bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of global changes upon regional ozone pollution in the United States
Authors: Chen J. , Avise J. , Lamb B. , Salathé E. , Mass C. , Guenther A. , Wiedinmyer C. , Lamarque J.-F. , O'Neill S. , McKenzie D. , Larkin N.
Published: April 2010

Abstract. A comprehensive numerical modeling framework was developed to estimate the effects of collective global changes upon ozone pollution in the US in 2050. The framework consists of the global climate and chemistry models, PCM (Parallel Climate Model) and MOZART-2 (Model for Ozone and Related Chemical Tracers v.2), coupled with regional meteorology and chemistry models, MM5 (Mesoscale Meteorological model) and CMAQ (Community Multi-scale Air Quality model). The modeling system was applied for two 10-year simulations: 1990–1999 as a present-day base case and 2045–2054 as a future case. The regional simulations employed 36-km grid cells covering the continental US with boundary conditions taken from the global models. For the current decade, the distributions of summer daily maxima 8-h (DM8H) ozone showed good agreement with observed distributions throughout the US. The future case simulation followed the Intergovernmental Panel on Climate Change (IPCC) A2 scenario together with business-as-usual US emission projections and projected alterations in land use, land cover (LULC) due to urban expansion and changes in vegetation. For these projections, US anthropogenic NOx (NO + NO2) and VOC (volatile organic carbon) emissions increased by approximately 8% and 50%, respectively, while biogenic VOC emissions decreased, in spite of warmer temperatures, due to decreases in forested lands and expansion of croplands, grasslands and urban areas. A stochastic model for wildfire emissions was applied that projected 25% higher VOC emissions in the future. For the global and US emission projection used here, regional ozone pollution becomes worse in the 2045–2054 period for all months. Annually, the mean DM8H ozone was projected to increase by 9.6 ppbv (22%). The changes were higher in the spring and winter (25%) and smaller in the summer (17%). The area affected by elevated ozone within the US continent was projected to increase; areas with levels exceeding the 75 ppbv ozone standard at least once a year increased by 38%. In addition, the length of the ozone season was projected to increase with more pollution episodes in the spring and fall. For selected urban areas, the system projected a higher number of pollution events per year and these events had more consecutive days when DM8H ozone exceed 75 ppbv.
Loading-dependent elemental composition of α-pinene SOA particles
Authors: Shilling J. E. , Chen Q. , King S. M. , Rosenoern T. , Kroll J. H. , Worsnop D. R. , DeCarlo P. F. , Aiken A. C. , Sueper D. , Jimenez J. L. , Martin S. T.
Published: April 2010

Abstract. The chemical composition of secondary organic aerosol (SOA) particles, formed by the dark ozonolysis of α-pinene, was characterized by a high-resolution time-of-flight aerosol mass spectrometer. The experiments were conducted using a continuous-flow chamber, allowing the particle mass loading and chemical composition to be maintained for several days. The organic portion of the particle mass loading was varied from 0.5 to >140 μg/m3 by adjusting the concentration of reacted α-pinene from 0.9 to 91.1 ppbv. The mass spectra of the organic material changed with loading. For loadings below 5 μg/m3 the unit-mass-resolution m/z 44 signal intensity exceeded that of m/z 43, suggesting more oxygenated organic material at lower loadings. Composition measurements displayed a greater dependence for lower loadings (0.5 to 15 μg/m3) compared to higher loadings (15 to >140 μg/m3). The high-resolution mass spectra showed that from >140 to 0.5 μg/m3 the mass percentage of fragments containing carbon and oxygen (CxHyOz+) monotonically increased from 48% to 54%. Correspondingly, the mass percentage of fragments representing CxHy+ decreased from 52% to 46%, and the atomic oxygen-to-carbon ratio increased from 0.29 to 0.45. The atomic ratios were accurately parameterized by a four-product basis set of decadal volatility (viz. 0.1, 1.0, 10, 100 μg/m−3) employing products with the empirical formulas C1H1.32O0.48, C1H1.36O0.39, C1H1.57O0.24, and C1H1.76O0.14. These findings suggest considerable caution is warranted in the extrapolation of laboratory results that were obtained under conditions of relatively high loading (i.e., >15 μg/m3) to modeling applications relevant to the atmosphere, for which loadings of 0.1 to 20 μg/m3 are typical. For the lowest loadings, the particle mass spectra resembled observations reported in the literature for some atmospheric particles.
Evolution of Asian aerosols during transpacific transport in INTEX-B
Authors: Dunlea E. J. , DeCarlo P. F. , Aiken A. C. , Kimmel J. R. , Peltier R. E. , Weber R. J. , Tomlison J. , Collins D. R. , Shinozuka Y. , McNaughton C. S. , Howell S. G. , Clarke A. D. , Emmons L. K. , Apel E. C. , Pfister G. G. , van Donkelaar A. , Martin R. V. , Millet D. B. , Heald C. L. , Jimenez J. L.
Published: April 2010

Abstract. Measurements of aerosol composition were made with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) on board the NSF/NCAR C-130 aircraft as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) field campaign over the Eastern Pacific Ocean. The HR-ToF-AMS measurements of non-refractory submicron aerosol mass are shown to compare well with other aerosol instrumentation in the INTEX-B field study. Two case studies are described for pollution layers transported across the Pacific from the Asian continent, intercepted 3–4 days and 7–10 days downwind of Asia, respectively. Aerosol chemistry is shown to be a robust tracer for air masses originating in Asia, specifically the presence of sulfate dominated aerosol is a distinguishing feature of Asian pollution layers that have been transported to the Eastern Pacific. We examine the time scales of processing for sulfate and organic aerosol in the atmosphere and show that our observations confirm a conceptual model for transpacific transport from Asia proposed by Brock et al. (2004). Our observations of both sulfate and organic aerosol in aged Asian pollution layers are consistent with fast formation near the Asian continent, followed by washout during lofting and subsequent transformation during transport across the Pacific. Our observations are the first atmospheric measurements to indicate that although secondary organic aerosol (SOA) formation from pollution happens on the timescale of one day, the oxidation of organic aerosol continues at longer timescales in the atmosphere. Comparisons with chemical transport models of data from the entire campaign reveal an under-prediction of SOA mass in the MOZART model, but much smaller discrepancies with the GEOS-Chem model than found in previous studies over the Western Pacific. No evidence is found to support a previous hypothesis for significant secondary organic aerosol formation in the free troposphere.
Hydration of the lower stratosphere by ice crystal geysers over land convective systems
Authors: Khaykin S. , Pommereau J.-P. , Korshunov L. , Yushkov V. , Nielsen J. , Larsen N. , Christensen T. , Garnier A. , Lukyanov A. , Williams E.
Published: April 2010

Abstract. The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to MesoScale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of this instrument show the presence of enhanced water vapour layers between the tropopause at 370 K and the 450 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images, over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets up to 18.5 km by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers, up to 8 ppmv higher than that of saturation at the tropopause, and the coincidence with the presence of ice crystals strongly suggest hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like structure of the water vapour seen by the high-resolution hygrometer in contrast to smooth profiles reported by a coarse vertical-resolution satellite observation, suggests that the hydration mechanism described above may be responsible for the known summer seasonal increase of moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause may be an important contributor to the stratospheric water vapour budget.
Cloud phase identification of low-level Arctic clouds from airborne spectral radiation measurements: test of three approaches
Authors: Ehrlich A. , Bierwirth E. , Wendisch M. , Gayet J.-F. , Mioche G. , Lampert A. , Heintzenberg J.
Published: April 2010

Abstract. Boundary layer clouds were investigated with a complementary set of remote sensing and in situ instruments during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. The clouds that formed in a cold air outbreak over the open Greenland sea showed a variety in their thermodynamic state. Beside the predominant mixed-phase clouds pure liquid and ice clouds were observed. Utilizing the measurements of solar radiation reflected by the clouds three methods to retrieve the thermodynamic phase of the cloud were defined and compared. Two ice indices IS and IP were obtained by analyzing the spectral pattern of the cloud top reflectance in the near infrared (1500–1800 nm wavelength) characterized by ice and water absorption. A third ice index IA is based on the different side scattering of spherical liquid water particles and nonspherical ice crystals which was recorded in simultaneous measurements of cloud albedo and reflectance. Radiative transfer simulations showed that IS, IP and IA range between 5 to 80, 0 to 20 and 1 to 1.25, respectively, with lowest values indicating pure liquid water clouds and highest values pure ice clouds. IS and IP were found to be strongly sensitive to the effective diameter of the ice crystals present in the cloud. Therefore the identification of mixed-phase clouds requires a priori knowledge of the ice crystal dimension. IA has the disadvantage that this index is mainly dominated by the uppermost cloud layer (τ<1.5). Typical boundary layer mixed-phase clouds with a liquid cloud top layer will be identified as pure liquid water clouds. All three methods were applied to measurements above a cloud field observed during ASTAR 2007. The comparison with independent in situ microphysical measurements showed a good agreement in identifying the dominant mixed-phase clouds and a pure ice cloud at the edge of the cloud field.
Role of convective transport on tropospheric ozone chemistry revealed by aircraft observations during the wet season of the AMMA campaign
Authors: Ancellet G. , Leclair de Bellevue J. , Mari C. , Nedelec P. , Kukui A. , Borbon A. , Perros P.
Published: April 2010

Abstract. During the wet season of the African Monsoon Multidisciplinary Analyses (AMMA) campaign, airborne measurements of several chemical species were made onboard the French Falcon-20 (FF20) aircraft. The scientific flights were planned in order to document, on one hand the regional distribution of trace gas species related to the oxidizing capacity of the troposphere, and on the other hand their spatial variability in the outflow of mesoscale convective systems (MCSs). The main objectives of this paper are the analysis of the main transport processes responsible for the observed variability, and the discussion of differences and similarities related to the convective transport by 4 different MCSs. This work is needed before using this data set for future studies of the convective transport of chemical species or for modeling work in the frame of the AMMA project. Regarding the regional distribution, five air masses types have been identified using the Lagrangian particle dispersion model FLEXPART, and by considering relationship between the measured trace gas concentrations (O3, CO, NOx, H2O, and hydroperoxides). This paper specifically discusses the advantage of hydroperoxide measurements in order to document the impact of recent or aged convection. The highest values of O3 are found to be related to transport from the subtropical tropopause region into the mid-troposphere at latitudes as low as 10° N. The lowest ozone values have been always explained by recent uplifting from the monsoon layer where O3 is photochemically destroyed. Regarding the analysis of the MCS outflow, the CO and H2O2 enhancements are related to the age and the southernmost position of the MCS. The analysis of the long range transport of the air masses where convection occurred, shows a connection with the Persian Gulf emissions for the largest CO concentrations in MCS outflow. However for our observations, Lagrangian particle dispersion modelling shows that this possible source is always modified by the convective transport of CO from the African lower troposphere when the air masses encounter a convective system at latitudes below 10° N.
Seasonal variation of temperatures between 1 and 105 km altitude at 54° N observed by lidar
Authors: Gerding M. , Höffner J. , Lautenbach J. , Rauthe M. , Lübken F.-J.
Published: April 2010

Abstract. Temperature soundings are performed by lidar at the mid-latitude station of Kühlungsborn (Germany, 54° N, 12° E). The profiles cover the complete range from the lower troposphere (~1 km) to the lower thermosphere (~105 km) by simultaneous and co-located operation of a Rayleigh-Mie-Raman lidar and a potassium resonance lidar. Observations have been done during 266 nights between June 2002 and July 2007, each of 3–15 h length. This large and unique data set provides comprehensive information on the altitudinal and seasonal variation of temperatures from the troposphere to the lower thermosphere. The remaining day-to-day-variability is strongly reduced by harmonic fits at constant altitude levels and a representative data set is achieved. This data set reveals a two-level mesopause structure with an altitude of about 86–87 km (~144 K) in summer and ~102 km (~170 K) during the rest of the year. The average stratopause altitude is ~48 km throughout the whole year, with temperatures varying between 258 and 276 K. From the fit parameters amplitudes and phases of annual, semi-annual, and quarter-annual variations are derived. The amplitude of the annual component is largest with amplitudes of up to 30 K in 85 km, while the quarter-annual variation is smallest and less than 3 K at all altitudes. The lidar data set is compared with ECMWF temperatures below about 70 km altitude and reference data from the NRLMSISE-00 model above. Apart from the temperature soundings the aerosol backscatter ratio is measured between 20 and 35 km. The seasonal variation of these values is presented here for the first time.
Spatial heterogeneity of satellite derived land surface parameters and energy flux densities for LITFASS-area
Authors: Tittebrand A. , Berger F. H.
Published: April 2010

Abstract. Remote sensing data provide area integrated information of surface properties in different spatial or temporal resolutions according to different sensor features. Landsat ETM+, Terra MODIS and NOAA-AVHRR surface temperature and spectral reflectance were used to infer further surface parameters and radiant- and energy flux densities for LITFASS-area, a 20×20 km2 heterogeneous area in Eastern Germany, mainly characterized by the land use types forest, crop, grass and water. Based on the Penman-Monteith-approach the actual latent heat flux (L.E), as key quantity of the hydrological cycle, is determined for each sensor in the accordant spatial resolution with an improved parametrization. However, using three sensors, significant discrepancies between the inferred parameters can cause flux distinctions resultant from differences of the sensor filter response functions or atmospheric correction methods. The approximation of MODIS- and AVHRR- derived surface parameters to the reference parameters of ETM (via regression lines and histogram stretching, respectively), further the use of accurate land use classifications (CORINE and a new Landsat-classification), and a consistent parametrization for the three sensors were realized to obtain a uniform base for investigations of the spatial variability. For the target area the spatial heterogeneity is analysed investigating frequency distribution functions (PDF) for surface parameters and energy fluxes. PDF is the most promising way to describe subgrid heterogeneity due to the given data in different spatial resolution. Aim of this study is to find typical distribution pattern of parameters (albedo, NDVI) for the determination of L.E determined from the highly resolved ETM data within pixel on coarser scale (MODIS, AVHRR). The analyses for 4 scenes in 2002 and 2003 showed that clear distribution-pattern for forest for NDVI and albedo are found. Grass and crop distributions show higher variability and differ significantly to each other in NDVI but only marginal in albedo. Regarding NDVI-distribution functions NDVI was found to be the key variable for L.E-determination.
Ozone mixing ratios inside tropical deep convective clouds from OMI satellite measurements
Authors: Ziemke J. R. , Joiner J. , Chandra S. , Bhartia P. K. , Vasilkov A. , Haffner D. P. , Yang K. , Schoeberl M. R. , Froidevaux L. , Levelt P. F.
Published: April 2010

Abstract. We have developed a new technique for estimating ozone mixing ratio inside deep convective clouds. The technique uses the concept of an optical centroid cloud pressure that is indicative of the photon path inside clouds. Radiative transfer calculations based on realistic cloud vertical structure as provided by CloudSat radar data show that because deep convective clouds are optically thin near the top, photons can penetrate significantly inside the cloud. This photon penetration coupled with in-cloud scattering produces optical centroid pressures that are hundreds of hPa inside the cloud. We use the measured column ozone and the optical centroid cloud pressure derived using the effects of rotational-Raman scattering to estimate O3 mixing ratio in the upper regions of deep convective clouds. The data are obtained from the Ozone Monitoring Instrument (OMI) aboard NASA's Aura satellite. Our results show that low O3 concentrations in these clouds are a common occurrence throughout much of the tropical Pacific. Ozonesonde measurements in the tropics following convective activity also show very low concentrations of O3 in the upper troposphere. These low amounts are attributed to vertical injection of ozone poor oceanic boundary layer air during convection into the upper troposphere followed by convective outflow. Over South America and Africa, O3 mixing ratio inside deep convective clouds often exceeds 50 ppbv which is comparable to mean background (cloud-free) concentrations. These areas contain higher amounts of ozone precursors due to biomass burning and lightning. Assuming that O3 is well mixed (i.e. constant mixing ratio with height) up to the tropopause, we can estimate the stratospheric column O3 over clouds. Stratospheric column ozone derived in this manner agrees well with that retrieved independently with the Aura Microwave Limb Sounder (MLS) instrument and thus provides a consistency check of our method.
Negatively charged nanoparticles produced by splashing of water
Authors: Tammet H. , Hõrrak U. , Kulmala M.
Published: April 2010

Abstract. The production of splashing-generated balloelectric intermediate ions was studied by means of mobility spectrometry in the atmosphere during the rain and in a laboratory experiment simulating the heavy rain. The partial neutralization of intermediate ions with cluster ions generated by beta rays suppressed the space charge of intermediate ions but preserved the shape of the mobility distribution. The balloelectric ions produced from the waterworks water of high TDS (Total Dissolved Solids) had about the same mobilities as the ions produced from the rainwater of low TDS. This suggests that the balloelectric ions can be considered as singly charged water nanodroplets. By different measurements, the diameter mode of these droplets was 2.2–2.7 nm, which is close to the diameter of 2.5 nm of the Chaplin's 280-molecule magic icosahedron superclusters. The measurements can be explained by a hypothesis that the pressure of saturated vapor over the nanodroplet surface is suppressed by a number of magnitudes due to the internal structure of the droplets near the size of 2.5 nm. The records of the concentration bursts of balloelectric ions in the atmosphere are formally similar to the records of the nucleation bursts but they cannot be qualified as nucleation bursts because the particles are not growing but shrinking.
Primary and secondary contributions to aerosol light scattering and absorption in Mexico City during the MILAGRO 2006 campaign
Authors: Paredes-Miranda G. , Arnott W. P. , Jimenez J. L. , Aiken A. C. , Gaffney J. S. , Marley N. A.
Published: April 2010

Abstract. A photoacoustic spectrometer, a nephelometer, an aetholemeter, and an aerosol mass spectrometer were used to measure at ground level real-time aerosol light absorption, scattering, and chemistry at an urban site located in north east Mexico City (Instituto Mexicano del Petroleo, Mexican Petroleum Institute, denoted by IMP), as part of the Megacity Impact on Regional and Global Environments field experiment, MILAGRO, in March 2006. Photoacoustic and reciprocal nephelometer measurements at 532 nm accomplished with a single instrument compare favorably with conventional measurements made with an aethelometer and a TSI nephelometer. The diurnally averaged single scattering albedo at 532 nm was found to vary from 0.60 to 0.85 with the peak value at midday and the minimum value at 7 a.m. local time, indicating that the Mexico City plume is likely to have a net warming effect on local climate. The peak value is associated with strong photochemical generation of secondary aerosol. It is estimated that the same-day photochemical production of secondary aerosol (inorganic and organic) is approximately 40 percent of the aerosol mass concentration and light scattering in association with the peak single scattering albedo. A strong correlation of aerosol scattering at 532 nm and total aerosol mass concentration was found, and an average mass scattering efficiency factor of 3.8 m2/g was determined. Comparisons of photoacoustic and aethalometer light absorption with oxygenated organic aerosol concentration (OOA) indicate a very small systematic bias of the filter based measurement associated with OOA and the peak aerosol single scattering albedo.
The Cloud Condensation Nuclei (CCN) properties of 2-methyltetrols and C3–C6 polyols from osmolality and surface tension measurements
Authors: Ekström S. , Nozière B. , Hansson H.-C.
Published: April 2010

Abstract. A significant fraction of the organic material in aerosols is made of highly soluble compounds such as sugars (mono- and polysaccharides) and polyols, including the 2-methyltetrols, methylerythritol and methyltreitol. The high solubility of these compounds has brought the question of their potentially high CCN efficiency. For the 2-methyltetrols, this would have important implications for cloud formation at global scale because they are thought to be produced by the atmospheric oxidation of isoprene. To investigate this question, the complete Köhler curves for C3–C6 polyols and the 2-methyltetrols have been determined experimentally from osmolality and surface tension measurements. Contrary to what expected, none of these compounds displayed a critical supersaturation lower than those of inorganic salts or organic acids. Their Raoult terms show that this limited CCN efficiency is due to their absence of dissociation in water, this in spite of slight surface-tension effects for the 2-methyltetrols. Thus, compounds such as sugars and polyols would not contribute more to cloud formation in the atmosphere than any other organic compounds studied so far. In particular, the presence of 2-methyltetrols in aerosols would not particularly enhance cloud formation in the atmosphere, contrary to what has been suggested.
Oligomers, organosulfates, and nitroxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry
Authors: Altieri K. E. , Turpin B. J. , Seitzinger S. P.
Published: April 2010

Abstract. Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental compositions of 552 unique molecular species were determined in the mass range 50–500 Da in the rainwater. Three main groups of organic compounds were identified: compounds containing carbon, hydrogen, and oxygen (CHO) only, sulfur (S) containing CHOS compounds, and S- and nitrogen containing CHONS compounds. Organic acids commonly identified in precipitation were detected, as well as linear alkylbenzene sulfonates, which are persistent pollutants commonly measured in river water, seawater, and sediments, but to our knowledge, not previously documented in atmospheric samples. Within the three main groups of compounds detected in the rainwater, oligomers, organosulfates, and nitroxy-organosulfates were identified. The majority of the compounds identified are products of atmospheric reactions and are known contributors to secondary organic aerosol (SOA) formed from gas phase, aerosol phase, and in-cloud reactions in the atmosphere. It is suggested that the large uncharacterized component of SOA is the main contributor to the large uncharacterized component of rainwater organic matter.
Eddy covariance fluxes of acyl peroxy nitrates (PAN, PPN, and MPAN) above a Ponderosa pine forest
Authors: Wolfe G. M. , Yatavelli R. L. N. , Thornton J. A. , McKay M. , Goldstein A. H. , LaFranchi B. , Min K.-E. , Cohen R. C.
Published: April 2010

Abstract. During the Biosphere Effects on AeRosols and Photochemistry EXperiment 2007 (BEARPEX-2007), we observed eddy covariance (EC) fluxes of speciated acyl peroxy nitrates (APNs), including peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN) and peroxymethacryloyl nitrate (MPAN), above a Ponderosa pine forest in the western Sierra Nevada. All APN fluxes are net downward during the day, with a median midday PAN exchange velocity of −0.3 cm s−1; nighttime storage-corrected APN EC fluxes are smaller than daytime fluxes but still downward. Analysis with a standard resistance model shows that loss of PAN to the canopy is not controlled by turbulent or molecular diffusion. Stomatal uptake contributes to 25–50% of the observed downward PAN flux. Vertical gradients in the PAN thermal decomposition (TD) rate explain a similar fraction of the flux, suggesting that a significant portion of the PAN flux into the forest results from chemical processes in the canopy. The remaining "unidentified" portion of the net PAN flux (~15%) is ascribed to deposition or reactive uptake on non-stomatal surfaces (e.g. leaf cuticles or soil). Shifts in temperature, moisture and ecosystem activity during the summer – fall transition alter the relative contribution of stomatal uptake, non-stomatal uptake and thermochemical gradients to the net PAN flux. Daytime PAN and MPAN exchange velocities are a factor of 3 smaller than those of PPN during the first two weeks of the measurement period, consistent with strong intra-canopy chemical production of PAN and MPAN during this period. The depositional loss of APNs can be 3–21% of the gross gas-phase TD loss depending on temperature. As a source of nitrogen to the biosphere, PAN deposition is approximately 4–19% of that due to dry deposition of nitric acid at this site.
Large surface radiative forcing from surface-based ice crystal events measured in the High Arctic at Eureka
Authors: Lesins G. , Bourdages L. , Duck T. J. , Drummond J. R. , Eloranta E. W. , Walden V. P.
Published: April 2010

Abstract. Ice crystals, also known as diamond dust, are suspended in the boundary layer air under clear sky conditions during most of the Arctic winter in Northern Canada. Occasionally ice crystal events can produce significantly thick layers with optical depths in excess of 2.0 even in the absence of liquid water clouds. Four case studies of high optical depth ice crystal events at Eureka in the Nunavut Territory of Canada during the winter of 2006–2007 are presented. They show that the measured ice crystal surface infrared downward radiative forcing ranged from 8 to 36 W m−2 in the wavelength band from 5.6 to 20 μm for visible optical depths ranging from 0.2 to 1.7. MODIS infrared and visible images and the operational radiosonde wind profile were used to show that these high optical depth events were caused by surface snow being blown off 600 to 800 m high mountain ridges about 20 to 30 km North-West of Eureka and advected by the winds towards Eureka as they settled towards the ground within the highly stable boundary layer. This work presents the first study that demonstrates the important role that surrounding topography plays in determining the occurrence of high optical depth ice crystal events and points to a new source of boundary layer ice crystal events distinct from the classical diamond dust phenomenon.
Severe ozone air pollution in the Persian Gulf region
Authors: Lelieveld J. , Hoor P. , Jöckel P. , Pozzer A. , Hadjinicolaou P. , Cammas J.-P.
Published: April 2010

Abstract. Recently it was discovered that over the Middle East during summer ozone mixing ratios can reach a pronounced maximum in the middle troposphere. Here we extend the analysis to the surface and show that especially in the Persian Gulf region conditions are highly favorable for ozone air pollution. Model results indicate that the region is a hot spot of photo-smog where air quality standards are violated throughout the year. Long-distance transports of air pollution from Europe, the Middle East, natural emissions and stratospheric ozone conspire to bring about high background ozone mixing ratios. This provides a hotbed to indigenous air pollution in the dry local weather conditions, which are likely to get worse in future.
Scaling behaviour of the global tropopause
Authors: Varotsos C. , Efstathiou M. , Tzanis C.
Published: April 2010

Abstract. Detrended fluctuation analysis is applied to the time series of the global tropopause height derived from the 1980–2004 daily radiosonde data, in order to detect long-range correlations in its time evolution. Global tropopause height fluctuations in small time-intervals are found to be positively correlated to those in larger time intervals in a power-law fashion. The exponent of this dependence is larger in the tropics than in the middle and high latitudes in both hemispheres. Greater persistence is observed in the tropopause of the Northern than in the Southern Hemisphere. This finding for the tropopause height variability should reduce the existing uncertainties in assessing the climatic characteristics.
Online coupled meteorology and chemistry models: history, current status, and outlook
Authors: Zhang Y.
Published: April 2010

Abstract. The climate-chemistry-aerosol-cloud-radiation feedbacks are important processes occurring in the atmosphere. Accurately simulating those feedbacks requires fully-coupled meteorology, climate, and chemistry models and presents significant challenges in terms of both scientific understanding and computational demand. This paper reviews the history and current status of development and application of online coupled models. Several representative online coupled meteorology and chemistry models developed in the U.S. such as GATOR-GCMOM, WRF/Chem, CAM3, MIRAGE, and Caltech unified GCM are included along with case studies. Major model features, physical/chemical treatments, as well as typical applications are compared with a focus on aerosol microphysics treatments, aerosol feedbacks to planetary boundary layer meteorology, and aerosol-cloud interactions. Recommendations for future development and improvement of online coupled models are provided.
Air-sea fluxes of biogenic bromine from the tropical and North Atlantic Ocean
Authors: Carpenter L. J. , Jones C. E. , Dunk R. M. , Hornsby K. E.
Published: April 2010

Abstract. Air-sea fluxes and bulk seawater and atmospheric concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) were measured during two research cruises in the northeast Atlantic (53–59° N, June–July 2006) and tropical eastern Atlantic Ocean including over the African coastal upwelling system (16–35° N May–June 2007). Saturations and sea-air fluxes of these compounds generally decrease in the order coastal>upwelling>shelf>open ocean, and a broad trend of elevated surface seawater concentrations with high chlorophylla was observed. From limited data from eastern Atlantic coastlines, we tentatively suggest that globally, coastal and coastally-influenced waters together contribute ~2.4 Gmol Br yr−1 (24–56%) of CHBr3. We show that upwelling regions (coastal and equatorial) represent regional hot spots of bromocarbons, but are probably not of major significance globally, contributing only a few percent of the total global emissions of CHBr3 and CH2Br2. We also show that the concentration ratio of CH2Br2/CHBr3 in seawater is a strong function of concentration (and location), with a lower CH2Br2/CHBr3 ratio found in coastal regions near to macroalgal sources.
Evidence for Asian dust effects from aerosol plume measurements during INTEX-B 2006 near Whistler, BC
Authors: Leaitch W. R. , Macdonald A. M. , Anlauf K. G. , Liu P. S. K. , Toom-Sauntry D. , Li S.-M. , Liggio J. , Hayden K. , Wasey M. A. , Russell L. M. , Takahama S. , Liu S. , van Donkelaar A. , Duck T. , Martin R. V. , Zhang Q. , Sun Y. , McKendry I. , Shantz N. C. , Cubison M.
Published: April 2010

Abstract. Several cases of aerosol plumes resulting from trans-Pacific transport were observed between 2 km and 5.3 km at Whistler, BC from 22 April 2006 to 15 May 2006. The fine particle (<1 μm) chemical composition of most of the plumes was dominated by sulphate that ranged from 1–5 μg m−3 as measured with a Quadrapole Aerosol Mass Spectrometer (Q-AMS). Coarse particles (>1 μm) were enhanced in all sulphate plumes. Fine particle organic mass concentrations were relatively low in most plumes and anti-correlated with the increases in the coarse particles. The chemistry of coarse particles sampled at Whistler Peak was dominated by calcium, sodium, nitrate, sulphate and formate. Scanning transmission X-ray microscopy of coarse particles sampled from the NCAR C-130 aircraft relatively close to Whistler indicated carbonate, potassium and organic functional groups, in particular the carboxyl group. Asian plumes reaching Whistler, BC during the INTEX-B study were not only significantly reduced of fine particle organic material, but organic compounds were attached to coarse particles in significant quantities. Scavenging of organic aerosol precursors by dust near source regions is suggested, and any formation of secondary organic aerosol (SOA) during transport from Asian source regions across the Pacific was principally associated with the coarse particles. An average of profiles indicates that trans-Pacific transport between 2 and 5 km during this period increased ozone by about 10 ppbv and fine particle sulphate by 0.2–0.5 μg m−3. The mean sizes of the fine particles in the sulphate plumes were larger when dust particles were present and smaller when the fine particle organic mass concentration was larger and dust was absent. The coarse particles of dust act to accumulate sulphate, nitrate and organic material in larger particles, diminishing the role of these compounds in indirect radiative forcing, but potentially enhancing their roles in direct radiative forcing.
Gaseous mercury distribution in the upper troposphere and lower stratosphere observed onboard the CARIBIC passenger aircraft
Authors: Slemr F. , Ebinghaus R. , Brenninkmeijer C. A. M. , Hermann M. , Kock H. H. , Martinsson B. G. , Schuck T. , Sprung D. , van Velthoven P. , Zahn A. , Ziereis H.
Published: April 2010

Abstract. Total gaseous mercury (TGM) was measured onboard a passenger aircraft during monthly CARIBIC flights (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrumented Container) made between May 2005 and March 2007 on the routes Frankfurt-São Paulo-Santiago de Chile and back (seven times four flights) and Frankfurt-Guangzhou-Manila and back (twelve times four flights). The data provide for the first time an insight into the seasonal distributions of TGM in the upper troposphere and lower stratosphere (UT/LS) of both hemispheres and demonstrate the importance of mercury emissions from biomass burning in the Southern Hemisphere. Numerous plumes were observed in the upper troposphere, the larger of which could be characterized in terms of Hg/CO emission ratios and their probable origins. During the flights to China TGM correlated with CO in the upper troposphere with a seasonally dependent slope reflecting the longer lifetime of elemental mercury when compared to that of CO. A pronounced depletion of TGM was always observed in the extratropical lowermost stratosphere. TGM concentrations there were found to decrease with the increasing concentrations of particles. Combined with the large concentrations of particle bond mercury in the stratosphere observed by others, this finding suggests either a direct conversion of TGM to particle bound mercury or an indirect conversion via a semivolatile bivalent mercury compound. Based on concurrent measurements of SF6 during two flights, the rate of this conversion is estimated to 0.4 ng m−3 yr−1. A zero TGM concentration was not observed during some 200 flight hours in the lowermost stratosphere suggesting an equilibrium between the gaseous and particulate mercury.
Concentrations of higher dicarboxylic acids C5-C13 in fresh snow samples collected at the High Alpine Research Station Jungfraujoch during CLACE 5 and 6
Authors: Winterhalter R. , Kippenberger M. , Williams J. , Fries E. , Sieg K. , Moortgat G. K.
Published: April 2010

Abstract. Samples of freshly fallen snow were collected at the high alpine research station Jungfraujoch (Switzerland) in February and March 2006 and 2007, during the Cloud and Aerosol Characterization Experiments (CLACE) 5 and 6. In this study a new technique has been developed and demonstrated for the measurement of organic acids in fresh snow. The melted snow samples were subjected to solid phase extraction and resulting solution analysed for organic acids by HPLC-MS-TOF using negative electrospray ionization. A series of linear dicarboxylic acids from C5 to C13 and phthalic acid, were identified and quantified. In several samples the biogenic acid pinonic acid was also observed. In fresh snow the median concentration of the most abundant acid, adipic acid, was 0.69 μg L−1 in 2006 and 0.70 μg L−1 in 2007. Glutaric acid was the second most abundant dicarboxylic acid found with median values of 0.46 μg L−1 in 2006 and 0.61 μg L−1 in 2007, while the aromatic acid phthalic acid showed a median concentration of 0.34 μg L−1 in 2006 and 0.45 μg L−1 in 2007. The concentrations in the samples from various snowfall events varied significantly, and were found to be dependent on the back trajectory of the air mass arriving at Jungfraujoch. Air masses of marine origin showed the lowest concentrations of acids whereas the highest concentrations were measured when the air mass was strongly influenced by boundary layer air.
Implications of Lagrangian transport for coupled chemistry-climate simulations
Authors: Stenke A. , Dameris M. , Grewe V. , Garny H.
Published: April 2010

Abstract. For the first time a purely Lagrangian transport algorithm is applied in a fully coupled chemistry-climate model (CCM). We use the Lagrangian scheme ATTILA for the transport of water vapour, cloud water and chemical trace species in the ECHAM4.L39(DLR)/CHEM (E39C) CCM. The advantage of the Lagrangian approach is that it is numerically non-diffusive and therefore maintains steeper and more realistic gradients than the operational semi-Lagrangian transport scheme. In case of radiatively active species changes in the simulated distributions feed back to model dynamics which in turn affect the modelled transport. The implications of the Lagrangian transport scheme for stratospheric model dynamics and tracer distributions in the upgraded model version E39C-ATTILA (E39C-A) are evaluated by comparison with observations and results of the E39C model with the operational semi-Lagrangian advection scheme. We find that several deficiencies in stratospheric dynamics in E39C seem to originate from a pronounced modelled wet bias and an associated cold bias in the extra-tropical lowermost stratosphere. The reduction of the simulated moisture and temperature bias in E39C-A leads to a significant advancement of stratospheric dynamics in terms of the mean state as well as annual and interannual variability. As a consequence of the favourable numerical characteristics of the Lagrangian transport scheme and the improved model dynamics, E39C-A generally shows more realistic stratospheric tracer distributions: Compared to E39C high stratospheric chlorine (Cly) concentrations extend further downward and agree now well with analyses derived from observations. Therefore E39C-A realistically covers the altitude of maximum ozone depletion in the stratosphere. The location of the ozonopause, i.e. the transition from low tropospheric to high stratospheric ozone values, is also clearly improved in E39C-A. Furthermore, the simulated temporal evolution of stratospheric Cly in the past is realistically reproduced which is an important step towards a more reliable projection of future changes, especially of stratospheric ozone.
Development of a global model of mineral dust aerosol microphysics
Authors: Lee Y. H. , Chen K. , Adams P. J.
Published: April 2010

Abstract. A mineral dust module is developed and implemented into the global aerosol microphysics model, GISS-TOMAS. The model is evaluated against long-term measurements of dust surface mass concentrations and deposition fluxes. Predicted mass concentrations and deposition fluxes are in error on average by a factor of 3 and 5, respectively. The comparison shows that the model performs better near the dust source regions but underestimates surface concentrations and deposition fluxes in more remote regions. For example, including only sites with measured dust concentrations of at least 0.5 μg m−3, the model prediction agrees with observations to within a factor of 2. It was hypothesized that the lifetime of dust, 2.6 days in our base case, is too short and causes the underestimation in remote areas. However, a sensitivity simulation with smaller dust particles and increased lifetime, 3.7 days, does not significantly improve the comparison. We conclude that the underestimation of mineral dust in remote areas results from local factors and sources not well described by the dust source function and/or the GCM meteorology. The effect of dust aerosols on CCN(0.2%) concentrations is negligible in most regions of the globe; however, CCN(0.2%) concentrations decrease by 10–20% in dusty regions as a result of coagulational scavenging of CCN particles by dust and a decrease in H2SO4 condensation to CCN particles due to the additional surface area of dust.
Anthropogenic influence on SOA and the resulting radiative forcing
Authors: Hoyle C. R. , Myhre G. , Berntsen T. K. , Isaksen I. S. A.
Published: April 2010

Abstract. The pre-industrial and present day distributions and burdens of Secondary Organic Aerosol (SOA) have been calculated using the off-line aerosol chemistry transport model Oslo CTM2. The production of SOA was found to have increased from about 43 Tg yr−1 to 69 Tg yr−1 since pre-industrial times, leading to an increase in the global annual mean SOA burden from 0.44 Tg to 0.70 Tg, or about 59%. The increases are greatest over industrialised areas, as well as over regions with high biogenic precursor emissions. The contribution of emissions from different sources to the larger SOA burdens has been calculated. The results suggest that the majority of the increase is caused by emissions of primary organic aerosols (POA), from fossil fuel and bio fuel combustion. When SOA partitioning to ammonium sulphate aerosol was not accounted for, the increase in SOA burden between pre-industrial times and the present was found to be lower (51%), with a production increase of 55%. As yet, very few radiative forcing estimates of SOA exist, and no such estimates were provided in the latest IPCC report. In this study, we find that the change in SOA burden caused a radiative forcing of −0.09 W m−2, when SOA was allowed to partition to both organic and sulphate aerosols, and −0.06 W m−2 when only partitioning to organic aerosols was assumed. Therefore, the radiative forcing of SOA is found to be substantially stronger than the best estimate for POA in the latest IPCC assessment.