bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of convective transport and lightning NOx production over North America: dependence on cumulus parameterizations
Authors: Zhao C. , Wang Y. , Choi Y. , Zeng T.
Published: April 2010

Abstract. A 3-D regional chemical transport model (REAM) is applied to examine the uncertainties in modeling the effects of convective transport and lightning NOx production on upper tropospheric chemical tracer distributions. To assess the model uncertainties, two different cumulus convective parameterizations, KF-eta and Grell, are adopted in REAM from the respective meteorological models, WRF and MM5. The model simulations are evaluated using INTEX-NA aircraft measurements and satellite measurements of NO2 columns and cloud top pressure, and we find that mid and upper tropospheric trace gas concentrations are affected strongly by convection and lightning NOx productions. A major improvement of the KF-eta scheme is its inclusion of cloud entrainment and detrainment processes. KF-eta scheme simulates larger convective updraft mass fluxes below 150 hPa than the Grell scheme, resulting in more outflow of pollutants in the mid troposphere. The ratio of C2H6/C3H8 is found to be a sensitive parameter to convective outflow; the simulation by WRF-REAM is in closer agreement with INTEX-NA measurements than MM5-REAM, implying that convective mass fluxes by KF-eta scheme are more realistic. The inclusion of entrainment and detrainment processes in the KF-eta scheme also leads to lower cloud top heights (10–12 km) than the Grell scheme (up to 16 km), and hence smaller amounts of estimated (intra-cloud) lightning NOx and lower emission altitudes. WRF simulated cloud top heights are in better agreement with GOES satellite measurements than MM5. The model divergence on lightning NOx mostly is above 12 km. As a result, both models suggest that lightning NOx production enhances the concentrations of upper tropospheric NO2 by a factor of >5 (~100 pptv) and increases O3 by up to ~20 ppbv at 8–12 km.
Characterization of non-photochemically formed oligomers from methylglyoxal: a pathway to produce secondary organic aerosol through cloud processing during night-time
Authors: Yasmeen F. , Sauret N. , Gal J. F. , Maria P.-C. , Massi L. , Maenhaut W. , Claeys M.
Published: April 2010

Abstract. Aqueous-phase oligomer formation from methylglyoxal, a major atmospheric photooxidation product, has been investigated in a simulated cloud matrix under dark conditions. The aim of this study was to explore an additional path producing secondary organic aerosol (SOA) through cloud processes without photochemistry during night-time. Indeed, atmospheric models still underestimate SOA formation, as field measurements have revealed more SOA than predicted. Soluble oligomers (n=1–8) formed in the course of acid-catalyzed aldol condensation and acid-catalyzed hydration followed by acetal formation have been detected and characterized by positive and negative ion electrospray ionization mass spectrometry. Aldol condensation proved to be a favorable mechanism under simulated cloud conditions, while hydration/acetal formation was found to strongly depend on the pH of the system. The aldol oligomer series starts with a β-hydroxy ketone via aldol condensation, where oligomers are formed by multiple additions of C3H4O2 units (72 Da) to the parent β-hydroxy ketone. Ion trap mass spectrometry experiments were performed to structurally characterize the major oligomer species. A mechanistic pathway for the growth of oligomers under cloud conditions and in the absence of UV-light and OH radicals, which could substantially enhance in-cloud SOA yields, is proposed here for the first time.
Tracing the fate of atmospheric nitrate deposited onto a forest ecosystem in eastern Asia using Δ17O
Authors: Tsunogai U. , Komatsu D. D. , Daita S. , Abbas Kazemi G. , Nakagawa F. , Noguchi I. , Zhang J.
Published: April 2010

Abstract. The stable isotopic compositions of nitrate in precipitation (wet deposition) and groundwater (spring, lake, and stream water) were determined for the island of Rishiri, Japan, so as to use the 17O anomalies (Δ17O) to trace the fate of atmospheric nitrate that had deposited onto the island ecosystem, which is a representative background forest ecosystem for eastern Asia. The deposited nitrate had large 17O anomalies with Δ17O values ranging from +20.8‰ to +34.5&permil (n= 32) with +26.2‰ being the annual average. The maximum Δ17O value of +34.5‰, obtained for precipitation on 23 to 24 February 2007, was an extraordinarily large value among values for all samples of precipitation. Most nitrate in the sample might have been produced through the heterogeneous reaction of NO3 radical with hydrocarbons in a highly polluted air mass that had been supplied from megacities on the eastern coast of the Asian continent. On the other hand, nitrate in groundwater had small Δ17O values ranging from +0.9‰ to 3.2‰ (n=19), which corresponds to an average mixing ratio of atmospheric nitrate to total nitrate of 7%. Comparing the inflow and outflow of atmospheric nitrate in groundwater within the island, we estimated that the direct drainage accounts for 10.5±5.2% of atmospheric nitrate that has deposited on the island and that the residual portion has undergone biological processing before being exported from the forest ecosystem.
Measurements of electric charge separated during the formation of rime by the accretion of supercooled droplets
Authors: Lighezzolo R. A. , Pereyra R. G. , Avila E. E.
Published: April 2010

Abstract. In these experiments, the electric charge carried by single particles ejected from the surface of a graupel particle growing by riming was measured. Simulated graupel pellets were grown by accretion of supercooled water drops, at temperatures ranging from −2 to −10°C in a wind tunnel at air velocities between 5 and 10 m s−1, with the goal of studying the charging of graupel pellets under conditions of secondary ice crystal production (Hallett-Mossop mechanism). The graupel, and induction rings upstream and downstream of the graupel, were connected to electrometers and analyzing circuits of sufficient sensitivity and speed to measure, correlate and display individual charging events. The results suggest that fewer than 1% of the ejected particles carry a measurable electric charge (>2 fC). Further, it was observed that the graupel pellets acquire a positive charge and the average charge of a single splinter ejected is −14 fC. This mechanism of ejection of charged particles seems adequate to account for a positive charge of around 1 pC that individual precipitation particles of mm-size could acquire in the lower part of the cloud, which in turn could contribute to the lower positive charge region of thunderstorms.
Sensitivity of isoprene emission estimates to the time resolution of input climate data
Authors: Ashworth K. , Wild O. , Hewitt C. N.
Published: April 2010

Abstract. We evaluate the effect of varying the temporal resolution of the input climate data on isoprene emission estimates generated by the community emissions model MEGAN (Model of Emissions of Gases and Aerosols from Nature). The estimated total global annual emissions of isoprene is reduced from 766 Tg y−1 for hourly input data to 746 Tg y−1 (a reduction of 3%) for daily average input data and 711 Tg y−1 (down 7%) for monthly average input data. The impact on a local scale can be more significant with reductions of up to 65% for some locations when using monthly average data. If the daily and monthly average temperature data are used without the imposition of a diurnal cycle the global emissions estimates fall by 27–32%, and local annual emissions by up to 77%. A similar pattern emerges if hourly isoprene fluxes are considered. Given the importance of land-atmosphere interactions in the Earth system and the low computational cost of the MEGAN algorithms, we recommend that chemistry-climate models and the new generation of Earth system models input biogenic emissions at the highest temporal resolution possible.
Uncertainties in estimating mercury emissions from coal-fired power plants in China
Authors: Wu Y. , Streets D. G. , Wang S. X. , Hao J. M.
Published: April 2010

Abstract. A detailed multiple-year inventory of mercury emissions from anthropogenic activities in China has been developed. Coal combustion and nonferrous metals production continue to be the two leading mercury sources in China, together contributing ~80% of total mercury emissions. Within our inventory, a new comprehensive sub-module for estimation of mercury emissions from coal-fired power plants in China is constructed for uncertainty case-study. The new sub-module integrates up-to-date information regarding mercury content in coal by province, coal washing and cleaning, coal consumption by province, mercury removal efficiencies by control technology or technology combinations, etc. Based on these detailed data, probability-based distribution functions are built into the sub-module to address the uncertainties of these key parameters. The sub-module incorporates Monte Carlo simulations to take into account the probability distributions of key input parameters and produce the mercury emission results in the form of a statistical distribution. For example, the best estimate for total mercury emissions from coal-fired power plants in China in 2003 is 90.5 Mg, with the uncertainty range from 57.1 Mg (P10) to 154.6 Mg (P90); and the best estimate for elemental mercury emissions is 43.0 Mg, with the uncertainty range from 25.6 Mg (P10) to 75.7 Mg (P90). The results further indicate that the majority of the uncertainty in mercury emission estimation comes from two factors: mercury content in coal and mercury removal efficiency.
On the roles of circulation and aerosols in the decline of mist and dense fog in Europe over the last 30 years
Authors: van Oldenborgh G. J. , Yiou P. , Vautard R.
Published: April 2010

Abstract. Fog and mist are meteorological phenomena that have significant contributions to temperature variations. Understanding and predicting them is also crucial for transportation risk management. It has been shown that low visibility phenomena over Europe have been declining over the past three decades. The trends in mist and haze have been correlated to atmospheric aerosol trends. However, dense fog has not received yet such focus. The goal of this paper is to examine the roles of synoptic atmospheric circulation and aerosol content on the trends of dense fog. We show that sulphur emission trends are spatially correlated with visibility trends, with a maximum correlation when visibility is between 1 km and 10 km. We find that atmospheric dynamics overall contributes up to 40% of the variability of the frequency of fog occurrences. This contribution is spatially variable and highly depends on the topography and the season, with higher values in the winter. The observed long-term circulation changes do not contribute much to the trends in low visibility found in the data. This process is illustrated on three stations (De Bilt, Zürich Airport and Potsdam) for which a long-term visibility data and a thorough meteorological description are available. We conclude that to properly represent fog in future climate simulations, it is necessary to include realistic representations of aerosol emissions and chemistry, land surface properties and atmospheric dynamics.
Mercury emission and speciation of coal-fired power plants in China
Authors: Wang S. , Zhang L. , Li G. , Wu Y. , Hao J. , Pirrone N. , Sprovieri F. , Ancora M. P.
Published: April 2010

Abstract. Comprehensive field measurements are needed to understand the mercury emissions from Chinese power plants and to improve the accuracy of emission inventories. Characterization of mercury emissions and their behavior were measured in six typical coal-fired power plants in China. During the tests, the flue gas was sampled simultaneously at inlet and outlet of selective catalyst reduction (SCR), electrostatic precipitators (ESP), and flue gas desulfurization (FGD) using the Ontario Hydro Method (OHM). The pulverized coal, bottom ash, fly ash and gypsum were also sampled in the field. Mercury concentrations in coal burned in the measured power plants ranged from 17 to 385 μg/kg. The mercury mass balances for the six power plants varied from 87 to 116% of the input coal mercury for the whole system. The total mercury concentrations in the flue gas from boilers were at the range of 1.92–27.15 μg/m3, which were significantly related to the mercury contents in burned coal. The mercury speciation in flue gas right after the boiler is influenced by the contents of halogen, mercury, and ash in the burned coal. The average mercury removal efficiencies of ESP, ESP plus wet FGD, and ESP plus dry FGD-FF systems were 24%, 73% and 66%, respectively, which were similar to the average removal efficiencies of pollution control device systems in other countries such as US, Japan and South Korea. The SCR system oxidized 16% elemental mercury and reduced about 32% of total mercury. Elemental mercury, accounting for 66–94% of total mercury, was the dominant species emitted to the atmosphere. The mercury emission factor was also calculated for each power plant.
Effect of hygroscopic seeding on warm rain clouds – numerical study using a hybrid cloud microphysical model
Authors: Kuba N. , Murakami M.
Published: April 2010

Abstract. The effect of hygroscopic seeding on warm rain clouds was examined using a hybrid cloud microphysical model combining a Lagrangian cloud condensation nuclei (CCN) activation model, a semi-Lagrangian droplet growth model, and an Eulerian spatial model for advection and sedimentation of droplets. This hybrid cloud microphysical model accurately estimated the effects of CCN on cloud microstructure and suggested the following conclusions for a moderate continental air mass (an air mass with a large number of background CCN). (1) Seeding can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount and radius of seeding particles are appropriate. (2) The optimal radius of monodisperse particles to increase rainfall becomes larger with the increase in the total mass of seeding particles. (3) Seeding with salt micro-powder can hasten the onset of surface rainfall and increase the accumulated amount of surface rainfall if the amount of seeding particles is sufficient. (4) Seeding by a hygroscopic flare decreases rainfall in the case of large updraft velocity (shallow convective cloud) and increases rainfall slightly in the case of small updraft velocity (stratiform cloud). (5) Seeding with hygroscopic flares including ultra-giant particles (r>5 μm) hastens the onset of surface rainfall but may not significantly increase the accumulated surface rainfall amount. (6) Hygroscopic seeding increases surface rainfall by two kinds of effects: the ''competition effect'' by which large soluble particles prevent the activation of smaller particles and the ''raindrop embryo effect'' in which giant soluble particles can immediately become raindrop embryos. In some cases, one of the effects works, and in other cases, both effects work, depending on the updraft velocity and the amount and size of seeding particles.
Freezing of water droplets colliding with kaolinite particles
Authors: Svensson E. A. , Delval C. , von Hessberg P. , Johnson M. S. , Pettersson J. B. C.
Published: April 2010

Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under dry conditions freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed at high relative humidity. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. The data recorded at high humidity should be most relevant to atmospheric conditions, and the results indicate that parameterizations currently used in modelling studies to describe freezing rates are appropriate for kaolinite aerosol particles. Mechanisms for contact freezing are briefly discussed.
Long-term changes in UT/LS ozone between the late 1970s and the 1990s deduced from the GASP and MOZAIC aircraft programs and from ozonesondes
Authors: Schnadt Poberaj C. , Staehelin J. , Brunner D. , Thouret V. , De Backer H. , Stübi R.
Published: April 2010

Abstract. We present ozone measurements of the Global Atmospheric Sampling Program (GASP) performed from four commercial and one research aircraft in the late 1970s to compare them with respective measurements of the ongoing MOZAIC project. Climatologies of UT/LS ozone were built using the aircraft data sets (1975–1979 and 1994–2001), and long-term changes between the 1970s and 1990s were derived by comparison. The data were binned relative to the dynamical tropopause to separate between UT and LS air masses. LS data were analysed using equivalent latitudes. In the UT, pronounced increases are found over the Middle East and South Asia in the spring and summer seasons. Increases are also found over Japan, Europe, and the eastern parts of the Unites States depending on season. LS ozone over northern mid- and high latitudes was found to be lower in the 1990s compared to the 1970s in all seasons of the year. In addition, a comparison with long-term changes deduced from ozonesondes is presented. An altitude offset was applied to the sonde data to account for the slow response time of the ozone sensors. The early 1970s European Brewer-Mast (BM) sonde data agree with GASP within the range of uncertainty (UT) or measured slightly less ozone (LS). In contrast, the 1990s BM sensors show consistently and significantly higher UT/LS ozone values than MOZAIC. This unequal behaviour of aircraft/sonde comparisons in the 1970s and 1990s leads to differences in the estimated long-term changes over Europe: while the comparison between GASP and MOZAIC indicates ozone changes of −5% to 10% over Europe, the sondes suggest a much larger increase of 10%–35% depending on station and season, although statistical significance is not conclusive due to data sample limitations. In contrast to the BM sondes, the Electrochemical Cell (ECC) sonde at Wallops Island, USA, measured higher UT ozone than both GASP and MOZAIC. Hence, long-term changes from GASP/MOZAIC agree within the range of uncertainty with the changes deduced from Wallops Island. The comparison of GASP with BM and ECC ozonesonde data over Europe and the eastern USA, respectively, corroborates earlier studies stating that early BM instruments measured less ozone than ECC sensor by 10–25%.
NO3 radical measurements in a polluted marine environment: links to ozone formation
Authors: McLaren R. , Wojtal P. , Majonis D. , McCourt J. , Halla J. D. , Brook J.
Published: April 2010

Abstract. Nighttime chemistry in polluted regions is dominated by the nitrate radical (NO3) including its direct reaction with natural and anthropogenic hydrocarbons, its reaction with NO2 to form N2O5, and subsequent reactions of N2O5 to form HNO3 and chlorine containing photolabile species. We report nighttime measurements of NO3, NO2, and O3, in the polluted marine boundary layer southwest of Vancouver, BC during a three week study in summer of 2005. The concentration of N2O5 was calculated using the well known equilibrium, NO3+NO2↔N2O5. Median overnight mixing ratios of NO3, N2O5 and NO2 were 10.3 ppt, 122 ppt and 8.3 ppb with median N2O5/NO3 molar ratios of 13.1 and median nocturnal partitioning of 4.9%. Due to the high levels of NO2 that can inhibit approach to steady-state, we use a method for calculating NO3 lifetimes that does not assume the steady-state approximation. Median and average lifetimes of NO3 in the NO3-N2O5 nighttime reservoir were 1.1–2.3 min. We have determined nocturnal profiles of the pseudo first order loss coefficient of NO3 and the first order loss coefficients of N2O5 by regression of the NO3 inverse lifetimes with the [N2O5]/[NO3] ratio. Direct losses of NO3 are highest early in the night, tapering off as the night proceeds. The magnitude of the first order loss coefficient of N2O5 is consistent with recommended homogeneous rate coefficients for reaction of N2O5 with water vapor early in the night, but increases significantly in the latter part of the night when relative humidity increases beyond 75%, consistent with heterogeneous reactions of N2O5 with sea salt and/or other aerosols with rate constant khet=1.2×10−3 s−1. Analysis indicates that a correlation exists between overnight integrated N2O5 concentrations in the marine boundary layer, a surrogate for the accumulation of chlorine containing photolabile species, and maximum 1-h average O3 at stations in the Lower Fraser Valley the next day when there is clear evidence of a sea breeze transporting marine air into the valley. The range of maximum 1-h average O3 increase attributable to the correlation is ΔO3=+1.1 to +8.3 ppb throughout the study for the average of 20 stations, although higher increases are seen for stations far downwind of the coastal urban area. The correlation is still statistically significant on the second day after a nighttime accumulation, but with a different spatial pattern favouring increased O3 at the coastal urban stations, consistent with transport of polluted air back to the coast.
Parameterization of subgrid aircraft emission plumes for use in large-scale atmospheric simulations
Authors: Naiman A. D. , Lele S. K. , Wilkerson J. T. , Jacobson M. Z.
Published: April 2010

Abstract. Aircraft emissions differ from other anthropogenic pollution in that they occur mainly in the upper troposphere and lower stratosphere where they can form condensation trails (contrails) and affect cirrus cloud cover. In determining the effect of aircraft on climate, it is therefore necessary to examine these processes. Previous studies have approached this problem by treating aircraft emissions on the grid scale, but this neglects the subgrid scale nature of aircraft emission plumes. We present a new model of aircraft emission plume dynamics that is intended to be used as a subgrid scale model in a large scale atmospheric simulation. The model shows good agreement with a large eddy simulation of aircraft emission plume dynamics and with an analytical solution to the dynamics of a sheared Gaussian plume. We argue that this provides a reasonable model of line-shaped contrail dynamics and give an example of how it might be applied in a global climate model.
A review of the theoretical basis for bulk mass flux convective parameterization
Authors: Plant R. S.
Published: April 2010

Abstract. Most parameterizations for precipitating convection in use today are bulk schemes, in which an ensemble of cumulus elements with different properties is modelled as a single, representative entraining-detraining plume. We review the underpinning mathematical model for such parameterizations, in particular by comparing it with spectral models in which elements are not combined into the representative plume. The chief merit of a bulk model is that the representative plume can be described by an equation set with the same structure as that which describes each element in a spectral model. The equivalence relies on an ansatz for detrained condensate introduced by Yanai et al. (1973) and on a simplified microphysics. There are also conceptual differences in the closure of bulk and spectral parameterizations. In particular, we show that the convective quasi-equilibrium closure of Arakawa and Schubert (1974) for spectral parameterizations cannot be carried over to a bulk parameterization in a straightforward way. Quasi-equilibrium of the cloud work function assumes a timescale separation between a slow forcing process and a rapid convective response. But, for the natural bulk analogue to the cloud-work function (the dilute CAPE), the relevant forcing is characterised by a different timescale, and so its quasi-equilibrium entails a different physical constraint. Closures of bulk parameterization that use the non-entraining parcel value of CAPE do not suffer from this timescale issue. However, the Yanai et al. (1973) ansatz must be invoked as a necessary ingredient of those closures.
Characterization of aerosol chemical composition by aerosol mass spectrometry in Central Europe: an overview
Authors: Lanz V. A. , Prévôt A. S. H. , Alfarra M. R. , Mohr C. , DeCarlo P. F. , Weimer S. , Gianini M. F. D. , Hueglin C. , Schneider J. , Favez O. , D'Anna B. , George C. , Baltensperger U.
Published: April 2010

Abstract. Real-time measurements of non-refractory submicron aerosols (NR-PM1) were conducted within the greater Alpine region (Switzerland, Germany, Austria, France and Liechtenstein) during several week-long field campaigns in 2002–2009. A large variety of sites was covered including urban backgrounds, motorways, rural, remote, and high-Alpine stations, and also mobile on-road measurements were performed. Inorganic and organic aerosol (OA) fractions were determined by means of aerosol mass spectrometry (AMS). The average mass concentration of NR-PM1 for the different campaigns typically ranged between 10 and 30 μg m−3. Overall, the organic portion was most abundant, ranging from 36% to 81% of NR-PM1. Other main constituents comprised ammonium (5–15%), nitrate (8–36%), sulfate (3–26%), and chloride (0–5%). These latter anions were, on average, fully neutralized by ammonium. The OA was further divided (based on factor analysis, FA) into its underlying components, such as oxygenated (mostly secondary) organic aerosol (OOA), hydrocarbon-like and freshly emitted organic aerosol (HOA), as well as primary OA from biomass burning (P-BBOA). OOA was ubiquitous, ranged between 36% and 94% of OA, and could be separated into a low-volatility and a semi-volatile fraction (LV-OOA and SV-OOA) for all summer campaigns at low sites. Primary wood combustion (P-BBOA) accounted for a considerable fraction during wintertime (17–49% OA). HOA/OA ratios were comparatively low for all campaigns (6–16%) with the exception of on-road, mobile measurements (23%).
36Cl bomb peak: comparison of modeled and measured data
Authors: Heikkilä U. , Beer J. , Feichter J. , Alfimov V. , Synal H.-A. , Schotterer U. , Eichler A. , Schwikowski M. , Thompson L.
Published: April 2010

Abstract. The extensive nuclear bomb testing of the fifties and sixties and the final tests in the seventies caused a strong 36Cl peak that has been observed in ice cores world-wide. The measured 36Cl deposition fluxes in eight ice cores (Dye3, Fiescherhorn, Grenzgletscher, Guliya, Huascarán, North GRIP, Inylchek (Tien Shan) and Berkner Island) were compared with an ECHAM5-HAM general circulation model simulation (1952–1972). We find a good agreement between the measured and the modeled 36Cl fluxes assuming that the bomb test produced global 36Cl input was ~80 kg. The model simulation indicates that the fallout of the bomb test produced 36Cl is largest in the subtropics and mid-latitudes due to the strong stratosphere-troposphere exchange. In Greenland the 36Cl bomb signal is quite large due to the relatively high precipitation rate. In Antarctica the 36Cl bomb peak is small but is visible even in the driest areas. The model suggests that the large bomb tests in the Northern Hemisphere are visible around the globe but the later (end of sixties and early seventies) smaller tests in the Southern Hemisphere are much less visible in the Northern Hemisphere. The question of how rapidly and to what extent the bomb produced 36Cl is mixed between the hemispheres depends on the season of the bomb test. The model results give an estimate of the amplitude of the bomb peak around the globe.
Chemical characterisation of iron in Dust and Biomass burning aerosols during AMMA-SOP0/DABEX: implication on iron solubility
Authors: Paris R. , Desboeufs K. V. , Formenti P. , Nava S. , Chou C.
Published: April 2010

Abstract. Chemical composition and the soluble fraction (in MilliQ water) has been determined in aerosol samples collected during flights of AMMA-SOP0/DABEX campaign conducted in the West African Sahel during dry season (2006). Two types of samples are encountered in this period: dust particles (DUST) and biomass burning aerosol (BB). Chemical analysis and microscope observations show that iron (Fe) found in BB samples is mainly issued from dust particles externally mixed in the biomass burning layer. Chemical analyses of samples show that solubilities determined for Fe in samples of African dust were significantly lower than the solubilities in aerosols of biomass burning. Our data provide a first idea of the variability of iron dust solubility in the source region (0.1% and 3.4%). We found a relationship between iron solubility/clay content/source which partly confirms that the variability of iron solubility in this source region is related to the character and origin of the aerosols themselves. In the biomass burning samples, no relationship could be found between Fe solubility and the concentrations of acid species (SO42−,NO3− or oxalate) nor the content of carbon (TC, OC, BC) so we are unable to determine what are the processes involved in this increase of iron solubility. In terms of the supply of soluble Fe to oceanic ecosystems on a global scale, the observed higher solubility for Fe in biomass burning could imply an indirect source of Fe to marine ecosystem, but these aerosols are probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic.
The hygroscopicity parameter (κ) of ambient organic aerosol at a field site subject to biogenic and anthropogenic influences: Relationship to degree of aerosol oxidation
Authors: Chang R. Y.-W. , Slowik J. G. , Shantz N. C. , Vlasenko A. , Liggio J. , Sjostedt S. J. , Leaitch W. R. , Abbatt J. P. D.
Published: April 2010

Abstract. Cloud condensation nuclei (CCN) concentrations were measured at a rural site in Ontario, Canada during the spring of 2007. The CCN concentrations were compared to values predicted from the aerosol chemical composition and size distribution using κ-Köhler theory. The hygroscopicity of the organic component was characterised by two methods, both of which are based on the aerosol's degree of oxygenation as determined by the mass spectra measured with an Aerodyne aerosol mass spectrometer. The first approach uses a statistical technique, positive matrix factorization (PMF), to separate hygroscopic and non-hygroscopic factors while the second uses the O/C, which is an indication of the aerosol's degree of oxygenation. In both cases, the hygroscopicity parameter (κ) of the organic component is varied so that the predicted and measured CCN concentrations are internally consistent and in good agreement. By focussing on a small number of organic components defined by their composition, we can simplify the estimates needed to describe the aerosol's hygroscopicity. We find that κ of the oxygenated organic component from the PMF analysis is 0.20±0.03 while κ of the entire organic component can be parameterized as κorg=(0.30±0.05)×(O/C).
Atmospheric diurnal and semi-diurnal variations observed with GPS radio occultation soundings
Authors: Xie F. , Wu D. L. , Ao C. O. , Mannucci A. J.
Published: April 2010

Abstract. Diurnal and semi-diurnal variations, driven by solar forcing, are two fundamental modes in the Earth's weather and climate system. Radio occultation (RO) measurements from the six COSMIC satellites (Constellation Observing System for Meteorology Ionosphere and Climate) provide rather uniform global coverage with high vertical resolution, all-weather and diurnal sampling capability. This paper analyzes the diurnal and semi-diurnal variations of both temperature and refractivity from two-year (2007–2008) COSMIC RO measurements in the troposphere and stratosphere. The RO observations reveal both propagating and trapped vertical structures of diurnal and semi-diurnal variations, including transition regions near the tropopause where data with high vertical resolution are critical. In the tropics the diurnal amplitude in refractivity decreases with altitude from a local maximum in the planetary boundary layer and reaches the minimum around 14 km and then further increase amplitude in the stratosphere. The upward propagating component of the migrating diurnal tides in the tropics is clearly captured by the GPS RO measurements, which show a downward progression in phase from upper troposphere to the stratopause with a vertical wavelength of about 25 km. Below 500 hPa (~5.5 km), seasonal variations of the peak diurnal amplitude in the tropics follow the solor forcing change in latitude, while at 30 km the seasonal pattern reverses with the diurnal amplitude peaking at the opposite side of the equator relative to the solar forcing. Polar regions shows large diurnal variations in the stratosphere with strong seasonal variations and the cause(s) of these variations require further investigations.
Synoptically-induced variability in the microphysical properties of the South East Pacific stratocumulus deck
Authors: Painemal D. , Zuidema P.
Published: April 2010

Abstract. Synoptic variations associated with changes in satellite-derived cloud droplet number concentrations (Nd) for the southeast Pacific stratocumulus deck were examined using a composite analysis applied to daily values from the five October months of 2001, 2005, 2006, 2007 and 2008. MAX and MIN Nd composites were defined by the top and bottom terciles of daily area-mean Nd values over the Arica Bight, the region with the largest mean oceanic Nd. Nd and ship-based accumulation mode aerosol concentrations (Na) correlate well (r=0.65), with a best-fit aerosol activation value dln Nddln Na of 0.53 for pixels with Nd>50 cm−3. The adiabatically-derived MODIS cloud depths also correlate well with the ship-based cloud depths (r=0.7), though are consistently higher (mean bias of almost 60 m). The MAX-Nd composite is characterized by a weaker subtropical anticyclone and weaker winds both at the surface and the lower free troposphere than the MIN-Nd composite. The MAX-Nd composite clouds over the Arica Bight are thinner than the MIN-Nd composite clouds, have lower cloud tops, and occur within warmer, drier free tropospheres (as deduced from radiosondes) that imply greater coastal subsidence. The cloud thinning compensates radiatively for increased reflectance from increases in Nd, most apparent near the coast. CloudSat radar reflectivities do not imply significant aerosol scavenging by precipitation near the coast, indicating that variability in wind transport contributes to the aerosol variability. The co-occurrence of more boundary-layer aerosol/higher Nd within a more stable atmosphere suggests a boundary layer source for the aerosol, rather than the free troposphere. Along 85° W, the top-of-atmosphere shortwave fluxes are significantly higher (~50%) for the MAX-Nd composite than for the MIN-Nd composite, with thicker clouds and higher cloud fractions. The change in Nd at this location is small (though positive), so that the composite difference primarily reflects synoptic changes. A one-point spatial correlation map reveals anomalous northerly winds at 850 hPa account for an anomalous warm temperature advection. The increase in the static stability along 85° W is highly correlated to the increased cloud fraction, despite accompanying weaker free tropospheric subsidence. This synoptic impact on offshore cloud properties is arguably our most radiatively important finding, and draws attention to the free tropospheric meridional flow as a meteorological control.
Aerosol analysis using a Proton-Transfer-Reaction Thermo-Desorption Mass Spectrometer (PTR-TD-MS): a new approach to study processing of organic aerosols
Authors: Holzinger R. , Williams J. , Herrmann F. , Lelieveld J. , Donahue N. M. , Röckmann T.
Published: April 2010

Abstract. We present a novel analytical approach to measure the chemical composition of organic aerosol. The new instrument combines proton-transfer-reaction mass-spectrometry (PTR-MS) with a collection-thermo-desorption aerosol sampling technique. For secondary organic aerosol produced from the reaction of ozone with isoprenoids in a laboratory reactor, the PTR-TD-MS instrument detected typically 80% of the mass that was measured with a scanning mobility particle sizer (SMPS). The first field deployment of the instrument was the EUCAARI-IOP campaign at the CESAR tall tower site in the Netherlands. For masses with low background values (~30% of all masses) the detection limit of aerosol compounds was below 0.2 ng/m3 which corresponds to a sampled compound mass of 35 pg. Comparison of thermograms from ambient samples and from chamber-derived secondary organic aerosol shows that, in general, organic compounds from ambient aerosol samples desorb at much higher temperatures than chamber samples. This suggests that chamber aerosol is not a good surrogate for ambient aerosol and therefore caution is advised when extrapolating results from chamber experiments to ambient conditions.
Effect of chemical mixing state on the hygroscopicity and cloud nucleation properties of calcium mineral dust particles
Authors: Sullivan R. C. , Moore M. J. K. , Petters M. D. , Kreidenweis S. M. , Roberts G. C. , Prather K. A.
Published: April 2010

Abstract. Atmospheric mineral dust particles can alter cloud properties and thus climate by acting as cloud condensation nuclei (CCN) that form cloud droplets. The CCN activation properties of various calcium mineral dust particles were studied experimentally to investigate the consequences of field observations showing the segregation of sulfate from nitrate and chloride between individual aged Asian dust particles, and the enrichment of oxalic acid in Asian dust. Each mineral's observed apparent hygroscopicity was primarily controlled by its solubility, which determines the degree to which the mineral's intrinsic hygroscopicity can be expressed. The significant increase in hygroscopicity caused by mixing soluble hygroscopic material with insoluble mineral particles is also presented. Insoluble minerals including calcium carbonate, representing fresh unprocessed dust, and calcium sulfate, representing atmospherically processed dust, had similarly small apparent hygroscopicities. Their activation is accurately described by a deliquescence limit following the Kelvin effect and corresponded to an apparent single-hygroscopicity parameter, κ, of ~0.001. Soluble calcium chloride and calcium nitrate, representing atmospherically processed mineral dust particles, were much more hygroscopic, activating similar to ammonium sulfate with κ~0.5. Calcium oxalate monohydrate (κ=0.05) was significantly less CCN-active than oxalic acid (κ=0.3), but not as inactive as its low solubility would predict. These results indicate that the common assumption that all mineral dust particles become more hygroscopic and CCN-active after atmospheric processing should be revisited. Calcium sulfate and calcium oxalate are two realistic proxies for aged mineral dust that remain non-hygroscopic. The dust's apparent hygroscopicity will be controlled by its chemical mixing state, which is determined by its mineralogy and the chemical reaction pathways it experiences during transport.
Intermediate and high resolution numerical simulations of the transition of a tropical wave critical layer to a tropical storm
Authors: Montgomery M. T. , Wang Z. , Dunkerton T. J.
Published: April 2010

Abstract. Recent work has hypothesized that tropical cyclones in the deep Atlantic and eastern Pacific basins develop from the cyclonic Kelvin cat's eye of a tropical easterly wave critical layer located equatorward of the easterly jet axis that typifies the trade wind belt. The cyclonic critical layer is thought to be important to tropical cyclogenesis because its cat's eye provides (i) a region of cyclonic vorticity and weak deformation by the resolved flow, (ii) containment of moisture entrained by the developing flow and/or lofted by deep convection therein, (iii) confinement of mesoscale vortex aggregation, (iv) a predominantly convective type of heating profile, and (v) maintenance or enhancement of the parent wave until the developing proto-vortex becomes a self-sustaining entity and emerges from the wave as a tropical depression. This genesis sequence and the overarching framework for describing how such hybrid wave-vortex structures become tropical depressions/storms is likened to the development of a marsupial infant in its mother's pouch, and for this reason has been dubbed the "marsupial paradigm". Here we conduct the first multi-scale test of the marsupial paradigm in an idealized setting by revisiting the problem of the transformation of an easterly wave-like disturbance into a tropical storm vortex using the WRF model. An analysis of the evolving winds, equivalent potential temperature, and relative vertical vorticity is presented from coarse (28 km) and high resolution (3.1 km) simulations. The results are found to support key elements of the marsupial paradigm by demonstrating the existence of a vorticity dominant region with minimal strain/shear deformation within the critical layer pouch that contains strong cyclonic vorticity and high saturation fraction. This localized region within the pouch serves as the "attractor" for an upscale "bottom up" development process while the wave pouch and proto-vortex move together. Implications of these findings are discussed in relation to an upcoming field experiment for the most active period of the Atlantic hurricane season in 2010 that is to be conducted collaboratively between the National Oceanic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and the National Aeronautics and Space Adminstration (NASA).
The ground-based FTIR network's potential for investigating the atmospheric water cycle
Authors: Schneider M. , Yoshimura K. , Hase F. , Blumenstock T.
Published: April 2010

Abstract. We present tropospheric H216O and HD16O/H216O vapour profiles measured by ground-based FTIR (Fourier Transform Infrared) spectrometers between 1996 and 2008 at a northern hemispheric subarctic and subtropical site (Kiruna, Northern Sweden, 68° N and Izaña, Tenerife Island, 28° N, respectively). We compare these measurements to an isotope incorporated atmospheric general circulation model (AGCM). If the model is nudged towards meteorological fields of reanalyses data the agreement is very satisfactory on time scales ranging from daily to inter-annual which demonstrates the good quality of the FTIR data. Taking the Izaña and Kiruna measurements as an example we document the FTIR network's unique potential for investigating the atmospheric water cycle. For the subtropical site the FTIR observations confirm the central role of the Hadley circulation, but in addition they reveal a strong connection between the Northern Atlantic Oscillation (NAO) and the middle/upper tropospheric water vapour transport pathways. Concerning the subarctic site the observations indicate that water transport to the lower troposphere is affected by the northern Atlantic sea surface temperature and correlated to the Arctic Oscillation (AO). For the middle troposphere we observe that spring and autumn water transport pathways are different. We document in detail where the AGCM is able to capture these complexities of the water cycle and where it fails.
Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation
Authors: Spracklen D. V. , Carslaw K. S. , Merikanto J. , Mann G. W. , Pickering S. , Ogren J. A. , Andrews E. , Baltensperger U. , Weingartner E. , Boy M. , Kulmala M. , Laakso L. , Lihavainen H. , Kivekäs N. , Mihalopoulos N. , Kouvarakis G. , Jennings S. G. , Birmili W. , Wiedensohler A. , Weller R. , Laj P. , Sellegri K. , Bonn B. , Krejci R.
Published: April 2010

Abstract. We use observations of total particle number concentration at 36 worldwide sites and a global aerosol model to quantify the primary and secondary sources of particle number. We show that emissions of primary particles can reasonably reproduce the spatial pattern of observed condensation nuclei (CN) (R2=0.51) but fail to explain the observed seasonal cycle at many sites (R2=0.1). The modeled CN concentration in the free troposphere is biased low (normalised mean bias, NMB=−88%) unless a secondary source of particles is included, for example from binary homogeneous nucleation of sulfuric acid and water (NMB=−25%). Simulated CN concentrations in the continental boundary layer (BL) are also biased low (NMB=−74%) unless the number emission of anthropogenic primary particles is increased or an empirical BL particle formation mechanism based on sulfuric acid is used. We find that the seasonal CN cycle observed at continental BL sites is better simulated by including a BL particle formation mechanism (R2=0.3) than by increasing the number emission from primary anthropogenic sources (R2=0.18). Using sensitivity tests we derive optimum rate coefficients for this nucleation mechanism, which agree with values derived from detailed case studies at individual sites.
Simultaneous retrieval of aerosol and surface optical properties from combined airborne- and ground-based direct and diffuse radiometric measurements
Authors: Gatebe C. K. , Dubovik O. , King M. D. , Sinyuk A.
Published: April 2010

Abstract. This paper presents a new method for simultaneously retrieving aerosol and surface reflectance properties from combined airborne and ground-based direct and diffuse radiometric measurements. The method is based on the standard Aerosol Robotic Network (AERONET) method for retrieving aerosol size distribution, complex index of refraction, and single scattering albedo, but modified to retrieve aerosol properties in two layers, below and above the aircraft, and parameters on surface optical properties from combined datasets (Cloud Absorption Radiometer, CAR, and AERONET data). A key advantage of this method is the inversion of all available spectral and angular data at the same time, while accounting for the influence of noise in the inversion procedure using statistical optimization. The wide spectral (0.34–2.30 μm) and angular range (180°) of the CAR instrument, combined with observations from an AERONET sunphotometer, provide sufficient measurement constraints for characterizing aerosol and surface properties with minimal assumptions. The robustness of the method was tested on observations made during four different field campaigns: (a) the Southern African Regional Science Initiative 2000 over Mongu, Zambia, (b) the Intercontinental Transport Experiment-Phase B over Mexico City, Mexico (c) Cloud and Land Surface Interaction Campaign over the Atmospheric Radiation Measurement (ARM) Central Facility, Oklahoma, USA, and (d) the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) over Elson Lagoon in Barrow, Alaska, USA. The four areas are dominated by different surface characteristics and aerosol types, and therefore provide good test cases for the new inversion method.