bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-year (2004–2008) record of nonmethane hydrocarbons and halocarbons in New England: seasonal variations and regional sources
Authors: Russo R. S. , Zhou Y. , White M. L. , Mao H. , Talbot R. , Sive B. C.
Published: April 2010

Abstract. Multi-year time series records of C2-C6 alkanes, C2-C4 alkenes, ethyne, isoprene, C6-C8 aromatics, trichloroethene (C2HCl3), and tetrachloroethene (C2Cl4) from canister samples collected during January 2004–February 2008 at the University of New Hampshire (UNH) AIRMAP Observatory at Thompson Farm (TF) in Durham, NH are presented. The objectives of this work are to identify the sources of nonmethane hydrocarbons (NMHCs) and halocarbons observed at TF, characterize the seasonal and interannual variability in ambient mixing ratios and sources, and estimate regional emission rates of NMHCs. Analysis of correlations and comparisons with emission ratios indicated that a ubiquitous and persistent mix of emissions from several anthropogenic sources is observed throughout the entire year. The highest C2-C8 anthropogenic NMHC mixing ratios were observed in mid to late winter. Following the springtime minimums, the C3-C6 alkanes, C7-C8 aromatics, and C2HCl3 increased in early to mid summer, presumably reflecting enhanced evaporative emissions. Mixing ratios of C2Cl4 and C2HCl3 decreased by 0.7±0.2 and 0.3±0.05 pptv/year, respectively, which is indicative of reduced usage and emissions of these halogenated solvents. Emission rates of C3-C8 NMHCs were estimated to be 109 to 1010 molecules cm-2 s-1 in winter 2006. The emission rates extrapolated to the state of New Hampshire and New England were ~2–60 Mg/day and ~12–430 Mg/day, respectively. The 2002 and 2005 EPA National Emissions Inventory (NEI) emission rates of benzene, ethylbenzene, and xylenes for New Hampshire agreed within ±<5–20% of the emission rates estimated from the TF data, while toluene emissions were overestimated (20–35%) in both versions of the NEI.
UV absorption cross sections of nitrous oxide (N2O) and carbon tetrachloride (CCl4) between 210 and 350 K and the atmospheric implications
Authors: Rontu Carlon N. , Papanastasiou D. K. , Fleming E. L. , Jackman C. H. , Newman P. A. , Burkholder J. B.
Published: April 2010

Abstract. Absorption cross sections of nitrous oxide (N2O) and carbon tetrachloride (CCl4) are reported at five atomic UV lines (184.95, 202.548, 206.200, 213.857, and 228.8 nm) at temperatures in the range 210–350 K. In addition, UV absorption spectra of CCl4 are reported between 200–235 nm as a function of temperature (225–350 K). The results from this work are critically compared with results from earlier studies. For N2O, the present results are in good agreement with the current JPL recommendation enabling a reduction in the estimated uncertainty in the N2O atmospheric photolysis rate. For CCl4, the present cross section results are systematically greater than the current recommendation at the reduced temperatures most relevant to stratospheric photolysis. The new cross sections result in a 5–7% increase in the modeled CCl4 photolysis loss, and a slight decrease in the stratospheric lifetime, from 51 to 50 years, for present day conditions. The corresponding changes in modeled inorganic chlorine and ozone in the stratosphere are quite small. A CCl4 cross section parameterization for use in atmospheric model calculations is presented.
Optical extinction by upper tropospheric/stratospheric aerosols and clouds: GOMOS observations for the period 2002–2008
Authors: Vanhellemont F. , Fussen D. , Mateshvili N. , Tétard C. , Bingen C. , Dekemper E. , Loodts N. , Kyrölä E. , Sofieva V. , Tamminen J. , Hauchecorne A. , Bertaux J.-L. , Dalaudier F. , Blanot L. , Fanton d'Andon O. , Barrot G. , Guirlet M. , Fehr T. , Saavedra L.
Published: April 2010

Abstract. Although the retrieval of aerosol extinction coefficients from satellite remote measurements is notoriously difficult (in comparison with gaseous species) due to the lack of typical spectral signatures, important information can be obtained. In this paper we present an overview of the current operational nighttime UV/Vis aerosol extinction profile results for the GOMOS star occultation instrument, spanning the period from August 2002 to May 2008. Some problems still remain, such as the ones associated with incomplete scintillation correction and the aerosol spectral law implementation, but good quality extinction values can be expected at a wavelength of 500 nm. Typical phenomena associated with atmospheric particulate matter in the Upper Troposphere/Lower Stratosphere (UTLS) are easily identified: Polar Stratospheric Clouds, tropical subvisual cirrus clouds, background stratospheric aerosols, and post-eruption volcanic aerosols (with their subsequent dispersion around the globe). In this overview paper we will give a summary of the current results.
Cluster analysis of midlatitude oceanic cloud regimes – Part 2: Temperature sensitivity of cloud properties
Authors: Gordon N. D. , Norris J. R.
Published: April 2010

Abstract. Clouds have a large impact on Earth's radiation budget by reflecting incoming solar radiation and trapping longwave radiation emitted from the surface. The present balance could change as the atmosphere warms from increasing anthropogenic greenhouse gases, thus altering the net radiation flux and mitigating or exacerbating the initial temperature increase. To ascertain the sign and magnitude of cloud-climate feedback, we must better understand the way in which clouds interact with their environment and how temperature modifies cloud and radiative properties. Since global climate models do not consistently and correctly simulate clouds, we undertake an observational analysis of how midlatitude oceanic clouds change with temperature when dynamical processes are held constant (i.e., partial derivative with respect to temperature). For each of the seven cloud regimes identified through k-means clustering of daily satellite data in the companion study, we examine the difference in cloud and radiative properties between warm and cold subsets. To avoid misinterpreting a cloud response to large-scale dynamical forcing as a cloud response to temperature, we require horizontal and vertical temperature advection in the warm and cold subsets to have near-median values in three layers of the troposphere. Across all of the seven clusters, we find that cloud fraction is smaller and cloud optical thickness is mostly larger for the warm subset. Cloud top pressure is higher for the three low-level cloud regimes and lower for the cirrus regime. The net upwelling radiation flux at the top of the atmosphere is larger for the warm subset in every cluster except cirrus, and larger when averaged over all clusters. This implies that the direct response of midlatitude oceanic clouds to increasing temperature acts as a negative feedback on the climate system. Note that the cloud response to atmospheric dynamical changes produced by global warming, which we do not consider in this study, may differ, and the total cloud feedback may be positive.
Aged organic aerosol in the Eastern Mediterranean: the Finokalia aerosol measurement experiment-2008
Authors: Hildebrandt L. , Engelhart G. J. , Mohr C. , Kostenidou E. , Lanz V. A. , Bougiatioti A. , DeCarlo P. F. , Prévôt A. S. H. , Baltensperger U. , Mihalopoulos N. , Donahue N. M. , Pandis S. N.
Published: April 2010

Abstract. Aged organic aerosol (OA) was measured at a remote coastal site on the island of Crete, Greece during the Finokalia Aerosol Measurement Experiment-2008 (FAME-2008), which was part of the EUCAARI intensive campaign of May 2008. The site at Finokalia is influenced by air masses from different source regions, including long-range transport of pollution from continental Europe. A quadrupole aerosol mass spectrometer (Q-AMS) was employed to measure the size-resolved chemical composition of non-refractory submicron aerosol (NR-PM1), and to estimate the extent of oxidation of the organic aerosol. Factor analysis was used to gain insights into the processes and sources affecting the OA composition. The particles were internally mixed and liquid. The largest fraction of the dry NR-PM1 sampled was ammonium sulfate and ammonium bisulfate, followed by organics and a small amount of nitrate. The variability in OA composition could be explained with two factors of oxygenated organic aerosol (OOA) with differing extents of oxidation but similar volatility. Hydrocarbon-like organic aerosol (HOA) was not detected. There was no statistically significant diurnal variation in the bulk composition of NR-PM1 such as total sulfate or total organic aerosol concentrations. However, the OA composition exhibited statistically significant diurnal variation with more oxidized OA in the afternoon. The organic aerosol was highly oxidized, regardless of the source region. Total OA concentrations also varied little with time of day, suggesting that local sources had only a small effect on OA concentrations measured at Finokalia. The aerosol was transported for about one day before arriving at the site, corresponding to an OH exposure of approximately 4×1011 molecules cm−3 s. The constant extent of oxidation suggests that atmospheric aging results in a highly oxidized OA at these OH exposures, regardless of the aerosol source.
Aerosol-induced changes of convective cloud anvils produce strong climate warming
Authors: Koren I. , Remer L. A. , Altaratz O. , Martins J. V. , Davidi A.
Published: April 2010

Abstract. The effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. In contrast, even small human-induced perturbations in cloud coverage, lifetime, height or optical properties can change the instantaneous radiative energy flux by hundreds of watts per unit area, and this forcing can be either warming or cooling. Clouds and aerosols form a complex coupled system that, unlike greenhouse gases, have relatively short lifetime (hours to days) and inhomogeneous distribution. This and the inherent complexity of cloud microphysics and dynamics, and the strong coupling with meteorology explain why the estimation of the overall effect of aerosol on climate is so challenging. Here we focus on the effect of aerosol on cloud top properties of deep convective clouds over the tropical Atlantic. The tops of these vertically developed clouds consist of mostly ice and can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing. This study demonstrates the deep link between cloud shape and aerosol loading and that the overall aerosol effect in regions of deep convective clouds might be warming. Moreover we show how averaging the cloud height and optical properties over large regions may lead to a false cooling estimation.
A trajectory analysis of atmospheric transport of black carbon aerosols to Canadian High Arctic in winter and spring (1990–2005)
Authors: Huang L. , Gong S. L. , Sharma S. , Lavoué D. , Jia C. Q.
Published: April 2010

Abstract. Black carbon (BC) particles accumulated in the Arctic troposphere and deposited over snow have significant effects on radiative forcing of the Arctic regional climate. Applying cluster analysis technique on 10-day backward trajectories, transport pathways affecting Alert (82.5° N, 62.5° W), Nunavut in Canada are identified in this work, along with the associated transport frequency. Based on the atmospheric transport frequency and the estimated BC emission intensity from surrounding regions, a linear regression model is constructed to investigate the inter-annual variations of BC observed at Alert in January and April, representative of winter and spring respectively, between 1990 and 2005. Strong correlations are found between BC concentrations predicted with the regression model and measured at Alert for both seasons (R2 equals 0.77 and 0.81 for winter and spring, respectively). Results imply that atmospheric transport and BC emission are the major contributors to the inter-annual variations in BC concentrations observed at Alert in the cold seasons for the 16-year period. Based on the regression model the relative contributions of regional BC emissions affecting Alert are attributed to the Eurasian sector, composed of the European Union and the former USSR, and the North American sector. Considering both seasons, the model suggests that Eurasia is the major contributor to the near-surface BC levels at the Canadian High Arctic site with an average contribution of over 85% during the 16-year period. In winter, the atmospheric transport of BC aerosols from Eurasia is found to be even more predominant with a multi-year average of 94%. The model estimates smaller contribution from the Eurasian sector in spring (70%) than that in winter. It is also found that the change in Eurasian contributions depends mainly on the reduction of emission intensity, while the changes in both emission and atmospheric transport contributed to the inter-annual variation of North American contributions.
Spectral optical properties of long-range transport Asian dust and pollution aerosols over Northeast Asia in 2007 and 2008
Authors: Jung J. , Kim Y. J. , Lee K. Y. , -Cayetano M. G. , Batmunkh T. , Koo J.-H. , Kim J.
Published: April 2010

Abstract. As a part of the IGAC (International Global Atmospheric Chemistry) Mega-cities program, aerosol physical and optical properties were continuously measured from March 2007 to March 2008 at an urban site (37.57° N, 126.94° E) in Seoul, Korea. Spectral optical properties of long-range transported Asian dust and pollution aerosols have been investigated based on the year long measurement data. Optically measured black carbon/thermally measured elemental carbon (BC/EC) ratio showed clear monthly variation with high values in summer and low values in winter mainly due to the enhancement of light attenuation by the internal mixing of EC. Novel approach has been suggested to retrieve the spectral light absorption coefficient (babs) from Aethalometer raw data by using BC/EC ratio. Mass absorption efficiency, σabs(=babs/EC) at 550 nm at the measurement site was determined to be 9.0±1.3, 8.9±1.5, 9.5±2.0, and 10.3±1.7 m2 g−1 in spring, summer, fall, and winter, respectively with an annual mean of 9.4±1.8 m2 g−1. Threshold values to classify severe haze events were suggested in this study. Increasing trend of aerosol single scattering albedo (SSA) with wavelength was observed during Asian dust events while little spectral dependence of SSA was observed during long-range transport pollution (LTP) events. Satellite aerosol optical thickness (AOT) and Hysplit air mass backward trajectory analyses as well as chemical analysis were performed to characterize the dependence of spectral optical properties on aerosol type. Results from this study can provide useful information for studies on regional air quality and aerosol's effects on climate change.
Uncertainty assessment of current size-resolved parameterizations for below-cloud particle scavenging by rain
Authors: Wang X. , Zhang L. , Moran M. D.
Published: April 2010

Abstract. A detailed review has been conducted of current size-resolved parameterizations of below-cloud scavenging by rain, including their formulation in terms of scavenging coefficient (Λ), their associated input parameters and comparisons with size-resolved Λ values obtained from field measurements. The three dominant factors in the theoretical formulations of Λ – raindrop-particle collection efficiency, raindrop number size distribution and raindrop terminal fall velocity – are investigated through numerical sensitivity tests. It is found that the use of different formulations for raindrop-particle collection efficiency can cause uncertainties in the Λ values of nearly one order of magnitude for particles smaller than 3 μm. The use of different formulations of raindrop number size distribution can cause the Λ values to vary by a factor of 3 to 5 for all particle sizes. The uncertainty in Λ, caused by the use of different droplet terminal velocity formulations, is generally smaller than a factor of 2. All of the current theoretical Λ parameterizations, however, underpredict the Λ values by one to two orders of magnitude for particles smaller than 3 μm, compared with most available field measurements or with empirical formulas generated from field observations. The combined uncertainties from known sources are, thus, not enough to explain the large discrepancies between the theoretical and experimental studies, suggesting a need for further investigations of the collection mechanisms through field, laboratory and numerical studies. The differences in the predicted particle concentrations, due to the use of different Λ parameterizations, can be larger than a factor of 10 for ultrafine and coarse particles even after a small amount of rain (e.g., 2–5 mm). The differences for submicron-sized particles can also be larger than a factor of 2 if sufficient rainfall occurs. Lastly, predicted bulk concentrations (integrated over the particle size distribution) from using different theoretical and empirical Λ parameterizations can differ by up to 50% for particle number and by up to 25% for particle mass after just 2–5 mm of rain.
CityFlux perfluorocarbon tracer experiments
Authors: Petersson F. K. , Martin D. , White I. R. , Henshaw S. J. , Nickless G. , Longley I. , Percival C. J. , Gallagher M. , Shallcross D. E.
Published: April 2010

Abstract. In June 2006, two perfluorocarbon tracer experiments were conducted in central Manchester UK as part of the CityFlux campaign. The main aim was to investigate vertical dispersion in an urban area during convective conditions, but dispersion mechanisms within the street network were also studied. Paired receptors were used in most cases where one receptor was located at ground level and one at roof level. One receptor was located on the roof of Portland Tower which is an 80 m high building in central Manchester. Source receptor distances in the two experiments varied between 120 and 600 m. The results reveal that maximum concentration was sometimes found at roof level rather than at ground level implying the effectiveness of convective forces on dispersion. The degree of vertical dispersion was found to be dependent on source receptor distance as well as on building height in proximity to the release site. Evidence of flow channelling in a street canyon was also found. Both a Gaussian profile and a street network model were applied and the results show that the urban topography may lead to highly effective flow channelling which therefore may be a very important dispersion mechanism should the right meteorological conditions prevail. The experimental results from this campaign have also been compared with a simple urban dispersion model that was developed during the DAPPLE framework and show good agreement with this. The results presented here are some of the first published regarding vertical dispersion. More tracer experiments are needed in order to further characterise vertical concentration profiles and their dependence on, for instance, atmospheric stability. The impact of urban topography on pollutant dispersion is important to focus on in future tracer experiments in order to improve performance of models as well as for our understanding of the relationship between air quality and public health.
A new method for deriving aerosol solar radiative forcing and its first application within MILAGRO/INTEX-B
Authors: Schmidt K. S. , Pilewskie P. , Bergstrom R. , Coddington O. , Redemann J. , Livingston J. , Russell P. , Bierwirth E. , Wendisch M. , Gore W. , Dubey M. K. , Mazzoleni C.
Published: April 2010

Abstract. We introduce a method for deriving aerosol spectral radiative forcing, along with single scattering albedo, asymmetry parameter and surface albedo from airborne vertical profile measurements of shortwave spectral irradiance and spectral aerosol optical thickness. The new method complements the traditional, direct measurement of aerosol radiative forcing efficiency from horizontal flight legs below gradients of aerosol optical thickness, and is particularly useful over heterogeneous land surfaces or for homogeneous aerosol layers where the horizontal gradient method is impractical. Using data collected by the Solar Spectral Flux Radiometer (SSFR) and the Ames Airborne Tracking Sunphotometer (AATS-14) during the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiment, we validate an over-ocean spectral aerosol forcing efficiency from the new method by comparing with the traditional method. Retrieved over-land aerosol optical properties are compared with in-situ measurements and AERONET retrievals. The spectral forcing efficiencies over ocean and land are remarkably similar, and agree with results from other field experiments.
Molecular hydrogen (H2) emissions and their isotopic signatures (H/D) from a motor vehicle: implications on atmospheric H2
Authors: Vollmer M. K. , Walter S. , Bond S. W. , Soltic P. , Röckmann T.
Published: April 2010

Abstract. Molecular hydrogen (H2), its isotopic signature (deuterium/hydrogen, δD), carbon monoxide (CO) and other compounds were studied in the exhaust of a passenger car engine fuelled with gasoline or methane and run under variable air-fuel ratios and operating modes. H2 and CO concentrations were largely reduced downstream of the three-way catalytic converter (TWC) compared to levels upstream, and showed a strong dependence on the air-fuel ratio (expressed as lambda, λ). The isotopic composition of H2 ranged from δD=–140‰ to δD=–195‰ upstream of the TWC but these values decreased to –270‰ to –370‰ after passing through the TWC. Post-TWC δD values for the fuel-rich range showed a strong dependence on TWC temperature with more negative δD for lower temperatures. These effects are attributed to a rapid temperature-dependent H-D isotope equilibration between H2 and water (H2O). In addition, post TWC δD in H2 showed a strong dependence on the fraction of removed H2, suggesting isotopic enrichment during catalytic removal of H2 with enrichment factors (ε) ranging from –39.8‰ to –15.5‰ depending on the operating mode. Our results imply that there may be considerable variability in real-world δD emissions from vehicle exhaust, which may mainly depend on TWC technology and exhaust temperature regime. This variability is suggestive of a δD from traffic that varies over time, by season, and by geographical location. An earlier-derived integrated pure (end-member) δD from anthropogenic activities of –270‰ (Rahn et al., 2002) can be explained as a mixture of mainly vehicle emissions from cold starts and fully functional TWCs, but enhanced δD values by >50‰ are likely for regions where TWC technology is not fully implemented. Our results also suggest that a full hydrogen isotope analysis on fuel and exhaust gas may greatly aid at understanding process-level reactions in the exhaust gas, in particular in the TWC.
Quantification of DMS aerosol-cloud-climate interactions using ECHAM5-HAMMOZ model in current climate scenario
Authors: Thomas M. A. , Suntharalingam P. , Pozzoli L. , Rast S. , Devasthale A. , Kloster S. , Feichter J. , Lenton T. M.
Published: April 2010

Abstract. The contribution of ocean dimethyl sulfide (DMS) emissions to changes in cloud microphysical properties is quantified seasonally and globally for present day climate conditions using an aerosol-chemistry-climate general circulation model, ECHAM5-HAMMOZ, coupled to a cloud microphysics scheme. We evaluate DMS aerosol-cloud-climate linkages over the southern oceans where anthropogenic influence is minimal. The changes in the number of activated particles, cloud droplet number concentration (CDNC), cloud droplet effective radius, cloud cover and the radiative forcing are examined by analyzing two simulations: a baseline simulation with ocean DMS emissions derived from a prescribed climatology and one in which the ocean DMS emissions are switched off. Our simulations show that the model realistically simulates the seasonality in the number of activated particles and CDNC, peaking during Southern Hemisphere (SH) summer coincident with increased phytoplankton blooms and gradually declining with a minimum in SH winter. In comparison to a simulation with no DMS, the CDNC level over the southern oceans is 128% larger in the baseline simulation averaged over the austral summer months. Our results also show an increased number of smaller sized cloud droplets during this period. We estimate a maximum decrease of up to 15–18% in the droplet radius and a mean increase in cloud cover by around 2.5% over the southern oceans during SH summer in the simulation with ocean DMS compared to when the DMS emissions are switched off. The global annual mean top of the atmosphere DMS aerosol all sky radiative forcing is −2.03 W/m2, whereas, over the southern oceans during SH summer, the mean DMS aerosol radiative forcing reaches −9.32 W/m2.
Co-located column and in situ measurements of CO2 in the tropics compared with model simulations
Authors: Warneke T. , Petersen A. K. , Gerbig C. , Jordan A. , Rödenbeck C. , Rothe M. , Macatangay R. , Notholt J. , Schrems O.
Published: April 2010

Abstract. The first ground-based remote sensing measurements of the column averaged volume mixing ratio of CO2 (XCO2) for the inner tropics have been obtained at Paramaribo, Suriname (5.8° N, 55.2° W). The remote sensing observations are complemented by surface air-samples collected at the site, analyzed for CO2 and 13CO2. The surface in-situ measurements are strongly influenced by local sources. From the isotopic composition of the air samples the local source component is suggested to be dominated by the terrestrial biosphere. Using δ13C from the NOAA/ESRL stations Ascension Is. (ASC), 7.9° S, 14.4° W, and Ragged Point (RPB), 7.9° S, 14.4° W, the data has been corrected for the local source component. Due to the migration of the ITCZ over the measurement site the probed air masses belong to the Northern or Southern Hemisphere depending on the time of the year. Comparison to analyzed CO2 fields based on TM3 model simulations using optimized fluxes indicate agreement for XCO2 as well as for the corrected CO2 mixing ratios at the surface for the long dry season, when Paramaribo belongs to the Southern Hemisphere. A slightly worse agreement during the short dry season is attributed to a larger representation error during this time of the year. Overall the comparison demonstrates that the TM3 model is capable to simulate surface concentrations as well as column densities of CO2 correctly at the same location.
Ozone predictabilities due to meteorological uncertainties in Mexico City basin using ensemble forecasts
Authors: Bei N. , Lei W. , Zavala M. , Molina L. T.
Published: April 2010

Abstract. The purpose of the present study is to investigate the sensitivity of ozone concentration ([O3]) predictions in Mexico City to meteorological initial uncertainties and planetary boundary layer (PBL) parameterization schemes using state-of-the-art meteorological and photochemical prediction models through ensemble forecasts. The simulated periods (3, 9, 15, and 29 March 2006), represent four typical meteorological episodes ("South-Venting", "O3-North", "O3-South" and "Convection-North", respectively) in the Mexico City basin during the MCMA-2006/MILAGRO campaign. Our results demonstrate that uncertainties in meteorological initial conditions have significant impacts on O3 predictions, including the peak time [O3], as well as the horizontal and vertical [O3] distributions, and temporal variations. The ensemble spread of the simulated peak [O3] averaged over the city's ambient monitoring sites can reach up to 10 ppb. The magnitude of the ensemble spreads varies with different PBL schemes and meteorological episodes. The uncertainties in O3 predictions caused by PBL schemes mainly come from their ability to represent the mixing layer height, but overall, these uncertainties are smaller than those from uncertainties in meteorological initial conditions.
Detection of dust aerosol by combining CALIPSO active lidar and passive IIR measurements
Authors: Chen B. , Huang J. , Minnis P. , Hu Y. , Yi Y. , Liu Z. , Zhang D. , Wang X.
Published: April 2010

Abstract. The version 2 Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) dust layer detection method, which is based only on lidar measurements, misclassified about 43% dust layers (mainly dense dust layer) as cloud layers over the Taklamakan Desert. To address this problem, a new method was developed by combining the CALIPSO Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and passive Infrared Imaging Radiometer (IIR) measurements. This combined lidar and IR measurement (hereafter, CLIM) method uses the IIR tri-spectral IR brightness temperatures to discriminate between ice cloud and dense dust layers, and lidar measurements alone to detect thin dust and water cloud layers. The brightness temperature difference between 10.60 and 12.05 μm (BTD11-12) is typically negative for dense dust and generally positive for ice cloud, but it varies from negative to positive for thin dust layers, which the CALIPSO lidar correctly identifies. Results show that the CLIM method could significantly reduce misclassification rates to as low as ~7% for the active dust season of spring 2008 over the Taklamakan Desert. The CLIM method also revealed 18% more dust layers having greatly intensified backscatter between 1.8 and 4 km altitude over the source region compared to the CALIPSO version 2 data. These results allow a more accurate assessment of the effect of dust on climate.
Impact of Mexico City emissions on regional air quality from MOZART-4 simulations
Authors: Emmons L. K. , Apel E. C. , Lamarque J.-F. , Hess P. G. , Avery M. , Blake D. , Brune W. , Campos T. , Crawford J. , DeCarlo P. F. , Hall S. , Heikes B. , Holloway J. , Jimenez J. L. , Knapp D. J. , Kok G. , Mena-Carrasco M. , Olson J. , O'Sullivan D. , Sachse G. , Walega J. , Weibring P. , Weinheimer A. , Wiedinmyer C.
Published: April 2010

Abstract. An extensive set of measurements was made in and around Mexico City as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiments in March 2006. Simulations with the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4), a global chemical transport model, have been used to provide a regional context for these observations and assist in their interpretation. These MOZART-4 simulations reproduce the aircraft observations generally well, but some differences in the modeled volatile organic compounds (VOCs) from the observations result from incorrect VOC speciation assumed for the emission inventories. The different types of CO sources represented in the model have been "tagged" to quantify the contributions of regions outside Mexico, as well as the various emissions sectors within Mexico, to the regional air quality of Mexico. This analysis indicates open fires have some, but not a dominant, impact on the atmospheric composition in the region around Mexico City, when averaged over the month. However, considerable variation in the fire contribution (2–15% of total CO) is seen during the month. The transport and photochemical aging of Mexico City emissions were studied using tags of CO emissions for each day, showing that typically the air near Mexico City was a combination of many ages. Ozone production in MOZART-4 is shown to agree well with the net production rates from box model calculations constrained by the MILAGRO aircraft measurements. Ozone production efficiency derived from the ratio of Ox to NOz is higher in MOZART-4 than in the observations for moderately polluted air. OH reactivity determined from the MOZART-4 results shows the same increase in relative importance of oxygenated VOCs downwind of Mexico City as the reactivity inferred from the observations. The amount of ozone produced by emissions from Mexico City and surrounding areas has been quantified in the model by tracking NO emissions, showing little influence beyond Mexico's borders, and also relatively minor influence from fire emissions on the monthly average tropospheric ozone column.
Thermodynamics of climate change: generalized sensitivities
Authors: Lucarini V. , Fraedrich K. , Lunkeit F.
Published: April 2010

Abstract. Using a recent theoretical approach, we study how the impact of global warming of the thermodynamics of the climate system by performing experiments with a simplified yet Earth-like climate model. In addition to the globally averaged surface temperature, the intensity of the Lorenz energy cycle, the Carnot efficiency, the material entropy production and the degree of irreversibility of the system are linear with the logarithm of the CO2 concentration. These generalized sensitivities suggest that the climate becomes less efficient, more irreversible, and features higher entropy production as it becomes warmer.
Bromine measurements in ozone depleted air over the Arctic Ocean
Authors: Neuman J. A. , Nowak J. B. , Huey L. G. , Burkholder J. B. , Dibb J. E. , Holloway J. S. , Liao J. , Peischl J. , Roberts J. M. , Ryerson T. B. , Scheuer E. , Stark H. , Stickel R. E. , Tanner D. J. , Weinheimer A.
Published: April 2010

Abstract. In situ measurements of ozone, photochemically active bromine compounds, and other trace gases over the Arctic Ocean in April 2008 are used to examine the chemistry and geographical extent of ozone depletion in the arctic marine boundary layer (MBL). Data were obtained from the NOAA WP-3D aircraft during the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study and the NASA DC-8 aircraft during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) study. Fast (1 s) and sensitive (detection limits at the low pptv level) measurements of BrCl and BrO were obtained from three different chemical ionization mass spectrometer (CIMS) instruments, and soluble bromide was measured with a mist chamber. The CIMS instruments also detected Br2. Subsequent laboratory studies showed that HOBr rapidly converts to Br2 on the Teflon instrument inlets. This detected Br2 is identified as active bromine and represents a lower limit of the sum HOBr+Br2. The measured active bromine is shown to likely be HOBr during daytime flights in the arctic. In the MBL over the Arctic Ocean, soluble bromide and active bromine were consistently elevated and ozone was depleted. Ozone depletion and active bromine enhancement were confined to the MBL that was capped by a temperature inversion at 200–500 m altitude. In ozone-depleted air, BrO rarely exceeded 10 pptv and was always substantially lower than soluble bromide that was as high as 40 pptv. BrCl was rarely enhanced above the 2-pptv detection limit, either in the MBL, over Alaska, or in the arctic free troposphere.
Uptake of NO3 and N2O5 to Saharan dust, ambient urban aerosol and soot: a relative rate study
Authors: Tang M. J. , Thieser J. , Schuster G. , Crowley J. N.
Published: April 2010

Abstract. The uptake of NO3 and N2O5 to Saharan dust, ambient aerosols and soot was investigated using a novel and simple relative rate method with simultaneous detection of both NO3 and N2O5. The use of cavity ring down spectroscopy to detect both trace gases enabled the measurements to be carried out at low mixing ratios (<500 pptv or 1×1010 molecule cm-3). The uptake coefficient ratio, γ(3)/γ(N2O5), was determined to be 0.9±0.4 for Saharan dust, independent of relative humidity, NO3 or N2O5 mixing ratio and exposure time. Ambient (urban) aerosols showed a very limited capacity to take up N2O5 but were reactive towards 3 with γ(NO3)/γ(N2O5)>15. A value of γ(NO3)/γ(N2O5)≈1.5–3 was obtained when using candle generated soot. The relative rate obtained for Saharan dust can be placed on an absolute basis using our recently determined value of γ(N2O5)=1×10−2 to give γ(NO3)=9×10-3, which is significantly smaller than the single previous value. With the present uptake coefficient, reaction of NO3 with mineral dust will generally not contribute significantly to its NO3 loss in the boundary atmosphere or to the nitration of mineral dust.
The role of the particle size distribution in assessing aerosol composition effects on simulated droplet activation
Authors: Ward D. S. , Eidhammer T. , Cotton W. R. , Kreidenweis S. M.
Published: April 2010

Abstract. Variations in the chemical composition of atmospheric aerosols alter their hygroscopicity and can lead to changes in the cloud-active fraction of the aerosols, or cloud condensation nuclei (CCN) number concentration. To investigate the importance of this effect under different atmospheric conditions, cloud droplet formation was simulated with a Lagrangian parcel model. Initial values of updraft speed and temperature were systematically varied along with aerosol number concentration, size and hygroscopicity (represented by the hygroscopicity parameter, κ). A previous study classifies the sensitivity of CCN activity to compositional changes based on the supersaturation reached in the parcel model. We found that these classifications could not be generalized to a range of aerosol size distribution median radii. Instead, variations in sensitivity with size depend on the location of the dry critical radius for droplet activation relative to the size distribution median radius. The parcel model output was used to construct droplet activation lookup tables based on κ that were implemented in the Regional Atmospheric Modeling System (RAMS) microphysical scheme. As a first application of this system, aerosol hygroscopicity and size were varied in a series of RAMS mesoscale simulations designed to investigate the sensitivity of a mixed-phase orographic cloud case to the parameter variations. Observations from a recent field campaign in northwestern Colorado provided the basis for the aerosol field initializations. Model results show moderate sensitivity in the distribution of total case precipitation to extreme changes in κ, and minimal sensitivity to observed changes in estimated κ. The impact of varying aerosol hygroscopicity diminished with increasing median radius, as expected from the parcel model results. The conclusions drawn from these simulations could simplify similar research in other cloud regimes by defining the need, or lack of need, for detailed knowledge of aerosol composition.
Transport of Saharan dust from the Bodélé Depression to the Amazon Basin: a case study
Authors: Ben-Ami Y. , Koren I. , Rudich Y. , Artaxo P. , Martin S. T. , Andreae M. O.
Published: April 2010

Abstract. Through long-range transport of dust, the Sahara desert supplies essential minerals to the Amazon rain forest. Since Saharan dust reaches South America mostly during the Northern Hemisphere winter, the dust sources active during winter are the main contributors to the forest. Given that the Bodélé depression area in Southwestern Chad is the main winter dust source, a close link is expected between the Bodélé emission patterns and volumes and the mineral supply flux to the Amazon. Until now, the particular link between the Bodélé and the Amazon forest was based on sparse satellite measurements and modeling studies. In this study, we combine a detailed analysis of space-borne and ground data with reanalysis model data and surface measurements taken in the Central Amazon during the Amazonian Aerosol Characterization Experiment (AMAZE-08) in order to explore the validity and the nature of the proposed link between the Bodélé depression and the Amazon forest. This case study follows the dust events of 11–16 and 18–27 February 2008, from the emission in the Bodélé over West Africa, the crossing of the Atlantic Ocean, to the observed effects above the Amazon canopy about 10 days after the emission. The dust was lifted by surface winds stronger than 14 m s−1, usually starting early in the morning. The lofted dust mixed with biomass burning aerosols over Nigeria, was transported over the Atlantic Ocean, and arrived over the South American continent. The top of the aerosol layer reached above 3 km, and the bottom merged with the marine boundary layer. The arrival of the dusty air parcel over the Amazon forest increased the average concentration of aerosol crustal elements by an order of magnitude.
Atmospheric deposition of mercury and major ions to the Pensacola Bay (Florida) watershed: spatial, seasonal, and inter-annual variability
Authors: Caffrey J. M. , Landing W. M. , Nolek S. D. , Gosnell K. , Bagui S. S. , Bagui S. C.
Published: April 2010

Abstract. Atmospheric deposition was measured at three sites in the Pensacola Bay watershed, Florida, between November 2004 and December 2007. Mercury deposition in the Pensacola Bay watershed was similar to that from nearby Mercury Deposition Network sites along the Northern Gulf of Mexico coast. Mercury deposition during the summer months is higher than other months due to higher concentrations in rainfall throughout the region. Deposition of constituents like H+, sulfate, nitrate, ammonium, chloride and sodium, were much higher in Pensacola Bay that at National Atmospheric Deposition Program (NADP) sites. Chloride and sodium fluxes are higher because Pensacola Bay sites are closer to the Gulf of Mexico which is a source of sea salt aerosols. Acid rain constituents, H+, sulfate, nitrate and ammonium are most likely higher at Pensacola Bay sites because these sites are much closer to emission sources of these constituents than NADP sites, particularly two Florida NADP sites, FL14 and FL23, which are located in rural counties far from major industrial activities.
Structure-activity relationships to estimate the effective Henry's law coefficients of organics of atmospheric interest
Authors: Raventos-Duran T. , Camredon M. , Valorso R. , Aumont B.
Published: April 2010

Abstract. The Henry's law coefficient is a key property needed to address the multiphase behaviour of organics in the atmosphere. Methods that can reliably predict the values for the vast number of organic compounds of atmospheric interest are therefore required. The effective Henry's law coefficient H* in air-water systems at 298 K was compiled from literature for 488 organic compounds bearing functional groups of atmospheric relevance. This data set was used to assess the reliability of the HENRYWIN bond contribution method and the SPARC approach for the determination of H*. Moreover, this data set was used to develop GROMHE, a new Structure Activity Relationship (SAR) based on a group contribution approach. These methods estimate logH* with a Root Mean Square Error (RMSE) of 0.38, 0.61, and 0.73 log unit for GROMHE, SPARC and HENRYWIN respectively. The results show that for all these methods the reliability of the estimates decreases with increasing solubility. The main differences among these methods lie in H* prediction for compounds with H* greater than 103 M atm−1. For these compounds, the predicted values of logH* using GROMHE are more accurate (RMSE=0.53) than the estimates from SPARC or HENRYWIN (RMSE=0.98 and 1.12).
A modelling study of air quality impact of odd-even day traffic restriction scheme before, during and after the 2008 Beijing Olympic Games
Authors: Cai H. , Xie S. D.
Published: April 2010

Abstract. Systematic air pollution control measures were designed and implemented to improve air quality for the 2008 Beijing Olympics. This study focuses on the evaluation of the air quality impacts of a short-term odd-even day traffic restriction scheme (TRS) implemented before, during and after the Games, based on modelling simulation by a well validated urban-scale air quality model. Concentration levels of CO, PM10, NO2 and O3 were predicted for the pre- (10–19 July), during- (20 July–20 September) and post-TRS (21–30 September) periods, based on the on-line monitored traffic flows on a total of 334 road segments constituting the 2nd, 3rd, 4th Ring Roads (RR) and the major Linkage Roads (LRs) that were subject to the TRS policy and distributed around the main urban area of Beijing, and on the hourly sequential meteorological data from a representative Observatory. Subsequently, we used the predictions and observations at a roadside air quality monitoring site to evaluate the model, based on a widely used statistical framework for model evaluation, as well as on the dependence of model performance on time-of-the-day and on wind direction, and the model predictions turned out satisfactory. Results showed that daily average concentrations on the 2nd, 3rd, 4th RR and LRs during the TRS period decreased significantly, by about 35.8%, 38.5%, 34.9% and 35.6% for CO, about 38.7%, 31.8%, 44.0% and 34.7% for PM10, about 30.3%, 31.9%, 32.3% and 33.9% for NO2, and about 36.7%, 33.0%, 33.4% and 34.7% for O3, respectively, compared with the pre-TRS period. Besides, hourly average concentrations were also reduced significantly, particularly for the morning and evening peaks for CO and PM10, for the evening peak for NO2, and for the afternoon peak for O3. Consequently, both the daily and hourly concentration level of CO, PM10, NO2 and O3 conformed to the CNAAQS (China National Ambient Air Quality Standards) Grade II during the Games. Besides, a notable ozone weekend effect was revealed for the pre- and post-TRS periods, and was virtually removed for the during-TRS period. In addition, notable reduction of concentration levels were achieved in different regions of Beijing in response to the TRS policy, with the air quality in the downwind northern and western regions improved most significantly. The TRS policy was therefore effective in improving short-term air quality in Beijing during the Games.
Simulation of aerosol optical thickness during IMPACT (May 2008, The Netherlands) with ECHAM5-HAM
Authors: Roelofs G.-J. , ten Brink H. , Kiendler-Scharr A. , de Leeuw G. , Mensah A. , Minikin A. , Otjes R.
Published: April 2010

Abstract. In May 2008 the measurement campaign IMPACT for observation of atmospheric aerosol and cloud properties was conducted in Cabauw (The Netherlands). With a nudged version of the coupled aerosol-climate model ECHAM5-HAM we simulate aerosol and aerosol optical thickness (AOT) for the campaign period. Synoptic scale meteorology is represented realistically and simulated concentrations of aerosol sulfate and organics at the surface are generally within a factor of two from observed values. The monthly averaged AOT from the model is 0.33, about 20% larger than observed. For selected periods of the month with relatively dry and moist conditions discrepancies are approximately −30% and +15%, respectively. Discrepancies during the dry period are partly caused by inaccurate representation of boundary layer (BL) dynamics by the model affecting the simulated AOT. The model simulates too strong exchange between the BL and the free troposphere, resulting in weaker concentration gradients at the BL top than observed for aerosol and humidity, while upward mixing from the surface layers into the BL appears to be underestimated. The results indicate that beside aerosol sulfate and organics also aerosol ammonium and nitrate significantly contribute to aerosol water uptake. The relation between particle concentration and AOT is rather weak during IMPACT. The simulated day-to-day variability of AOT follows synoptic scale advection of humidity rather than particle concentration. Even for relatively dry conditions AOT appears to be strongly influenced by the diurnal cycle of RH in the lower boundary layer, further enhanced by uptake and release of nitric acid and ammonia by aerosol water.