bluuebunny/crossref_metadata_2025 huggingface dataset:
Implications of AAOE observations for proposed chemical explanations of the seasonal and interannual behavior of Antarctic ozone
Authors: Ko M. K. W. , Rodriguez J. M. , Sze N. D. , Proffitt M. H. , Starr W. L. , Krueger A. , Browell E. V. , McCormick M. P.
Published: February 2008

A number of numerical experiments using different assumptions on the initial odd nitrogen content and the efficiencies and durations of heterogeneous reactions is selected based on the simulations of the observed trace gas concentrations during the Airborne Antarctic Ozone Experiment (AAOE) in 1987 (Rodriguez et al., this issue). The model is used to calculate the seasonal behavior of O3 in 1987 and its possible interannual variations as the chlorine content of the atmosphere increases from 1 to 6 ppbv. The seasonal behavior in 1987 is compared with the total ozone mapping spectrometer (TOMS) and AAOE data. In all the cases considered, the catalytic cycle associated with the formation and photolysis of Cl2O2 could account for more than half of the photochemical removal of O3 within the Antarctic vortex through mid‐September. The reaction of BrO with ClO, which accounts for 15–20% of the removal in the same period, tends to play a more important role toward the end of September, when the concentration of ClO is expected to decrease. The detailed behavior of the calculated O3 depends on the assumptions for the spatial and temporal extent of denitrification, the initial concentrations of odd nitrogen species sequestered in the vortex in July, and the efficiencies and durations of the heterogeneous reactions in the months that follow. Additional observations of ClO, odd nitrogen species, and O3 similar to those obtained in the campaign covering the period in July and October will be useful in providing additional constraints to narrow down the possibilities. There is no simple relationship between the increase in chlorine level and the interannual decrease in Antarctic O3. It is difficult to explain both the 40% decrease in October mean O3 within the hole since 1979 and the much slower decrease prior to the mid‐1970s without invoking effects from interannual variations of heterogeneous activities and initial odd nitrogen concentrations in July. Such effects must be isolated before the observed trends in the Antarctic O3 hole in the past 8 years can be used to predict future behavior of O3 based solely on projected increase in the chlorine content of the atmosphere.
Stratospheric nitrous oxide distribution in the southern hemisphere
Authors: Podolske J. R. , Loewenstein M. , Strahan S. E. , Chan K. R.
Published: February 2008

Nitrous oxide measurements were made in the southern hemisphere (latitude, 42°S to 72°S) as part of the Airborne Antarctic Ozone Experiment (AAOE) in late winter and early spring 1987, covering the altitude range 14–21 km. This paper reports on N2O measurements made by the airborne tunable laser absorption spectrometer (ATLAS), which was flown on board the NASA ER‐2 aircraft. Average vertical N2O profiles at latitudes 72°S, 54°S, and 42°S are presented and compared, when possible, with equivalent summer profiles. Latitudinal gradients of N2O on isentropic surfaces are presented and discussed in terms of their implications about the inhibition of horizontal mixing near the polar vortex. Finally, a large‐scale distribution of N2O for the region 72°S to 42°S latitude is presented. The reader is directed to the note added in proof regarding the recent recalibration of this data set.
Evidence for diabatic cooling and poleward transport within and around the 1987 Antarctic ozone hole
Authors: Proffitt M. H. , Kelly K. K. , Powell J. A. , Gary B. L. , Loewenstein M. , Podolske J. R. , Strahan S. E. , Chan K. R.
Published: February 2008

Combining in situ measurements of nitrous oxide, total water, and NOy with meteorological data, including potential vorticity, taken during the 1987 Airborne Antarctic Ozone Experiment, a consistent picture emerges of a gradual poleward movement of air extending from about 10° in latitude outside the boundary of the ozone hole to about 5° inside. The data analysis is concentrated in the potential temperature range of 425–450 K, corresponding to geometric altitudes of 17.5–19 km. Evidence of ongoing diabatic cooling throughout this region is presented, and cooling rates of about 1.75 K in potential temperature per day (approximately 0.8 K per day in temperature at constant pressure) are calculated from the data outside the boundary of the ozone hole. An interpretation of the data is presented that describes the movement of air that has come from lower latitudes into the ozone hole, as diabatically descending and spiraling poleward. The result of this spiraling motion is a dominantly advective flow of ozone rich air across the boundary and into the ozone hole. This simple picture precludes requiring extensive isentropic mixing with accompanying vertical descent to maintain the steep poleward isentropic gradients found in nitrous oxide. Data are presented to show that the necessary accompanying outflow of stratospheric air from within the ozone hole occurs at potential temperatures less than 425 K and that, during the mission, there was no significant transport of processed air across the boundary and out of the ozone hole from 425 to 450 K. Arguments involving conservation of angular momentum are also used to support this model.
The 13C/12C kinetic isotope effect for soil oxidation of methane at ambient atmospheric concentrations
Authors: King Stagg L. , Quay Paul D. , Lansdown John M.
Published: February 2008

During a survey of the Alaskan North Slope to estimate the isotopic composition and fluxes of methane (CH4) from the tundra, two sites were encountered that showed net methane consumption within flux chambers. Methane concentrations decreased from ambient (1.78 ppmv) by up to 50% and the δ13C increased by up to 10‰ in the two chamber deployments showing CH4 consumption. CH4 consumption rates were measured to be 1.2 and 0.6 mg CH4 m−2 d−1; the corresponding carbon kinetic isotope effects (k13/k12) were 0.974 and 0.984, respectively. For comparison, the carbon kinetic isotope effect for CH4 oxidation by hydroxyl radical has been recently measured to be 0.990 (Davidson et al., 1987). These data are briefly discussed with reference to the potential effect of soil oxidation on the stable carbon isotope budget of atmospheric methane.
Absorption line profiles in a moving atmosphere: A single scattering linear perturbation theory
Authors: Hays P. B. , Abreu V. J.
Published: February 2008

An integral equation is derived which linearly relates Doppler perturbations in the spectrum of atmospheric absorption features to the wind system which creates them. The perturbation theory is developed using a single scattering model, which is validated against a multiple scattering calculation. The nature and basic properties of the kernels in the integral equation are examined. It is concluded that the kernels are well behaved and that wind velocity profiles can be recovered using standard inversion techniques.
An analysis of gravity wave ducting in the atmosphere: Eckart's resonances in thermal and Doppler ducts
Authors: Fritts David C. , Yuan Li
Published: February 2008

We present simple examples of gravity wave ducting due to the background thermal and velocity structure in the atmosphere and examine the consequences of such ducts lying in close proximity. The dispersion curves for individual thermal and Doppler ducts exhibit similar behavior, with normal and inverse dispersion at higher and lower frequencies, respectively, and with smaller phase velocities and larger group velocities for higher modes. In the presence of two ducts of different character, the dispersion curves are given approximately by the intersection of the curves for the individual ducts, with modal character changing dramatically at resonance points near which the dispersion curves for individual ducts cross. Such ducting of gravity wave activity is likely to be a common occurrence in the atmosphere and the oceans and may provide a means of transporting vertically the energy and momentum associated with high‐frequency wave motions.
Statistical comparison of spatial fields in model validation, perturbation, and predictability experiments
Authors: Wigley T. M. L. , Santer B. D.
Published: February 2008

The comparison of spatial fields of meteorological variables is an essential component of model validation studies and is central in assessing the significance of any change between a perturbed and control run of a general circulation model. Comparisons may be made of statistics which define the time‐mean state, the temporal variability about this state, and/or spatial variability. Comparisons may also be made of the two time‐mean spatial patterns, or of the temporal evolutions of spatial patterns. We consider here a suite of univariate and multivariate statistics which may be used to make these comparisons. Some of these statistics have been used previously, while others are either new or have not previously been used in the present context. The use of these statistics, their differences and similarities, and their relative performances are illustrated by considering mean sea level pressure changes between the decades 1951–1960 and 1971–1980 over an area covering North America, the North Atlantic Ocean, and Europe. Significance levels are assessed using the pool‐permutation procedure of Preisendorfer and Barnett (1983) (henceforth P+B). This overcomes problems arising from nonideal behavior of the data (particularly spatial autocorrelation), unknown sampling distributions, and multiplicity in the case of univariate statistics. A subset of statistics is identified as most useful. For tests of differences in means these are the grid point by grid point t‐test, a test comparing the overall means, and P+B's SITES statistic. For tests of differences in temporal variability they are the grid point by grid point F‐test, and SPRET1 (the ratio of the spatial means of the time variances). SPRET1 is a modification of P+B's SPRED statistic designed to identify the direction of any variance difference. As a test of spatial variability differences, we identify SPREX1 (the ratio of the time means of the spatial variances), and for comparing spatial patterns the best statistic is the (spatial) correlation coefficient between the time‐mean fields. For comparing the temporal evolution of spatial patterns, we recommend using the time‐mean anomaly field correlation which is a more easily interpreted equivalent to P+B's SHAPE statistic.
Haze and other aerosol components in late winter Arctic Alaska, 1986
Authors: Li Shao‐Meng , Winchester John W.
Published: February 2008

Three coarse and five fine aerosol components of different elemental compositions were identified at Barrow, Alaska, from March 17 to April 21, 1986, resolved by absolute principal component analyses of element concentrations in 280 sequential coarse and fine size fraction time step samples. In the coarse (> 2.5 μm), two components C‐1 and C‐2 had abundant Si, S, Cl, K, and Ca, but no Al, and together contained 85% of coarse S. Their compositions resembled expected products of carbonaceous fuel combustion, with Si being volatilized by carbon reduction and other metals volatilized perhaps as chloride salts. C‐1, with high trace metal contents, might be from nonferrous smelting, whereas C‐2, with high Fe, might be associated with conventional coal combustion. Both appeared semi‐aged with respect to acidic gas uptake because the S chemical equivalents were less than those of metals contributing to alkalinity. When combined with Cl, S was close to the metal equivalents, indicating complete acid‐base titration. A strong concentration rise of C‐1 and C‐2 occurred from March 25 to April 2 during a haze event, although C‐1 was also present at other times. Air trajectories showed that air masses arrived at Barrow during the haze event from eastern or northern Europe. The third component C‐3 was a dust aerosol rich in Al that contained high S but low Cl, suggesting saturation with H2SO4 and therefore aged and regional aerosols perhaps typical of the late winter Arctic. No major change in its concentration was observed to correspond to synoptic events. In the fine (< 2.5 μm), five components represent a sea‐salt aerosol, an S‐rich aerosol with some Si, K, Ca, and Fe, a trace metal aerosol, an Al‐rich dust, and a marine product with Br, S, and Cl. The sea‐salt was found only in three plumes when synoptic meteorology and air trajectories suggested origins in the North Pacific. The S‐rich aerosol, accounting for 73% of S and 40% of Si, was enhanced during the haze event by 75%, and existed over the entire period at rather high levels and might be due to SO2 oxidation and condensation on fine Si‐rich particles. The trace metal aerosol was always present and could have been generated from nonferrous smelters at lower latitudes. The Al‐rich dust particles contained 7% of S and were similar to component C‐3. The marine aerosol contained 74% of Br, 69% of Cl, and 20% of S, and could be from oxidation of marine biogenic Br and S gases. All but the sea‐salt were present at Barrow throughout the period, with no clear relation to air trajectories or synoptic meteorology. The results show that certain winter meteorological conditions favor pollutant transport from lower latitudes to the Arctic. But while haze is related to industrial pollutants, other nonpollution products are present in the winter Arctic and may be important constituents of haze. They also show that by careful data reduction and meteorological analysis, the sources and transport pathways of haze may be better understood.
Three‐dimensional simulations of the atmospheric cycle of desert dust particles using a general circulation model
Authors: Joussaume Sylvie
Published: February 2008

A modeling of the atmospheric cycle of desert dust particles has been introduced within an atmospheric general circulation model. This approach, which allows a modeling of the full cycle of dust particles, should help to investigate the link between desert dust and climate and, in particular, to study how the dust transport can be affected by climatic changes (for example, glacial age). In this paper we present a detailed description of the modeling and of the results obtained from simulations of the present‐day climate (February and August) performed to test the dust model. The modeling considers particles as passive scalars, in the 1‐μm range, and includes transport from all the desert areas. The simulated results exhibit a strong seasonal cycle, with twice more dust in August than in February, resulting from more dust uplifting in the troposphere over the Sahara and Arabia‐Asia in the summer. Compared to the available observations, the simulated results are fairly reasonable, showing, however, some deficiencies which are discussed.
Multiscaling properties of spatial rainfall and river flow distributions
Authors: Gupta Vijay K. , Waymire Ed
Published: February 2008

Two common properties of empirical moments shared by spatial rainfall, river flows, and turbulent velocities are identified: namely, the log‐log linearity of moments with spatial scale and the concavity of corresponding slopes with respect to the order of the moments. A general class of continuous multiplicative processes is constructed to provide a theoretical framework for these observations. Specifically, the class of log‐Levy‐stable processes, which includes the lognormal as a special case, is analyzed. This analysis builds on some mathematical results for simple scaling processes. The general class of multiplicative processes is shown to be characterized by an invariance property of their probability distributions with respect to rescaling by a positive random function of the scale parameter. It is referred to as (strict sense) multiscaling. This theory provides a foundation for studying spatial variability in a variety of hydrologic processes across a broad range of scales.
Sampling errors for satellite‐derived tropical rainfall: Monte Carlo study using a space‐time stochastic model
Authors: Bell Thomas L. , Abdullah A. , Martin Russell L. , North Gerald R.
Published: February 2008

Estimates of monthly average rainfall based on satellite observations from a low Earth orbit will differ from the true monthly average because the satellite observes a given area only intermittently. This sampling error inherent in satellite monitoring of rainfall would occur even if the satellite instruments could measure rainfall perfectly. We estimate the size of this error for a satellite system being studied at NASA, the Tropical Rainfall Measuring Mission (TRMM). We first examine in detail the statistical description of rainfall on scales from 1 to 103 km, based on rainfall data from the Global Atmospheric Research Project Atlantic Tropical Experiment (GATE). A TRMM‐like satellite is flown over a two‐dimensional time‐evolving simulation of rainfall using a stochastic model with statistics tuned to agree with GATE statistics. The distribution of sampling errors found from many months of simulated observations is found to be nearly normal, even though the distribution of area‐averaged rainfall is far from normal. For a range of orbits likely to be employed in TRMM, sampling error is found to be less than 10% of the mean for rainfall averaged over a 500 × 500 km2 area.
Global impact of the Antarctic ozone hole: Dynamical dilution with a three‐dimensional chemical transport model
Authors: Prather Michael , Garcia Maria M. , Suozzo Robert , Rind David
Published: February 2008

A study of the Antarctic ozone hole has been made with a three‐dimensional chemical transport model (CTM) using a linearized photochemistry for ozone. The tracer model uses the winds and convection from the Goddard Institute for Space Studies general circulation model (8° × 10° × 23 layers). The general circulation model (GCM) develops an Antarctic circumpolar vortex in early winter with strong westerlies that reverse in austral spring; the circulation compares favorably with the observed climatologies. A 4‐year control run of the CTM with annually repeating winds produces ozone distributions that compare reasonably with the observed climatology. We examine different linearizations of the ozone chemistry and show that the calculated column ozone is sensitive to the chemical time constants in the lower stratosphere. In separate numerical experiments a hypothetical Antarctic ozone “hole” is induced on September 1 and on October 1; the CTM is integrated for 1 year with a linearized model that assumes standard photochemistry, not including the heterogeneous reactions and unusual chemistry associated with formation of the ozone hole. The initial depletion, assumed to be 90% of the O3 poleward of 70°S between 22 and 200 mbar, amounts to about 5% of the total O3 in the southern hemisphere. As the vortex breaks down and the ozone hole is dispersed, significant depletions to column ozone, of order 10 Dobson units (3%) occur as far north as 40°S during austral summer. One year later, only 30% of the original depletion remains, mostly below 100 mbar and poleward of 30°S. The October 1 initialization is continued for a second year, the ozone hole being reinduced 1 year later with the same parameterization. The cumulative effects from the year before are noticeable but add only 20% to the depletion. A budget analysis for the southern high‐latitude stratosphere (10–350 mbar × 31°–90°S) indicates the ozone hole is replenished equally by photochemical regeneration and by reduced transport of ozone into the troposphere, with a lesser fraction being filled in by an increased flux from the tropical stratosphere.
n‐Alkanes, fatty acid esters, and fatty acid salts in size fractionated aerosols collected over the Mediterranean Sea
Authors: Sicre M.‐A. , Marty J.‐C. , Saliot A.
Published: February 2008

The n‐alkanes, fatty acid esters, and fatty acid salts have been analyzed in size fractionated aerosols collected over the Mediterranean Sea using a five‐stage cascade impactor. Two main sources of n‐alkanes have been identified: terrestrially derived n‐alkanes evenly distributed over the whole particle size spectrum and anthropogenic n‐alkanes predominantly carried by submicron particles. The comparison between the fatty acid ester (FAE) and fatty acid salt (FAS) particle size distributions allowed an important contribution to be ascertained of the marine source in aerosols ranging from 7.2 to 3.0 μm under rough weather conditions that may be due to larger bubble produced particles. In contrast, FAE and FAS were evenly distributed from the first to the fifth stage, when collected during calm sea surface conditions. Higher values of the degree of unsaturation of FAE and FAS were associated with mass concentration maxima observed on stages 2 and 3 in IMPI aerosol sample whereas lower values were found on the other stages in the same sample, and over the whole particle size spectrum in IMP2 aerosol sample collected during calm weather conditions. The data we present here are discussed in terms of jet and film drop ejections and degradation processes.
Uptake of HCl molecules by aqueous sulfuric acid droplets as a function of acid concentration
Authors: Watson Lyn R. , Van Doren Jane M. , Davidovits Paul , Worsnop Douglas R. , Zahniser Mark S. , Kolb Charles E.
Published: February 2008

The uptake of HCl molecules by aqueous sulfuric acid droplets was measured at 283 K as a function of acid mole fraction. In the apparatus a controllable stream of monodispersed droplets is produced by a vibrating orifice jet. The droplets enter a flow system containing HCl(g). The droplets are switched on and off while the density of the species is continuously monitored by infrared absorption. From the on‐off signal a coefficient for the probability of gas uptake upon collision with the liquid surface is calculated. This coefficient is 0.15 for pure water, remains constant up to 0.1 mole fraction of H2SO4 (40 wt %) and then drops sharply to <10−2 at 0.2 mole fraction (60 wt %). The results are in accord with calculations based on the decrease in the solubility of HCl with increasing H2SO4 mole fraction. Increasing acidity reduces the dissociation of HCl into H+ and Cl− in solution. Our results indicate that mass accommodation coefficients are large enough so that the HCl content of stratospheric aerosols will be determined entirely by this solubility.
Observations of the chemical properties of dew on vegetation that affect the dry deposition of SO2
Authors: Wesely M. L. , Sisterson D. L. , Jastrow J. D.
Published: February 2008

Experiments were conducted to examine the chemical properties of dew (and guttation) that affect the dry deposition of SO2 to prairie grasses of tall stature and mixed broadleaf plants of short stature. For 2–3 hours after sunrise, liquid samples were extracted directly from the upper of the plant canopies and from surrogate surfaces, concurrently with selected atmospheric observations. Chemical analyses showed that aqueous concentrations of S(IV), SO42‐, and several other ions in the leaf wetness were often high compared to values typically found in rain, while NH4+ was not very abundant. Guttation produced substantial amounts of liquid, which mainly contributed Cl− to the leaf wetness. The dry deposition of S(IV) to leaf wetness was not always apparently limited by aqueous oxidation by O3, especially when aerodynamic resistances limited the maximum potential deposition velocity to less than 0.5 cm/s at a height of 8 m. A more effective oxidant than atmospheric O3 or NO2 could have been present and could have lessened the inferred substantial contributions of particle deposition to leaf wetness SO42‐. Foliar uptake of NO3‐ and SO42‐ was significant after sunrise. The pH of the leaf wetness in the broadleaf vegetation seemed to have a lower limit of about 5.3, possibly because of neutralization by substances leached from leaves, while the pH of the grasses reached values as low as 4.5 when the amount of leaf wetness was small. The potassium ion concentration in leaf wetness appeared to be an effective marker for leaf leaching.
Monoterpene emission rate measurements from a Monterey pine
Authors: Juuti Soile , Arey Janet , Atkinson Roger
Published: February 2008

The monoterpenes emitted from a Monterey pine (Pinus radiata) were investigated using a dynamic flow‐through enclosure technique. The monoterpenes identified and quantified were α‐ and β‐pinene, d‐limonene + β‐phellandrene, myrcene, camphene and Δ3‐carene, with α‐ and β‐pinene accounting for over 80% of the total monoterpene emissions. The monoterpene emission rate increased with temperature, in good agreement with previous data for other coniferous species. The absence of added CO2 to the synthetic air flow stream, exposure to elevated levels (300–500 ppb mixing ratio) of O3 for 3–4 hours, and increased air movement within the enclosure had no observable effect on the monoterpene emission rate at a given temperature. In contrast, “rough handling” of the pine during the sampling protocol resulted in increases in the monoterpene emission rate by factors of 10–50. These results will be useful to those designing enclosure sampling protocols for the determination of the emission rates of biogenic organic compounds from vegetation.
An assessment of a generalized Waymire‐Gupta‐Rodriguez‐Iturbe model for GARP Atlantic Tropical Experiment rainfall
Authors: Phelan Michael J. , Goodall Colin R.
Published: February 2008

We assess a generalized Waymire‐Gupta‐Rodriguez‐Iturbe model for rainfall intensity from GARP Atlantic Tropical Experiment rainfall fields. The generalization allows the rain cells' characteristics to be variable and models both their intensive and dissipative stages. In a detailed analysis of the rainfall trace from a cloud cluster over a 5‐hour period, we fit the model using nonlinear least squares, and we assess its ability to represent rainfall intensity in space and time. We find that the geometry and kinematics of the actual cloud cluster are more complex than is hypothesized in the model.
Perturbations to tropospheric oxidants, 1985–2035: 1. Calculations of ozone and OH in chemically coherent regions
Authors: Thompson Anne M. , Ann Huntley Mary , Stewart Richard W.
Published: February 2008

A one‐dimensional photochemical model has been used to calculate future changes in tropospheric O3 and OH due to CO/NOx/CH4 emissions and to possible changes in stratospheric O3 and tropospheric H2O. Perturbations are simulated for various chemically coherent regions (e.g., urban and continental mid‐latitudes, and marine and continental low latitudes) from 1985 to 2035. Estimates of global changes in O3 and OH are made by averaging over these regions. Two types of scenarios are simulated. “Global” scenarios assume that increases of CH4 and CO continue at current rates in all regions. A second set of scenarios, based on an analysis Of CH4, CO, and NO budgets in each region, assumes that emissions will be controlled in some regions and not in others. Both global and region‐specific scenarios predict a global tropospheric O3 increase of ∼10–15% from 1985 to 2035 with OH decreasing 10–15%. In the regionally varying scenarios, O3 will increase in some regions and decrease in others; for examples in regions of rapid CH4 and CO increase, growth in boundary layer O3 may be as high as 40%. Calculations that assume stratospheric O3 depletion and climate warming from 1985 to 2035 show near cancellation of the tropospheric O3 enhancement and OH loss. All scenarios of CH4/CO/NO changes considered in this study imply a 1–1.5% increase in total ozone from 1985 to 2035, assuming that tropospheric O3 is 10% of the total O3 column. This may complicate detection of stratospheric O3 change by monitoring of total O3.
Radiative forcing of climate by changes in the vertical distribution of ozone
Authors: Lacis Andrew A. , Wuebbles Donald J. , Logan Jennifer A.
Published: February 2008

We describe a simple method for evaluating the radiative forcing of surface temperature caused by changes in the vertical distribution of ozone. The method employs a parameterization based on one‐dimensional radiative‐convective equilibrium calculations; these calculations predict that the surface temperature should warm in response to both decreases in ozone above 30 km and increases in ozone below 30 km. The parameterization is used to investigate the response of surface temperature to observed changes in the vertical distribution of ozone at northern mid‐latitudes. We show that the observed ozone trends, taken at face value, suggest a cooling of the surface temperature at northern mid‐latitudes during the 1970s equal in magnitude to about half the warming predicted for CO2 for the same time period. However, the measurement uncertainty of the observed trends is large, with the best estimates for mid‐latitude cooling being −0.05±0.05°C. The surface cooling is caused by ozone decreases in the lower stratosphere, which outweigh the warming effects of ozone increases in the troposphere. The results obtained differ from predictions based on one‐dimensional photochemical model simulations of ozone trends for the 1970s, which suggest a warming of the surface temperature equal to ∼20% of the warming contributed by CO2. Also, the ozone decreases observed in the lower stratosphere during the 1970s produce atmospheric cooling by several tenths of a degree in the 12‐ to 20‐km altitude region over the northern mid‐latitudes. This temperature decrease is larger than the cooling due to CO2 and thus may obscure the expected stratospheric CO2 greenhouse signature.
Operational overview of NASA GTE/CITE 2 airborne instrument intercomparisons: Nitrogen dioxide, nitric acid, and peroxyacetyl nitrate
Authors: Hoell James M. , Albritton Daniel L. , Gregory Gerald L. , McNeal Robert J. , Beck Sherwin M. , Bendura Richard J. , Drewry Joseph W.
Published: February 2008

This paper provides the rationale, objectives, approach, and a brief description of the instrumentation included in the second airborne Chemical Instrumentation Test and Evaluation (CITE 2) mission conducted by NASA. This mission, conducted on NASA's Electra aircraft, was based at Moffett Field, California, and intercompared data from instruments measuring NO2, HNO3, and PAN in the troposphere. Ancillary measurements augmented the intercpmparison data in order to address specific questions related to the budget and partitioning of odd nitrogen species in the troposphere. This study, conducted in August 1986, encountered marine and continental air with free tropospheric mixing ratios of NO2, HNO3, and PAN typically less than 120, 150, and 200 parts per trillion by volume, respectively. Other papers in this issue provide the detailed results of the intercomparison tests and also discuss issues related to the budget and distribution of odd nitrogen species in the troposphere.
Peroxyacetyl nitrate measurements during CITE 2: Atmospheric distribution and precursor relationships
Authors: Singh H. B. , Condon E. , Vedder J. , O'Hara D. , Ridley B. A. , Gandrud B. W. , Shetter J. D. , Salas L. J. , Huebert B. , Hübler G. , Carroll M. A. , Albritton D. L. , Davis D. D. , Bradshaw J. D. , Sandholm S. T. , Rodgers M. O. , Beck S. M. , Gregory G. L. , LeBel P. J.
Published: February 2008

Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO2, HNO3, and NOy) were performed over the continental United States and the eastern Pacific during August–September 1986 at all altitudes between O and 6 km as part of CITE 2. PAN measurements were conducted by two independent groups, allowing both intercomparisons and greater confidence in its observed atmospheric structure. PAN was found to be a dominant reactive nitrogen species in the troposphere with 98% of the mixing ratios falling in a range of 5–400 ppt. Typically, the highest mixing ratios (100–300 ppt) were observed aloft (4–6 km) with extremely low values (5–20 ppt) in the marine boundary layer. In the lower troposphere, continental air contained significantly more PAN than marine air. The vertical structure of PAN was largely dictated by its thermal destruction rate and equilibrium with available NO2. PAN mixing ratios showed a high degree of variability in both continental and marine atmospheres. Westerly marine air trajectories did not guarantee well‐mixed air of uniform composition. Mixing ratios of O3, NOy, NOx, HNO3, C2H6, CO, and CFCl3 were strongly correlated with those of PAN, indicating the important role played by transport processes. High PAN to NOx ratios in the mid‐troposphere further support the importance of long‐range transport from continental sources. Frequently, descending air masses from the upper troposphere suggested that PAN mixing ratios probably continued to increase above the 6‐km ceiling altitude. Air masses with O3 <20 ppb, CO <60 ppb, and C2H6 <500 ppt contained only miniscule amounts of PAN and are expected to be of tropical origin. Reasons for the observed PAN variability are discussed.
Low‐frequency oscillations in total ozone measurements
Authors: Gao X. H. , Stanford J. L.
Published: February 2008

Low‐frequency oscillations with periods of approximately 1 to 2 months are found in 8 years of global grids of total ozone data from the total ozone mapping spectrometer (TOMS) satellite instrument. The low‐frequency oscillations corroborate earlier analyses based on 4 years of TOMS data. In addition, both annual and seasonal one‐point correlation maps based on the 8‐year TOMS data are presented. The analyses reveal a clear standing “dipole” in ozone perturbations, oscillating with 1‐ to 2‐month periods over the equatorial Indian ocean‐west Pacific region. In a number of instances, large‐scale, exceptionally strong correlations (satisfying a posteriori statistics) are found in the total ozone fields. Very strong correlations occur in the southern midlatitudes at zonal wave one scale. Large‐scale standing patterns are also found in the extratropics of both hemispheres, correlated with ozone fluctuations over the tropical dipole region. In the northern hemisphere, one wave train appears to emanate from the tropical dipole source, extending across the north Pacific and North America and crossing the Atlantic ocean into central Africa. This is interpreted as Rossby wave radiation from the tropical source region.
Atmospheric NO3 3. Sunrise disappearance and the stratospheric profile
Authors: Smith Joseph P. , Solomon Susan
Published: February 2008

New ground‐based measurements of NO3 absorption in the band near 662 nm were carried out using the moon as a light source during sunrise on July 1, 1988. As the sun rose, the observed slant column abundance of atmospheric NO3 decreased systematically. This time‐dependent decrease is expected, due to the progression of the solar terminator down through the atmosphere, and provides a basis for inferring the nighttime vertical profile of NO3. This approach represents a new means of measuring the vertical profile of stratospheric species whose distributions change rapidly at sunrise. The profile inferred from the time‐dependent NO3 decrease is sensitive to the NO3 absorption cross section and the adopted photolysis rate, and these sensitivities are investigated. The inferred vertical profile on July 1, 1988, is in excellent agreement with theoretical predictions in the altitude range from about 20 to 33 km. At higher levels near 40 km, the NO3 abundance is found to be quite sensitive to the adopted rate constant for thermal decomposition of N2O5. The profile inferred from these measurements suggests a relatively slow rate of N2O5 thermal decomposition in this region.
Active nitrogen partitioning and the nighttime formation of N2O5 in the stratosphere: Simultaneous in situ measurements of NO, NO2, HNO3, O3, and N2O using the BLISS diode laser spectrometer
Authors: Webster Christopher R. , May Randy D. , Toumi Ralf , Pyle John A.
Published: February 2008

Simultaneous in situ measurements of NO, NO2, HNO3, O3, N2O, pressure, and temperature at 30 km have been made from Palestine, Texas (32°N) on September 13, 1988, using the Jet Propulsion Laboratory Balloon‐Borne Laser In‐Situ Sensor (BLISS) instrument, with the NOAA dual‐channel balloon UV ozone spectrometer on the same gondola. Using tunable diode laser absorption spectroscopy over a long path length, measurements were made during a 24‐hour flight of the daytime concentrations of NO, NO2, and O3 and of the diurnal variation in the concentration of NO2. Postsunset measurements of NO2, made every half minute throughout much of the night, show the NO2 mixing ratio falling from a sunset value of 10.5 ppbv to 5.2 ppbv at night's end. According to the simple identity (d/dt)[NO2] = ‐2k[NO2][O3] for the rate of decay of the NO2 concentration, where k is the rate constant for the reaction between NO2 and O3, an exponential fit to the observed decay agrees with that calculated to better than 10%, with a standard deviation of the fit of only ±3%. Photochemical model calculations constrained to the measured temperature and O3 values, and incorporating both N2O5 and ClONO2 chemistry, predict in detail the observed NO2 diurnal behavior. From the sunset/sunrise difference in the volume mixing ratio of NO2 is derived a value of 2.7±0.4 ppbv for the sunrise N2O5 mixing ratio, in excellent agreement with the model predictions of 2.9 ppbv at this latitude. The measured daytime NO2/NO ratio was found to be in good agreement with model predictions at 30 km. The measured presunset sum NO +NO2 of 10.1±0.8 ppbv agreed well with the measured postsunset NO2 amount of 10.5±0.8 ppbv. Simultaneous measurements of the mixing ratios of HNO3 and postsunset NO2 allow an estimate of total reactive nitrogen, approximated at this time by NO2 + HNO3 + 2(N2O5) + ClONO2, of 16.4±1.2 ppbv at 30 km, and (from an earlier flight) of 13.7±1.7 ppbv at 37 km. Using model predictions incorporating corrections for non‐steady state and for diurnal chemistry, an OH mixing ratio of 8±4 pptv is derived from the measured HNO3/NO2 ratio of 0.72±0.17 at 30 km.
Ice particles and electron “bite‐outs” at the summer polar mesopause
Authors: Reid George C.
Published: February 2008

Rocket measurements of electron density profiles in the vicinity of the high‐latitude summer mesopause have frequently shown the existence of a sharply bounded layer of thickness ∼1 km in which the electron density is depleted by as much as an order of magnitude below the value that would be inferred from the densities above and below. The most plausible explanation of these “bite‐outs” is that they are caused by scavenging of the electrons by small ice particles that exist in the cold environment of the polar summer mesopause and that are related to those responsible for noctilucent and polar mesospheric clouds. This possibility is explored quantitatively using a simplified version of relations developed earlier (Natanson, 1960) to describe the charging of aerosols. It is shown that the radius of the ice particles must be of the order of 10 nm in order to satisfy the number density requirement and at the same time keep the water content within reasonable bounds. These particles would be too small to produce a visible cloud but may form a semipermanent substrate from which the larger cloud particles can develop under suitable conditions.
Particle size distribution and chemistry of late winter Arctic aerosols
Authors: Li Shao‐Meng , Winchester John W.
Published: February 2008

Mass size distributions of element concentrations in Arctic aerosols at Barrow, Alaska, were measured from March 16 to May 6, 1986, and their correlations were examined statistically by absolute principal component analysis. In eight particle size fractions from <0.25 to >16 μm aerodynamic diameter (μmad), from eight‐stage cascade impactor sampling and proton‐induced X‐ray emission (PIXE) analysis, four types of aerosol components were resolved. One, resembling sea salt in composition, shows a maximum mass at 2–4 μmad and not detected at <0.25 μmad. Sulfur is enriched in fine particles 0.25–1 μmad but not in coarse; chlorine is depleted in 0.5–1 μmad particles, conforms to sea salt composition >8 μmad, but is about 50% enriched in other fine and coarse fractions, suggesting gas‐particle chemical interactions during aerosol aging. The sea salt aerosols appear only in a few elevated concentration periods, with transport likely from open ocean areas. Dust components are found in all size fractions, with a maximum concentration at 1–2 μmad and a rough symmetry about the maximum when sulfur is not included, suggesting eolian dust particles. Their compositions resemble average crust materials. On these dust particles, sulfur contents show a linear relationship with surface areas, suggesting uptake of gaseous sulfur compounds. Carbonaceous fuel combustion pollutants are indicated by the presence of Si, Cl, and several trace metals and the absence of Al. They are present in all size fractions, usually rich in sulfur with the highest concentration in ultrafine particles <0.25 μmad, strongly suggesting a gas phase origin and consistent with condensation of chloride salt and SiO vapors formed during coal or other fuel combustion. Bromine‐sulfur components are in every size fraction and contain most of the measured bromine, greatly in excess of sea salt Br. The greatest mass is at <0.25 μmad, suggesting a gas phase origin that may involve both nucleation and surface adsorption.
A field study of the oxidation of SO2 in cloud
Authors: Clark P. A. , Gervat G. P. , Hill T. A. , Marsh A. R. W. , Chandler A. S. , Choularton T. W. , Gay M. J.
Published: February 2008

This paper describes the execution and analysis of one of a series of field experiments performed at Great Dun Fell in the northern Pennines of England designed to study the oxidation of SO2 in cloud. The experiments are designed to isolate the effect on cloud chemistry by artificially releasing SO2 gas into the air entering cloud base. Observations made in cloud on April 30, 1986, clearly and unequivocally demonstrated the production of sulphate ions in cloudwater. A simultaneous decrease in H2O2 concentration demonstrated that about 40% of this arises from rapid reaction between H2O2 and SO2. The results of a comprehensive model of the cloud physical and chemical development at the site show good agreement with the observations, and indicate that the remaining fraction of sulphate produced resulted from the reaction of O3 with SO2 in cloudwater, promoted by the relatively high pH found in the cloud. Extrapolation of the results to other input gaseous concentrations by means of the model demonstrates the importance of gaseous ammonia in controlling cloudwater pH and hence the oxidation of SO2 by O3, in that it is found that over a wide range of SO2 concentrations, the total sulphate produced by the time air reaches a given point in the cloud is virtually independent of the initial SO2 concentration, and roughly proportional to the ambient ammonia concentration.
Model calculations of tropospheric ozone production potential following observed convective events
Authors: Pickering Kenneth E. , Thompson Anne M. , Dickerson Russell R. , Luke Winston T. , McNamara Donna P. , Greenberg James P. , Zimmerman Patrick R.
Published: February 2008

Photochemical modeling and analysis of field data have been used to evaluate the effects of convective clouds on tropospheric trace gas chemistry. Observations were made during a 1985 field campaign over the rural south‐central United States. Meteorological data and measurements of CO, NO, NOy, O3, and hydrocarbons were collected in air surrounding and inside clouds during and immediately following cloud convection. A one‐dimensional photochemical model has been used to calculate O3 production potential before and after cloud redistribution of O3 precursor gases. Four distinct types of convective events have been analyzed. Fair weather cumulus clouds increase O3 production in a layer immediately above the boundary layer (to 4 km in the case studied). Outflow from deeper convection can cause enhanced O3 production in the upper troposphere hundreds of kilometers downstream from the clouds. A comparison of trace gas profiles measured in and around a large cumulonimbus during dissipation shows O3 production in the upper troposphere may be increased fourfold by convection relative to undisturbed air. Convective enhancement of O3 production for the entire tropospheric column is about 50%. Compared to nonurban continental regions with no convection, the rate of O3 production potential in air processed by convection is up to 3–4; times greater. Catalysis of O3 production becomes more efficient when NO becomes more dilute after being transported from the boundary layer to the free troposphere. Free tropospheric NO may also be enhanced by lightning, adding to O3 production, particularly when sufficient hydrocarbons are transported to such locations.
Calculation of infrared limb emission by ozone in the terrestrial middle atmosphere: 1. Source functions
Authors: Mlynczak Martin G. , Drayson S. Roland
Published: February 2008

Two statistical equilibrium models are compared to analyze the departure from local thermodynamic equilibrium (LTE) in the vibration‐rotation bands of ozone in the middle atmosphere. The bands that emit in the 9–11 μm spectral interval depart from LTE due to chemical pumping, spontaneous emission, radiative absorption, and photochemical reaction. The diurnal variation in the ν1 and ν3 fundamental band source functions is determined by the diurnal changes in the rate of photolysis of ozone by solar radiation. The hot band source functions (υ > 2) are invariant above 85 km due to the diurnal invariance in the chemical pumping process. The magnitude of the hot‐band source functions is uncertain because of the lack of understanding of the chemical pumping process. Collisional quenching of vibrationally excited ozone by atomic oxygen may reduce the magnitude of the ν3 and ν1 fundamental source functions by 10% near 100 km.
Interpretation of an 8‐year record of Nimbus 7 wide‐field‐of‐view infrared measurements
Authors: Cess Robert D.
Published: February 2008

An 8‐year record of global‐mean infrared emission from the surface‐atmosphere system, as measured by instruments on the Nimbus 7 satellite, shows an interesting downward trend with time. While it is tempting to attribute this trend to increasing atmospheric CO2 and other greenhouse gases, the present study demonstrates that such a greenhouse gas radiative signal is well below the level of instrument detectability. It is shown instead that the temporal variability of the Nimbus 7 infrared measurements is strongly correlated with observed variability of global‐mean surface air temperature, so that the Nimbus 7 measurements actually provide an independent means of appraising global climate variability. Although the last two decades have, on average, been a period of global warming, embedded within this is a period of global cooling that is a significant cause of the downward temporal trend in the Nimbus 7 emission measurements.
The solar flare of August 18, 1979: Incoherent scatter radar data and photochemical model comparisons
Authors: Zinn John , Sutherland C. D. , Ganguly Suman
Published: February 2008

Measurements of electron density at seven D region altitudes were made with the Arecibo radar during a class X solar flare on August 18, 1979. Measurements of solar X ray fluxes during the same period were available from the GOES 2 satellite (0.5–4 Å and 1–8 Å) and from ISEE 3 (in four bands between 26 and 400 keV). From the X ray flux data we computed ionization rates in the D region and the associated chemical changes, using a coupled atmospheric chemistry and diffusion model (with 997 chemical reactions and 19 vertical levels). The computed electron densities matched the data quite well after we had adjusted the rate coefficients of three reactions, namely, O−2 + O2(1Δ) → e + O2 + O2, O+2 + O2 + M → O+4 + M, and O+4 + O → O+2 + O3. We also discuss the hierarchies among the many flare‐induced chemical reactions in two altitude ranges within the D region and the possible effects of two separate isomeric forms of O+4.