bluuebunny/crossref_metadata_2025 huggingface dataset:
Real time chemical characterization of local and regional nitrate aerosols
Authors: Dall'Osto M. , Harrison R. M. , Coe H. , Williams P. I. , Allan J. D.
Published: April 2010

Abstract. Nitrate aerosols make a very major contribution to PM2.5 and PM10 in western Europe, but their sources and pathways have not been fully elucidated. An Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS) and a Compact Time of Flight Aerosol Mass Spectrometer (C-ToF-AMS) were deployed in an urban background location in London, UK, collecting data as part of the REPARTEE-I experiment. During REPARTEE-I, daily PM10 concentrations ranged up to 43.6 µg m−3, with hourly nitrate concentrations (measured by AMS) of up to 5.3 µg m−3. The application of the ART-2a neural network algorithm to the ATOFMS data characterised the nitrate particles as occurring in two distinct clusters (i.e. particle types). The first (33.6% of particles by number) appeared to be locally produced in urban locations during nighttime, whilst the second (22.8% of particles by number) was regionally transported from continental Europe. Nitrate in locally produced aerosol was present mainly in particles smaller than 300 nm, whilst the regional nitrate presented a coarser mode, peaking at 600 nm. In both aerosol types, nitrate was found to be internally mixed with sulphate, ammonium, elemental and organic carbon. Nitrate in regional aerosol appeared to be more volatile than that locally formed. During daytime, a core of the regionally transported nitrate aerosol particle type composed of organic carbon and sulphate was detected.
Impact of primary formaldehyde on air pollution in the Mexico City Metropolitan Area
Authors: Lei W. , Zavala M. , de Foy B. , Volkamer R. , Molina M. J. , Molina L. T.
Published: April 2010

Abstract. Formaldehyde (HCHO) is a radical source that plays an important role in urban atmospheric chemistry and ozone formation. The Mexico City Metropolitan Area (MCMA) is characterized by high anthropogenic emissions of HCHO (primary HCHO), which together with photochemical production of HCHO from hydrocarbon oxidation (secondary HCHO), lead to high ambient HCHO levels. The CAMx chemical transport model was employed to evaluate the impact of primary HCHO on its ambient concentration, on the ROx radical budget, and on ozone (O3) formation in the MCMA. Important radical sources, including HCHO, HONO, and O3-olefin reactions, were constrained by measurements from routine observations of the local ambient air monitoring network and the MCMA-2003 field campaign. Primary HCHO was found not only contributing significantly to the ambient HCHO concentration, but also enhancing the radical budget and O3 production in the urban atmosphere of the MCMA. Overall in the urban area, total daytime radical production is enhanced by up to 10% and peak O3 concentration by up to 8%. While primary HCHO contributes predominantly to the ambient HCHO concentration between nighttime and morning rush hours, significant influence on the radical budget and O3 production starts early morning, culminates at mid-morning and is sustained until early afternoon.
Springtime warming and reduced snow cover from carbonaceous particles
Authors: Flanner M. G. , Zender C. S. , Hess P. G. , Mahowald N. M. , Painter T. H. , Ramanathan V. , Rasch P. J.
Published: April 2010

Abstract. Boreal spring climate is uniquely susceptible to solar warming mechanisms because it has expansive snow cover and receives relatively strong insolation. Carbonaceous particles can influence snow coverage by warming the atmosphere, reducing surface-incident solar energy (dimming), and reducing snow reflectance after deposition (darkening). We apply a range of models and observations to explore impacts of these processes on springtime climate, drawing several conclusions: 1) Nearly all atmospheric particles (those with visible-band single-scatter albedo less than 0.999), including all mixtures of black carbon (BC) and organic matter (OM), increase net solar heating of the atmosphere-snow column. 2) Darkening caused by small concentrations of particles within snow exceeds the loss of absorbed energy from concurrent dimming, thus increasing solar heating of snowpack as well (positive net surface forcing). Over global snow, we estimate 6-fold greater surface forcing from darkening than dimming, caused by BC+OM. 3) Equilibrium climate experiments suggest that fossil fuel and biofuel emissions of BC+OM induce 95% as much springtime snow cover loss over Eurasia as anthropogenic carbon dioxide, a consequence of strong snow-albedo feedback and large BC+OM emissions from Asia. 4) Of 22 climate models contributing to the IPCC Fourth Assessment Report, 21 underpredict the rapid warming (0.64°C decade−1) observed over springtime Eurasia since 1979. Darkening from natural and anthropogenic sources of BC and mineral dust exerts 3-fold greater forcing on springtime snow over Eurasia (3.9 W m−2) than North America (1.2 W m−2). Inclusion of this forcing significantly improves simulated continental warming trends, but does not reconcile the low bias in rate of Eurasian spring snow cover decline exhibited by all models.
Estimates of mercury flux into the United States from non-local and global sources: results from a 3-D CTM simulation
Authors: Drewniak B. A. , Kotamarthi V. R. , Streets D. , Kim M. , Crist K.
Published: April 2010

Abstract. The sensitivity of Hg concentration and deposition in the United States to emissions in China was investigated by using a global chemical transport model: Model for Ozone and Related Chemical Tracers (MOZART). Two forms of gaseous Hg were included in the model: elemental Hg (HG(0) and oxidized or reactive Hg (HGO). We simulated three different emission scenarios to evaluate the model's sensitivity. One scenario included no emissions from China, while the others were based on different estimates of Hg emissions in China. The results indicated, in general, that when Hg emissions were included, HG(0) concentrations increased both locally and globally. Increases in Hg concentrations in the United States were greatest during spring and summer, by as much as 7%. Ratios of calculated concentrations of Hg and CO near the source region in eastern Asia agreed well with ratios based on measurements. Increases similar to those observed for HG(0) were also calculated for deposition of HGO. Calculated increases in wet and dry deposition in the United States were 5–7% and 5–9%, respectively. The results indicate that long-range transcontinental transport of Hg has a non-negligible impact on Hg deposition levels in the United States.
Estimating surface CO2 fluxes from space-borne CO2 dry air mole fraction observations using an ensemble Kalman Filter
Authors: Feng L. , Palmer P. I. , Bösch H. , Dance S.
Published: April 2010

Abstract. We have developed an ensemble Kalman Filter (EnKF) to estimate 8-day regional surface fluxes of CO2 from space-borne CO2 dry-air mole fraction observations (XCO2
Comparison of tropospheric chemistry schemes for use within global models
Authors: Emmerson K. M. , Evans M. J.
Published: April 2010

Abstract. Methane and ozone are two important climate gases with significant tropospheric chemistry. Within chemistry-climate and transport models this chemistry is simplified for computational expediency. We compare the state of the art Master Chemical Mechanism (MCM) with six tropospheric chemistry schemes (CRI-reduced, GEOS-CHEM and a GEOS-CHEM adduct, MOZART, TOMCAT and CBM-IV) that could be used within composition transport models. We test the schemes within a box model framework under conditions derived from a composition transport model and from field observations from a regional scale pollution event. We find that CRI-reduced provides much skill in simulating the full chemistry, yet with greatly reduced complexity. We find significant variations between the other chemical schemes, and reach the following conclusions. 1) The inclusion of a gas phase N2O5+H2O reaction in some schemes and not others is a large source of uncertainty in the inorganic chemistry. 2) There are significant variations in the calculated concentration of PAN between the schemes, which will affect the long range transport of reactive nitrogen in global models. 3) The representation of isoprene chemistry differs hugely between the schemes, leading to significant uncertainties on the impact of isoprene on composition. 4) Night-time chemistry is badly represented with significant disagreements in the ratio of NO3 to NOx. Resolving these four issues through further investigative laboratory studies will reduce the uncertainties within the chemical schemes of global tropospheric models.
Atmospheric oxygen and carbon dioxide observations from two European coastal stations 2000–2005: continental influence, trend changes and APO climatology
Authors: Sirignano C. , Neubert R. E. M. , Meijer H. A. J. , Rödenbeck C.
Published: April 2010

Abstract. Seeking for baseline conditions has biased the carbon dioxide (CO2) monitoring networks towards remote marine stations, missing part of the variability that is due to regional anthropogenic as well as land biota activity. We present here a five-year record of atmospheric CO2 mixing ratios and oxygen/nitrogen ratios (O2/N2) from the coastal stations Lutjewad (LUT), the Netherlands and Mace Head (MHD), Ireland, derived from flask samples. Oxygen mixing ratios, concurrently measured with CO2, help determine regional CO2 fluxes by separating land fluxes from sea fluxes. Mace Head is the closest marine baseline station to Lutjewad, located at the same latitude, and therefore is taken as a reference. During the period of this study, we observed an average increase of CO2 in the atmosphere of (1.7±0.2) μmol*(mol dry air)−1 per year, and a change of the O2 fraction of (−20±1) per meg per year. The observed acceleration of the oxygen decrease during the study period seems to confirm the existence of a net oxygen sink other than the combustion processes alone. The difference between the CO2 summer minimum and the winter maximum is 14.4 μmol*(mol dry air)−1 and 16.1 μmol*(mol dry air)−1 at Mace Head and Lutjewad, respectively, while the opposite variation in the O2 signal equals 113 per meg and 153 per meg, respectively. We also studied the APO (atmospheric potential oxygen) tracer at both stations. By this analysis, evidence has been found that we need to be careful when using APO close to anthropogenic CO2 sources. It could be biased by combustion-derived CO2, and models have to take into account daily and seasonal variations in the anthropogenic CO2 production in order to be able to simulate APO over the continents.
Assessing the regional impacts of Mexico City emissions on air quality and chemistry
Authors: Mena-Carrasco M. , Carmichael G. R. , Campbell J. E. , Zimmerman D. , Tang Y. , Adhikary B. , D'allura A. , Molina L. T. , Zavala M. , García A. , Flocke F. , Campos T. , Weinheimer A. J. , Shetter R. , Apel E. , Montzka D. D. , Knapp D. J. , Zheng W.
Published: April 2010

Abstract. The impact of Mexico City (MCMA) emissions is examined by studying its effects on air quality, photochemistry, and on ozone production regimes by combining model products and aircraft observations from the MILAGRO experiment. The influence of MCMA emissions to enhancements in surface level NOx, CO, and O3 concentrations are confined to distances <200 km. However, the extent of the influence is significantly larger at higher altitudes. Broader MCMA impacts (some 900 km Northeast of the city) are shown for specific outflow conditions in which enhanced ozone, NOy, and MTBE mixing ratios over the Gulf of Mexico are linked to MCMA by source tagged tracers and sensitivity runs. This study shows that the "footprint" of MCMA on average is fairly local, with exception to reactive nitrogen, which can be transported long range in the form of PAN, acting as a reservoir and source of NOx with important regional ozone formation implications. The simulated effect of MCMA emissions of anthropogenic aerosol on photochemistry showed a maximum regional decrease of 40% in J[NO2→NO+O], and resulting in the reduction of ozone production by 5–10%. Observed ozone production efficiencies and photolysis rates are evaluated as a function of distance from MCMA, and by modeled influence from MCMA. These tend to be much lower closer to MCMA, and with higher MCMA influence. This research shows that MCMA emissions have a discernible effect on regional air quality and photochemistry, both contributing large amounts of ozone and its precursors, but with caveat that aerosol concentrations hinder formation of ozone to its potential due to its reduction in photolysis rates.
Source apportionment of PM2.5 in Seoul, Korea
Authors: Heo J.-B. , Hopke P. K. , Yi S.-M.
Published: April 2010

Abstract. PM2.5 samples were collected at a centrally located urban monitoring site in Seoul, Korea, every third day from March 2003 to December 2006 and analyzed for their chemical constituents. Sources were identified using Positive Matrix Factorization (PMF). A total of 393 samples were obtained during the sampling period, and 20 chemical species were measured. Nine PM2.5 sources were identified providing physically realistic profiles and interesting insights into the source contributions to the ambient mass concentrations. The major sources of PM2.5 were secondary nitrate (20%), secondary sulfate (20%), gasoline-fueled vehicles (17%), and biomass burning (12%), with lesser contributions from diesel emissions (8%), soil (7%), industry (6%), road salt and two-stroke engine (5%), and aged sea salt (2%). PM2.5 levels in Seoul were influenced by both local urban activities and regional-scale transport. Conditional Probability Function (CPF) results identified possible source directions of local sources such as motor vehicles (gasoline and diesel), industry, and road salt. Potential Source Contribution Function (PSCF) results showed that possible source areas contributing to the elevated secondary particle concentrations (sulfate and nitrate) in Seoul to be the major industrial areas in China.
Reactive nitrogen in Mexico City and its relation to ozone-precursor sensitivity: results from photochemical models
Authors: Sillman S. , West J. J.
Published: April 2010

Abstract. We use results of a 3-D photochemistry/transport model for ozone formation in Mexico City during events in 1997 to investigate ambient concentrations of reactive nitrogen in relation to ozone-precursor sensitivity. Previous results from other locations suggest that ratios such as O3/NOy and H2O2/HNO3 might provide measurement-based indicators for NOx-sensitive or VOC-sensitive conditions. Mexico City presents a different environment due to its high concentrations of VOC and high level of pollutants in general. The model predicts a correlation between PAN and O3 with relatively high PAN/O3 (0.07), which is still lower than measured values. The model PAN is comparable with results from a model for Paris but much higher than were found in Nashville in both models and measurements. The difference can be explained by the lower temperature in Mexico City relative to Nashville. Model HNO3 in Mexico City is unusually low for an urban area and PAN/HNO3 is very high, probably due to the high ratio of reactivity-weighted VOC to NOx. The model predicts that VOC-sensitive chemistry in Mexico is associated with high NOx, NOy and NOx/NOy and with low O3/NOy and H2O2/HNO3, suggesting that these indicators work well for Mexico City. The relation between ozone-precursor sensitivity and either O3/NOz or O3/HNO3 is more ambiguous. VOC-sensitive conditions are associated with higher O3/HNO3 than would be found in NOx-sensitive conditions, but model O3/HNO3 associated with both NOx-sensitive and VOC-sensitive chemistry is higher in Mexico than in other cities. The model predicts mixed sensitivity to NOx and VOC in Mexico City, with a tendency towards VOC-sensitive chemistry in the morning and NOx-sensitive in the afternoon, in contrast to model results for more recent events that predicted strongly VOC-sensitive conditions. The difference in predicted ozone-precursor sensitivity is most likely due to changes in emission rates over time. The model with mixed sensitivity predicts much lower ambient NOx and NOx/NOy than the strongly VOC-sensitive model.
Statistical properties of cloud lifecycles in cloud-resolving models
Authors: Plant R. S.
Published: April 2010

Abstract. A new technique is described for the analysis of cloud-resolving model simulations, which allows one to investigate the statistics of the lifecycles of cumulus clouds. Clouds are tracked from timestep-to-timestep within the model run. This allows for a very simple method of tracking, but one which is both comprehensive and robust. An approach for handling cloud splits and mergers is described which allows clouds with simple and complicated time histories to be compared within a single framework. This is found to be important for the analysis of an idealized simulation of radiative-convective equilibrium, in which the moist, buoyant, updrafts (i.e., the convective cores) were tracked. Around half of all such cores were subject to splits and mergers during their lifecycles. For cores without any such events, the average lifetime is 30 min, but events can lengthen the typical lifetime considerably.
Size-resolved aerosol chemistry on Whistler Mountain, Canada with a High-Resolution Aerosol Mass Spectrometer during INTEX-B
Authors: Sun Y. , Zhang Q. , MacDonald A. M. , Hayden K. , Li S. M. , Liggio J. , Liu P. S. K. , Anlauf K. G. , Leaitch W. R. , Cubison M. , Worsnop D. , van Donkelaar A. , Martin R. V.
Published: April 2010

Abstract. An Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) was deployed at the peak of Whistler Mountain (elevation 2182 m-MSL), British Columbia, from 19 April to 16 May 2006, as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) campaign. The mass concentrations and size distributions of non-refractory submicron particle (NR-PM1) species (i.e., sulfate, nitrate, ammonium, chloride, and organics) were measured in situ every 5 min. The HR-ToF-AMS results agreed well with collocated measurements. The average concentration of non-refractory submicron particulate matter (NR-PM1; 1.9 μg m−3) is similar to those observed at other remote, high elevation sites in North America. Episodes of enhanced aerosol loadings were observed, due to influences of regional and trans-Pacific transport of air pollution. Organics and sulfate were the dominant species, on average accounting for 55% and 30%, respectively, of the NR-PM1 mass. The average size distributions of sulfate and ammonium both showed a~large accumulation mode peaking around 500–600 nm in Dva while those of organic aerosol (OA) and nitrate peaked at ~300 nm. The size differences suggest that sulfate and OA were mostly present in external mixtures from different source origins. We also quantitatively determined the elemental composition of OA using the high resolution mass spectra. Overall, OA at Whistler Peak was highly oxygenated, with an average organic-mass-to-organic-carbon ratio (OM/OC) of 2.28±0.23 and an atomic ratio of oxygen-to-carbon (O/C) of 0.83±0.17. The nominal formula for OA was C1H1.66N0.03O0.83 for the entire study. Two significant trans-Pacific dust events originated from Asia were observed at Whistler Peak during this study. While both events were characterized with significant enhancements of coarse mode particles and mineral contents, the composition and characteristics of NR-PM1 were significantly different between them. One trans-Pacific event occurred on 15 May 2006, during which ammonium sulfate contributed >90% of the total NR-PM1 mass. This event was followed by a~high OA episode likely associated with regional emissions. The trans-Pacific OA were more oxidized and aged than the regional OA.
Glyoxal uptake on ammonium sulphate seed aerosol: reaction products and reversibility of uptake under dark and irradiated conditions
Authors: Galloway M. M. , Chhabra P. S. , Chan A. W. H. , Surratt J. D. , Flagan R. C. , Seinfeld J. H. , Keutsch F. N.
Published: April 2010

Abstract. Chamber studies of glyoxal uptake onto neutral ammonium sulphate aerosol were performed under dark and irradiated conditions to gain further insight into processes controlling glyoxal uptake onto ambient aerosol. Organic fragments from glyoxal dimers and trimers were observed within the aerosol under dark and irradiated conditions; glyoxal oligomer formation and overall organic growth were found to be reversible under dark conditions. Analysis of high-resolution time-of-flight aerosol mass spectra provides evidence for irreversible formation of carbon-nitrogen (C-N) compounds in the aerosol. These compounds are likely to be imidazoles formed by reaction of glyoxal with the ammonium sulphate seed. To the authors' knowledge, this is the first time C-N compounds resulting from condensed phase reactions with ammonium sulphate seed have been detected in aerosol. Organosulphates were not detected under dark conditions. However, active oxidative photochemistry, similar to that found in cloud processing, was found to occur within aerosol during irradiated experiments. Organosulphates, carboxylic acids, and organic esters were identified within the aerosol. Our study suggests that both C-N compound formation and photochemical processes should be considered in models of secondary organic aerosol formation via glyoxal.
Single ice crystal measurements during nucleation experiments with the depolarization detector IODE
Authors: Nicolet M. , Stetzer O. , Lohmann U. , Möhler O.
Published: April 2010

Abstract. In order to determine the efficiency of aerosol particles of several types to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175° in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one gives the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, peaks were detected in both channels, generating depolarization signals. Mean values of δ ranged from 0.24 to 0.37.
All weather IASI single field-of-view retrievals: case study – validation with JAIVEx data
Authors: Zhou D. K. , Smith W. L. , Larar A. M. , Liu X. , Taylor J. P. , Schlüssel P. , Strow L. L. , Mango S. A.
Published: April 2010

Abstract. Atmospheric thermodynamic parameters, such as atmospheric temperature and moisture profiles, cloud optical/microphysical properties, and surface properties are basic meteorological variables for weather forecasting. In addition, they are critical parameters in tropospheric chemistry studies. A physical, geophysical parameter retrieval scheme dealing with cloudy and cloud-free radiances observed with satellite ultraspectral infrared sounders has been developed to determine simultaneously surface, atmospheric thermodynamic, and cloud microphysical parameters. A one-dimensional variational (1-D Var.) multivariable inverse solution of the radiative transfer equation is used to iteratively improve a background state defined by eigenvector regression. This algorithm has been applied to data from the Infrared Atmospheric Sounding Interferometer (IASI) on the EUMETSAT Metop-A satellite. The IASI retrieved parameters presented herein are from radiance data gathered during the Joint Airborne IASI Validation Experiment (JAIVEx). JAIVEx provided intensive aircraft observations obtained from airborne Fourier Transform Spectrometer (FTS) systems, such as the NPOESS Airborne Sounder Testbed – Interferometer (NAST-I), in-situ measurements, and dedicated dropsonde and radiosonde measurements for the validation of the IASI products. Here, IASI atmospheric profile retrievals are compared with those obtained from dedicated dropsondes, radiosondes, and the airborne FTS system. The IASI examples presented here demonstrate the ability to retrieve fine-scale horizontal features with high vertical resolution from satellite ultraspectral sounder radiance spectra.
Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF6 and CO2
Authors: Bönisch H. , Engel A. , Curtius J. , Birner T. , Hoor P.
Published: April 2010

Abstract. The seasonality of transport and mixing of air into the lowermost stratosphere (LMS) is studied using distributions of mean age of air and a~mass balance approach, based on in-situ observations of SF6 and CO2 during the SPURT (Spurenstofftransport in der Tropopausenregion, trace gas transport in the tropopause region) aircraft campaigns. Combining the information of the mean age of air and the water vapour distributions we demonstrate that the tropospheric air transported into the LMS above the extratropical tropopause layer (ExTL) originates predominantly from the tropical tropopause layer (TTL). The concept of our mass balance is based on simultaneous measurements of the two passive tracers and the assumption that transport into the LMS can be described by age spectra which are superposition of two different modes. Based on this concept we conclude that the stratospheric influence on LMS composition is strongest in April with tropospheric fractions (α1) below 20% and that the strongest tropospheric signatures are found in October with (α1 greater than 80%. Beyond the fractions, our mass balance concept allows to calculate the associated transit times for transport of tropospheric air from the tropics into the LMS. The shortest transit times (<0.3 years) are derived for the summer, continuously increasing up to 0.8 years by the end of spring. These findings suggest that strong quasi-horizontal mixing across the weak subtropical jet from summer to mid of autumn and the considerably shorter residual transport time-scales within the lower branch of the Brewer-Dobson circulation in summer than in winter dominates the tropospheric influence in the LMS until the beginning of next year's summer.
Emission and chemistry of organic carbon in the gas and aerosol phase at a sub-urban site near Mexico City in March 2006 during the MILAGRO study
Authors: de Gouw J. A. , Welsh-Bon D. , Warneke C. , Kuster W. C. , Alexander L. , Baker A. K. , Beyersdorf A. J. , Blake D. R. , Canagaratna M. , Huey L. G. , Junkermann W. , Onasch T. B. , Sjostedt S. J. , Sullivan A. P. , Tanner D. J. , Vargas O. , Weber R. J. , Worsnop D. R. , Yu X. Y. , Zaveri R.
Published: April 2010

Abstract. Volatile organic compounds (VOCs) and carbonaceous aerosol were measured at a sub-urban site near Mexico City in March of 2006 during the MILAGRO study (Megacity Initiative: Local and Global Research Objectives). Diurnal variations of hydrocarbons, elemental carbon (EC) and hydrocarbon-like organic aerosol (HOA) were dominated by a high peak in the early morning when local emissions accumulated in a shallow boundary layer, and a minimum in the afternoon when the emissions were diluted in a significantly expanded boundary layer and, in case of the reactive gases, removed by OH. In comparison, diurnal variations of species with secondary sources such as the aldehydes, ketones, oxygenated organic aerosol (OOA) and water-soluble organic carbon (WSOC) stayed relatively high in the afternoon indicating strong photochemical formation. Emission ratios of many hydrocarbon species relative to CO were higher in Mexico City than in the US, but we found similar emission ratios for most oxygenated VOCs and organic aerosol. Secondary formation of acetone may be more efficient in Mexico City than in the US, due to higher emissions of alkane precursors from the use of liquefied petroleum gas. Secondary formation of organic aerosol was similar between Mexico City and the US. Combining the data for all measured gas and aerosol species, we describe the budget of total observed organic carbon (TOOC), and find that the enhancement ratio of TOOC relative to CO is conserved between the early morning and mid afternoon despite large compositional changes. Finally, the influence of biomass burning is investigated using the measurements of acetonitrile, which was found to correlate with levoglucosan in the particle phase. Diurnal variations of acetonitrile indicate a contribution from local burning sources. Scatter plots of acetonitrile versus CO suggest that the contribution of biomass burning to the enhancement of most gas and aerosol species was not dominant and perhaps not dissimilar from observations in the US.
A method to generate near real time UV-Index maps of Austria
Authors: Schallhart B. , Blumthaler M. , Schreder J. , Verdebout J.
Published: April 2010

Abstract. A method is presented that combines individual ground based ultraviolet (UV) measurements from the Austrian UVB monitoring network and area-wide data of the distribution of clouds derived from satellite images to generate a UV-Index map all over the region. The Austrian UVB Monitoring network provides near real time ground based measurements of surface UV irradiance from fifteen selected locations throughout and in the vicinity of Austria. The amount of ultraviolet radiation passing through the atmosphere as measured by the UVB detectors is indicated in units of the UV-Index, the internationally agreed unit for erythemally weighted solar UV irradiance. Together with clear sky model calculations the measured UV-Index is used to determine the cloud modification factor (CMF), a scaling factor giving the reduction of radiation due to the presence of clouds. Moreover satellite images from MSG (Meteosat Second Generation) with a time resolution of 15 min and a spatial resolution of 0.05° are received. From the satellite images the CMFs for the area of Austria are obtained using an algorithm provided by Jean Verdebout. Then both independent data sets of cloud modification factors are checked for consistency by comparing satellite derived and ground based values at the positions of the monitoring stations. If necessary the satellite derived cloud modification factors are corrected by about ±20% according to the results of the ground based measurements. Afterwards realistic UV-Index maps of the whole area are generated by scaling model derived UV-Indexes with the corresponding cloud modification factors. Since all the data is available in almost real time, the calculated UV-Index maps are available in the web at http://www.uv-index.at/ with a time delay of about 30 min.
Characteristics of the NO-NO2-O3 system in different chemical regimes during the MIRAGE-Mex field campaign
Authors: Shon Z.-H. , Madronich S. , Song S.-K. , Flocke F.  M. , Knapp D. J. , Anderson R. S. , Shetter R. E. , Cantrell C. A. , Hall S. R.
Published: April 2010

Abstract. The NO-NO2 system was analyzed in different chemical regimes/air masses based on observations of reactive nitrogen species and peroxy radicals made during the intensive field campaign MIRAGE-Mex (4 to 29 March 2006). In general, NO2/NO ratios, which can be used as an indicator to test current understanding of tropospheric chemistry mechanism, are near photostationary state. The air masses were categorized into 5 groups: boundary layer (labeled as "BL"), free troposphere (continental, "FTCO" and marine, "FTMA"), biomass burning ("BB"), and Tula industrial complex ("TIC"). The time- and air mass-dependent NO2/NO ratios ranged from 2.35 (TIC) to 5.18 (BB), while the NOx/NOy ratios varied from 0.17 (FTCO) to 0.54 (BL). The ozone production efficiency for the 5 air mass categories ranged from 5.0 (TIC) to 10.2 (BL), indicating photochemically young and reactive air masses.
Mixing ratios and eddy covariance flux measurements of volatile organic compounds from an urban canopy (Manchester, UK)
Authors: Langford B. , Davison B. , Nemitz E. , Hewitt C. N.
Published: April 2010

Abstract. Concentrations and fluxes of six volatile organic compounds (VOC) were measured above the city of Manchester (UK) during the summer of 2006. A proton transfer reaction-mass spectrometer was used for the measurement of concentrations, and fluxes were calculated using both the disjunct and the virtual disjunct eddy covariance techniques. The two flux systems, which operated in alternate half hours, showed reasonable agreement, with R2 values ranging between 0.2 and 0.8 for the individual analytes. On average, fluxes measured in the disjunct mode were lower than those measured in the virtual mode by approximately 19%, of which at least 8% can be attributed to the differing measurement frequencies of the two systems and the subsequent attenuation of high frequency flux contributions. Observed fluxes are thought to be largely controlled by anthropogenic sources, with vehicle emissions the major contributor. However both evaporative and biogenic emissions may account for a fraction of the isoprene present. Fluxes of the oxygenated compounds were highest on average, ranging between 60–89 μg m−2 h−1, whereas the fluxes of aromatic compounds were lower, between 19–42 μg m−2 h−1. The observed fluxes of benzene were up-scaled to give a city wide emission estimate which was found to be significantly lower than that of the National Atmospheric Emissions Inventory (NAEI).
Probing ETEX-II data set with inverse modelling
Authors: Krysta M. , Bocquet M. , Brandt J.
Published: April 2010

Abstract. We give here an account on the results of source inversion of the ETEX-II experiment. Inversion has been performed with the maximum entropy method on the basis of non-zero measurements and in conjunction with a transport model Polair3D. The discrepancy scaling factor between the true and the reconstructed mass has been estimated to be equal to 7. The results contrast with the method's performance on the ETEX-I source. In the latter case its mass has been reconstructed with an accuracy exceeding 80%. The large value of the discrepancy factor for ETEX-II could be ascribed to modelling difficulties, possibly linked not to the transport model itself but rather to the quality of the measurements.
Airborne measurements of nucleation mode particles II: boreal forest nucleation events
Authors: O'Dowd C. D. , Yoon Y. J. , Junkerman W. , Aalto P. , Kulmala M. , Lihavainen H. , Viisanen Y.
Published: April 2010

Abstract. Airborne measurements of nucleation mode aerosol concentrations during nucleation events over the boreal forest of southern Finland are reported. Three case studies are analysis in an attempt to characterise the spatial scales over which these events occur and to identify the source region for particle production. For the cases presented, there is no evidence of nucleation mode particles in the Free Troposphere. Nucleation mode particles are first detected in the surface layer as the nocturnal inversion breaks up and develops into the current-day's new boundary layer. In terms of spatial variability, significant variability in the concentration of nucleation mode particles was observed and was attributed to changes in the topography which comprised a mix of forest canopy and frozen lakes. Measurements over the Gulf of Bothnia indicated no nucleation mode over the sea and confirm that the scale of the events is associated with the boreal forest scale and that the new particles are produced directly above the forest canopy.
Correlation between equatorial Kelvin waves and the occurrence of extremely thin ice clouds at the tropical tropopause
Authors: Immler F. , Krüger K. , Fujiwara M. , Verver G. , Rex M. , Schrems O.
Published: April 2010

Abstract. A number of field-campaigns in the tropics have been conducted in the recent years with two different LIDAR systems at Paramaribo in Suriname (5.8° N, 55.2° W). The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). Radiosonde as well as operational ECMWF analysis show that temperature anomalies caused by equatorial Kelvin waves propagate downward, well below the cold point tropopause (CPT). We find a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus in the TTL. In particular we found that extremely thin ice clouds form regularly where cold anomalies shift the tropopause to high altitudes. This finding suggests an influence of Kelvin wave activity on the dehydration in the TTL and thus on the global stratospheric water vapour concentration.
Assessing positive matrix factorization model fit: a new method to estimate uncertainty and bias in factor contributions at the daily time scale
Authors: Hemann J. G. , Brinkman G. L. , Dutton S. J. , Hannigan M. P. , Milford J. B. , Miller S. L.
Published: April 2010

Abstract. A Positive Matrix Factorization receptor model for aerosol pollution source apportionment was fit to a synthetic dataset simulating one year of daily measurements of ambient PM2.5 concentrations, comprised of 39 chemical species from nine pollutant sources. A novel method was developed to estimate model fit uncertainty and bias at the daily time scale, as related to factor contributions. A balanced bootstrap is used to create replicate datasets, with the same model then fit to the data. Neural networks are trained to classify factors based upon chemical profiles, as opposed to correlating contribution time series, and this classification is used to align factor orderings across results associated with the replicate datasets. Factor contribution uncertainty is assessed from the distribution of results associated with each factor. Comparing modeled factors with input factors used to create the synthetic data assesses bias. The results indicate that variability in factor contribution estimates does not necessarily encompass model error: contribution estimates can have small associated variability yet also be very biased. These results are likely dependent on characteristics of the data.
Modelling UV irradiances on arbitrarily oriented surfaces: effects of sky obstructions
Authors: Hess M. , Koepke P.
Published: April 2010

Abstract. A method is presented to calculate UV irradiances on inclined surfaces that additionally takes into account the influence of sky obstructions caused by obstacles such as mountains, houses, trees, or umbrellas. Thus the method allows calculating the impact of UV radiation on biological systems, such as for instance the human skin or eye, in any natural or artificial environment. The method, a combination of radiation models, is explained and the correctness of its results is demonstrated. The effect of a natural skyline is shown for an Alpine ski area, where the UV irradiance even on a horizontal surface may increase due to reflection at snow by more than 10%. In contrast in a street canyon the irradiance on a horizontal surface is reduced down to 30% in shadow and to about 75% for a position in the sun.
Validation of ACE-FTS v2.2 measurements of HCl, HF, CCl3F and CCl2F2 using space-, balloon- and ground-based instrument observations
Authors: Mahieu E. , Duchatelet P. , Demoulin P. , Walker K. A. , Dupuy E. , Froidevaux L. , Randall C. , Catoire V. , Strong K. , Boone C. D. , Bernath P. F. , Blavier J.-F. , Blumenstock T. , Coffey M. , De Mazière M. , Griffith D. , Hannigan J. , Hase F. , Jones N. , Jucks K. W. , Kagawa A. , Kasai Y. , Mebarki Y. , Mikuteit S. , Nassar R. , Notholt J. , Rinsland C. P. , Robert C. , Schrems O. , Senten C. , Smale D. , Taylor J. , Tétard C. , Toon G. C. , Warneke T. , Wood S. W. , Zander R. , Servais C.
Published: April 2010

Abstract. Hydrogen chloride (HCl) and hydrogen fluoride (HF) are respectively the main chlorine and fluorine reservoirs in the Earth's stratosphere. Their buildup resulted from the intensive use of man-made halogenated source gases, in particular CFC-11 (CCl3F) and CFC-12 (CCl2F2), during the second half of the 20th century. It is important to continue monitoring the evolution of these source gases and reservoirs, in support of the Montreal Protocol and also indirectly of the Kyoto Protocol. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) is a space-based instrument that has been performing regular solar occultation measurements of over 30 atmospheric gases since early 2004. In this validation paper, the HCl, HF, CFC-11 and CFC-12 version 2.2 profile data products retrieved from ACE-FTS measurements are evaluated. Volume mixing ratio profiles have been compared to observations made from space by MLS and HALOE, and from stratospheric balloons by SPIRALE, FIRS-2 and Mark-IV. Partial columns derived from the ACE-FTS data were also compared to column measurements from ground-based Fourier transform instruments operated at 12 sites. ACE-FTS data recorded from March 2004 to August 2007 have been used for the comparisons. These data are representative of a variety of atmospheric and chemical situations, with sounded air masses extending from the winter vortex to summer sub-tropical conditions. Typically, the ACE-FTS products are available in the 10–50 km altitude range for HCl and HF, and in the 7–20 and 7–25 km ranges for CFC-11 and CFC-12, respectively. For both reservoirs, comparison results indicate an agreement generally better than 5–10%, when accounting for the known offset affecting HALOE measurements of HCl and HF. Larger positive differences are however found for comparisons with single profiles from FIRS-2 and SPIRALE. For CFCs, the few coincident measurements available suggest that the differences probably remain within ±20%.
Airborne measurements of HCl from the marine boundary layer to the lower stratosphere over the North Pacific Ocean during INTEX-B
Authors: Kim S. , Huey L. G. , Stickel R. E. , Pierce R. B. , Chen G. , Avery M. A. , Dibb J. E. , Diskin G. S. , Sachse G. W. , McNaughton C. S. , Clarke A. D. , Anderson B. E. , Blake D. R.
Published: April 2010

Abstract. Gas phase HCl was measured from the marine boundary layer (MBL) to the lower stratosphere from the NASA DC-8 during five science flights (41 h) of the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B) field campaign. In the upper troposphere/lower stratosphere (UT/LS, 8–12 km) HCl was observed to range from a few tens to 100 pptv due to stratospheric influence with a background tropospheric level of less than 2 pptv. In the 8–12 km altitude range, a simple analysis of the O3/HCl correlation shows that pure stratospheric and mixed tropospheric/stratospheric air masses were encountered 30% and 15% of the time, respectively. In the mid troposphere (4–8 km) HCl levels were usually below 2 pptv except for a few cases of stratospheric influence and were much lower than reported in previous work. These data indicate that background levels of HCl in the mid and upper troposphere are very low and confirm its use in these regions as a tracer of stratospheric ozone. However, a case study suggests that HCl may be produced in the mid troposphere by the dechlorination of dust aerosols. In the remote marine boundary layer HCl levels were consistently above 20 pptv (up to 140 pptv) and strongly correlated with HNO3. Cl atom levels were estimated from the background level of HCl in the MBL. This analysis suggests a Cl concentration of ~3×103 atoms cm−3, which corresponds to the lower range of previous studies. Finally, the observed HCl levels are compared to predictions by the Real-time Air Quality Modeling System (RAQMS) to assess its ability to characterize the impact of stratospheric transport on the upper troposphere.
Steady-state aerosol distributions in the extra-tropical, lower stratosphere and the processes that maintain them
Authors: Wilson J. C. , Lee S.-H. , Reeves J. M. , Brock C. A. , Jonsson H. H. , Lafleur B. G. , Loewenstein M. , Podolske J. , Atlas E. , Boering K. , Toon G. , Fahey D. , Bui T. P. , Diskin G. , Moore F.
Published: April 2010

Abstract. Measurements of aerosol, N2O and OCS made in the Northern Hemisphere below 21 km altitude following the eruption of Pinatubo are presented and analyzed. After September 1999, the oxidation of OCS and the sedimentation of particles in the extra-tropical overworld maintain the aerosol in a steady state. This analysis empirically links precursor gas to aerosol abundance throughout this region. These processes are tracked with age-of-air which offers advantages over tracking as a function of latitude and altitude. In the extra-tropical, lowermost stratosphere, normalized volume distributions appear constant in time after the fall of 1999. Exchange with the troposphere is important in understanding aerosol evolution there. Size distributions of volcanically perturbed aerosol are included to distinguish between volcanic and non-volcanic conditions. This analysis suggests that model failures to correctly predict OCS and aerosol properties below 20 km in the Northern Hemisphere extra tropics result from inadequate descriptions of atmospheric circulation.
The role of sea-salt emissions and heterogeneous chemistry in the air quality of polluted coastal areas
Authors: Athanasopoulou E. , Tombrou M. , Pandis S. N. , Russell A. G.
Published: April 2010

Abstract. Open-ocean and surf-zone sea-salt aerosol (SSA) emissions algorithms are incorporated in the CAMx aerosol model and applied over an area with an extended Archipelago (Greece), with a fine grid nested over the highly populated Attica peninsula. The maximum indirect impact of SSA on PM10 mass (35%) is located over a marine area with moderate SSA production and elevated shipping emissions (central Aegean Sea) where SSA interacts with anthropogenic nitric acid forming sodium nitrate. SSA increases PM10 levels in the Athens city center up to 27% during stable onshore winds. Under such conditions both open-ocean and surf-zone mechanisms contribute to aerosol production over Attica. A hybrid scheme for gas-to-particle mass transfer is necessary for accurately simulating semi-volatile aerosol components when coarse SSA is included. Dynamically simulating mass transfer to the coarse particles leads to a quadrupling of predicted PM10 nitrate in the Athens city center and up to two orders of magnitude in its coarse mass in comparison to using a bulk equilibrium approach.
Gap filling and noise reduction of unevenly sampled data by means of the Lomb-Scargle periodogram
Authors: Hocke K. , Kämpfer N.
Published: April 2010

Abstract. The Lomb-Scargle periodogram is widely used for the estimation of the power spectral density of unevenly sampled data. A small extension of the algorithm of the Lomb-Scargle periodogram permits the estimation of the phases of the spectral components. The amplitude and phase information is sufficient for the construction of a complex Fourier spectrum. The inverse Fourier transform can be applied to this Fourier spectrum and provides an evenly sampled series (Scargle, 1989). We are testing the proposed reconstruction method by means of artificial time series and real observations of mesospheric ozone, having data gaps and noise. For data gap filling and noise reduction, it is necessary to modify the Fourier spectrum before the inverse Fourier transform is done. The modification can be easily performed by selection of the relevant spectral components which are above a given confidence limit or within a certain frequency range. Examples with time series of lower mesospheric ozone show that the reconstruction method can reproduce steep ozone gradients around sunrise and sunset and superposed planetary wave-like oscillations observed by a ground-based microwave radiometer at Payerne.