.47+0. 38 = 3.381itre min and v 05 1.8x10 3 litre min ] The values of X„s m m„og determined for each measurement time are listed in row 10 of Table 3. The NO concentration of air is measured as nitric oxide at point J ΔTT + All. For this example the values obtained ( χ NQ ) are listed in Table 3, row 3, and are also listed as the NO concentrations at the time of air sampling (χ N t Q ) in row 11 of Tabl ■ e 3. The nitric oxide concentration of air is measured at Point Al and the values obtained ( Al y.t Q are listed in Table 3, row 2, and are also listed in row 12, Table 3, as the nitric oxide concentrations at the time of air sampling (X NQ )- The ozone concentration of air is calculated from the values of X smo , X N0 and χ NQ according to equation (44). The y t values thus determined (χ n ) are listed in row 13, Table 3 for each 3 sampling time. -94- The concentration at ti me t of N0 y that woul d exi st i n the absence of N0 y removal processes from ai r (°χjj 0 ) , and whi ch y represents the cumulative emissions of N0 y into air is calculated from the values determined for J Q , x Jj 0 and xj as fol l ows. t y 3 Q ^ The value of G is determined by equation (58) and-the value of X N0 determined by equation ( 59 ) when G^l otherwise by equation ( 60 ) . T he va l ue of G and corresponding value of °χj f or air y at each time of sampling are listed in Table 3, rows 14 and 1 5 respectively. formation in air equation (3 1 ). each time of sampling is given in Table 3, row 16. The extent of prior smog formation in air ( f χ * ) i s calculated from the measurements according to equation 9 (61) and accor d ing to the value of G* and where P 7 = 0.125 and °F Mft = 0 .9. The ■P 4*** ' INU values thus determined for r χJ mQg are given in Table- 3, row 17 . The extent of smog formation in air at time t (E* ) is calculated fr« f * og and -V Jccord ,- g fa «*- equation (35). The values of E^ determined for air at each time of sampling are given in Table 3, row 18. The concentration of reactive organic compounds χ^ QC in air i s d etermined from the measured reactivity coefficient for smo g formation in a1r (R smog ) and a known a1ue f °r the activity coefficient for smo g formation of the ROC mixture as previously emitted into the air and sampled at time t ( a^). Now the value of a^ can be separately determined by introducing a known amount of the ROC mixture into the system as described for calibration or, alternatively , a value can be assumed. For the range of compositions of ROC mixtures commonly emitte d into urban air the value of a RQC is approximately constant over the range of R O C compositions. Hence it is satisfactory to use a general value o f - R o O c C. The general value is not determined for the particular RO C mixture present in air at the time of samplin g . SUBSTITUTE SHeET For the air being monitored in the present application a value of +• a Rnr of 0.0067 moles smog/moles of ROC carbon/unit illumination/unit f(T) was chosen as applicable. The concentration of reactive organic compounds in air at time t (χ R0C ) is given by equation (105) '^R*OC - ~ R l smog/a d R* (105) 0C The concentration of ROC in air thus determined for each time of air sampling according to equation (105) are given in row 19 of Table 3 in units of carbon atoms of ROC/million molecules of air, (ppmC). To a good approximation the activity coefficient for smog formation in air (a R0 ~) is independent of the amount of illumination to which the ROC/air mixture has been exposed. Thus to a good approximation the concentration of ROC carbon measured by the system according to equation (105) is equivalent to the total amount of ROC carbon previously introduced into the air thus, where °X Rnr denotes the total concentration of ROC carbon previously introduced into the air. Table 3 lists in row 20 the value of °X RO thus determined by equation (106) for each time of air sampling. The reactive organic compounds to nitrogen oxides emission ratio ( X nQ c*-/ X ) of smog precursor emissions is a characteristic of air commonly used in air quality evaluations and in the assessment of the smog forming characteristics of air. The value of °X OC // ° X NO x is determined by operation of system 100. For fresh emissions and as indicated by equation (10) and also given relation (106) then: , t _ t /0 t (108) λ R0C λ N0 ~ λ R0C *N0 y The values of ° or* / ° x NO determined according to x equation (108) for each time of air sampling of the example are given in Table 3, row 21. System 100 can be used to determine the nitric oxide and ozone concentrations in air by an alternative procedure to that yielding the results of Table 3, rows 12 and 13. The temperature and illumination intensity of air is measured by sensors 123 and 124 respectively and the value of k 3 , the rate coefficient for N0 ? photolysis in the air determined from the readings. The values of k 3 determined for this example are listed in Table 2. The nitric oxide and ozone concentrations X , X n ) of air determined according to equations (68), 3 (69) or (73) and (74) depending on the domain of χ as given 3 smog - by expression (70). Now (70) can be evaluated because, following equation (11): and substituting equation (109) into (78) the specified domain of V Λ smog is- (110 ) The values defining the range of X ςmnα and the applicability of equations (68) and (69) are calculated on the basis of the determined values of χ N0 and expression (127) and are listed in Table 3, y rows 22 and 23 wherein H and L have been assigned the value 1/2. The truth or falsity of expression (110) is determined by inspection from the data of Table 3, rows 22 and 23 and the results are tabulated in Table 3, t t row 24. When test (110) has value false χ NQ and xi are 3 calculated according to equations (68) and (69) otherwise equations (73) and (74) are employed. The concentrations so determined for each time of sampling air are given in Table 3, rows 25 and 26. The value of k . employed in this calculation was taken from the literature, kψ = 2.66xl0 3 e- 1370/τt ppm-1 min- 1 The time period required for production of selected amount of smog SUBSTITUTE SHEET ( se ec xsmog) in air of composition as determined at time t can be determined by application of system 100 and calculation of time period according to equations (82) and (83). Two applications of this method are of special interest, namely determination of the time period of prior smog formation in air and time period required for smog formation in air to reach maximum extent under selected conditions of temperature and i1lumination. The time period required for maximum smog formation for air of composition as determined for each time of sampling and for temperature and illumination conditions for the day as measured and tabulated in Table 2 is determined as follows. The amount of extra smog required to be p ^roduced to reach max χs m mo Λ g„ is determined from the measurements according to equation (79). The time period (t„ - t,) where t, is the time of sampling and t2 is the time of onset of max χ f s. m m Λ o Λ g is determined for the conditions according to equation (80). The integral can be evaluated for the data according to the trap ■^ ez-ooiiddaall rruullee aanndd wwhheerree RI is the value of R„sm m og determined for air at time of sampling, t, . t=t t t The value of the integral -^-- ==cjawn - f (τ ^-d where + -4700(1/Tt-1/316) f(T ) = e and where td.aw,„n = 0622hr was evaluated for each time of air sampling and the values obtained are tabulated in Table 2. Now from eq^uations (79) and (80) max χ*smo„g is attained at time t for air sampled at time t when J Thus the time at which the maximum smog formation would be reached under the selected conditions of temperature and sunlight intensity observed during the day at the sampling site and in the absence of further NO emissions into the air after the time of air sampling is determined for each sampling time by evaluation of the left hand side of equation (112) and by determining the time corresponding to this value by interpolation of the values of t=t . . J" ltf(τt).dt listed in Table 2 t=0622 SUBSTITUTE SHSE1 The values obtained for the left hand side of expression (112) are given in Table 3, row 27 and the corresponding time of day when maximum smog formation v/as attained determined by interpolation of data listed in Table 2 for each time of sampling are given in Table 3, row 28 and where the value > 18 indicates that the potential maximum formation of smog is not reached before sunset (i.e. t=18) on that day. The time period (t,-t ) during which smog formation in air has occurred may be determined according to equation (81), given that when the conditions i s true the period determined is a minimum period. Knowledge of the time period and the time of measurement (t,) enables the apparent time of emission of ROC (ie an average time of the ROC emissions weighted with respect to the ROC emission strengths and sunlight intensities) into the air (t ) to be determined by equation (113), the time corresponding to the beginning of the smog forming period. It is convenient to calculate the value of .dt throughout the day, as given in Table 2. From equations (81) and (113) equation (114) is obtained. t=to t=t S I t f(T t )dt = (J I t f(T t ) . dt) - X* R 1 (114) t=dawn t=dawn smog The times (t ) corresponding to the values determined by equation (114) for t=to S I t f(T t ).dt t=dawn may be obtained by interpolation from Table 2. The values thus determined by application of equation (114) for t=to J * I t f(T t ).dt t=dawn and the corresponding values for t , the apparent time of ROC emissions, for air at each time of sampling are given in Table 3 rows 29 and 30 and where the value t of <06 indicates that the ROC entered the air previous to the day of measurement. For air that was sampled ^ nu Tl^ during the period 11.29 to 12.30 hrs and at 14.04 hrs the data is consistent with significant quantities of ROC having been emitted into the air at about dawn otherwise the results indicate that the smog forming activity of the air sampled during the day is attributable to ROC emitted to the air on days previous to the day of measurement. The general case for determination of time period for production of selected amount of smog in air is here illustrated by way of example for one air analysis. For air of the same characteristics as the sample the smog, ozone and nitric oxide concentrations to be expected throughout the selected time period, namely from dawn to dusk on the day of sampling are determined. The air sample for this example is arbitrarily chosen as air sampled at 1145 hrs. The procedure described is applicable to air sampled at other times. Smog concentrations to be expected at selected times are determined from the data obtained by operation of system 100 using equation (81). For this example the nitrogen oxides determined as present in the air at time of sampling are assumed to have been present throughout the previous daylight hours. The ROC is taken to be emitted into the air at a single time corresponding to the determined mean time of. ROC emission (t ), i.e. 08.30 hr on- the day of sampling. t=t The value of X I f(T t ).dt, where t=0 is the time of ROC emission as previously determined for the 1145 sample (i.e. t=0 corresponding to 0830 hrs), is calculated from the data listed in Table 2 for selected times. The values obtained are given in Table 4. The value for all values of t is as determined for the sample y air at 1145, i .e o„t NΩ = 4 ^ P* 3111 * See T a - *)' ' e - ' The value for R„ prior to the determined time of R emiss ,t smog r OC .ion is: Rs m mo Λ „g (t<[t=o]_),= 0.0 while for all times t≥[t=o], Rsmog = 8.5 x 10 as determined for the 1145 sample and as listed in Table 3. The air temperature at selected times is given in Table 2. The predicted concentrations of smog f (f t - ormed s m m„og) calculated using the sunlight data of Table 4 by equation (81) for each selected time and the results are listed in Table 4. The initial value for the nitric oxide concentration is determined from the value for °X M0 by SUBSTITUTE SHEET appl i cati on of equati on ( 109) and hence (°oF t N Mn O havi ng the val ue 0.9) ° X NΩ° ^ aS ^ e v l ue °^ O * 1 *** PP m * χ smog i s tested by i neq - i ual i ty ( 110) The value, true (T) or false (F), thus determined for each time are given in Table 4. When condition (110) has value false the nitric oxide concentrations to be expected at those selected times (X N0 ) are calculated according to equation (68) when the value is true χ N0 is obtained by application of equation (73). Similarly ozone concentrations are determined by equation (69) when the value is false and by (74) when the value is true. The predicted concentrations of nitric oxide and ozone thus determined for selected times and for conditions of no dispersion or dilution of the air are given in Table 4. The values for light intensity and air temperature used are given in Table 2. INDUSTRIAL APPLICABILITY The methods and systems of the invention have the following industrial applicabilities: (a) Total smog concentration of air can be determined by measurement of a single species, NO, instead of needing to determine N0 χ , NO, 0 3 , ROC's etc. (b) Smog forming activity of the air can be directly measured instead of having to estimate it by determination of ROC's, their composition and foncentrations and as well separately modelling the detailed chemistry of the smog-forming process which requires carrying out of complex and approximate chemical kinetic calculations. (c) Prospects for smog formation can be assessed in real time. (d) Ozone and nitrogen oxides concentrations can be determined via the one detector (an NO detector). (e) The duration of prior smog formation can be determined in a straightforward manner. Prior art gives no satisfactory means of determining duration of prior smog formation. (f) Prospective course of smog formation can be quantitatively predicted from measurement of a single air sample. Prior art offers no alternative means for making such predictions from a single instrumental analysis. (g) A sensitive means for determining the amount of prior ROC and nitrogen oxides emissions into the air, independently of the reaction or length of the period of residence in the air is made available. Determination of ROC by alternative means gives results which are biased low due to transformation by reaction of the ROC emissions into chemical forms which are not easily detected by existing ROC analysis methods. (h) A measure of smog formation is made available which varies in proportion to the total amount of smog formation (unlike prior types of measurements which determine the concentration of a single species, e.g. NO or O , the concentrations of which vary nonlinearly with total smog formation) . (i) Smog formation can be characterised by only three measured parameters, namely NO concentration, smog concentration and rate coefficient for smog formation, instead of having to specify the behaviour of numerous chemical species. (j) The location of the sources of ROC emissions can be estimated from the duration of smog formation in air and knowledge of the trajectory and speed of the air during smog formation. (k) The most effective option for controlling formation of excessive ozone concentrations in air can be determined from the value of extent of smog formation in air. When the extent approaches the value 1 then minimization of nitrogen oxides is the indicated strategy. When extent is less than 1 then control of ROC emissions is the indicated strategy. (1) The concentrations of nitrogen oxides converted to nitric acid or lost from the gas phase can be determined. This is of particular practical importance as it is a measure of the quantity of nitrogen available for acidic or nitrate deposition from the air. SUBSTITUTE SHEET TABLE 1 Data measured for calibration of Reactor 107 Line of best fit: (CI J 0 CIIχ 0 > = °' 0139 te " °- 0852t + 0.0029 SUBSTITUTE ;HE£ι TABLE 2 Measured temperature and sunlight intensities of the atmosphere for selected period including the period of operation of System 100 in Fig. 12 SUBSTITUTE SHEET TABLE 2 (Cont. ) Measured temperature and sunlight intensities of the atmosphere for selected period including the period of operation of System 100 in Fig. 12 j SUBSTITUTE SK .i£-E. i TABLE 3 Example of Smog Monitoring Data obtained b operation of System 100 depicted in Fig. 12 t Time of air 0958 1013 1029 1044 1059 1113 Sampling (hr. in) A1 χjj 0 <ppm ) 0.001 0.006 0.005 0.004 0.004 0.011 AII χ|j 0 (ppm> 0.016 0.028 0.027 0.031 0.038 0.086 BI N 0 ( P m) 0.260 0.291 0.284 0.266 0.249 0.241 0.331 0.343 0.342 0.346 0.353 0.401 BII XN0 ( PP m) CI xJjo ( PP m) 0.293 0.292 0.285 0.269 0.254 0.243 CII xJjθ ( PP m 0.292 0.290 0.285 0.272 0.251 0.241 T,I Q t xlO 4 0.9 1.7 0.0 (-2.6) 2.6 1.7 v smog (ppm/min) R 4.4 8. ' 8 0.0 (-13) 13 8.8 sm Λ oπg xl ° 4 χ* _ (ppm) 0.07 0.05 0.06 0.08 0.10 0.16 smog 0.02 0.03 0.03 0.03 0.04 0.09 *N0y (ppιη) X N0 (ppm ) 0.00 0.01 0.00 0.00 0.00 0.01 xj (ppm) 0.06 0.03 0.04 0.05 0.07 0.08 3 0.68 0.27 0.32 0.40 0.42 0.25 °x£o, < P" 0.03 0.03 0.03 0.04 0.05 0.11 fmax t x smog (ppm) 0.10 0.14 0.14 0.17 0.21 0.43 0.08 0.06 0.06 0.09 0.11 0.17 0.75 0.40 0.44 0.52 0.54 0.44 0.07 0.13 0.00 -0.20 0.20 0.13 °χ 0C (ppmC) 0.07 0.13 0.00 -0.20 0.20 0.13 SUBSTITUTE S.HEE * TABLE 3 (Cont.) Row t 1 Time of air 0958 1013 1029 1044 1059 1113 Sampling (hr,min) 2.5 3.7 0.0 3.8 1.2 0.010 0.014 0.014 0.017 0.005 0.010 0.036 0.049 0.049 0.059 0.073 0.149 F F F F F F 0.00 0.00 0.00 0.00 0.00 0.00 (ppm) 0.05 0.02 0.03 0.05 0.07 0.07 27 t=tmax S I t f(T t ).dt t=dawn 69 107 89 311 28 max^t 16 >18 >18 >18 smog (hr) 29 t=to S I t f(T t ).dt t=dawn -168 -52 -69 -176 30 t o (hr) <06 <06 <06 <06 SUB5TSTUTE SH ΞT TABLE 3 (Continued) Example of Smog Monitoring Data obtained by operation of System 100 depicted in Fig. 12 t Time of air 1129 1145 1200 1231 1302 1333 Sampling (hr.min) TABLE 3 (Cont.) t Time of air 1129 1145 1200 1231 1302 1333 Sampling (hr.min) 5.6 6.6 3.9 4.2 2.9 3.5 0.060 0.071 0.074 0.062 0.046 0.030 0.211 0.249 0.259 0.218 0.159 0.105 T T T F F F 0.02 0.02 0.02 0.00 0.00 0.00 SUBSTITUTE SHEET TABLE 3 (Continued) Example of Smog Monitoring Data obtained by operation of System 100 depicted in Fig. 12 t Time of air 1404 1451 1522 1553 1624 1654 Sampling (hr,min) -0.001 -0.001 -0.003 -0.003 -0.002 -0.002 0.024 0.017 0.006 0.007 0.005 0.006 0.173 0.190 0.185 0.191 0.208 0.206 0.339 0.332 0.308 0.315 0.317 0.316 0.169 0.191 0.203 0.190 0.205 0.206 0.161 0.186 0.202 0.188 0.202 0.205 6.9 4.3 0.9 1.7 2.6 0.9 0.98 1.06 1.64 1.50 1.60 1.56 0.05 0.04 0.04 0.04 0.03 0.04 10.9 8.4 1.5 3.5 6.0 1.8 SUBSTITUTE SH£E7 TABLE 3 (Cont.) t Time of air 1404 1451 1522 1553 1624 1654 Sampling (hr . in) ,o χ t NO . "1/2 y > 0.019 0.016 0.017 0.148 0.013 0.014 ,o t ( ι iiNV; 0.067 0.055 0.060 0.052 0.046 0.050 NOy' 0.00 0.00 0.00 0.00 0.00 0.00 (ppm) 0.15 0.12 0.14 0.12 0.10 0.11 t=tmax X I t f(T t ).dt t=dawn 46 44 44 57 66 59 max t* ) 14 14 14 15 16 15 smog Chr t-to X I t f(T t ).dt t=dawn -8 ≤-26 ≤-347 ≤-112 <-36 ≤-268 t Q (hr) 08 <06 <06 <06 <06 <06 I SUBSTITUTE S EWT • TABLE 4 Concentration-Time Profiles predicted for air with characteristics as air sampled at 11.45 hrs and conditions of temperature and illumination as determined at the sampling site on that day. SUBSTITUTE SHEET TABLE 4 (Contd. ) Concentration-Time Profiles predicted for air with characteristics as air sampled at 11.45 hrs and conditions of temperature and i11umination as determined at the sampling site on that day. SUBSTITUTE SHEET |

Claims: -113- Claims 1. A method for determining rate coefficient of smog formation in air, the method comprising: ( a ) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; ( b ) permitting the mixture to react for a first selected per i od wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; . ( c ) determining a first nitric oxide concentration of the m i xture after the first selected period; ( d ) illuminating the mixture of (a) or the mixture after the f i rst selected period for a second selected period under reference temperature and illumination conditions; ( e ) permitting the mixture, after illumination, to react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; ^ ( f ) determining a second nitric oxide concentration of the m i xture after the third selected period; and ( g ) determining the rate coefficient of smog formation from the first and second nitric oxide concentrations, the reference temperature and Illumination conditions and the duration of the second selected period. 2. A method for determining rate coefficient of smog formation in air, the method comprising: . ( a ) adding excess ozone to the air to provide an excess ozone/a i r mixture; , . , . . ( b ) permitting the mixture to react for a first selected per i od wherein excess ozone in the mixture reacts with substantially all n i tr i c oxide in the mixture; ( c> determining a first ozone concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the f i rst selected period for a second selected period under reference temperature and illumination conditions; ( e ) permitting the mixture, after illumination, to react for a third selected period wherein excess ozone in the mixture reacts with any SUBSTITUTE SHEET nitric oxide present in the mixture; (f) determining a second ozone concentration of the mixture after the third selected period; and (g) determining the rate coefficient from the first and second ozone concentrations, the reference temperature and illumination conditions and the duration of the second selected period. 3. A method for determining rate coefficient of smog formation in air according to claim 2, further comprising the step of: (a)(1) adding a quantity of nitrogen oxides to the mixture prior to step (b). 4. A method for determining rate of smog formation in air under selected temperature and illumination conditions, which method comprises: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (b) permitting the mixture to react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) determining a first nitric oxide concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under selected temperature and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; (f) determining a second nitric oxide concentration of the mixture after the third selected period; and (g) determining the rate from the first and second nitric oxide concentrations and the duration of the second selected period. 5. A method for determining rate of smog formation in air under selected temperature and illumination conditions, which method comprises: (a) adding excess ozone to the air to provide an excess ozone/air mixture; (b) permitting the mixture to react for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric -1 15- oxide in the mixture; , ( c ) determining a first ozone concentration of the m i xture after the first selected period; ( d> illuminating the mixture of (a) or the mixture after the f i rst selected period for a second selected period under selected temperature and illumination conditions; ( e ) permitting the mixture, after illumination, to react for a th i rd selected period wherein excess ozone in the mixture reacts with any n i tnc oxide present in the mixture; <f> determining second ozone concentration of the m i xture after the third selected period; and g) determining the rate from the first and second ozone concentrations and the duration of the second selected per i od. . A method for determining rate of s^g formation in air under selected 6. temperature and illumination conditions according to claim 5, further including the step of: . ( a )( 1 ) adding a quantity of nitrogen oxides to the m i xture pr i or to step ( b ) . 7 A method for determining time required for maximum smog formation in air under selected conditions of illumination and temperature, the method ""^ ( ^determining rate coefficient of smog formation In the air by the method of claim 1, 2 or 3; _ ( B ) determining maximum potential smog format i on i n the a i r by. ( B )( 1 ) determining the amount of prior smog formation in the a i r by: ( I ) determining NO concentration in the a i r; ( 1X1 ) determining the concentration of smog in the air by: ( IIX1 ) adding excess nitric oxide to the air to prov i de an excess nitric oxide/air mixture; ( 11X11 ) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; ( 11X111 ) determining the nitric oxide concentration of the mixture after the selected period; ( ID ( iv ) determining the total oxidized nitrogen ( N0 y ) concentration of the mixture after the selected period; and SUBSTITUTE SHEET (II)(v) determining the concentration of smog formation from the nitric oxide concentration of ( 11X111 ) and the NO concentration of (ID ( iv ) . (1X11) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (IXiii) determining the amount of prior smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air as determined in step ( I )( 11 ) and the concentration of smog in the air as determined in ( IXi ) ; (BXii) determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; (BXiii) determining the maximum potential smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air; and (C) determining the time required for maximum smog formation, under selected temperature and illumination conditions, from the maximum potential smog formation and the rate coefficient. 8. A method for determining time required for maximum smog formation in air under selected conditions of illumination and temperature, the method comprising: (A) determining rate of smog formation in the air under the selected conditions by the method of claim 4, 5 or 6; (B) determining maximum potential smog formation in the air by: (BXi) determining the amount of prior smog formation in the air by: (I) determining NO concentration in the air; (IXi) determining the concentration of smog in the air by: (H)(1) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (II)(ii) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; (11X111) determining the nitric oxide concentration of the mixture after the selected period; (ID(iv) determining the total oxidized nitrogen ( NO ) concentration of the mixture after the selected period; and SUBSTITUTE SHEET I -117- <II )( v ) determining the concentration of smog formation from the nitric oxide concentration of .IIX111> and the from ^ concentration of total nitrogen oxides previously em i tted i nto the a1r; "c, determining the time required for maximum smog formation, under selected temperature and illumination conditions, from the max i mum potential smog formation and the rate. the method of claim 1, 2 or 3; ( D> determining the amount of prior smo, format i on i n the a,r at end of the time period by: ( I ) determining NO concentration in the a i r, ( II ) determining the concentration of smog in the a i r by: ( H )( 1 ) adding excess nitric oxide to the air to prov i de an excess nitric oxide/air mixture; ( ID ( ii ) reacting the mixture for a selected per i od wherein the excess nitric oxide reacts with substantially all ozone in the mixture; SUBSTITUTE SHEET (ID(iii) determining the nitric oxide concentration of the mixture after the selected period; (ID(iv) determining the total oxidized nitrogen (NO ) concentration of the mixture after the selected period; and (II)(v) determining the concentration of smog formation from the nitric oxide concentration of (ID(iii) and the NO concentration of (ID(iv). (III) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (IV) determining the amount of prior smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (III) and the concentration of smog in the air as determined in (II); and (E) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation, the rate coefficient, and the determined temperatures and sunlight intensities. 10. A method for determining time period during which smog formation in air has occurred, the time period being substantially the same as or within a predetermined period for which the illumination and temperature conditions are known, wherein the end of the predetermined period coincides with the end of the time period, the method comprising: (A) determining temperatures of the air for the predetermined period; (B) determining sunlight intensities for the predetermined period; (C) determining rate of smog formation in the air under temperatures and light intensities corresponding to the determined temperatures and sunlight intensities by the method of claim 4, 5 or 6; (D) determining the amount of prior smog formation in the air at the end of the time period by: (I) determining NO concentration in the air; (II) determining the concentration of smog in the air by: (II)(i) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (ID(ii) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; (ID(iii) determining the nitric oxide concentration of Γ SUBSTITUTE SHEET the mixture after the selected period; (ID(iv) determining the total oxidized nitrogen (NO ) concentration of the mixture after the selected period; and (IIXv) determining the concentration of smog formation from the nitric oxide concentration of (ID(iii) and the NO concentration of (ID(iv). (III) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (IV) determining the amount of prior smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (III) and the concentration of smog in the air as determined in (II); and (E) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation and the rate of smog formation. 11. A method of locating a source of Reactive Organic Compounds (ROC) present in air, the method comprising: (α) determining a time period during which smog formation in the air has occurred, the time period being substantially the same as or within a predetermined period for which the illumination and temperature conditions are known, wherein the end of the predetermined period coincides with the end of the time period by: (A) determining temperatures of the air for the predetermined period; (B) determining sunlight intensities for the predetermined period; (C) determining the rate coefficient of smog formation in the air by the method of claim 1 , 2 or 3; (D) determining the amount of prior smog formation in the air at the end of the time period by: (I) determining NO concentration in the air; (II) determining the concentration of smog in the air by: (IlXi) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (ID(ii) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; (ID(iii) determining the nitric oxide concentration of SUBSTITUTE SHEET the mixture after the selected period; (ID(iv) determining the total oxidized nitrogen ( NO ) concentration of the mixture after the selected period; and (IIXv) determining the concentration of smog formation from the nitric oxide concentration of ( ID ( iii ) and the NO concentration of (II)(iv). (III) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and the concentration of smog in the air; and (IV) determining the amount of prior smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air as determined in step ( III ) and the concentration of smog in the air as determined in ( II ) ; and (E) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation, the rate coefficient, and the determined temperatures and sunlight intensities; and (β) determining speed of movement and trajectory in the air during the time period; and (γ) locating said source of ROC from said time period and said speed and trajectory in the air over said time period. 12. A method of locating a source of Reactive Organic Compounds ( ROC ) present in air, the method comprising: (α) determining a time period during which smog formation in the air has occurred, the time period being substantially the same as or within a predetermined period for which the illumination and temperature conditions are known, wherein the end of the predetermined period coincides with the end of the time period by: (A) determining temperatures of the air for the predetermined period; (B) determining sunlight intensities for the predetermined period; (C) determining rate of smog formation in the air under temperatures and light intensities corresponding to the determined temperatures and sunlight intensities by the method of claim 4, 5 or 6; (D) determining the amount of prior smog formation in the air at the end of the time period by: (I) determining NO concentration in the air; (II) determining the concentration of smog in the air by: (IlXi) adding excess nitric oxide to the air to provide SUBSTITUTE SHEET an excess nitric oxide/air mixture; (11X11) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; (11X111) determining the nitric oxide concentration of the mixture after the selected period; (ID(iv) determining the total oxidized nitrogen ( NO ) concentration of the mixture after the selected period; and (IIXv) determining the concentration of smog formation from the nitric oxide concentration of ( 11X111 ) and the NO concentration of (ID(iv ) . (III) determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; and (IV) determining the amount of prior smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air as determined in step ( III ) and the concentration of smog in the air as determined in ( II ) ; and ( E) determining the time period during which the smog formation in the air has occurred from the amount of prior smog formation and the rate of smog formation; (β ) determining speed of movement and trajectory in the air during the time period; and (γ) locating said source of ROC from said time period and said speed and trajectory in the air over said time period. 13. A method for determining time required for production of a selected amount of smog in air under selected temperature and illumination conditions and with selected initial amount of smog in the air, the method comprising: (A) determining rate coefficient of smog formation in the air according to the method of claim 1, 2 or 3; (B) determining NO concentration in the air; ( C) determining the amount of N0 y previously emitted into the air from the NO concentration of (B) and the selected initial amount of smog in the air; ( D ) determining the time required for production of selected amount of smog in the air for the selected conditions of temperature and SUBSTITUTE SHEET i11umination from the rate coefficient and the amount of NO . 14. A method for determining time required for production of a selected amount of smog in air under selected temperature and illumination conditions and with selected initial amount of smog in the air, the method comprising: (A) determining rate of smog formation in the air under the selected temperature and illumination conditions according to the method of claim 4, 5 or 6; (B) determining NO concentration in the air; (C) determining the amount of NO previously emitted into the air from the NO concentration of (B) and the selected initial amount of smog in the air; (D) determining the time required for production of the selected amount of smog in the air for the selected conditions of temperature and illumination from the rate and the amount of NO previously emitted into the air. 15. A method for determining concentration of smog in air, which method comprises: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (b) reacting the mixture for a selected period wherein the excess nitric oxide reacts with substantially all ozone in the mixture; (c) determining the nitric oxide concentration of the mixture after the selected period; (d) determining the total oxidized nitrogen (NO ) concentration of the mixture after the selected period; and (e) determining the concentration of smog in the air from the nitric oxide concentration of (c) and the NO concentration of (d). 16. A method for determining the amount of prior smog formation in air, which method comprises: (A) determining NO concentration in the air; (B) determining the concentration of smog in the air by the method according to claim 15; (C) determining the concentration of total nitrogen oxides previously emitted into the air from the NO concentration in the air and SUBSTITUTE SHEET -123- the concentration of smog in the air; and ( D ) determining the amount of prior smog formation in air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (C) and the concentration of smog in the air as determined in ( B ) . 17. A method for determining maximum potential smog formation in air, which method comprises: ( α ) determining the amount of prior smog formation in air by: ( A ) determining NO concentration in the air; ( B ) determining the concentration of smog in the air by the method according to claim 15; ( C ) determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; and ( D ) determining the amount of prior smog formation in air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (C) and the concentration of smog in the air as determined in ( B ) ; (β) determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; and ( γ ) determining the maximum potential smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air. 18. A method for determining the current extent of smog formation in air, which method comprises the steps of: ( I ) determining maximum potential smog formation in the air by: ( α ) determining the amount of prior smog formation in air by: ( A ) determining NO concentration in the air; ( B ) determining the concentration of smog in the air by the method according to claim 15; ( C ) determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; and ( D ) determining the amount of prior smog formation in air from the concentration of total nitrogen oxides previously emitted into the SUBSTITUTE SHEET -124- air as determined in step (C) and the concentration of smog in the air as determined in ( B ) ; (β) determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; and ( γ ) determining the maximum potential smog formation in the air from the concentration of total nitrogen oxides previously emitted into the air * ( II ) determining the amount of prior smog formation in the air by: ( AA) determining NO concentration in the air; ( BB ) determining the concentration of smog in the air by the method according to claim 15; ( CO determining the concentration of total nitrogen oxides previously emitted into the air from the N0 y concentration in the air and the concentration of smog in the air; and ( DD ) determining the amount of prior smog formation in air from the concentration of total nitrogen oxides previously emitted into the air as determined in step (CO and the concentration of smog in the air as determined in (BB ) ; and ( III ) calculating the current extent of smog formation in the air as the ratio of the amount of prior smog formation in the air to the maximum potential concentration of smog in the air. 19. A method for determining ozone concentration in air, which method comprises: ( A ) determining nitric oxide concentration in the air; ( B) determining NO concentration in the air; ( O determining concentration of smog in the air according to the method of claim 15; and ( D ) calculating the ozone concentration in the air from the measured nitric oxide concentration, N0 y concentration in the air and the concentration of smog in the air. 20. A method for determining nitric oxide and/or ozone concentrations in air, which method comprises: ( A ) determining the sunlight intensity in the air; (B) determining the temperature of the air; ( C ) determining the NO concentration in the air; SUBSTITUTE SHEET -125- ( D ) determining the smog concentration in the air according to the method of claim 15; and ( E ) determining the concentrations of nitric oxide and/or ozone in the air from the N0 y and smog concentrations, the sunlight intensity and the temperature. 21. A method for determining ROC concentration in air, which method comprises: ( a ) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; ( b ) permitting the mixture to react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; ( c ) determining a first nitric oxide concentration of the mixture after the first selected period; ( d ) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under reference temperature and illumination conditions; ( e ) permitting the mixture, after illumination, to. react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; ( f ) determining a second nitric oxide concentration of the mixture after the third selected period; and ( g ) determining the ROC concentration in the air from the first and second nitric oxide concentrations, the duration of the second selected period and the reference temperature and illumination conditions. 22. A method for determining ROC concentration in air, which method comprises: ( a ) adding excess ozone to the air to provide an excess ozone/air mixture and optionally adding a quantity of nitrogen oxides to the mixture; ( b ) permitting the mixture to react for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; ( c ) determining a first ozone concentration of the mixture after the first selected period; ( d ) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under reference temperature SUBSTITUTE SHEET and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess ozone in the mixture reacts with any nitric oxide present in the mixture; (f) determining a second ozone concentration of the mixture after the third selected period; and (g) determining the ROC concentration in the air from the first and second ozone concentrations, the reference temperature and illumination conditions and the duration of the second selected period. 23. A method for determining total concentration of prior ROC emissions into air, which method comprises: (a) adding excess nitric oxide to the air to provide an excess nitric oxide/air mixture; (b) permitting the mixture to react for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) determining a first nitric oxide concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under reference temperature and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess nitric oxide in the mixture reacts with any ozone present in the mixture; (f) determining a second nitric oxide concentration of the mixture after the third selected period; and (g) determining the total concentration of prior ROC emissions into the air from the first and second nitric oxide concentrations and the reference temperature and illumination conditions. 24. A method for determining total concentration of prior ROC emissions into air, which method comprises: (a) adding excess ozone to the air to provide an excess ozone/air mixture and optionally adding a quantity of nitrogen oxides to the mixture; (b) permitting the mixture to react for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; SUBSTITUTE SHEET (c) determining a first ozone concentration of the mixture after the first selected period; (d) illuminating the mixture of (a) or the mixture after the first selected period for a second selected period under reference temperature and illumination conditions; (e) permitting the mixture, after illumination, to react for a third selected period wherein excess ozone in the mixture reacts with any nitric oxide present in the mixture; (f) determining a second ozone concentration of the mixture after the third selected period; and (g) determining the total concentration of prior ROC emissions into the air from the first and second ozone concentrations, the reference temperature and illumination conditions and the duration of the second selected period. 25. A system for determining rate coefficient of smog formation in air, which system comprises: (a) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a) in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under reference temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (f) a nitric oxide analyser operatively associated with the first reactor, to determine a first nitric oxide concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second nitric oxide concentration of the mixture after the third selected period; SUBSTITUTE SHEET -128- <„ a tem p erature sensor operatively associate d w i t h th e ph otoreactor to d etermine the temperature o f t h e m i xture ; P an i l lumination sensor operatively assoc i ate w,t t Halat i on source to determine the amount of i ll um i nat i on o f t h e Illuminated m i xture; and assoc i ated w i t h t h e temperature secon d selected period. 26 . A system f or d etermining ra * te„ c r o rn e f fψfi' r cϊieen-τ t oo f r ssmmo o g g formation in a i r , oxιde ;:, th : s^ op.™* * .* «.«.«.- «« ■ «. — » < : lne a second ozone concentration of the mi xture after the th i rd Se, eCt ;;> P erature sensor operatively associated with the photoreactor to determine the temperature of the **»" ■ (h) an i llumination sensor operatively assoc i ate w i th t illumi nation source to determine the amount of i ll um i nat i on of the ' SUBSTITUTE SHEE illuminated mixture; and (i) calculating means operatively associated with the temperature and illumination sensors and the ozone analyser to calculate the rate coefficient from the first and second ozone concentrations, the reference temperature and illumination conditions and the duration of the second selected period. 27. A system for determining rate coefficient of smog formation in air according to claim 26, further comprising a second combiner operatively associated with the first combiner for combining a quantity of nitrogen oxides with the air. 28. A system for determining rate of smog formation in air under selected temperature and illumination conditions, which system comprises: (a) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a), in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under selected temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can in the second reactor react for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (f) a nitric oxide analyser operatively associated with the first reactor to determine a first nitric oxide concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second nitric oxide concentration of the mixture after the third selected period; and (g) calculating means operatively associated with the nitric oxide analyser to calculate the rate from the first and second nitric oxide concentrations and the duration of the second selected period. SUBSTITUTE SHEET 29. A system for determining rate of smog formation in air under selected temperature and illumination conditions, which system comprises: (a) a first combiner for combining excess ozone is combined with the air to provide an excess ozone/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the reactor for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mi ture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a), in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under selected temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (f) an ozone analyser operatively associated with the first reactor to determine a first ozone concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second ozone concentration of the mixture after the third selected period; and (g) calculating means operatively associated with the ozone analyser to calculate the rate from the first and second ozone concentrations and the duration of the second selected period. 30. A system for determining ROC concentration in air, which system comprises: (a) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; SUBSTITUTE SHEET ( d ) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a), in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under reference temperature and illumination conditions; ( e ) a second reactor operatively associated with the photoreactor wherein the mixture can in the second reactor react for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; ( f ) a nitric oxide analyser operatively associated with the first reactor to determine a first nitric oxide concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second nitric oxide concentration of the mixture after the third selected period; and ( g ) calculating means operatively associated with the nitric oxide analyser to calculate the ROC concentration in the air from the first and second nitric oxide concentrations, the second selected period and the reference temperature and illumination conditions. 31. A system for determining ROC concentration in air, the system • comprising: ( a ) a combiner for combining excess ozone with the air to provide an excess ozone/air mixture; ( b ) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; ( c ) a photoreactor operatively associated with the combiner and optionally the first reactor; ( d ) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a) in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under reference temperature and illumination conditions; ( e ) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; ( f ) an ozone analyser operatively associated with the first reactor to determine a first ozone concentration of the SUBSTITUTE SHEET -132- ixture after the first selected period and operatively associated with the second reactor to determine a second ozone concentration of the mixture after the third selected period; ( g) a temperature sensor operatively associated with the photoreactor to determine the temperature of the mixture; (h) an illumination sensor operatively associated with the illumination source to determine the amount of illumination of the illuminated mixture; and (i) calculating means operatively associated with the temperature and illumination sensors and the ozone analyser to calculate the ROC concentration in the air from the first and second ozone concentrations, the reference temperature and illumination conditions and the duration of the second selected period. 32. A system for determining the total concentration of prior ROC emissions into air, which system comprises: ( a ) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; ( b ) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess nitric oxide ' in the mixture reacts with substantially all ozone in the mixture; ( c ) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate- the mixture of (a ) , in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under reference temperature and illumination conditions; ( e ) a second reactor operatively associated with the photoreactor wherein the mixture can in the second reactor react for a third selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; ( f ) a nitric oxide analyser operatively associated with the first reactor to determine a first nitric oxide concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second nitric oxide concentration of the mixture after the third selected period; and I SUBSTITUTE SHEET (g) calculating means operatively associated with the nitric oxide analyser to calculate the total concentration of prior ROC emissions into the air from the first and second nitric oxide concentrations, the second selected period and the reference temperature and illumination conditions. 33. A system for determining the total concentration of prior ROC emissions into air, the system comprising: (a) a first combiner for combining excess ozone with the air to provide an excess ozone/air mixture; (b) a first reactor operatively associated with the combiner wherein the mixture can react in the first reactor for a first selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (c) a photoreactor operatively associated with the combiner and optionally the first reactor; (d) an illumination source operatively disposed about the photoreactor to illuminate the mixture of (a) in the photoreactor, or the mixture after the first selected period, in the photoreactor for a second selected period under reference temperature and illumination conditions; (e) a second reactor operatively associated with the photoreactor wherein the mixture can react in the second reactor for a third selected period wherein excess ozone in the mixture reacts with substantially all nitric oxide in the mixture; (f) an ozone analyser operatively associated with the first reactor to determine a first ozone concentration of the mixture after the first selected period and operatively associated with the second reactor to determine a second ozone concentration of the mixture after the third selected period; (g) a temperature sensor operatively associated with the photoreactor to determine the temperature of the mixture; (h) an illumination sensor operatively associated with the illumination source to determine the amount of illumination of the illuminated mixture; and (i) calculating means operatively associated with the temperature and illumination sensors and the ozone analyser to calculate the total concentration of prior ROC emissions into the air from the first and second ozone concentrations, the reference temperature and illumination conditions and the duration of the second selected period. SUBSTITUTE SHEET -134- 34 A system according to claim 25, 26, 27, 28, 29, 30 or 32, wherein the first and second reactors and the photoreactor are the same reactor. 35. A system according to claim 25, 26, 27, 28, 29, 30 or 32, wherein the first reactor and the photoreactor are the same reactor. 36. A system according t _-.o c„ila,i. m m 25c, 2b-, iI , ^28e, 29, 3 J 0 U o U r I 32, wherein the second reactor and the photoreactor are the same reactor. 37 A system according to claim 25, 26, 27, 28, 29, 30 or 32, wherein the first reactor and photoreactor are two separate vessels through which the mixture can continuously flow in separate streams and the second reactor i s a separate vessel through which the mixture from the photoreactor can continuously flow. 38 A system according to claim 37, wherein the first reactor provides a first residence time for the mixture when continuously flowing therethrough and the photoreactor and the second reactor in combination provide a second residence time for the mixture when continuously flowing therethrough, the ' first and second residence times being substantially the same. 39 A system for determining rate of smog formation in air according to claim 29, further comprising a second combiner operatively associated w i th said first combiner in which second combiner a quantity of N0 χ is added to air. 40 A system for determining time required for maximum smog formation in air under selected conditions of illumination and temperature wherein the system includes: ( A ) a NO analyser to determine the N0 y concentration of the al r; ( B ) a system for determining rate coefficient of smog formation in air according to either claim 25, 26 or 27; ( C ) a system for determining the maximum potential smog formation i n the air, which system comprises; ( C )(i) a first NO analyser for determining the N0 y concentrat i on of the air; . ( C )( ϋ ) a combiner for combining excess nitric oxide with the a i r to provide an excess nitric oxide/air mixture; SUBSTITUTE SHEET -135- ( CX111 ) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone i n the ( C )( iv ) a nitric oxide analyser operatively assoc i ated w i th the reactor to determine the nitric oxide concentration of the mixture after the selected period; ( C )( v ) a second NO analyser operatively associated w i th the reactor to determine the N0 y concentration of the mixture; and ( C )( vi ) calculating means operatively associated and coupled w i th the nitric oxide analyser and the first and second N0 y analysers to calculate the maximum potential smog formation in the air from the N0 y concentration of the air and the NO and N0 y concentrations of the excess nitric oxide/air mixture; and ( D ) calculating means operatively associated with the analyser of ( A ) and the systems of <B> and (C) to calculate the maximum time for smog formation, under the selected temperature and illumination conditions from the NO concentration, the maximum potential smog format i on and the rate coefficient. 41 A system for determining time required for maximum smog formation in air under selected conditions of illumination and temperature wherein the system includes: ( A ) a NO analyser to determine the N0 y concentration of the air; ( B ) a system for determining rate of smog formation in air accord i ng to either claim 28, 29 or 39; . ( C ) a system for determining the maximum potential smog format i on i n the air, which system comprises; ( CXI ) a first N0 y analyser for determining the N0 y concentrat i on of the air; .^ ,, . , Λ ( C )( Ti ) a combiner for combining excess nitric oxide w i th the a i r to provide an excess nitric oxide/air mixture; ( CX11D reactor operatively associated with the combiner where i n the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone i n the mixture; ( CXiv ) a nitric oxide analyser operatively associated w i th the reactor to determine the nitric oxide concentration of the mixture after the selected period; SUBSTITUTE SHEE -136- ( C )( v ) a second NO analyser operatively associated with the reactor to determine the NO concentration of the mixture; and ( O ( vi ) calculating means operatively associated and coupled with the nitric oxide analyser and the first and second N0 y analysers to calculate the maximum potential smog formation in the air from the N0 y concentrat i on of the air and the NO and N0 y concentrations of the excess nitric oxide/air mixture; and ( D ) calculating means operatively associated with the analyser of ( A ) and the systems of (B) and (C) to calculate the maximum time for smog formation, under the selected temperature and illumination conditions from the NO concentration, the maximum potential smog formation and the rates. 42 A system for determining time required for maximum smog formation in air according to claim 40 or 41, wherein said N0 y analyser of ( A ) includes a N0 V converter to convert all the N0 y in the air to n i tr i c oxide and a nitric oxide analyser to determine the total nitric ox i de. 43. A system for determining time period during which smog formation in air has occurred, the time period being substantially the same as, or within a predetermined period for which the illumination and temperature conditions are known, wherein the end of the predetermined period coinc i des with the end of the time period, the system comprising: ( A ) a system for determining the rate coefficient of smog formation in the air according to either claim 25, 26 or 27; ( B ) a system for determining concentration of smog in " air, which system comprises: ( BXi ) a combiner for combining excess nitric oxide with the a i r to provide an excess nitric oxide/air mixture; ( BXii ) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; ( BXiii ) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; ( BXiv ) a NO analyser operatively associated with the reactor to determine the N0 y concentration of the mixture; and SUBSTITUTE SHEET (BXv) calculating means operatively associated with the nitric oxide analyser and the NO analyser to calculate the concentration of smog from the NO and nitric oxide concentrations; (C) an NO analyser for determining the NO concentration in the air; (D) a temperature sensor to determine the temperature of the air for the duration of the selected period; (E) a light sensor to determine the sunlight illumination during the selected period; and (F) calculating means operatively associated with the temperature sensor, the light sensor, the NO analyser and the systems for determining the rate coefficient of smog formation and smog concentration, to calculate the time period during which smog formation in air has occurred under the measured sunlight and temperature conditions. 44. A system for determining time period during which smog formation in air has occurred, the time period being substantially the same as, or within a predetermined period for which the illumination and temperature conditions are known, wherein the end of the predetermined period coincides with the end of the time period, the system comprising: (A) a system for determining the rate of smog formation in the air according to either claim 28, 29 or 39; (B) a system for determining concentration of smog in air, which system comprises: (BXi) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (BXii) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (BXiii) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; (BXiv) a NO analyser operatively associated with the reactor to determine the NO concentration of the mixture; and (BXv) calculating means operatively associated with the nitric oxide analyser and the NO analyser to calculate the concentration of smog from the NO and nitric oxide concentrations; SUBSTITUTE SHEET (C) an NO analyser for determining the NO concentration in the air; (D) a temperature sensor to determine the temperature of the air for the duration of the selected period; (E) a light sensor to determine the sunlight illumination during the selected period; and (F) calculating means operatively associated with the temperature sensor, the light sensor, the NO analyser and the systems for determining the rate of smog formation and smog concentration, to calculate the time period during which smog formation in air has occurred under the measured sunlight and temperature conditions. 45. A system for determining time period during which smog formation in air has occurred according to claim 43 or 44, wherein the NO analyser of (C) includes a NO converter to convert substantially all NO in the mixture to nitric oxide, the converter being operatively associated with a nitric oxide analyser. 46. A system for determining time period during which smog formation in air has occurred according to claim 43, 44 or 44 further comprising means of determining the speed and trajectory of the air during the selected period and calculating means to determine the location of emission sources of ROC present in air on the basis of the time period of smog formation, the air speed and trajectory. 47. A system for determining time required for production of a selected amount of smog in air under selected temperature and illumination conditions, the system comprising (A) a system of determining rate coefficient of smog formation in the air according to claim 25, 26 or 27; (B) a system for determining concentration of smog in air, which system comprises: (BXi ) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (BXii) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; SUBSTITUTE SHEET -139- ( B )( iii ) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; ( BXI. ) a NO analyser operatively associated w i th the reactor to determine the NO concentration of the mixture; and ( B )( v ) calculating means operatively associated w i th the n i tπc ox i de analyser and the N0 y analyser to calculate the concentration of smog from the NO and nitric oxide concentrations; ΪO an N0 y analyser for determining the N0 y concentrat i on of the a,r: "co ) calculating means operatively associated with the systems for determining: the rate coefficient, smog concentration and the analyser, to calculate the time required for the product i on of a elected amount of smog In the air under selected temperature and ll1u. n.t on conditions. 48 A system for determining time required for production of a selected amount of smog in air under selected temperature and illuminat i on conditions, the system comprising ( A ) a system for determining the rates of smog format i on i n the a i r according to claim 28, 29 or 39; _ ( B ) a system for determining concentration of smog i n a i r, wh i ch system comprises: ... ,, ,, r tn ( B )( 1 ) a combiner for combining excess nitric ox ! de w,th the a,r to provide an excess nitric oxide/air mixture; ( BXii ) a reactor operatively associated with the combmer wherem the mixture can react in the reactor for a selected period wherein excess nitric oxide n the mixture reacts with substantially all ozone ,n the ( BX111 ) nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; ( BXiv ) a N0 y analyser operatively associated with the reactor to determine the NO concentration of the mixture; and ( B )( v ) calculating means operatively associated w i th the n i tr i c ox i analyser and ' the N0 y analyser to calculate the concentration of smog fro the NO and nitric oxide concentrations; ?C> an N0 y analyser for determining the N0 y concentrat i on of the SUBSTITUTE SHE -140- a1r: "a ) calculating means operatively associated with the systems of <«-» and ( B ) and the N0 y analyser, to calculate the time requ i red for the production of a selected amount of smog n air under selected temperature and illumination conditions. 49 A system for determining time required for production of a selected amount of smog in air under selected temperature and illuminat i on conditions according to Cairn 47 or 48 wherein the NOy analyse of ( C, includes a NO converter to convert substantially all NO i n the l to n.ϊr.c oxide, the converter being operatively associated w i th the nitric oxide analyser of ( B ) . 50 A system according to claim 25, 26, 27, 28, 29, 30, 32 or 3 further c-prlsin a temperature controller/programmer operatively assoc i a ed w i th the photoreactor whereby the temperature of the mixture can be lc.pt cons ant during illumination, can be allowed to vary and opt i on ly lltored or the temperature of the mixture can be varied accord i ng to a preselected or selected temperature prof i le. 51 A system according to claim 25, 26, 27, 28, 29, 30, 32 or 39 furthe comprising an Hlumlnator controller/programmer operatively assoc i ated w,t Tcoupl to the illumination source whereby the illumination can be Kep constant or can be varied according to a preselected or selected illumination profile. 52. A system according to Cairn 25, 26, 27, 28, 29, 30, 32 or 39 furth comprising first metered delivery means to deliver metered doses of t . a to Z combiner and second metered delivery means to deliver metered dose of nitric oxide to the combiner. 53 A system according to claim 52, further comprising third metered ddvery means to deliver metered doses of ozone to the combiner and an ozone filter to filter ozone prior to injection into the comb i ner. 54 A system according to Cairn 25, 26, 27, 28, 29, 30, 32 or 39, furt comprising an air filter to filter the air prior to injection ,n o the combiner and a nitric oxide filter to filter nitric oxide pr i or to injection into the combiner. SUBSTITUTE SHEE 55. A system for determining concentration of smog in air, which system COmPri ( i a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; ^ ^ ( b ) a reactor operatively associate d WI LD m i xture can react In the reactor for a selected period wherein excess " o"de " the mixture reacts with substantially all ozone in the " iXtUr ( c, a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the Se,eCt ;: o ; analyser operatively associated with the reactor to determine the NO concentration of the mixture; and ( . ) calculating means operatively associated w i th the n i tr i c ox de analyst and the N0 y analyser to calculate the concentration of smo, from the NO and nitric oxide concentrations. 56 A system for determining concentration of smog in air according to aim 5 wherein the NO, analyser includes a N0 y converter to conver in the mixture tZ nitric oxide, the converter being operat i vely associated with the nitric oxide analyser. 57 A system for determining concentration of smog In air according to Calm 56, wherein the N0 y analyser consists of the N0 y converter and the nitric oxide analyser. 58. A system for determining a»unt of prior smog formation in air, whi N0 y analyser to determine the N0 y concentration of thβ '' , a combiner for combining excess nitric oxide with the air to m irie an excess nitric oxide/air mixture; P c l ector operatively associated with the combiner where i n the mixture can react in the reactor for a selected period wherein excess nitric oxide n the mixture reacts with substant i ally all ozone i n mixture; SUBSTITUTE SHEE E -142- (d) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the the reactor n i tr i c ox i de the amount the a,r and m i xture. 59 A system for determining amount of prior smog formation in air cord ng to claim 58, wherein said first and said second NO analysers as to determine the N0 y concentration of the air before excess mtπc oxide is combined with the air. 60 A system for determining amount of prior smog formation in air according to claim 59, .wherein said N0 y analyser includes a NO converter to convert all N0 y in the mixture to nitr i c ox,de, the Z being operativel assoclated with said nitric oxide analyser. 6, A system for determining amount of prior smog formation in air according to claim 60, wherein said N0 y analyser consists of sa i d N0 y converter and said nitric oxide analyser. U A system for determining maximum potential and optionally the curre extent of smog formation in air, which system compr i ses ; ( a, a first N0 y analyser for determining the N0 y concentrat i on ° f combiner for combining excess nitric oxide with the air to p rovide an excess nitric oxide/air mixture; ( c ) a reactor operatively associated with the combiner wherem the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone ,n the m1XtUr ( d ) a nitric oxide analyser operatively associated with the react to determine the nitric oxide concentration of the mixture after the selected period; SUBSTITUTE SHEET (e) a second NO analyser operatively associated with the reactor to determine the NO concentration of the mixture; and (f) calculating means operatively associated and coupled with the nitric oxide analyser and the first and second NO analysers to calculate the maximum potential and optionally the current extent of smog formation in air from the NO concentration of the air and the NO and NO concentrations of the excess nitric oxide/air mixture. 63. A system for determining amount of prior smog formation in air according to claim 62, wherein said first and said second NO analysers are the same analyser which is operatively associated with said combiner so as to determine the NO concentration of the air before excess nitric oxide is combined with the air. 64. A system for determining amount of prior smog formation in air according to claim 63, wherein said NO analyser includes a NO converter to convert all NO in the mixture to nitric oxide, the converter being operatively associated with said nitric oxide analyser. 65. A system for determining amount of prior smog formation in air aaccccoorrddiinngg ttoo ccllaaiimm 6644,, wwhheerreeiinn ssaaiidd NNOO Eanalyser consists of said NO converter and said nitric oxide analyser. 66. A system for determining ozone concentration in air, which system comprises: (A) a nitric oxide analyser to determine the nitric oxide concentration of the air; (B) a NO analyser to determine the NO concentration of the air; (C) a system for determining the concentration of smog in the air according to claim 55, 56 or 58; and (D) calculating means operatively associated with the nitric oxide analyser of (A) the NO analyser of (B) and the system of (C) to calculate the ozone concentration from the nitric oxide concentration, the NO concentration of the air and the smog concentration of the air. 67. A system for determining ozone concentration in air according to claim 66, wherein the nitric oxide analyser of (A) and the NO analyser of (B) are the same nitric oxide and NO analysers of the system of (C). SUBSTITUTE SHZZT 68. A system for determining nitric oxide and/or ozone concentrations in air, which system comprises: (A) a light sensor to determine the sunlight intensity of the air; (B) a temperature sensor to determine the temperature of the air; (C) an NO analyser to determine the NO concentration of the (D) a system for determining the smog concentration of the air according to claim 55, 56 or 58; and (E) calculating means operatively associated with the light and temperature sensors and the NO analyser and smog concentration measurement systems for calculating the nitric oxide and/or ozone concentrations of the air from the sunlight intensity, air temperature and the NO and smog concentrations. 69. A system for determining nitric oxide and NO or ozone or both concentrations in air according to claim 68, wherein the N0 y analyser of (C) is the same NO analyser of the system ( D ) . 70. A system for determining concentration of smog in air according to claim 55, further comprising first metered delivery means to del.iver metered doses of air to the combiner and second metered delivery means to deliver metered doses of nitric oxide to the combiner. 71. A system for determining amount of prior smog formation in air according to claim 58, further comprising first metered delivery means to deliver metered doses of air to the combiner and second metered delivery means to deliver metered doses of nitric oxide to the combiner. 72. A system for determining maximum potential and optionally the curren extent of smog formation in air according to claim 62, further comprising first metered delivery means to deliver metered doses of air to the combiner and second metered delivery means to deliver metered doses of nitric oxide to the combiner. 73. A system for determining concentration of smog in air according to claim 55, further comprising an air filter to filter air prior to injectio into the combiner and a nitric oxide filter to filter nitric oxide prior t injection into the combiner. SUBSTITUTE SHEET 74. A system for determining amount of prior smog formation in air according to claim 58, further comprising an air filter to filter air prior to injection into the combiner and a nitric oxide filter to filter nitric oxide prior to injection into the combiner. 75. A system for determining maximum potential and optionally the current extent of smog formation in air according to claim 62, further comprising an air filter to filter air prior to injection into the combiner and a nitric oxide filter to filter nitric oxide prior to injection into the combiner. 76. A system for locating a source of Reactive Organic Compounds (ROC) present in air, the system comprising: (a) means for determining a time period during which smog formation in air has occurred, the time period being substantially the same as, or within a predetermined period for which illumination and temperature conditions are known, wherein the end of the predetermined period coincides with the end of the time period: (b) a system for determining the rate coefficient of smog formation . in the air according to either claim 25, 26 or 27; (c) a system for determining concentration of smog in air, which system comprises: (cXi) a combiner for combining excess nitric oxide with the air to provide an excess nitric oxide/air mixture; (cXii) a reactor operatively associated with the combiner wherein the mixture can react in the reactor for a selected period wherein excess nitric oxide in the mixture reacts with substantially all ozone in the mixture; (cXiii) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture after the selected period; (cXiv) a NO analyser operatively associated with the reactor to determine the NO concentration of the mixture; and (cXv) first calculating means operatively associated with the nitric oxide analyser and the NO analyser to calculate the concentration of smog from the NO and nitric oxide concentrations; (d) an NO analyser for determining the NO concentration in the air; (e) a temperature sensor to determine the temperature of the air for SUBSTITUTE SKEE i -146- the ^r° i :: d:;Ile the sunlight Illumination during the calculate the location of said source of ROC. 77 A system for locating a source of Reactive Organic Compounds ( ROC ) * - f * Predetermined period coinci - h - : : e nlng the rate of smog formations the ai according to either claim 28, 29 or 39; ( c ) a system for determining concentration of smog i n a i r, wh i ch ^ X i riblner for combining excess nitric oxide with the air t tr'c oxide in the mixture reacts with substantially all ozone i n the ra,XtUr ( c )( i11 ) a nitric oxide analyser operatively associated with the reactor to determine the nitric oxide concentration of the mixture afte (d) an NO analyser for determi ni ng the NO concentration i n the (e) a temperature sensor to determine the temperature of the air fo the duration of the selected period; (f) a light sensor to determine the sunlight illumination during th selected period; (g) second calculating means operatively associated with the temperature sensor, the light sensor, the NO analyser and the systems for determining the rate coefficient of smog formation and smog concentration, to calculate the time period during which smog formation in air has occurred under the measured sunlight and temperature conditions; a (h) means for determining speed of movement and trajectory in the air during the time period; and (i) third calculating means operatively associated with the means for determining speed and trajectory and the second calculating means to calculate the location of said source of ROC. SUBSTITUTE SHEET

Inventors: JOHNSON GRAHAM MICHAEL, JOHNSON, GRAHAM, MICHAEL
Applicants: COMMW SCIENT IND RES ORG, COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH OR
Application year: 1989
Main classification: G01N31
IPC codes: G01N21, G01N31, G01N33