bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing
Authors: Ehrlich A. , Wendisch M. , Bierwirth E. , Gayet J.-F. , Mioche G. , Lampert A. , Mayer B.
Published: April 2010

Abstract. The vertical distribution of ice crystals in Arctic boundary-layer mixed-phase (ABM) clouds was investigated by airborne remote sensing and in situ measurements during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. From airborne measurements of spectral solar radiation reflected by the ABM clouds information on the spectral absorption of solar radiation by ice and liquid water cloud particles is derived. It is shown by calculation of the vertical weighting function of the measurements that the observed absorption of solar radiation is dominated by the upper cloud layers (50% within 200 m from cloud top). This vertical weighting function is shifted even closer to cloud top for wavelengths where absorption by ice is dominating. On this basis an indicator of the vertical distribution of ice crystals in ABM clouds is designed. Applying the in situ measured microphysical properties, the cloud top reflectance was calculated by radiative transfer simulations and compared to measurements. It is found that ice crystals near cloud top (mixed-phase cloud top layer) are necessary to reproduce the measurements at wavelengths where absorption by ice is dominating. The observation of backscatter glories on top of the ABM clouds generally indicating liquid water droplets does not contradict the postulated presence of ice crystals. Radiative transfer simulations reproduce the observed glories even if the cloud top layer is of mixed-phase character.
Atmospheric hydrogen variations and traffic emissions at an urban site in Finland
Authors: Aalto T. , Lallo M. , Hatakka J. , Laurila T.
Published: April 2010

Abstract. Atmospheric hydrogen (H2) mixing ratios were observed over one year period from summer 2007 to 2008 in Helsinki, Finland. Relatively stable background values of hydrogen were occasionally observed at the site, with minimum in October and maximum between March and May. High hydrogen mixing ratios occurred simultaneously with high carbon monoxide (CO) values and coincided with high traffic flow periods. Carbon monoxide and radon (222Rn) were continuously monitored at the same site and they were used in estimation of the hydrogen emissions from traffic. The morning rush hour slope of ΔH2/ΔCO was in average 0.43±0.03 ppb (H2)/ppb(CO). After correction due to soil deposition of H2 the slope was 0.49±0.07 ppb (H2)/ppb(CO). Using this slope and CO emission statistics, a road traffic emission of about 260 t (H2)/year was estimated for Helsinki in 2007.
Daytime SABER/TIMED observations of water vapor in the mesosphere: retrieval approach and first results
Authors: Feofilov A. G. , Kutepov A. A. , Pesnell W. D. , Goldberg R. A. , Marshall B. T. , Gordley L. L. , García-Comas M. , López-Puertas M. , Manuilova R. O. , Yankovsky V. A. , Petelina S. V. , Russell III J. M.
Published: April 2010

Abstract. This paper describes a methodology for water vapor retrieval using 6.6 μm daytime broadband emissions measured by SABER, the limb scanning infrared radiometer on board the TIMED satellite. Particular attention is given to accounting for the non-local thermodynamic equilibrium (non-LTE) nature of the H2O 6.6 μm emission in the mesosphere and lower thermosphere (MLT). The non-LTE H2O (ν2) vibrational level populations responsible for this emission depend on energy exchange processes within the H2O vibrational system as well as on interactions with vibrationally excited states of the O2, N2, and CO2 molecules. The paper analyzes current H2O non-LTE models and, based on comparisons with the ACE-FTS satellite solar occultation measurements, suggests an update to the rate coefficients of the three most important processes that affect the H2O(ν2) populations in the MLT: a) the vibrational-vibrational (V–V) exchange between the H2O and O2 molecules; b) the vibrational-translational (V–T) process of the O2(1) level quenching by collisions with atomic oxygen, and c) the V–T process of the H2O(010) level quenching by collisions with N2, O2, and O. We demonstrate that applying the updated H2O non-LTE model to the SABER radiances makes the retrieved H2O vertical profiles in 50–85 km region consistent with climatological data and model predictions.
On the distribution of formaldehyde in the western Po-Valley, Italy, during FORMAT 2002/2003
Authors: Junkermann W.
Published: April 2010

Abstract. Formaldehyde was measured in the area of Milano, Italy, during the 2002 and 2003 FORMAT campaigns at three ground field sites and from an ultralight aircraft. The horizontal distributions show a strong impact of local emissions at a site in the centre of Milano and more photochemically driven diurnal patterns in the remote locations north and south of the city. The mixing ratios in the agricultural areas upwind of Milano were comparable to those downwind indicating the importance of biogenic emissions and anthropogenic agricultural activities. The vertical distributions were dominated by transport processes with advection of CH2O above the planetary boundary layer by cloud venting. Comparison to model calculations show discrepancies in the diurnal patterns and regional distribution which allude to uncertainties in emission inventories.
Comment on "Quantitative performance metrics for stratospheric-resolving chemistry-climate models" by Waugh and Eyring
Authors: Grewe V. , Sausen R.
Published: April 2010

Abstract. This comment focuses on the statistical limitations of a model grading, as applied by D. Waugh and V. Eyring (2008) (WE08). The grade g is calculated for a specific diagnostic, which basically relates the difference of model and observational data to the standard deviation in the observational dataset. Monte Carlo simulations show that this method is not leading to statistical significant gradings. Moreover, the difference between two models is hardly significant. The results of the statistical tests performed in WE08 agree with our findings. However, most of those tests are based on special cases, which implicitely assume that observations are available without any errors and that the interannual variability of the observational data and the model data are equal. Without these assumptions the grading becomes basically insignificant. We further show that the inclusion of confidence intervals into the grading approach is necessary, since it has the potential to change the grading results drastically.
Atmospheric nitrogen budget in Sahelian dry savannas
Authors: Delon C. , Galy-Lacaux C. , Boone A. , Liousse C. , Serça D. , Adon M. , Diop B. , Akpo A. , Lavenu F. , Mougin E. , Timouk F.
Published: April 2010

Abstract. The atmospheric nitrogen budget depends on emission and deposition fluxes both as reduced and oxidized nitrogen compounds. In this study, a first attempt at estimating the Sahel nitrogen budget for the year 2006 is made, through measurements and simulations at three stations from the IDAF network situated in dry savanna ecosystems. Dry deposition fluxes are estimated from measurements of NO2, HNO3 and NH3 gaseous concentrations, and wet deposition fluxes are calculated from NH4+ and NO3− concentrations in samples of rain. Emission fluxes are estimated including biogenic emission of NO from soils (an Artificial Neural Network module has been inserted into the ISBA-SURFEX surface model), emission of NOx and NH3 from domestic fires and biomass burning, and volatilization of NH3 from animal excreta. This study uses original and unique data from remote and hardly-ever-explored regions. The monthly evolution of oxidized N compounds shows that deposition increases at the beginning of the rainy season because of large emissions of biogenic NO (pulse events). Emission of oxidized compounds is dominated by biogenic emission from soils (domestic fires and biomass burning account for 27% at the most, depending on the station), whereas emission of NH3 is dominated by the process of volatilization. Deposition fluxes are dominated by gaseous dry deposition processes (58% of the total), for both oxidized and reduced compounds. The average deposition flux in dry savanna ecosystems ranges from 8.6 to 10.9 kgN ha−1 yr−1, with 30% attributed to oxidized compounds, and the other 70% attributed to NHx. The average emission flux ranges from 7.8 to 9.7 kgN ha−1 yr−1, dominated by NH3 volatilization (67%) and biogenic emission from soils (24%). The annual budget is then balanced, with emission fluxes on the same order of magnitude as deposition fluxes. When scaled up to the Sahelian region (10° N:20° N, 15° W:10° E), the estimates of total emission range from 3.6 to 4.5 TgN yr−1 and total deposition ranges from 3.9 to 5 TgN yr−1. The N budget gives a net deposition flux ranging from 0.2 to 0.6 TgN yr−1. If scaled up to the global scale (in the tropical band), it is possible to calculate a total budget of oxidized and reduced N compounds for dry savannas, with a global nitrogen deposition flux ranging from 11.1 to 14.1 TgN yr−1, and a global emission flux ranging from 10.1 to 12.5 TgN yr−1. These ecosystems contribute a significant amount (around 12%) to the global nitrogen budget.
Est modus in rebus: analytical properties of multi-model ensembles
Authors: Potempski S. , Galmarini S.
Published: April 2010

Abstract. In this paper we investigate some basic properties of the multi-model ensemble systems, which can be deduced from a general characteristic of statistical distributions of the ensemble members with the help of mathematical tools. In particular we show how to find optimal linear combination of model results, which minimizes the mean square error both in the case of uncorrelated and correlated models. By proving basic estimations we try to deduce general properties describing multi-model ensemble systems. We show also how mathematical formalism can be used for investigation of the characteristics of such systems.
Impact of stratospheric intrusions and intercontinental transport on ozone at Jungfraujoch in 2005: comparison and validation of two Lagrangian approaches
Authors: Cui J. , Sprenger M. , Staehelin J. , Siegrist A. , Kunz M. , Henne S. , Steinbacher M.
Published: April 2010

Abstract. The particle dispersion model FLEXPART and the trajectory model LAGRANTO are Lagrangian models which are widely used to study synoptic-scale atmospheric air flows such as stratospheric intrusions (SI) and intercontinental transport (ICT). In this study, we focus on SI and ICT events particularly from the North American planetary boundary layer for the Jungfraujoch (JFJ) measurement site, Switzerland, in 2005. Two representative cases of SI and ICT are identified based on measurements recorded at Jungfraujoch and are compared with FLEXPART and LAGRANTO simulations, respectively. Both models well capture the events, showing good temporal agreement between models and measurements. In addition, we investigate the performance of FLEXPART and LAGRANTO on representing SI and ICT events over the entire year 2005 in a statistical way. We found that the air at JFJ is influenced by SI during 19% (FLEXPART) and 18% (LAGRANTO), and by ICT from the North American planetary boundary layer during 13% (FLEXPART) and 12% (LAGRANTO) of the entire year. Through intercomparsion with measurements, our findings suggest that both FLEXPART and LAGRANTO are well capable of representing SI and ICT events if they last for more than 12 h, whereas both have problems on representing short events. It is also shown that although the long-range transported air is characterized by relatively low NOy/CO ratios and elevated CO concentrations, using a combination of NOy/CO and CO as control parameters still encounters difficulty in distinguishing aged air masses by their source regions. Moreover, a sensitivity study indicates that the agreement between models and measurements depends significantly on the threshold values applied to the individual control parameters. Generally, the less strict the thresholds are, the better the agreement between models and measurements. Although the dependence of the agreement on the threshold values is appreciable, it nevertheless confirms the conclusion that both FLEXPART and LAGRANTO are well able to capture SI and ICT events with sustaining time longer than 12 h.
The comprehensive model system COSMO-ART – radiative impact of aerosol on the state of the atmosphere on the regional scale
Authors: Vogel B. , Vogel H. , Bäumer D. , Bangert M. , Lundgren K. , Rinke R. , Stanelle T.
Published: April 2010

Abstract. A new fully online coupled model system developed for the evaluation of the interaction of aerosol particles with the atmosphere on the regional scale is described. The model system is based on the operational weather forecast model of the Deutscher Wetterdienst. Physical processes like transport, turbulent diffusion, and dry and wet deposition are treated together with photochemistry and aerosol dynamics using the modal approach. Based on detailed calculations we have developed parameterizations to examine the impact of aerosol particles on photolysis and on radiation. Currently the model allows feedback between natural and anthropogenic aerosol particles and the atmospheric variables that are initialized by the modification of the radiative fluxes. The model system is applied to two summer episodes, each lasting five days, with a model domain covering Western Europe and adjacent regions. The first episode is characterised by almost cloud free conditions and the second one by cloudy conditions. The simulated aerosol concentrations are compared to observations made at 700 stations distributed over Western Europe. For each episode two model runs are performed; one where the feedback between the aerosol particles and the atmosphere is taken into account and a second one where the feedback is neglected. Comparing these two sets of model runs, the radiative feedback on temperature and other variables is evaluated. In the cloud free case a clear correlation between the aerosol optical depth and changes in global radiation and temperature is found. In the case of cloudy conditions the pure radiative effects are superposed by changes in the liquid water content of the clouds due to changes in the thermodynamics of the atmosphere. In this case the correlation between the aerosol optical depth and its effects on temperature is low. However, on average a decrease in the 2 m temperature is still found. In both cases a reduction in the daily temperature range, due to the aerosol optical depth, can be seen with an average value of −0.13 K over Germany.
Constraints on inorganic gaseous iodine in the tropical upper troposphere and stratosphere inferred from balloon-borne solar occultation observations
Authors: Butz A. , Bösch H. , Camy-Peyret C. , Chipperfield M. P. , Dorf M. , Kreycy S. , Kritten L. , Prados-Román C. , Schwärzle J. , Pfeilsticker K.
Published: April 2010

Abstract. We report upper limits of IO and OIO in the tropical upper troposphere and stratosphere inferred from solar occultation spectra recorded by the LPMA/DOAS (Limb Profile Monitor of the Atmosphere/Differential Optical Absorption Spectroscopy) payload during two stratospheric balloon flights from a station in Northern Brazil (5.1° S, 42.9° W). In the tropical upper troposphere and lower stratosphere, upper limits for both, IO and OIO, are below 0.1 ppt. Photochemical modelling is used to estimate the compatible upper limits for the total gaseous inorganic iodine burden (Iy) amounting to 0.09 to 0.16 (+0.10/−0.04) ppt in the tropical lower stratosphere (21.0 km to 16.5 km) and 0.17 to 0.35 (+0.20/−0.08) ppt in the tropical upper troposphere (16.5 km to 13.5 km). In the middle stratosphere, upper limits increase with altitude as sampling sensitivity decreases. Our findings imply that the amount of gaseous iodine transported into the stratosphere through the tropical tropopause layer is small and that iodine-mediated ozone loss plays only a minor role for stratospheric photochemistry. However, photochemical modelling uncertainties are large and iodine might be transported into the stratosphere in particulate form.
Nitric acid and particulate matter measurements at Athens, Greece, in connection with corrosion studies
Authors: Tzanis C. , Varotsos C. , Ferm M. , Christodoulakis J. , Assimakopoulos M. N. , Efthymiou C.
Published: April 2010

Abstract. For a long time, scientists have been concerned about the effects of air pollution on materials and especially on the monuments of the cultural heritage. The EU funded a project, entitled MULTI-ASSESS, to determine these effects and to develop dose-response functions appropriate for the new multi-pollutant environment. The University of Athens participated in this effort as a targeted field exposure test site. In the present paper, the measurements of the passive samplers, which were exposed during the same period with the samples for corrosion studies, at the Athens' station, are presented. The results have shown that only 16.5% of the deposited mass was water soluble. The vertical distribution of passive particle collectors has led to the conclusion that the height of maximum deposition of each ion is different. In addition, a variation of the water-soluble mass to total deposited mass between 8% and 31% is observed.
Numerical simulations of contrail-to-cirrus transition – Part 1: An extensive parametric study
Authors: Unterstrasser S. , Gierens K.
Published: April 2010

Abstract. Simulations of contrail-to-cirrus transition over up to 6 h were performed using a LES-model. The sensitivity of microphysical, optical and geometric contrail properties on relative humidity RHi, temperature T and vertical wind shear s was investigated in an extensive parametric study. The dominant parameter for contrail evolution is relative humidity. Substantial spreading is only visible for RHi≳120%. Vertical wind shear has a smaller effect on most contrail properties than human observers might expect from the visual impression. Our model shows that after a few hours the water vapour removed by falling ice crystals from the contrail layer can be several times higher than the ice mass that is actually present in the contrail at any instance.
A three-dimensional model study of methanesulphonic acid to non sea salt sulphate ratio at mid and high-southern latitudes
Authors: Castebrunet H. , Martinerie P. , Genthon C. , Cosme E.
Published: April 2010

Abstract. The Antarctic and sub-Antarctic methanesulphonic acid (MSA) to non sea salt sulphate (nssSO4) ratio is simulated with the Laboratoire de Météorologie Dynamique Atmospheric General Circulation Model including an atmospheric sulphur chemistry module. Spatial variations of the MSA/nssSO4 ratio in different regions have been suggested to be mostly dependent on temperature or sulphur source contributions. Its past variations in ice cores have been interpreted as related to the DMS precursor source location. Our model results are compared with available field measurements in the Antarctic and sub-Antarctic regions. This suggests that the MSA/nssSO4 ratio in the extra-tropical south hemisphere is mostly dependent on the relative importance of various DMS oxidation pathways. In order to evaluate the effect of a rapid conversion of dimethyl sulphoxide (DMSO) into MSA, not implemented in the model, the MSA+DMSO to nssSO4 ratio is also discussed. Using this modified ratio, the model mostly captures the seasonal variations of MSA/nssSO4 at mid and high-southern latitudes. In addition, the model qualitatively reproduces the bell shaped meridional variations of the ratio, which is highly dependent on the adopted relative reaction rates for the DMS+OH addition and abstraction pathways, and on the assumed reaction products of the MSIA+OH reaction. MSA/nssSO4 ratio in Antarctic snow is fairly well reproduced except at the most inland sites characterized with very low snow accumulation rates. Our results also suggest that atmospheric chemistry plays an important role in the observed decrease of the ratio in snow between coastal regions and central Antarctica. The still insufficient understanding of the DMS oxidation scheme limits our ability to model the MSA/nssSO4 ratio. Specifically, reaction products of the MSIA+OH reaction should be better quantified, and the impact of a fast DMSO conversion to MSA in spring to fall over Antarctica should be evaluated. Direct measurements of MSA and nssSO4 dry deposition velocities on Antarctic snow would improve our ability to model MSA and nssSO4 in ice cores.
Observations of boundary layer, mixed-phase and multi-layer Arctic clouds with different lidar systems during ASTAR 2007
Authors: Lampert A. , Ritter C. , Hoffmann A. , Gayet J.-F. , Mioche G. , Ehrlich A. , Dörnbrack A. , Wendisch M. , Shiobara M.
Published: April 2010

Abstract. During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR), which was conducted in Svalbard in March and April 2007, tropospheric Arctic clouds were observed with two ground-based backscatter lidar systems (micro pulse lidar and Raman lidar) and with an airborne elastic lidar. An increase in low-level (cloud tops below 2.5 km) cloud cover from 51% to 65% was observed above Ny-Ålesund during the time of the ASTAR campaign. Four different case studies of lidar cloud observations are analyzed: With the ground-based Raman lidar, a pre-condensation layer was observed at an altitude of 2 km. The layer consisted of small droplets with a high number concentration (around 300 cm−3) at low temperatures (−30°C). Observations of a boundary layer mixed-phase cloud by airborne lidar were evaluated with the measurements of concurrent airborne in situ and spectral solar radiation sensors. Two detailed observations of multiply layered clouds in the free troposphere are presented. The first case was composed of various ice layers with different optical properties detected with the Raman lidar, the other case showed a mixed-phase double layer and was observed by airborne lidar. The analysis of these four cases confirmed that lidar data provide information of the whole range from subvisible to optically thick clouds. Despite the attenuation of the laser signal in optically thick clouds and multiple scattering effects, information on the geometrical boundaries of liquid water clouds were obtained. Furthermore, the dominating phase of the clouds' particles in the layer closest to the lidar system could be retrieved.
27-day variation in cloud amount and relationship to the solar cycle
Authors: Takahashi Y. , Okazaki Y. , Sato M. , Miyahara H. , Sakanoi K. , Hong P. K.
Published: April 2010

Abstract. Linkages between solar activity and the earth's climate have been suggested in previous studies. The 11-year cycle in solar activity evident in sunspot numbers is the most examined example of periodicity, and it is clearly recognized in variations in the thermal structure and dynamical motion of the stratospheric atmosphere. Also the variations in the stratosphere related to the period of apparent solar rotation have also been suggested; however, for such a short period, no quantitative evidence indicating a relationship to the tropospheric phenomena. We clearly demonstrate a 27-day variation in the cloud amount in the region of the Western Pacific warm pool, which is only seen in the solar maximum years of the 11-year cycle. The average spectrum in solar maximum years also shows an enhancement in the range of MJO period. Long-term variations in the tropospheric phenomena, including the 11-year cycle, are generally investigated based on monthly or even yearly averaged data, but the present results may suggest an alternative possibility: short-period variations could modulate longer periodic phenomena.
Secondary organic material formed by methylglyoxal in aqueous aerosol mimics – Part 1: Surface tension depression and light-absorbing products
Authors: Schwier A. N. , Shapiro E. L. , Sareen N. , McNeill V. F.
Published: April 2010

Abstract. We show that methylglyoxal forms light-absorbing secondary organic material in aqueous ammonium sulfate and ammonium nitrate solutions mimicking tropospheric aerosol particles. The light-absorbing products form on the order of minutes, and solution composition continues to change over several days. The results suggest an aldol condensation pathway involving the participation of the ammonium ion. Aqueous solutions of methylglyoxal, with and without inorganic salts, exhibit surface tension depression. Methylglyoxal uptake could potentially change the optical properties, climate effects, and heterogeneous chemistry of the seed aerosol over its lifetime.
Estimating trajectory uncertainties due to flow dependent errors in the atmospheric analysis
Authors: Engström A. , Magnusson L.
Published: April 2010

Abstract. The uncertainty of a calculated trajectory is dependent on the uncertainty in the atmospheric analysis. Using the Ensemble Transform method (originally adapted for ensemble forecasting) we sample the analysis uncertainty in order to create an ensemble of analyses where a trajectory is started from each perturbed analysis. This method, called the Ensemble analysis method (EA), is compared to the Initial spread method (IS), where the trajectory receptor point is perturbed in the horizontal and vertical direction to create a set of trajectories used to estimate trajectory uncertainty. The deviation growth is examined for a one-month period and for 15 different locations. We find up to a 40% increase in trajectory deviation in the mid-latitudes using the EA method. A simple model for trajectory deviation growth speed is set up and validated. It is shown that the EA method result in a faster error growth compared to the IS method. In addition, two case studies are examined to qualitatively illustrate how the flow dependent analysis uncertainty can impact the trajectory calculations. We find a more irregular behavior for the EA trajectories compared to the IS trajectories and a significantly increased uncertainty in the trajectory origin. By perturbing the analysis in consistency with the analysis uncertainties the error in backward trajectory calculations can be more consistently estimated.
The influence of the vertical distribution of emissions on tropospheric chemistry
Authors: Pozzer A. , Jöckel P. , Van Aardenne J.
Published: April 2010

Abstract. The atmospheric chemistry general circulation model EMAC (ECHAM5/MESSy atmospheric chemistry) is used to investigate the effect of height dependent emissions on tropospheric chemistry. In a sensitivity simulation, anthropogenic and biomass burning emissions are released in the lowest model layer. The resulting tracer distributions are compared to those of a former simulation applying height dependent emissions. Although the differences between the two simulations in the free troposphere are small (less than 5%), large differences are present in polluted regions at the surface, in particular for NOx (more than 100%) and non-methane hydrocarbons (up to 30%), whereas for OH the differences at the same locations are somewhat lower (15%). Global ozone formation is virtually unaffected by the choice of the vertical distribution of emissions. Nevertheless, local ozone changes can be up to 30%. Model results of both simulations are further compared to observations from field campaigns and to data from measurement stations. The two simulations show no significant differences when compared to aircraft observations. In contrast, for measurements from surface stations, the simulation with emissions in the lowest model layer gives a 20% lower correlation to the observations compared to the simulation with height dependent emissions.
More evidence for very short-lived substance contribution to stratospheric chlorine inferred from HCl balloon-borne in situ measurements in the tropics
Authors: Mébarki Y. , Catoire V. , Berthet G. , Huret N. , Robert C.
Published: April 2010

Abstract. Volume mixing ratio (vmr) vertical profiles of hydrogen chloride (HCl) are retrieved from in situ measurements performed by a balloon-borne infrared tunable diode laser absorption spectrometer (SPIRALE) during two balloon flights in the tropics (Teresina, Brazil, 5.1° S–42.9° W) at three year interval in June 2005 and June 2008. HCl vertical profiles obtained from 15.0 to 31.0 km are presented and analysed to estimate the contribution of very short-lived substances (VSLS) to total stratospheric chlorine. Both retrieved vertical profiles of HCl from these flights globally agree very well with each other, with estimated overall uncertainties of 6% on vmr between 23 and 31 km. Upper limits of HCl vmr as low as (20±20) pptv in June 2008 and (30±30) pptv in June 2005 are inferred in the upper part of the tropical tropopause layer (TTL). Backward trajectory calculations suggest that these low amounts were sampled in air masses corresponding to typical background conditions, i.e. neither influenced by recent tropospheric nor stratospheric air. Taking into account the recently reported VSLS source gas measurements obtained in similar conditions (Laube et al., 2008) and the main intermediate product gas (COCl2), a VSLS contribution of about (85±35 pptv) to total stratospheric chlorine is inferred. This refines the WMO (2007) estimation of 50 to 100 pptv, which was not taking into account any HCl contribution. In addition, comparisons of HCl measurements between SPIRALE and MLS-Aura satellite instrument in the tropical lower and middle stratosphere lead to a very good agreement. Since HCl modelled values derived from a total stratospheric chlorine budget including 100 pptv of VSLS agree with MLS measurements in the upper stratosphere, the consistency between SPIRALE and MLS measurements provides another evidence for this VSLS contribution.
The time evolution of aerosol size distribution over the Mexico City plateau
Authors: Kleinman L. I. , Springston S. R. , Wang J. , Daum P. H. , Lee Y.-N. , Nunnermacker L. J. , Senum G. I. , Weinstein-Lloyd J. , Alexander M. L. , Hubbe J. , Ortega J. , Zaveri R. A. , Canagaratna M. R. , Jayne J.
Published: April 2010

Abstract. As part of the MILAGRO field campaign, the DOE G-1 aircraft was used to make measurements over and downwind of Mexico City with the objective of determining growth characteristics of aerosols from a megacity urban source. This study focuses on number concentration and size distributions. It is found that a 5-fold increase in aerosol volume is accompanied by about a 5-fold increase in accumulation mode number concentration. There is growth in aerosol volume because there are more accumulation mode particles, not because particles are larger. Condensation and volume growth laws were examined to see whether either is consistent with observations. Condensation calculations show that the growth of Aitken mode particles into the accumulation mode size range gives the required increase in number concentration. There are minimal changes in the accumulation mode size distribution with age, consistent with observations. Volume-growth in contrast yields a population of large particles, distinctly different from what is observed. Detailed model calculations are required to translate our observations into specific information on the volatility and properties of secondary organic aerosol.
Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide
Authors: Yang M. , Blomquist B. W. , Huebert B. J.
Published: April 2010

Abstract. The hydroxyl radical (OH) is an important oxidant in the troposphere due to its high reactivity and relative abundance. Measuring the concentration of OH in situ, however, is technically challenging. Here we present a robust yet simple method of estimating an OH-equivalent oxidant concentration ("effective OH") in the marine boundary layer (MBL) from the mass balance of dimethylsulfide (DMS). We use shipboard eddy covariance measurements of the sea-to-air DMS flux from the Vamos Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in October and November of 2008. The persistent stratocumulus cloud-cover off the west coast of South America and the associated strong inversion between MBL and the free troposphere (FT) greatly simplify the dynamics in this region and make our budget estimate possible. From the observed diurnal cycle in DMS concentration, the nighttime entrainment velocity at the inversion is estimated to be 4 mm s−1. We calculate 1.4×106 OH molecules cm−3 from the DMS budget, which represents a ~monthly effective OH concentration and is well within the range of previous estimates. Furthermore, when fitted to the measured intensity of solar flux, the resultant diel variation in OH concentration, together with the DMS surface and entrainment fluxes, enables us to accurately replicate the observed diurnal cycle in DMS (correlation coefficient exceeding 0.9). The nitrate radical is found to have little contribution to DMS oxidation during VOCALS-REx.
Aerosol vertical distribution and optical properties over M'Bour (16.96° W; 14.39° N), Senegal from 2006 to 2008
Authors: Léon J.-F. , Derimian Y. , Chiapello I. , Tanré D. , Podvin T. , Chatenet B. , Diallo A. , Deroo C.
Published: April 2010

Abstract. We present ground-based measurements of aerosol mass, optical properties and vertical extinction profiles acquired in M'Bour, Senegal (16.96° W; 14.39° N) from January 2006 to September 2008. This place of the word is all year long affected by the export of mineral dust as it moves westward to the north Atlantic ocean. The maximum in the dust activity is observed in summer (June–July), corresponding to a maximum in the aerosol optical thickness (above 0.5) and single scattering albedo (above 0.95). It also corresponds to a maximum in the top altitude of the transported aerosol layer (up to 6 km) and aerosol optical thickness scale height (up to 3.5 km) due to the presence of the Saharan Air Layer located between 2 and 6 km. The late summer shows an additional low level aerosol layer that increases in thickness in autumn. Severe dust storms are also systematically observed in spring (March) but with a lower vertical development and a stronger impact (factor 2 to 3) on the ground-level mass compared to summer. Sporadic events of biomass burning aerosols are observed in winter (January) and particularly in January 2006 when the biomass burning aerosol are advected between 1.5 and 3.5 km high. On average, the seasonal signal in the aerosol optical properties and vertical distribution is very similar from year to year over our 3 year monitoring.
Characteristics and source apportionment of atmospheric aerosols at the summit of Mount Tai during summertime
Authors: Xu H. , Wang Y. , Wen T. , Yang Y. , Zhao Y.
Published: April 2010

Abstract. To investigate the long-range transport of air pollutants in North China, aerosol samples were collected at the summit of Mount Tai (Shandong province) in June of 2006. Water-soluble ion and metal element concentrations were analyzed using ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. Results showed three different size distributions for the ions and metal elements characterized, including masses in: (i) the accumulation mode, with a peak at 0.43 to 1.1 μm (SO42−, NH4+, K+, Pb, Zn, Ti); (ii) the coarse particle mode, with a peak at 4.7 to 5.8 μm (Ca2+, Mg2+, Ca, Mg, Fe, Al, Ba, Mn); and (iii) a bimodal distribution, with peaks at 0.43 to 0.65 μm and 4.7 to 5.8 μm (NO3−, Na+, Cl−, Na, Co, Ni, Mo, Cu). When SO42− was in high concentration, the mass median diameter was between 0.5 μm and 0.8 μm, belonging to the "drop mode". The concentrations of SO42−, NO3−, NH4+, and K+ were quite variable. Interestingly, SO42−, NO3−, and NH4+ reached their highest concentrations when the humid air mass was coming from the south. Furthermore, crustal element concentrations increased when the air mass came from the north and pollution element concentrations were elevated when the air mass came from the south.
Trans-Pacific transport and evolution of aerosols and trace gases from Asia during the INTEX-B field campaign
Authors: Adhikary B. , Carmichael G. R. , Kulkarni S. , Wei C. , Tang Y. , Dallura A. , Mena-Carrasco M. , Streets D. G. , Zhang Q. , Pierce R. B. , Al-Saadi J. A. , Emmons L. K. , Pfister G. G. , Avery M. A. , Barrick J. D. , Blake D. R. , Brune W. H. , Cohen R. C. , Dibb J. E. , Fried A. , Heikes B. G. , Huey L. G. , O'Sullivan D. W. , Sachse G. W. , Shetter R. E. , Singh H. B. , Campos T. L. , Cantrell C. A. , Flocke F. M. , Dunlea E. J. , Jimenez J. L. , Weinheimer A. J. , Crounse J. D. , Wennberg P. O. , Schauer J. J. , Stone E. A. , Jaffe D. A. , Reidmiller D. R.
Published: April 2010

Abstract. The Sulfur Transport and dEposition Model (STEM) developed at the University of Iowa is applied to the analysis of observations obtained during the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B), conducted over the Pacific Ocean during the 2006 North American spring season. This paper reports on the model performance of meteorological parameters, trace gases, aerosols and photolysis rate (J-values) predictions with the NASA DC-8 and NSF/NCAR C-130 airborne measurements along with observations from three surface sites Mt. Bachelor, Trinidad Head and Kathmandu, Nepal. In general the model shows appreciable skill in predicting many of the important aspects of the observed distributions. The major meteorological parameters driving long range transport are accurately predicted by the WRF simulations used in this study. Furthermore, the STEM model predicts aerosols and trace gases concentrations within a standard deviation of most of the observed mean values. The results also point towards areas where model improvements are needed; e.g., the STEM model underestimates CO (15% for the DC8 and 6% for the C-130), whereas it overpredicts PAN (by a factor of two for both aircraft). The errors in the model calculations are attributed to uncertainty in emissions estimates and uncertainty in the top and lateral boundary conditions. Results from a series of sensitivity simulations examining the impact of the growth of emissions in Asia from 2000 to 2006, the importance of biomass burning, the effect of using boundary conditions from different global models, and the role of heterogeneous chemistry on the predictions are also presented. The impacts of heterogeneous reactions at specific times during dust transport episodes can be significant, and in the presence of dust both sulfate and nitrate aerosol production is increased and gas phase nitric acid levels are reduced appreciably (~50%). The aging of the air masses during the long range transport over the Pacific and the impact of various sources (source regions as well as energy and biomass burning) on targeted observations are analyzed using back-trajectories and tagged CO-tracer analysis.
Aerosol distribution around Svalbard during intense easterly winds
Authors: Dörnbrack A. , Stachlewska I. S. , Ritter C. , Neuber R.
Published: April 2010

Abstract. This paper reports on backscatter and depolarization measurements by an airborne lidar in the Arctic during the ASTAR 2004 campaign. A unique weather situation facilitated the observation of the aerosol concentration under strongly forced atmospheric conditions. The vigorous easterly winds distorted the flow past Svalbard in such a way that unique mesoscale features were visible in the remote-sensing observations. Mesoscale numerical modelling was applied to identify the sources of the aerosol plumes and to explain the observed patterns.
The role of mixing layer on changes of particle properties in lower troposphere
Authors: Ferrero L. , Bolzacchini E. , Perrone M. G. , Petraccone S. , Sangiorgi G. , Ferrini B. S. , Lo Porto C. , Lazzati Z. , Cocchi D. , Bruno F. , Greco F.
Published: April 2010

Abstract. Vertical profiles of atmospheric particulate matter number concentration, size distribution and chemical composition were directly measured in the city of Milan, over three years (2005–2008) of field campaigns. An optical particle counter, a portable meteorological station and a miniaturized cascade impactor were deployed on a tethered balloon. Mixing layer height was estimated by PM dispersion along height. More than 300 PM vertical profiles were measured both in the winter and summer, mainly in clear and dry sky conditions. Under these conditions, no significant changes in NO3−, SO42− or NH4+ into or over the mixing layer were found. From experimental measurements we observed changes in size distribution along height. An increase of the mean particle diameter, in the accumulation mode, passing through the mixing layer under stable conditions was highlighted; the mean relative growth was 2.1±0.1% in the winter and 3.9±0.3% in the summer. At the same time, sedimentation processes occurred across the ML height for coarse particles leading to a mean particle diameter reduction (14.9±0.6% in the winter and 10.7±1.0% in summer). A hierarchical statistical model for the PM size distribution has been developed to describe the aging process of the finest PM fraction along height. The proposed model is able to estimate the typical vertical profile that characterises launches within pre-specified groups. The mean growth estimated on the basis of the model was 1.9±0.5% in the winter and 6.1±1.2% in the summer, in accordance with experimental evidence.
Impact of Chinese SO2 emissions on submicron aerosol concentration at Mt. Tateyama, Japan
Authors: Osada K. , Ohara T. , Uno I. , Kido M. , Iida H.
Published: April 2010

Abstract. Rapid Asian economic development might engender secondary impacts of atmospheric aerosol particles over the western Pacific after conversion of gaseous pollutants such as SO2. To elucidate changes in aerosol concentrations in leeward areas undergoing remarkable industrialization, the number-size distributions of submicron (0.3–1.0 μm) aerosols were measured at Murododaira (36.6° N, 137.6° E, 2450 m a.s.l.) on the western flank of Mount Tateyama in central Japan during January 1999–February 2009. Nighttime data obtained from 24:00 to 05:00 (local time) were used to analyze free-tropospheric aerosol concentration. Monthly average volume concentrations were calculated for months with >50% daily data coverage. Volume concentrations of submicron aerosols were high in spring to early summer and low in winter. Significant increasing trends at 5% level were found for volume concentrations during December–January and March–April. Simulated monthly SO42− concentrations at Mt. Tateyama from results of regional aerosol modeling with SO2 emission inventory up to 2005 showed seasonal variation and winter–spring increasing trends similar to those of observed aerosol concentration. According to the model analyses, the contribution of Chinese SO42− concentration was high in winter–spring (ca. 80% of total SO42− at Mt. Tateyama). This accords with the increasing trend observed in winter–spring, suggesting that increasing SO2 emission in China engender enhancement of submicron aerosols over Japan, especially during winter–spring.
Increased cloud activation potential of secondary organic aerosol for atmospheric mass loadings
Authors: King S. M. , Rosenoern T. , Shilling J. E. , Chen Q. , Martin S. T.
Published: April 2010

Abstract. The effect of organic particle mass loading from 1 to ≥100 μg m−3 on the cloud condensation nuclei (CCN) properties of mixed organic-sulfate particles was investigated in the Harvard Environmental Chamber. Mixed particles were produced by the condensation of organic molecules onto ammonium sulfate particles during the dark ozonolysis of α-pinene. A continuous-flow mode of the chamber provided stable conditions over long time periods, allowing for signal integration and hence increased measurement precision at low organic mass loadings representative of atmospheric conditions. CCN activity was measured at eight mass loadings for 80- and 100-nm particles grown on 50-nm sulfate seeds. A two-component (organic/sulfate) Köhler model, which included the particle heterogeneity arising from DMA size selection and from organic volume fraction for the selected 80- and 100-nm particles, was used to predict CCN activity. For organic mass loadings of 2.9 μg m−3 and greater, the observed activation curves were well predicted using a single set of physicochemical parameters for the organic component. For mass loadings of 1.74 μg m−3 and less, the observed CCN activity increased beyond predicted values using the same parameters, implying changed physicochemical properties of the organic component. Of possible changes in surface tension, effective molecular weight, and effective density, a sensitivity analysis implicated a decrease of up to 10% in surface tension at low mass loadings as the plausible dominant mechanism for the observed increase in CCN activity.
Antarctic stratospheric warming since 1979
Authors: Hu Y. , Fu Q.
Published: April 2010

Abstract. In the present study, we show evidence of significant stratospheric warming over large portions of the Antarctic polar region in winter and spring seasons, with a maximum warming of 7–8°C in September and October, using satellite Microwave Sounding Unit observations for 1979–2006. It is found that this warming is associated with increasing wave activity from the troposphere into the stratosphere, suggesting that the warming is caused by enhanced wave-driven dynamical heating. We show that the Antarctic stratospheric warming has close correlations with sea surface temperature (SST) increases, and that general circulation model simulations forced with observed time-varying SSTs reproduce similar warming trend patterns in the Antarctic stratosphere. These findings suggest that the Antarctic stratospheric warming is likely induced by SST warming. As SST warming continues as a consequence of greenhouse gas increases due to anthropogenic activity, Antarctic stratospheric warming would also continue, which has important implications to the recovery of the Antarctic ozone hole.
The ARCTAS aircraft mission: design and execution
Authors: Jacob D. J. , Crawford J. H. , Maring H. , Clarke A. D. , Dibb J. E. , Ferrare R. A. , Hostetler C. A. , Russell P. B. , Singh H. B. , Thompson A. M. , Shaw G. E. , McCauley E. , Pederson J. R. , Fisher J. A.
Published: April 2010

Abstract. The NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission was conducted in two 3-week deployments based in Alaska (April 2008) and western Canada (June–July 2008). The goal of ARCTAS was to better understand the factors driving current changes in Arctic atmospheric composition and climate, including (1) transport of mid-latitude pollution, (2) boreal forest fires, (3) aerosol radiative forcing, and (4) chemical processes. ARCTAS involved three aircraft: a DC-8 with detailed chemical payload, a P-3 with extensive aerosol payload, and a B-200 with aerosol remote sensing instrumentation. The aircraft augmented satellite observations of Arctic atmospheric composition, in particular from the NASA A-Train, by (1) validating the data, (2) improving constraints on retrievals, (3) making correlated observations, and (4) characterizing chemical and aerosol processes. The April flights (ARCTAS-A) sampled pollution plumes from all three mid-latitude continents, fire plumes from Siberia and Southeast Asia, and halogen radical events. The June-July flights (ARCTAS-B) focused on boreal forest fire influences and sampled fresh fire plumes from northern Saskatchewan as well as older fire plumes from Canada, Siberia, and California. The June–July deployment was preceded by one week of flights over California sponsored by the California Air Resources Board (ARCTAS-CARB). The ARCTAS-CARB goals were to (1) improve state emission inventories for greenhouse gases and aerosols, (2) provide observations to test and improve models of ozone and aerosol pollution. Extensive sampling across southern California and the Central Valley characterized emissions from urban centers, offshore shipping lanes, agricultural crops, feedlots, industrial sources, and wildfires.