bluuebunny/crossref_metadata_2025 huggingface dataset:
Attribution of Modeled Atmospheric Sulfate and SO2 in the Northern Hemisphere for June–July 1997
Authors: Benkovitz C. M. , Schwartz S. E. , Jensen M. P. , Miller M. A.
Published: April 2010

Abstract. Anthropogenic sulfate aerosol is a major contributor to shortwave radiative forcing of climate change by direct light scattering and by perturbing cloud properties and to local concentrations of atmospheric particulate matter. Here we analyze results from previously published calculations with an Eulerian transport model for atmospheric sulfur species in the Northern Hemisphere in June–July, 1997 to quantify the absolute and relative contributions of specific source regions (North America, Europe, and Asia) and SO2-to-sulfate conversion mechanisms (gas-phase, aqueous-phase and primary sulfate) to sulfate and SO2 column burdens as a function of location and time. Although material emitted within a given region dominates the sulfate and SO2 column burden in that region, examination of time series at specific locations shows that material imported from outside can make a substantial and occasionally dominant contribution. Frequently the major fraction of these exogenous contributions to the sulfate column burden was present aloft, thus minimally impacting air quality at the surface, but contributing substantially to the burden and, by implication, to radiative forcing and diminution of surface irradiance. Although the dominant sulfate formation pathway in the domain as a whole is aqueous-phase reaction in clouds (61.7%), in regions with minimum opportunity for aqueous-phase reaction gas-phase oxidation can be dominant, albeit with considerable temporal variability depending on meteorological conditions. These calculations highlight the importance of transoceanic transport of sulfate, especially at the western margins of continents under the influence of predominantly westerly transport winds.
Direct observations of the atmospheric processing of Asian mineral dust
Authors: Sullivan R. C. , Guazzotti S. A. , Sodeman D. A. , Prather K. A.
Published: April 2010

Abstract. The accumulation of secondary acid products and ammonium on individual mineral dust particles during ACE-Asia has been measured in real-time using ATOFMS. Changes in the amounts of sulphate, nitrate, and chloride mixed with dust particles corresponded to different air mass source regions. During volcanically influenced periods, dust mixed with sulphate dominated. This rapidly switched to dust predominantly mixed with chloride when the first Asian dust front reached the R/V Ronald Brown. We hypothesise that the high degree of mixing of dust with chloride was caused by the prior reaction of NOy(g) and volcanic SO2(g) with sea salt particles, reducing the availability of nitrate and sulphate precursors while releasing HCl(g), which then reacted with the incoming dust front. The segregation of sulphate from nitrate and chloride in individual dust particles is demonstrated for the first time. This is likely caused by the dust plume encountering elevated SO2(g) in the Chinese interior before reaching coastal urban areas polluted by both SO2(g) and NOx(g). This caused the fractions of dust mixed with nitrate and/or chloride to be strongly dependent on the total dust loadings, whereas dust mixed with sulphate did not show this same dust concentration dependence. Ammonium was also significantly mixed with dust and the amount correlated strongly with the total amount of secondary acid reaction products in the dust. Submicron dust and ammonium sulphate were internally mixed, contrary to frequent statements that they exist as an external mixture. The size distribution of the mixing state of dust with these secondary species validates previous models and mechanisms of the atmospheric processing of dust. The uptake of secondary acids was also dependent on the individual dust particle mineralogy; nitrate accumulated on calcium-rich dust while sulphate accumulated on aluminosilicate-rich dust. Oxidation of S(IV) to S(VI) by iron in the aluminosilicate-rich dust is a probable explanation for this result, with important consequences for dust as a vector for the fertilization of remote oceans by soluble iron. This series of novel results has important implications for improving the treatment of dust in global chemistry models and highlights several key processes requiring further investigation through laboratory and field studies.
Organics in the Northeastern Pacific and their impacts on aerosol hygroscopicity in the subsaturated and supersaturated regimes
Authors: Crahan K. K. , Hegg D. A. , Covert D. S. , Santarpia J. L. , Jonsson H. , Buzorius G. , Collins D.
Published: April 2010

Abstract. Aerosol samples were collected by aircraft during the summer of 2004 in the Northeastern Pacific and compared to measurements of aerosol hygroscopicity. Chemical speciation analyses of the samples revealed that a significant portion of the marine aerosols was organic, and on average 8% of the total aerosol mass was insoluble organic material, tentatively attributed to natural marine emissions. Two chemical models were explored in an attempt to reproduce observed aerosol growth, both in the subsaturated and supersaturated regimes. Results suggest that at subsaturated relative humidities, the nonideal behavior of water activity with respect to aerosol chemistry is an important effect on aerosol growth. At supersaturations, the underprediction of critical supersaturations by all models suggests the hypothesis that formation of a complete monolayer by the insoluble organics may inhibit the activation of aerosols to form cloud droplets.
Observations of the diurnal and seasonal trends in nitrogen oxides in the western Sierra Nevada
Authors: Murphy J. G. , Day D. A. , Cleary P. A. , Wooldridge P. J. , Cohen R. C.
Published: April 2010

Abstract. Observations of speciated nitrogen oxides, namely NO2, total peroxy nitrates (ΣPNs), total alkyl nitrates (ΣANs), and HNO3 by thermal dissociation laser induced fluorescence (TD-LIF), and supporting chemical and meteorological measurements at Big Hill (1860 m), a high elevation site in California's Sierra Nevada Mountains, are described. From May through October, terrain-driven winds in the region routinely bring air from Sacramento, 100 km southwest of the site, upslope over oak and pine forests to Big Hill during the day, while at night, the site often samples clean, dry air characteristic of the free troposphere. Winter differs mainly in that the meteorology does not favour the buildup of Sacramento's pollution over the Sierra Nevada range, and the urban-influenced air that is seen has been less affected by biogenic VOC emissions, resulting in longer lifetime for NO2 and a predominance of the inorganic forms of nitrogen oxides. Summertime observations at Big Hill can be compared with those from Granite Bay, a Sacramento suburb, and from the University of California's Blodgett Forest Research Station to examine the evolution of nitrogen oxides and ozone within the urban plume. Nitrogen oxide radicals (NO and NO2), which dominate total nitrogen oxides (NOy) at Granite Bay, are rapidly converted into HNO3, ΣPNs, and ΣANs, such that these compounds contribute 29, 30, and 21% respectively to the NOy budget in the plume at Big Hill. Nevertheless, the decreasing concentrations of NO2 as the plume is advected to Big Hill lead to decreases in the production rate of HNO3 and ozone. The data also demonstrate the role that temperature plays in sequestering NO2 into peroxy nitrates, effectively decreasing the rate of ozone production. The important contribution of ΣANs to NOy in the region suggests that they should be considered with regards to export of NOy from the boundary layer. Nocturnal observations of airmasses characteristic of the free troposphere showed lower NOy concentrations, which were dominated by HNO3 with a relatively small contribution from the organic nitrates.
Cluster analysis of the organic peaks in bulk mass spectra obtained during the 2002 New England Air Quality Study with an Aerodyne aerosol mass spectrometer
Authors: Marcolli C. , Canagaratna M. R. , Worsnop D. R. , Bahreini R. , de Gouw J. A. , Warneke C. , Goldan P. D. , Kuster W. C. , Williams E. J. , Lerner B. M. , Roberts J. M. , Meagher J. F. , Fehsenfeld F. C. , Marchewka M. L. , Bertman S. B. , Middlebrook A. M.
Published: April 2010

Abstract. We applied hierarchical cluster analysis to an Aerodyne aerosol mass spectrometer (AMS) bulk mass spectral dataset collected aboard the NOAA research vessel Ronald H. Brown during the 2002 New England Air Quality Study off the east coast of the United States. Emphasizing the organic peaks, the cluster analysis yielded a series of categories that are distinguishable with respect to their mass spectra and their occurrence as a function of time. The differences between the categories mainly arise from relative intensity changes rather than from the presence or absence of specific peaks. The most frequent category exhibits a strong signal at m/z 44 and represents oxidized organic matter most probably originating from both, anthropogenic as well as biogenic sources. On the basis of spectral and trace gas correlations, the second most common category with strong signals at m/z 29, 43, and 44 contains contributions from isoprene oxidation products. The third through the fifth most common categories have peak patterns characteristic of monoterpene oxidation products and were most frequently observed when air masses from monoterpene rich regions were sampled. Taken together, the second through the fifth most common categories represent as much as 5 µg/m3 organic aerosol mass – 17% of the total organic mass – that can be attributed to biogenic sources. These numbers have to be viewed as lower limits since the most common category was attributed to anthropogenic sources for this calculation. The cluster analysis was also very effective in identifying a few contaminated mass spectra that were not removed during pre-processing. This study demonstrates that hierarchical clustering is a useful tool to analyze the complex patterns of the organic peaks in bulk aerosol mass spectra from a field study.
Technical note: Recursive rediscretisation of geo-scientific data in the Modular Earth Submodel System (MESSy)
Authors: Jöckel P.
Published: April 2010

Abstract. This technical note describes a method for the rediscretisation of "gridded'' geo-scientific data. A recursive algorithm (NREGRID) is derived to solve the rediscretisation problem for orthogonal grids (also curvilinear) of arbitrary dimension. The algorithm is used within the program NCREGRID to handle geo-scientific data. These data are typically 2-dimensional (latitude-longitude grid), or 3-dimensional (latitude-longitude grid with a vertical pressure, or hybrid pressure coordinate, as used in atmospheric modelling). NCREGRID can be used as stand-alone program for the transformation ("regridding'') of data from and to data files in netCDF format. Moreover, NCREGRID constitutes the core of the Modular Earth Submodel System (MESSy) data import interface, providing a powerful tool for accessing data independently of the applied grid resolution ("automatic regridding'').
Characterization of on-road vehicle emissions in the Mexico City Metropolitan Area using a mobile laboratory in chase and fleet average measurement modes during the MCMA-2003 field campaign
Authors: Zavala M. , Herndon S. C. , Slott R. S. , Dunlea E. J. , Marr L. C. , Shorter J. H. , Zahniser M. , Knighton W. B. , Rogers T. M. , Kolb C. E. , Molina L. T. , Molina M. J.
Published: April 2010

Abstract. A mobile laboratory was used to measure on-road vehicle emission ratios during the MCMA-2003 field campaign held during the spring of 2003 in the Mexico City Metropolitan Area (MCMA). The measured emission ratios represent a sample of emissions of in-use vehicles under real world driving conditions for the MCMA. From the relative amounts of NOx and selected VOC's sampled, the results indicate that the technique is capable of differentiating among vehicle categories and fuel type in real world driving conditions. Emission ratios for NOx, NOy, NH3, H2CO, CH3CHO, and other selected volatile organic compounds (VOCs) are presented for chase sampled vehicles and fleet averaged emissions. Results indicate that colectivos, particularly CNG-powered colectivos, are potentially significant contributors of NOx and aldehydes in the MCMA. Similarly, ratios of selected VOCs and NOy showed a strong dependence on traffic mode. These results are compared with the vehicle emissions inventory for the MCMA, other vehicle emissions measurements in the MCMA, and measurements of on-road emissions in US cities. Our estimates for motor vehicle emissions of benzene, toluene, formaldehyde, and acetaldehyde in the MCMA indicate these species are present in concentrations higher than previously reported. The high motor vehicle aldehyde emissions may have an impact on the photochemistry of urban areas.
The water vapour distribution in the Arctic lowermost stratosphere during LAUTLOS campaign and related transport processes including stratosphere-troposphere exchange
Authors: Karpechko A. , Lukyanov A. , Kyrö E. , Khaikin S. , Korshunov L. , Kivi R. , Vömel H.
Published: April 2010

Abstract. Balloon-borne water vapour measurements during January and February 2004, which were obtained as part of the LAUTLOS campaign at Sodankylä, Finland, 67° N, were used to analyse the water vapour distribution in the wintertime Arctic lowermost stratosphere. A 2.5 km thick layer (or 30 K in the potential temperature scale) above the local tropopause is characterized by a significant water vapour variability on a synoptic timescale with values between stratospheric and tropospheric, which is in good agreement with previously reported measurements. A cross-correlation analysis of ozone and water vapour confirms that this layer contains a mixture of stratospheric and tropospheric air masses. Some of the flights sampled laminae of enhanced water vapour above the tropopause. Meteorological analyses and backward trajectory calculations show that these features are related to filaments that had developed along the flanks of cut-off anticyclones, which had been active at this time over the Northern Atlantic. Cross-tropopause mass fluxes calculated following the Wei method are used to identify regions and processes that are important for stratosphere-troposphere exchange (STE) in high-latitudes. Intensive STE occurs around cut-off anticyclones in regions of strong winds, where calculations suggest the presence of developed clear-air turbulence. The decay of the filaments is also shown to be important for STE.
A global emission inventory of carbonaceous aerosol from historic records of fossil fuel and biofuel consumption for the period 1860–1997
Authors: Junker C. , Liousse C.
Published: April 2010

Abstract. Country by country emission inventories for carbonaceous aerosol for the period 1860 to 1997 have been constructed on the basis of historic fuel production, use and trade data sets published by the United Nation's Statistical Division UNSTAT (1997), Etemad et al. (1991) and Mitchell (1992, 1993, 1995). The inventories use emission factors variable over time, which have been determined according to changes in technological development. The results indicate that the industrialisation period since 1860 was accompanied by a steady increase in black carbon (BC) and organic carbon (OC) emissions up to 1910. The calculations show a moderate decrease of carbonaceous aerosol emissions between 1920 and 1930, followed by an increase up to 1990, the year when emissions began to decrease again. Changes in BC and OC emissions prior to the year 1950 are essentially driven by the USA, Germany and the UK. The USSR, China and India become substantial contributors to carbonaceous aerosol emissions after 1950. Emission maps have been generated with a 1°×1° resolution based on the relative population density in each country. They will provide a helpful tool for assessing the effect of carbonaceous aerosol emissions on observed climate changes of the past.
The atmospheric cycling of radiomethane and the ''fossil fraction'' of the methane source
Authors: Lassey K. R. , Lowe D. C. , Smith A. M.
Published: April 2010

Abstract. The cycling of 14CH4 (''radiomethane'') through the atmosphere has been strongly perturbed in the industrial era by the release of 14C-free methane from geologic reservoirs (''fossil methane'' emissions), and in the nuclear era, especially since ca 1970, by the direct release of nucleogenic radiomethane from nuclear power facilities. Contemporary measurements of atmospheric radiomethane have been used to estimate the proportion of fossil methane in the global methane source (the ''fossil fraction''), but such estimates carry high uncertainty due to the ill-determined nuclear-power source. We exploit an analysis in a companion paper of the global radiomethane budget through the nuclear era, using contemporary measurements of atmospheric radiomethane since 1986 to quantify both the fossil fraction and the strength of the nuclear power source. We deduce that 28.6±1.9% (1 s.d.) of the global methane source has fossil origin, a fraction which may include some 14C-depleted refractory carbon fraction such as in aged peat deposits. The co-estimated strength of the global nuclear-power source of radiomethane is consistent with values inferred independently from local nuclear facilities.
Radiative forcing by aerosols as derived from the AeroCom present-day and pre-industrial simulations
Authors: Schulz M. , Textor C. , Kinne S. , Balkanski Y. , Bauer S. , Berntsen T. , Berglen T. , Boucher O. , Dentener F. , Guibert S. , Isaksen I. S. A. , Iversen T. , Koch D. , Kirkevåg A. , Liu X. , Montanaro V. , Myhre G. , Penner J. E. , Pitari G. , Reddy S. , Seland Ø. , Stier P. , Takemura T.
Published: April 2010

Abstract. Nine different global models with detailed aerosol modules have independently produced instantaneous direct radiative forcing due to anthropogenic aerosols. The anthropogenic impact is derived from the difference of two model simulations with identically prescribed aerosol emissions, one for present-day and one for pre-industrial conditions. The difference in the energy budget at the top of the atmosphere (ToA) yields a new harmonized estimate for the aerosol direct radiative forcing (RF) under all-sky conditions. On a global annual basis RF is –0.2 Wm-2, with a standard deviation of ±0.2 Wm-2. Anthropogenic nitrate and dust are not included in this estimate. No model shows a significant positive all-sky RF. The corresponding clear-sky RF is –0.6 Wm-2. The cloud-sky RF was derived based on all-sky and clear-sky RF and modelled cloud cover. It was significantly different from zero and ranged between –0.16 and +0.34 Wm-2. A sensitivity analysis shows that the total aerosol RF is influenced by considerable diversity in simulated residence times, mass extinction coefficients and most importantly forcing efficiencies (forcing per unit optical depth). Forcing efficiency differences among models explain most of the variability, mainly because all-sky forcing estimates require proper representation of cloud fields and the correct relative altitude placement between absorbing aerosol and clouds. The analysis of the sulphate RF shows that differences in sulphate residence times are compensated by opposite mass extinction coefficients. This is explained by more sulphate particle humidity growth and thus higher extinction in models with short-lived sulphate present at lower altitude and vice versa. Solar absorption within the atmospheric column is estimated at +0.85 Wm-2. The local annual average maxima of atmospheric forcing exceed +5 Wm-2 confirming the regional character of aerosol impacts on climate. The annual average surface forcing is –1.03 Wm-2.
Water-side turbulence enhancement of ozone deposition to the ocean
Authors: Fairall C. W. , Helmig D. , Ganzeveld L. , Hare J.
Published: April 2010

Abstract. A parameterization for the deposition velocity of an ocean-reactive atmospheric gas (such as ozone) is developed. The parameterization is based on integration of the turbulent-molecular transport equation (with a chemical source term) in the ocean. It extends previous work that only considered reactions within the oceanic molecular sublayer. The sensitivity of the ocean-side transport to reaction rate and wind forcing is examined. A more complicated case with a much more reactive thin surfactant layer is also considered. The full atmosphere-ocean deposition velocity is obtained by matching boundary conditions at the interface. For an assumed ocean reaction rate of 103 s-1, the enhancement for ozone deposition by oceanic turbulence is found to be up to a factor of three for meteorological data obtained in a recent cruise off the East Coast of the U.S.
Regional lightning NOx sources during the TROCCINOX experiment
Authors: Mari C. , Chaboureau J. P. , Pinty J. P. , Duron J. , Mascart P. , Cammas J. P. , Gheusi F. , Fehr T. , Schlager H. , Roiger A. , Lichtenstein M. , Stock P.
Published: April 2010

Abstract. A lightning NOx source (LiNOx) has been implemented in the deep convection scheme of the Meso-NH mesoscale model following a mass-flux formalism coherent with the transport and scavenging of gases inside the convective scheme. No a-priori vertical placement of LiNOx is necessary with this approach. In this approach the vertical transport of NO inside clouds is calculated by the parameterization of deep convective transport, thus eliminating the need for a-priori LiNOx. Once produced inside the convective column, NO molecules are redistributed by updrafts and downdrafts and detrained in the environment when the conditions are favorable. The model was applied to three particular flights during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) campaign over the tropical area around Bauru on 3–4 March 2004. The convective activity during the three flights was investigated using brightness temperature at 10.7 µm observed from GOES-12 satellite. The use of a model-to-satellite approach reveals that the simulation appears rather realistic compared to the observations. The diurnal cycle of the simulated brightness temperature, CAPE, number of IC lightning, NO entrainment flux are in phase, with a succession of three marked peaks at 18:00 UTC (15:00 LT). These simulated peaks precede the observed afternoon one by about three hours. Comparison of the simulated NOx with observations along the flight tracks show that the model reproduces well the observed NOx levels when the LiNOx source is applied. The budget of entrainment, detrainment and LiNOx convective fluxes shows that the majority of the NO detrained back to the environment comes from lightning source inside the convective columns. Entrainment of NO from the environment and vertical transport from the boundary layer were not significant during the episode. The troposphere is impacted by detrainment fluxes of LiNOx from 4 km altitude to 16 km with maximum values around 14 km altitude. Detrainment fluxes vary between 75 kg(N)/s during nighttime to 400 kg(N)/s at the times of maximun convective activity. Extrapolation of these regional fluxes gives global LiNOx production between 39–55 Tg(N)/year which is above the upper range of current estimates.
Technical note: Water vapour concentration and flux measurements with PTR-MS
Authors: Ammann C. , Brunner A. , Spirig C. , Neftel A.
Published: April 2010

Abstract. The most direct approach for measuring the exchange of biogenic volatile organic compounds between terrestrial ecosystems and the atmosphere is the eddy covariance technique. It has been applied several times in the last few years using fast response proton-transfer-reaction mass spectrometry (PTR-MS). We present an independent validation of this technique by applying it to measure the water vapour flux in comparison to a common reference system comprising an infra-red gas analyser (IRGA). Water vapour was detected in the PTR-MS at mass 37 (atomic mass units) corresponding to the cluster ion H3O+·H2O. During a five-week field campaign at a grassland site, we obtained a non-linear but stable calibration function between the mass 37 signal and the reference water vapour concentration. With a correction of the high-frequency damping loss based on empirical ogive analysis, the eddy covariance water vapour flux obtained with the PTR-MS showed a very good agreement with the flux of the reference system. The application of the empirical ogive method for high-frequency correction led to significantly better results than using a correction based on theoretical spectral transfer functions. This finding is attributed to adsorption effects on the tube walls that are presently not included in the theoretical correction approach.
Sensitivity of meteoric smoke distribution to microphysical properties and atmospheric conditions
Authors: Megner L. , Rapp M. , Gumbel J.
Published: April 2010

Abstract. Meteoroids entering the Earth's atmopsphere experience strong deceleration and ablate, whereupon the resulting material is believed to re-condense to nanometre-size "smoke particles". These particles are thought to be of great importance for many middle atmosphere phenomena, such as noctilucent clouds, polar mesospheric summer echoes, metal layers, and heterogeneous chemistry. The properties and distribution of meteoric smoke depend on poorly known or highly variable factors such as the amount, composition and velocity of incoming meteoric material, the efficiency of coagulation, and the state and circulation of the atmosphere. This work uses a one-dimensional microphysical model to investigate the sensitivities of meteoric smoke properties to these poorly known or highly variable factors. The resulting uncertainty or variability of meteoric smoke quantities such as number density, mass density, and size distribution are determined. It is found that the two most important factors are the efficiency of the coagulation and background vertical wind. The seasonal variation of the vertical wind in the mesosphere implies strong global and temporal variations in the meteoric smoke distribution. This contrasts the simplistic picture of a homogeneous global meteoric smoke layer, which is currently assumed in many studies of middle atmospheric phenomena. In particular, our results suggest a very low number of nanometre-sized smoke particles at the summer mesopause where they are thought to serve as condensation nuclei for noctilucent clouds.
Aerosol nucleation over oceans and the role of galactic cosmic rays
Authors: Kazil J. , Lovejoy E. R. , Barth M. C. , O’Brien K.
Published: April 2010

Abstract. We investigate formation of sulfate aerosol in the marine troposphere from neutral and charged nucleation of H2SO4 and H2O. A box model of neutral and charged aerosol processes is run on a grid covering the oceans. Input data are taken from a model of galactic cosmic rays in the atmosphere, and from global chemistry and transport models. We find a weak aerosol production over the tropical oceans in the lower and middle troposphere, and a stronger production at higher latitudes, most notably downwind of industrial regions. The highest aerosol production, however, occurs in the upper troposphere, in particular in the tropics. This finding supports the proposition by which non-sea salt marine boundary layer aerosol in tropical regions does not form in situ, but nucleates in the upper troposphere from convectively lifted and cloud processed boundary layer air rich in aerosol precursor gases, from where it descends in subsiding air masses compensating convection. Convection of boundary layer air also appears to drive the formation of condensation nuclei in the tropical upper troposphere which maintains the stratospheric aerosol layer in the absence of volcanic activity. Neutral nucleation contributes only marginally to aerosol production in our simulations. This highlights the importance of charged binary and of ternary nucleation involving ammonia for aerosol formation. In clean marine regions however, ammonia concentrations seem too low to support ternary nucleation, making binary nucleation from ions a likely pathway for sulfate aerosol formation. On the other hand, our analysis indicates that the variation of ionization by galactic cosmic rays over the decadal solar cycle does not entail a response in aerosol production and cloud cover via the second indirect aerosol effect that would explain observed variations in global cloud cover. We estimate that the variation in radiative forcing resulting from a response of clouds to the change in galactic cosmic ray ionization and subsequent aerosol production over the decadal solar cycle is smaller than the concurrent variation of total solar irradiance.
Formation of secondary organic aerosol and oligomers from the ozonolysis of enol ethers
Authors: Sadezky A. , Chaimbault P. , Mellouki A. , Römpp A. , Winterhalter R. , Le Bras G. , Moortgat G. K.
Published: April 2010

Abstract. Formation of secondary organic aerosol has been observed in the gas phase ozonolysis of a series of enol ethers, among them several alkyl vinyl ethers (AVE, ROCH=CH2), such as ethyl, propyl, n-butyl, iso-butyl, t-butyl vinyl ether, and ethyl propenyl ether (EPE, C2H5OCH=CHCH3). The ozonolysis has been studied in a 570 l spherical glass reactor at atmospheric pressure (730 Torr) and temperature (296 K). Gas phase reaction products were investigated by in-situ FTIR spectroscopy, and secondary organic aerosol (SOA) formation was monitored by a scanning mobility particle sizer (SMPS). The chemical composition of the formed SOA was analysed by a hybrid mass spectrometer using electrospray ionization (ESI). The main stable gas phase reaction product is the respective alkyl formate ROC(O)H, formed with yields of 60 to 80%, implying that similar yields of the corresponding Criegee Intermediates (CI) CH2O2 for the AVE and CH3CHO2 for EPE are generated. Measured SOA yields are between 2 to 4% for all enol ethers. Furthermore, SOA formation is strongly reduced or suppressed by the presence of an excess of formic acid, which acts as an efficient CI scavenger. Chemical analysis of the formed SOA by ESI(+)/MS-TOF allows to identify oligomeric compounds in the mass range 200 to 800 u as its major constituents. Repetitive chain units are identified as CH2O2 (mass 46) for the AVE and C2H4O2 (mass 60) for EPE and thus have the same chemical compositions as the respective major Criegee Intermediates formed during ozonolysis of these ethers. The oligomeric structure and chain unit identity are confirmed by HPLC/ESI(+)/MS-TOF and ESI(+)/MS/MS-TOF experiments, whereby successive and systematic loss of a fragment with mass 46 for the AVE (and mass 60 for EPE) is observed. It is proposed that the oligomer has the following basic structure of an oligoperoxide, -[CH(R)-O-O]n-, where R=H for the AVE and R=CH3 for the EPE. Oligoperoxide formation is thus suggested to be another, so far unknown reaction of stabilized Criegee Intermediates in the gas phase ozonolysis of oxygen-containing alkenes leading to SOA formation.
Analysis of non-regulated vehicular emissions by extractive FTIR spectrometry: tests on a hybrid car in Mexico City
Authors: Reyes F. , Grutter M. , Jazcilevich A. , González-Oropeza R.
Published: April 2010

Abstract. A methodology to acquire valuable information on the chemical composition and evolution of vehicular emissions is presented. The analysis of the gases is performed by passing a constant flow of a sample gas from the tail-pipe into a 10 L multi-pass cell. The absorption spectra within the cell are obtained using an FTIR spectrometer at 0.5 cm-1 resolution along a 13.1 m optical path. Additionally, the total flow from the exhaust is continuously measured from a differential pressure sensor on a Pitot tube installed at the exit of the exhaust. This configuration aims to obtain a good speciation capability by coadding spectra during 30 s and reporting the emission (in g/km) of key and non-regulated pollutants, such as CO2, CO, NO, SO2, NH3, HCHO, NMHC, during predetermined driving routines. The advantages and disadvantages of increasing the acquisition frequency, as well as the effect of other parameters such as spectral resolution, cell volume and flow rate, are discussed. With the aim of testing and evaluating the proposed technique, experiments were performed on a dynamometer running FTP-75 and typical driving cycles of the Mexico City Metropolitan Area (MCMA) on a Toyota Prius hybrid vehicle. This car is an example of recent automotive technology to reach the market dedicated to reduce emissions and therefore pressing the need of low detection techniques. This study shows the potential of the proposed technique to measure and report in real time the emissions of a large variety of pollutants, even from a super ultra-low emission vehicle (SULEV). The emissions of HC's, NOx, CO and CO2 obtained here are similar to experiments performed in other locations with the same vehicle model. Some differences suggest that an inefficient combustion process and type of gasoline used in the MCMA may be partly responsible for lower CO2 and higher CO and NO emission factors. Also, a fast reduction of NO emission to very low values is observed after cold ignition, giving rise to moderate N2O and eventually NH3 emissions. The proposed technique provides a tool for future studies comparing in detail the emissions of different technologies using alternative fuels and emission control systems.
Kinetics and mechanism of heterogeneous oxidation of sulfur dioxide by ozone on surface of calcium carbonate
Authors: Li L. , Chen Z. M. , Zhang Y. H. , Zhu T. , Li J. L. , Ding J.
Published: April 2010

Abstract. Sulfate particles play a key role in the air quality and the global climate, but the heterogeneous formation mechanism of sulfates on surfaces of atmospheric particles is not well established. Carbonates, which act as a reactive component in mineral dust due to their special chemical properties, may contribute significantly to the sulfate formation by heterogeneous processes. This paper presents a study on the oxidation of SO2 by O3 on CaCO3 particles. Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), the formation of sulfite and sulfate on the surface was identified, and the roles of O3 and water in oxidation processes were determined. The results showed that in the presence of O3, SO2 can be oxidized to sulfate on the surface of CaCO3 particles. The reaction is first order in SO2 and zero order in O3. The reactive uptake coefficient for SO2 oxidation by O3 was determined to be (1.4±0.3)×10−7 using the BET area as the reactive area and (7.7±1.6)×10−4 using the geometric area. A two-stage mechanism that involves adsorption of SO2 followed by O3 oxidation is proposed and the adsorption of SO2 on the CaCO3 surface is the rate-determining step. The proposed mechanism can well explain the experiment results. The atmospheric implications were explored based on a box model calculation. It was found that the heterogeneous reaction might be an important pathway for sulfate formation in the atmosphere.
Differences between ground Dobson, Brewer and satellite TOMS-8, GOME-WFDOAS total ozone observations at Hradec Kralove, Czech
Authors: Vanicek K.
Published: April 2010

Abstract. This paper presents key results achieved on analysis of relation between high-quality simultaneous Dobson, Brewer ground and TOMS-V8, GOME-WFDOAS satellite total ozone observations for Hradec Kralove, Czech Republic. Statistically significant seasonal differences with maxima up to 4% of monthly averages have been found between Dobson and Brewer measurements in winter/spring months. These differences can influence estimation of ozone trends if combined data series are used after replacement of the Dobson instrument by the Brewer spectrophotometer. The differences are mostly attributed to the influence of ozone effective temperature on ozone absorption coefficients and to total sulphur dioxide. Similar seasonal differences exist between Dobson, GOME and Brewer, TOMS data sets at Hradec Kralove while Dobson versus TOMS and Brewer versus GOME observations fit well with each other within the instrumental accuracy of spectrophotometers. The above findings are supposed to be relevant to other mid and high latitude stations and they have been confirmed by several independent analyses. The conclusions should be considered by data users because the differences between particular ground and satellite data sets can influence validation of satellite ozone observing systems and analyses of recovery of the ozone layer in mid and high latitudes, among others.
Radiocarbon analysis in an Alpine ice core: record of anthropogenic and biogenic contributions to carbonaceous aerosols in the past (1650–1940)
Authors: Jenk T. M. , Szidat S. , Schwikowski M. , Gäggeler H. W. , Brütsch S. , Wacker L. , Synal H.-A. , Saurer M.
Published: April 2010

Abstract. Long-term concentration records of carbonaceous particles (CP) are of increasing interest in climate research due to their not yet completely understood effects on climate. Nevertheless, only poor data on their concentrations and sources in the past is available. We present a first long-term record of organic carbon (OC) and elemental carbon (EC) concentrations - the two main fractions of CP – along with the corresponding fraction of modern carbon (fM) derived from radiocarbon (14C) analysis. The combination of concentration measurements with 14C analysis of CP allows a distinction and quantification of natural, biogenic and anthropogenic fossil sources in the past. CP were extracted from an ice archive, with resulting carbon quantities in the microgram range. Analysis of 14C by accelerator mass spectrometry (AMS) was therefore highly demanding. We analysed 33 samples of 0.4 to 1 kg ice from a 150.5 m long ice core retrieved at Fiescherhorn glacier in December 2002 (46°33'3.2" N, 08°04'0.4'' E; 3900 m a.s.l.). Samples were taken from below the firn/ice transition down to bedrock, covering the time period 1650–1940 and thus the transition from the pre-industrial to the industrial era. Before 1800, OC was of pure biogenic origin with a mean concentration of 21±2 μg kg−1}. In 1940, OC concentration was more than a factor of 3 higher than this biogenic background, almost half of it originating from anthropogenic sources, i.e. from combustion of fossil fuels. The biogenic EC concentration was nearly constant over the examined time period with 6±1 μg kg−1. In 1940, the additional anthropogenic input of atmospheric EC was about 50 μg kg−1.
Implementation of a Markov Chain Monte Carlo Method to inorganic aerosol modeling of observations from the MCMA-2003 Campaign. Part II: Model application to the CENICA, Pedregal and Santa Ana sites
Authors: San Martini F. M. , Dunlea E. J. , Volkamer R. , Onasch T. B. , Jayne J. T. , Canagaratna M. R. , Worsnop D. R. , Kolb C. E. , Shorter J. H. , Herndon S. C. , Zahniser M. S. , Salcedo D. , Dzepina K. , Jimenez J. L. , Ortega J. M. , Johnson K. S. , McRae G. J. , Molina L. T. , Molina M. J.
Published: April 2010

Abstract. A Markov Chain Monte Carlo model for integrating the observations of inorganic species with a thermodynamic equilibrium model was presented in Part I of this series. Using observations taken at three ground sites, i.e. a residential, industrial and rural site, during the MCMA-2003 campaign in Mexico City, the model is used to analyze the inorganic aerosol and ammonia data and predict gas phase concentrations of nitric and hydrochloric acid. In general the model is able to accurately predict the observed inorganic aerosol concentrations at all three sites. The agreement between the predicted and observed gas phase ammonia concentration is excellent. The NOz concentration calculated from the NOy, NO and NO2 observations is of limited use in constraining the gas phase nitric acid concentration given the large uncertainties in this measure of nitric acid and additional reactive nitrogen species. Focusing on the acidic period of 9–11 April identified by Salcedo et al. (2006), the model accurately predicts the aerosol phase observations during this period with the exception of the nitrate predictions after 10:00 a.m. (CDT) on 9 April, where the model underpredicts the observations by, on average, 20%. For periods when the aerosol chloride observations are consistently above the detection limit, the model is able to both accurately predict the aerosol chloride predictions and provide well-constrained HCl (g) concentrations. When the aerosols are aqueous, the most likely concentrations of HCl (g) are in the sub-ppbv range. The most likely predicted concentration of HCl (g) was found to reach concentrations of order 10 ppbv if the aerosols are dry. Finally, the atmospheric relevance of HCl (g) is discussed in terms of its indicator properties for the possible influence of chlorine-mediated photochemistry in Mexico City.
Modeling of biomass smoke injection into the lower stratosphere by a large forest fire (Part I): reference simulation
Authors: Trentmann J. , Luderer G. , Winterrath T. , Fromm M. D. , Servranckx R. , Textor C. , Herzog M. , Graf H.-F. , Andreae M. O.
Published: April 2010

Abstract. Wildland fires in boreal regions have the potential to initiate deep convection, so-called pyro-convection, due to their release of sensible heat. Under favorable atmospheric conditions, large fires can result in pyro-convection that transports the emissions into the upper troposphere and the lower stratosphere. Here, we present three-dimensional model simulations of the injection of fire emissions into the lower stratosphere by pyro-convection. These model simulations are constrained and evaluated with observations obtained from the Chisholm fire in Alberta, Canada, in 2001. The active tracer high resolution atmospheric model (ATHAM) is initialized with observations obtained by radiosonde. Information on the fire forcing is obtained from ground-based observations of the mass and moisture of the burned fuel. Based on radar observations, the pyro-convection reached an altitude of about 13 km, well above the tropopause, which was located at about 11.2 km. The model simulation yields a similarly strong convection with an overshoot of the convection above the tropopause. The main outflow from the pyro-convection occurs at about 10.6 km, but a significant fraction (about 8%) of the emitted mass of the smoke aerosol is transported above the tropopause. In contrast to regular convection, the region with maximum updraft velocity in the pyro-convection is located close to the surface above the fire. This results in high updraft velocities >10 ms−1 at cloud base. The temperature anomaly in the plume decreases rapidly with height from values above 50 K at the fire to about 5 K at about 3000 m above the fire. While the sensible heat released from the fire is responsible for the initiation of convection in the model, the release of latent heat from condensation and freezing dominates the overall energy budget. Emissions of water vapor from the fire do not significantly contribute to the energy budget of the convection.
Modelling constraints on the emission inventory and on vertical diffusion for CO and SO2 in the Mexico City Metropolitan Area using Solar FTIR and zenith sky UV spectroscopy
Authors: de Foy B. , Lei W. , Zavala M. , Volkamer R. , Samuelsson J. , Mellqvist J. , Galle B. , Martínez A.-P. , Grutter M. , Molina L. T.
Published: April 2010

Abstract. Emissions of air pollutants in and around urban areas lead to negative health impacts on the population. To estimate these impacts, it is important to know the sources and transport mechanisms of the pollutants accurately. Mexico City has a large urban fleet in a topographically constrained basin leading to high levels of carbon monoxide (CO). Large point sources of sulfur dioxide (SO2) surrounding the basin lead to episodes with high concentrations. An Eulerian grid model (CAMx) and a particle trajectory model (FLEXPART) are used to evaluate the estimates of CO and SO2 in the current emission inventory using mesoscale meteorological simulations from MM5. Vertical column measurements of CO are used to constrain the total amount of emitted CO in the model and to identify the most appropriate vertical diffusion scheme. Zenith sky UV spectroscopy is used to estimate the emissions of SO2 from a large power plant and the Popocatépetl volcano. Results suggest that the models are able to identify correctly large point sources and that both the power plant and the volcano impact the MCMA. Modelled concentrations of CO based on the current emission inventory match observations suggesting that the current total emissions estimate is correct. Possible adjustments to the spatial and temporal distribution can be inferred from model results. Accurate source and dispersion modelling provides feedback for development of the emission inventory, verification of transport processes in air quality models and guidance for policy decisions.
Pronounced signature of arctic surface ozone depletion events after polar sunrise on Δ17O in atmospheric nitrate
Authors: Morin S. , Savarino J. , Bekki S. , Gong S. , Bottenheim J. W.
Published: April 2010

Abstract. We report in this paper the first measurements of the isotopic anomaly of oxygen in Arctic atmospheric inorganic nitrate. Data and samples were collected at Alert, Nunavut, Canada (82°30' N, 62°19' W) in spring 2004. Focusing on the polar sunrise period, characterized by the occurrence of severe boundary layer ozone depletion events (ODEs), our data show a significant correlation between the evolution of atmospheric ozone (O3) mixing ratios and Δ17O in nitrate Δ17O(NO−3)). This relationship can be expressed as: Δ17O(NO−3)/‰=0.15 O3/ (nmol mol−1) + 28.6, with R2=0.70 (n=12), for Δ17O(NO−3) ranging between 29 and 34. To quantitatively interpret this relationship, we derive from mechanisms at play in the arctic boundary layer isotopic mass-balance equations, which depend on the concentrations of reactive species and their isotopic characteristics. Changes in the relative importance of O3, RO2 and BrO in the oxidation of NOx during ODEs, and the large isotopic anomalies that O3 and BrO carry, are the driving force for the high variability in the measured Δ17O(NO−3). BrONO2 hydrolysis is found to be the major source of nitrate in the arctic boundary layer, in agreement with recent modeling studies. In addition, the isotopic fingerprint of the activity of ozone in a relatively stable compound appears somewhat promising in the perspective of using the isotopic composition of nitrate embedded in polar ice-cores as a paleo-indicator of the atmospheric ozone level that may yield an indirect proxy for the oxidative power of past atmospheres.
Investigating the composition of organic aerosol resulting from cyclohexene ozonolysis: low molecular weight and heterogeneous reaction products
Authors: Hamilton J. F. , Lewis A. C. , Reynolds J. , Carpenter L. J. , Lubben A.
Published: April 2010

Abstract. The composition of organic aerosol formed from the gas phase ozonolysis of cyclohexene has been investigated in a smog chamber experiment. Comprehensive gas chromatography with time of flight mass spectrometric detection was used to determine that dicarboxylic acids and corresponding cyclic anhydrides dominated the small gas phase reaction products found in aerosol sampled during the first hour after initial aerosol formation. Structural analysis of larger more polar molecules was performed using liquid chromatography with ion trap tandem mass spectrometry. This indicated that the majority of identified organic mass was in dimer form, built up from combinations of the most abundant small acid molecules, with frequent indication of the inclusion of adipic acid. Trimers and tetramers potentially formed via similar acid combinations were also observed in lower abundances. Tandem mass spectral data indicated dimers with either acid anhydride or ester functionalities as the linkage between monomers. High-resolution mass spectrometry identified the molecular formulae of the most abundant dimer species to be C10H16O6, C11H18O6, C10H14O8 and C11H16O8 and could be used in some cases to reduce uncertainty in exact chemical structure determination by tandem MS.