bluuebunny/crossref_metadata_2025 huggingface dataset:
Preindustrial-to-present-day radiative forcing by tropospheric ozone from improved simulations with the GISS chemistry-climate GCM
Authors: Shindell D. T. , Faluvegi G. , Bell N.
Published: April 2010

Abstract. The tropospheric chemistry model used at the Goddard Institute for Space Studies (GISS) within the GISS general circulation model (GCM) to study interactions between chemistry and climate change has been expanded and integrated into a version of the GCM with higher vertical resolution. The chemistry now includes peroxyacetylnitrates and non-methane hydrocarbons in addition to background NOx-HOx-Ox-CO-CH4 chemistry. The GCM has improved resolution and physics in the boundary layer, improved resolution near the tropopause, and contains a full representation of the stratosphere. Simulations of present-day conditions show that this coupled chemistry-climate model is better able to reproduce observed tropospheric ozone, especially in the tropopause region, which is critical to climate forcing. Comparison with simulations of preindustrial conditions gives a global annual average radiative forcing due to tropospheric ozone increases of 0.30 W/m2 with standard assumptions for preindustrial emissions. Locally, the forcing reaches more than 0.8 W/m2 in parts of the northern subtropics during spring and summer, and is more than 0.6 W/m2 through nearly all the Northern subtropics and mid-latitudes during summer. An alternative preindustrial simulation with soil NOx emissions reduced by two-thirds and emissions of isoprene, paraffins and alkenes from vegetation increased by 50% gives a forcing of 0.33 W/m2. Given the large uncertainties in preindustrial ozone amounts, the true value may lie well outside this range.
FTIR spectroscopic studies of the simultaneous condensation of HCl and H2O at 190 K – atmospheric applications
Authors: Xueref I. , Dominé F.
Published: April 2010

Abstract. Type II polar stratospheric cloud particles are made up of ice that forms by water vapor condensation in the presence of numerous trace gases, including HCl. These gaseous species can co-condense with water molecules and perturb ice structure and reactivity. In order to investigate the effect of co-condensing dopants on the structure of ice, we have designed an experimental system where ice films can be stabilized at 190 K, a temperature relevant to the polar stratosphere. We have co-condensed different HCl:H2O gaseous mixtures, with ratios 5:1, 1:10, 1:50 and 1:200 and studied the solids formed by infrared spectroscopy. The IR spectra obtained show that: (1) HCl undergoes ionic dissociation when it is incorporated by co-condensation into the ice at 190 K; (2) this dissociation is done by several water molecules per HCl molecule; and (3) furthermore, HCl and H2O do not form crystalline HCl hydrates, but rather form non-crystalline solids, that appear homogeneous, and in which HCl is solvated by several water molecules. Considering the major impact of HCl on ice structure observed here, and the well known impact of the structure of solids on their reactivity, we conclude that the actual reactivity of stratospheric ice particles, that catalyze reactions involved in ozone depletion, may be different from what has been measured in laboratory experiments that used pure ice.
Size-segregated aerosol mass closure and chemical composition in Monte Cimone (I) during MINATROC
Authors: Putaud J.-P. , Van Dingenen R. , Dell’Acqua A. , Raes F. , Matta E. , Decesari S. , Facchini M. C. , Fuzzi S.
Published: April 2010

Abstract. Physical and chemical characterizations of the atmospheric aerosol was carried out at Mt. Cimone (Italy) during the 4 June–4 July 2000 period. Particle size distributions in the size range 6 nm–10 μm were measured with a differential mobility analyzer (DMA) and a optical particle counter (OPC). Size-segregated aerosol was sampled using a 6-stage low pressure impactor. Aerosol samples were submitted to gravimetric and chemical analyses. Ionic, carbonaceous and refractory components of the aerosol were quantified. We compared the sub- and super-μm aerosol mass concentrations determined by gravimetric measurements (mGM), chemical analyses (mCA), and by converting particle size distribution to aerosol mass concentrations (mSC). Mean random uncertainties associated with the determination of mGM, mCA, and mSD were assessed. The three estimates of the sub-μm aerosol mass concentration agreed, which shows that within experimental uncertainty, the sub-μm aerosol was composed of the quantified components. The three estimates of the super-mm aerosol mass concentration did not agree, which indicates that random uncertainties and/or possible systematic errors in aerosol sampling, sizing or analyses were not adequately accounted for. Aerosol chemical composition in air masses from different origins showed differences, which were significant in regard to experimental uncertainties. During the Saharan dust advection period, coarse dust and fine anthropogenic particles were externally mixed. No anthropogenic sulfate could be found in the super-μm dust particles. In contrast, nitrate was shifted towards the aerosol super-μm fraction in presence of desert dust.
Stratospheric water vapour as tracer for vortex filamentation in the Arctic winter 2002/2003
Authors: Müller M. , Neuber R. , Fierli F. , Hauchecorne A. , Vömel H. , Oltmans S. J.
Published: April 2010

Abstract. During winter 2002/2003, three balloon-borne frost point hygrometers measured high-resolution profiles of stratospheric water vapour above Ny-Ålesund, Spitsbergen. All measurements reveal a high H2O mixing ratio of about 7 ppmv above 24 km, thus differing significantly from the 5 ppmv that are commonly assumed for the calculation of polar stratospheric cloud existence temperatures. The profiles obtained on 12 December 2002 and on 17 January 2003 provide an insight into the vertical distribution of water vapour in the core of the polar vortex. Unlike the earlier profiles, the water vapour sounding on 11 February 2003 detected the vortex edge region in the lower part of the stratosphere. Here, a striking diminuition in H2O mixing ratio stands out between 16 and 19 km. The according stratospheric temperatures clarify that this dehydration can not be caused by the presence of polar stratospheric clouds or earlier PSC particle sedimentation. On the same day, ozone observations by lidar indicate a large scale movement of the polar vortex, while an ozone sonde measurement even shows laminae in the same altitude range as in the water vapour profile. Tracer lamination in the vortex edge region is caused by filamentation of the vortex. The link between the observed water vapour diminuition and filaments in the vortex edge region is highlighted by results of the MIMOSA contour advection model. In the altitude of interest, adjoined filaments of polar and mid-latitudinal air can be identified above the Spitsbergen region. A vertical cross-section reveals that the water vapour sonde has flown through polar air in the lowest part of the stratosphere. Where the low water vapour mixing ratio was detected, the balloon passed through air from a mid-latitudinal filament from about 425 to 445 K, before it finally entered the polar vortex above 450 K. The MIMOSA model results elucidate the correlation that on 11 February 2003 the frost point hygrometer measured strongly variable water vapour concentrations as the sonde detected air with different origins, respectively. Instead of being linked to dehydration due to PSC particle sedimentation, the local diminuition in the stratospheric water vapour profile of 11 February 2003 has been found to be caused by dynamical processes in the polar stratosphere.
On the accuracy of analysed low temperatures in the stratosphere
Authors: Knudsen B. M.
Published: April 2010

Abstract. The accuracy of ECMWF (European Centre for Medium-Range Weather Forecasts) temperatures have been investigated by comparison to radiosonde temperatures. Particularly, the extent of temperatures below which Polar Stratospheric Clouds (PSCs) consisting of nitric acid trihydrate can exist (TNAT) has been studied. In the 1999/2000 winter analyses and in the 40 year reanalyses (ERA40) from the winter 1996/1997 the analysed extent agrees quite well with the radiosondes extent, whereas the 2002/2003 winter analyses considerably overestimate the extent from 40–11 hPa. Close to the frost point small-scale temperature variations, which ECMWF does not catch, substantially increase the extent of these low temperatures. Some of these small-scale variations are caused by lee-waves.
Intercontinental transport of tropospheric ozone: A study of its seasonal variability across the North Atlantic utilizing tropospheric ozone residuals and its relationship to the North Atlantic Oscillation
Authors: Creilson J. K. , Fishman J. , Wozniak A. E.
Published: April 2010

Abstract. Using the empirically-corrected tropospheric ozone residual (TOR) technique, which utilizes coincident observations of total ozone from the Total Ozone Mapping Spectrometer (TOMS) and stratospheric ozone profiles from the Solar Backscattered Ultraviolet (SBUV) instruments, the seasonal and regional distribution of tropospheric ozone across the North Atlantic from 1979–2000 is examined. Its relationship to the North Atlantic Oscillation (NAO) is also analyzed as a possible transport mechanism across the North Atlantic. Monthly climatologies of tropospheric ozone for five different regions across the North Atlantic exhibit strong seasonality. The correlation between these monthly climatologies of the TOR and adjacent ozonesonde profiles in both Region 1 (eastern North America-western North Atlantic) and Region 5 (eastern North Atlantic-western Europe) are highly significant (R values of +0.98 and +0.96, respectively) and help to validate the use of satellite retrievals of tropospheric ozone. Distinct springtime interannual variability over North Atlantic Region 5 (eastern North Atlantic-western Europe) is particularly evident and exhibits similar variability to the positive phase of the NAO (R=+0.61, ρ =<0.01). Positive phases of the NAO are indicative of a stronger Bermuda-Azores high and a stronger Icelandic low and thus faster more zonal flow across the North Atlantic from west to east. This flow regime appears to be causing the transport of tropospheric ozone across the North Atlantic and onto Europe. The consequence of such transport is the impact on a downwind region's ability to meet their ozone attainment goals. This link between the positive phase of the NAO and increased tropospheric ozone over Region 5 could be an important tool for prediction of such pollution outbreaks.
Lidar and in situ observations of continental and Saharan aerosol: closure analysis of particles optical and physical properties
Authors: Gobbi G. P. , Barnaba F. , van Dingenen R. , Putaud J. P. , Mircea M. , Facchini M. C.
Published: April 2010

Abstract. Single wavelength polarization lidar observations collected at Mt. Cimone (44.2° N, 10.7° E, 1870 m a.s.l.) during the June 2000 MINATROC campaign are analyzed to derive tropospheric profiles of aerosol extinction, depolarization, surface area and volume. Lidar retrievals for the 2170–2245 m level are compared to the same variables as computed from in situ measurements of particles size distributions, performed at the mountain top Station (2165 m a.s.l.) by a differential mobility analyzer (DMA) and an optical particle counter (OPC). A sensitivity analysis of this closure experiment shows that mean relative differences between the backscatter coefficients obtained by the two techniques undergo a 30% decrease when hygroscopic growth to ambient humidity is considered for the DMA dataset, otherwise representative of dry aerosols. Minimization of differences between lidar and size distribution-derived backscatter coefficients allowed to find values of the "best" refractive index, specific to each measurement. These results show the refractive index to increase for air masses proceeding from either continental Europe or Africa with respect to Mediterranean air. Lidar depolarization was observed to minimize mainly in airmasses proceeding from Western Europe, thus indicating a spherical, i.e. liquid nature for such aerosols. This analysis shows average relative differences between lidar and in-situ observations of 10% for backscatter, 37% for extinction and 44% for surface area and volume. These values are within the expected combined errors of the lidar and in situ retrievals. However, average differences strongly decrease during the Saharan dust transport event, when a lidar signal inversion model considering non-spherical scatterers is employed. The closure obtained between particle counter and lidar-derived aerosol surface area and volume constitutes a validation of the technique providing the latter estimates on the basis of single-wavelength lidar observations.
Cloud thermodynamic phase and particle size estimation using the 0.67 and 1.6 μm channels from meteorological satellites
Authors: Jolivet D. , Feijt A. J.
Published: April 2010

Abstract. A robust method to estimate the cloud microphysical properties from visible (0.67 μm) and near infrared (1.6 μm) measurements of reflected sunlight is presented. The method does not determine cloud particle phase and size separately. Instead it assigns a cloud particle type to every pixel that is most representative for the radiation measurements. The corresponding radiative transfer model calculations will yield the most accurate values for optical thickness. Furthermore, an estimate of the particle size is obtained, which is used in estimates of liquid water path. Radiative transfer calculations have been performed for eleven cloud particle models assuming a single, plane-parallel and homogeneous layer. Standard gamma distributions with varying effective radii have been chosen for liquid water droplet whereas imperfect hexagonal ice crystal with different aspect ratio and size were selected for ice particles. It is shown that the ratio of the visible reflectivity to the near infrared reflectivity as a function of the visible reflectivity allows a consistent classification of cloud particles with respect to size and phase over a large area. The method is tested with measurements from the Along Track Scanning Radiometer instrument (ATSR-2) on board ERS-2 for a marine stratocumulus cloud and a cirrus cloud over the North Sea. For both cases, the variation of the measured ratio as a function of the measured visible reflectivity is well simulated by liquid water droplet distribution with an effective radius between 4 and 10 micrometers for the stratocumulus and by imperfect hexagonal ice crystal with a size of 60 μm for cirrus. The method was used in the CLIWANET-project and will be the basis to the algorithm for AVHRR and SEVIRI radiances for EUMETSAT's Sattelite Application facility on climate monitoring.
Source-receptor matrix calculation with a Source-receptor matrix calculation with a backward mode
Authors: Seibert P. , Frank A.
Published: April 2010

Abstract. The possibility to calculate linear-source receptor relationships for the transport of atmospheric trace substances with a Lagrangian particle dispersion model (LPDM) running in backward mode is shown and presented with many tests and examples. The derivation includes the action of sources and of any first-order processes (transformation with prescribed rates, dry and wet deposition, radioactive decay, ...). The backward mode is computationally advantageous if the number of receptors is less than the number of sources considered. The combination of an LPDM with the backward (adjoint) methodology is especially attractive for the application to point measurements, which can be handled without artificial numerical diffusion. Practical hints are provided for source-receptor calculations with different settings, both in forward and backward mode. The equivalence of forward and backward calculations is shown in simple tests for release and sampling of particles, pure wet deposition, pure convective redistribution and realistic transport over a short distance. Furthermore, an application example explaining measurements of Cs-137 in Stockholm as transport from areas contaminated heavily in the Chernobyl disaster is included.
Characterization of African dust over southern Italy
Authors: Blanco A. , de Tomasi F. , Filippo E. , Manno D. , Perrone M. R. , Serra R. , Tafuro A. M. , Tepore A.
Published: April 2010

Abstract. Dust samples from rainfall residues have been collected in southeast Italy (40°20' N, 18°6 E) during dust outbreaks occurred from April to June 2002 to characterize morphological and elemental particle composition by different techniques, and investigate the dependence of particle properties on source regions. Four-day analytical back trajectories and satellite images have been used to infer source regions of the investigated dust samples. It has been found that the TOMS aerosol index product was in the range 0.7–2.2 over Southern Italy when samples have been collected. The particle-size and -shape analysis by a scanning electron microscope (SEM) has revealed either that the particle-diameter distribution was between 0.3 and 307μm with median-diameter values between 1.7–2.4 μm, and that the particles were characterized by a roundness factor varying from 0.8 to 2.5. The infrared transmission spectra have allowed recognizing that all dust samples contained a significant amount of illite. The X-ray energy dispersive (EDX) measurements have revealed that the Al/Si ratio of the transported dust varies from 0.41 to 0.50, and that the Al/Si, Ca/Al, K/Ca, and Fe/Ca ratios differ according to source regions and therefore can be used as indicators of dust source regions. Indeed, it has been found that dust samples with larger Ca/Al and Si/Al ratios and lower Fe/Ca and K/Ca ratios, have been collected along dust events with a source region in northwestern Sahara. On the contrary, the samples collected along dust events with the origin mainly in Chad, Niger, Algeria and Lybia were characterized by larger Fe/Ca and K/Ca ratios.
Halogen cycling and aerosol pH in the Hawaiian marine boundary layer
Authors: Pszenny A. A. P. , Moldanová J. , Keene W. C. , Sander R. , Maben J. R. , Martinez M. , Crutzen P. J. , Perner D. , Prinn R. G.
Published: April 2010

Abstract. Halogen species (HCl* (primarily HCl), Cl* (including Cl2 and HOCl), BrO, total gaseous inorganic Br and size-resolved particulate Cl− and Br −) and related chemical and physical parameters were measured in surface air at Oahu, Hawaii during September 1999. Aerosol pH as a function of particle size was inferred from phase partitioning and thermodynamic properties of HCl. Mixing ratios of halogen compounds and aerosol pHs were simulated with a new version of the photochemical box model MOCCA that considers multiple aerosol size bins. Inferred aerosol pHs ranged from 4.5 to 5.4 (median 5.1, n=22) for super-mm (primarily sea-salt) size fractions and 2.6 to 5.3 (median 4.6) for sub-μm (primarily sulphate) fractions. Simulated pHs for most sea-salt size bins were within the range of inferred values. However, simulated pHs for the largest size fraction in the model were somewhat higher (oscillating around 5.9) due to the rapid turnover rates and relatively larger infusions of sea-salt alkalinity associated with fresh aerosols. Measured mixing ratios of HCl* ranged from <30 to 250 pmol mol-1 and those for Cl* from <6 to 38 pmol mol-1. Simulated HCl and Cl* (Cl+ClO+HOCl+Cl2) mixing ratios ranged between 20 and 70 pmol mol−1 and 0.5 and 6 pmol mol−1, respectively. Afternoon HCl* maxima occurred on some days but consistent diel cycles for HCl* and Cl* were not observed. Simulated HCl did vary diurnally, peaking before dusk and reaching a minimum at dawn. While individual components of Cl* varied diurnally in the simulations, their sum did not, consistent with the lack of a diel cycle in observed Cl*. Mixing ratios of total gaseous inorganic Br varied from <1.5 to 9 pmol mol−1 and particulate Br − deficits varied from 1 to 6 pmol mol−1 with values for both tending to be greater during daytime. Simulated mixing ratios of Br species were consistent with those of observed total gaseous inorganic Br, however the diel cycle was reversed with higher values predicted at night. This may be due to cloud processing, which is not considered in the current version of MOCCA. Measured BrO was never above detection limit (~2 pmol mol-1) during the experiment, however relative changes in the BrO signal during the 3-hour period ending at 11:00 local time were mostly negative, averaging −0.3 pmol mol−1. Both of these results are consistent with MOCCA simulations of BrO mixing ratios. Increasing the sea-salt mixing ratio in MOCCA by ~25% (within observed range) led to a decrease in O3 of ~16%. The chemistry leading to this decrease is complex and is tied to NOx removal by heterogeneous reactions of BrNO3 and ClNO3. The sink of O3 due to the catalytic Cl-ClO and Br-BrO cycles was estimated at −1.0 to −1.5 nmol mol−1 day−1, a range similar to that due to O3 photolysis in the MOCCA simulations.
Ground-based water vapour soundings by microwave radiometry and Raman lidar on Jungfraujoch (Swiss Alps)
Authors: Gerber D. , Balin I. , Feist D. , Kämpfer N. , Simeonov V. , Calpini B. , van den Bergh H.
Published: April 2010

Abstract. Water vapour has been measured from the International Scientific Station Jungfraujoch (ISSJ, 47° N, 7° E, 3580 m a.s.l.) during the winters of 1999/2000 and 2000/2001 by microwave radiometry and Raman lidar. The abundance of atmospheric water vapour between the planetary boundary layer and the upper stratosphere varies over more than three orders of magnitude. The currently used measurement techniques are suited to determine the abundance of water vapour in different atmospheric regimes, however none can resolve by itself a vertical distribution profile over a full altitude range from ground level to the top of the stratosphere. We present such a water vapour profile where simultaneous measurements from a Raman lidar and a microwave radiometer are combined to cover both the troposphere and the stratosphere, respectively. We also present a study of the stratospheric and tropospheric water vapour variability for the two consecutive winters.
Laboratory studies of the homogeneous nucleation of iodine oxides
Authors: Burkholder J. B. , Curtius J. , Ravishankara A. R. , Lovejoy E. R.
Published: April 2010

Abstract. Laboratory experimental results of iodine oxide nucleation are presented. Nucleation was induced following UV photolysis of CF3I or CH2I2 in the presence of excess ozone. Measurements were performed in a 70 L Teflon reactor with new particles detected using an Ultrafine Condensation Particle Counter, UCPC. The experimental results are interpreted using a coupled chemical – aerosol model to derive model parameters assuming single component homogeneous nucleation of OIO. The aerosol model results have been applied in an atmospheric box-model to interpret the possible implications of iodine oxide nucleation in the marine boundary layer. The model calculations demonstrate that IO and OIO concentrations reported in recent field measurements (Allan et al., 2000, 2001) are not sufficient to account for significant aerosol production either in the coastal or open ocean marine boundary layer using the mechanism presented. We demonstrate that inhomogeneous sources of iodine oxides, i.e. "hot" spots with elevated iodine species emissions, could account for the aerosol production bursts observed in the coastal region near Mace Head, Ireland.
A climatological study of rural surface ozone in central Greece
Authors: Kalabokas P. D. , Repapis C. C.
Published: April 2010

Abstract. Recent studies show that surface ozone levels at rural sites in Greece are generally high when compared with rural ozone measurements at northern European sites. The area of SE Europe, including Greece, is not very well monitored regarding rural ozone in comparison to central and northern Europe. In order to have the best possible picture of the rural surface ozone climatology in the area, based on the available data-sets of long-term continuous monitoring stations, the 10-year measurement records (1987–1996) of the Athens peripheral station of Liossia, (12 km N of the city center) and the urban background station of Geoponiki (3 km W) as well as the 4-year record (1996–1999) of the rural station of Aliartos (100 km NW of Athens), are analyzed in this paper. The data for Liossia and Geoponiki stations are screened for cases of strong airflow from rural areas (N-NE winds stronger than 5 m/s). The variation characteristics of the average rural ozone afternoon levels (12:00–18:00), with the best vertical atmospheric mixing, are mainly examined since these measurements are expected to be representative of the broader area. In all three stations there is a characteristic seasonal variation of rural ozone concentrations with lowest winter afternoon values at about 50 μg/m3 in December-January and average summer afternoon values at about 120 μg/m3 in July–August, indicating that high summer values are observed all over the area. The rural summer afternoon ozone values are very well correlated between the three stations, implying spatial homogeneity all over the area but also temporal homogeneity, since during the 13-year period 1987–1999 the rural afternoon ozone levels remained almost constant around the value of 120 μg/m3.
Linking horizontal and vertical transports of biomass fire emissions to the Tropical Atlantic Ozone Paradox during the Northern Hemisphere winter season: climatology
Authors: Jenkins G. S. , Ryu J.-H.
Published: April 2010

Abstract. During the Northern hemisphere winter season, biomass burning is widespread in West Africa, yet the total tropospheric column ozone values (<30 DU) over much of the Tropical Atlantic Ocean (15° N–5° S) are relatively low. At the same time, the tropospheric column ozone values in the Southern Tropical Atlantic are higher than those in the Northern Hemisphere (ozone paradox). We examine the causes for low tropospheric column ozone values by considering the horizontal and vertical transport of biomass fire emissions in West Africa during November through March, using observed data which characterizes fires, aerosols, horizontal winds, precipitation, lightning and outgoing longwave radiation. We have found that easterly winds prevail in the lower troposphere but transition to westerly winds at pressure levels lower than 500 hPa. A persistent anticyclone over West Africa at 700 hPa is responsible for strong easterly winds, which causes a net outflow of ozone/ozone precursors from biomass burning in West Africa across the Atlantic Ocean towards South America. The lowest outgoing longwave radiation (OLR) and highest precipitation rates are generally found over the central Atlantic, some distance downstream of fires in West Africa making the vertical transport of ozone and ozone precursors less likely and ozone destruction more likely. However, lightning over land areas in Central Africa and South America can lead to enhanced ozone levels in the upper troposphere especially over the Southern tropical Atlantic during the Northern Hemisphere winter season.
Optimizing CO2 observing networks in the presence of model error: results from TransCom 3
Authors: Rayner P. J.
Published: April 2010

Abstract. We use a genetic algorithm to construct optimal observing networks of atmospheric CO2 concentration for inverse determination of net sources. Optimal networks are those that produce a minimum in average posterior uncertainty plus a term representing the divergence among source estimates for different transport models. The addition of this last term modifies the choice of observing sites, leading to larger networks than would be chosen under the traditional estimated variance metric. Model-model differences behave like sub-grid heterogeneity and optimal networks try to average over some of this. The optimization does not, however, necessarily reject apparently difficult sites to model. Although the results are so conditioned on the experimental set-up that the specific networks chosen are unlikely to be the best choices in the real world, the counter-intuitive behaviour of the optimization suggests the model error contribution should be taken into account when designing observing networks. Finally we compare the flux and total uncertainty estimates from the optimal network with those from the TransCom 3 control case. The comparison suggests that the TransCom 3 control case is robust.
New insights in the global cycle of acetonitrile: release from the ocean and acetonitrile: release from the ocean and Venezuela
Authors: Sanhueza E. , Holzinger R. , Kleiss B. , Donoso L. , Crutzen P. J.
Published: April 2010

Abstract. CUsing the proton transfer reaction mass spectrometry (PTR-MS) technique, acetonitrile was measured during the wet season in a Venezuelan woodland savanna. The site was located downwind of the Caribbean Sea and no biomass burning events were observed in the region. High boundary layer concentrations of  211 ±36 pmol/mol (median, ± standard deviation) were observed during daytime in the well mixed boundary layer, which is about 60 pmol/mol above background concentrations recently measured over the Mediterranean Sea and the Pacific Ocean. Most likely acetonitrile is released from the warm waters of the Caribbean Sea thereby enhancing mixing ratios over Venezuela. Acetonitrile concentrations will probably still be much higher in biomass burning plumes, however, the general suitability of acetonitrile as a biomass burning marker should be treated with care. During nights, acetonitrile dropped to levels typically around 120 pmol/mol, which is consistent with a dry deposition velocity of ~0.14 cm/s when a nocturnal boundary layer height of 100 m is assumed.
Measurements of reactive chlorocarbons over the Surinam tropical rain forest: indications for strong biogenic emissions
Authors: Scheeren H. A. , Lelieveld J. , Williams J. , Fischer H. , Warneke C.
Published: April 2010

Abstract. Contrary to the understanding of the emissions and chemical behavior of halocarbons from anthropogenic sources (e.g. CFCs and HCFCs), the biogeochemistry of naturally emitted halocarbons is still poorly understood. We present measurements of chloromethane (methyl chloride, CH3Cl), trichloromethane (chloroform, CHCl3), dichloromethane (CH2Cl2), and tetrachloroethylene (C2Cl4) from air samples taken over the Surinam rainforest during the 1998 LBA/CLAIRE campaign. The samples were collected in stainless steel canisters on-board a Cessna Citation jet aircraft and analyzed in the laboratory using a gas chromatograph equipped with FID and ECD. The chlorocarbons we studied have atmospheric lifetimes of ~1 year or less, and appear to have significant emissions from natural sources including oceans, soils and vegetations, as well as biomass burning. These sources are primarily concentrated in the tropics (30º N-30º S). We detected an increase as a function of latitude of methyl chloride, chloroform, and tetrachloroethylene mixing ratios, in pristine air masses advected from the Atlantic Ocean toward the central Amazon. In the absence of significant biomass burning sources, we attribute this increase to biogenic emissions from the Surinam rainforest. From our measurements, we deduce fluxes from the Surinam rainforest of 7.6±1.8 μg CH3Cl m−2 h−1, 1.11±0.08g CHCl3 μm−2 h−1, and 0.36±0.07 μg C2Cl4 m−2 h−1. Extrapolated to a global scale, our emission estimates suggest a large potential source of 2 Tg CH3Cl yr−1 from tropical forests, which could account for the net budget discrepancy (underestimation of sources), as indicated previously. In addition, our estimates suggest a potential emission of 57±17 Gg C2C4 yr−1 from tropical forest soils, equal to half of the currently missing C2Cl4 sources. We hypothesize that the extensive deforestation over the last two decades relates to the observed global downward trend of atmospheric methyl chloride.
Particle size distribution and particle mass measurements at urban, near-city and rural level in the Copenhagen area and Southern Sweden
Authors: Ketzel M. , Wåhlin P. , Kristensson A. , Swietlicki E. , Berkowicz R. , Nielsen O. J. , Palmgren F.
Published: April 2010

Abstract. Particle size distribution (size-range 3–900 nm) and PM10 was measured simultaneously at an urban background station in Copenhagen, a near-city background and a rural location during a period in September-November 2002. The study investigates the contribution from urban versus regional sources of particle number and mass concentration. The total particle number (ToN) and NOx are well correlated at the urban and near-city level and show a distinct diurnal variation, indicating the common traffic source. The average ToN at the three stations differs by a factor of 3. The observed concentrations are 2500 # cm−3, 4500 # cm−3 and 7700 # cm−3 at rural, near-city and urban level, respectively. PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar concentration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations. Measures to reduce the local urban emissions of NOx and ToN are likely to affect both the street level and urban background concentrations, while for PM10 and ToV only measurable effects at the street level are probable. Taking into account the supposed stronger health effects of ultrafine particles reduction measures should address particle number emissions. The traffic source contributes strongest in the 10–200 nm particle size range. The maximum of the size distribution shifts from about 20–30 nm at kerbside to 50–60 nm at rural level. We also observe particle formation events in the 3–20 nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of pre-existing aerosol particles. The maximum in the size distribution of the "traffic contribution" seems to be shifted to about 28 nm in the urban location compared to 22 nm at kerbside. Assuming NOx as an inert tracer on urban scale let us estimate that ToN at urban level is reduced by 15–30% compared to kerbside. Particle removal processes, e.g. deposition and coagulation, which are most efficient for smallest particle sizes (<20 nm) and condensational growth are likely mechanisms for the loss of particle number and the shift in particle size.
Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS)
Authors: Hönninger G. , von Friedeburg C. , Platt U.
Published: April 2010

Abstract. Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a novel measurement technique that represents a significant advance on the well-established zenith scattered sunlight DOAS instruments which are mainly sensitive to stratospheric absorbers. MAX-DOAS utilizes scattered sunlight received from multiple viewing directions. The spatial distribution of various trace gases close to the instrument can be derived by combining several viewing directions. Ground based MAX-DOAS is highly sensitive to absorbers in the lowest few kilometres of the atmosphere and vertical profile information can be retrieved by combining the measurements with Radiative Transfer Model (RTM) calculations. The potential of the technique for a wide variety of studies of tropospheric trace species and its (few) limitations are discussed. A Monte Carlo RTM is applied to calculate Airmass Factors (AMF) for the various viewing geometries of MAX-DOAS. Airmass Factors can be used to quantify the light path length within the absorber layers. The airmass factor dependencies on the viewing direction and the influence of several parameters (trace gas profile, ground albedo, aerosol profile and type, solar zenith and azimuth angles) are investigated. In addition we give a brief description of the instrumental MAX-DOAS systems realised and deployed so far. The results of the RTM studies are compared to several examples of recent MAX-DOAS field experiments and an outlook for future possible applications is given.
Space-borne observations link the tropical Atlantic ozone maximum and paradox to lightning
Authors: Jenkins G. S. , Ryu J.-H.
Published: April 2010

Abstract. The causes of high tropospheric column ozone values over the Tropical Atlantic Ocean during September, October, and November (SON) are investigated by examining lightning during 1998–2001. The cause for high tropospheric column ozone in the hemisphere opposite of biomass burning (tropical ozone paradox) is also examined. Our results show that lightning is central to high tropospheric column ozone during SON and responsible for the tropical ozone paradox during December, January, and February (DJF) and June, July and August (JJA). During SON large numbers of flashes are observed in South America, Central and West Africa enriching the tropospheric column ozone over the Tropical Atlantic Ocean. During JJA the largest numbers of lightning flashes are observed in West Africa, enriching tropospheric column ozone to the north of 5° S in the absence biomass burning. During DJF, lightning is concentrated in South America and Central Africa enriching tropospheric column ozone south of the Equator in the absence of biomass burning.
The vertical distribution of aerosols, Saharan dust and cirrus clouds at Rome (Italy) in the year 2001
Authors: Gobbi G. P. , Barnaba F.
Published: April 2010

Abstract. A set of 813 lidar profiles of tropospheric aerosol and cirrus clouds extinction and depolarization observed at Rome, Italy, between February 2001 and February 2002 is analyzed and discussed. The yearly record reveals a meaningful contribution of both cirrus clouds (38%) and Saharan dust (12%) to the total optical thickness (OT) of 0.26, at 532 nm. Seasonal analysis shows the planetary boundary layer (PBL) aerosols to be confined below 2 km in winter and 3.8 km in summer, with relevant OT shifting from 0.08 to 0.16, respectively. Cirrus clouds maximize in spring and autumn, in both cases with average OT similar to the PBL aerosols one. With the exception of winter months, Saharan dust is found to represent an important third layer mostly residing between PBL aerosols and cirrus clouds, with yearly average OT~0.03. Saharan dust and cirrus clouds were detected in 20% and in 45% of the observational days, respectively. Validation of the lidar OT retrievals against collocated sunphotometer observations show very good agreement. These results represent one of the few yearly records of tropospheric aerosol vertical profiles available in the literature.
Volatile particles formation during PartEmis: a modelling study
Authors: Vancassel X. , Sorokin A. , Mirabel P. , Petzold A. , Wilson C.
Published: April 2010

Abstract. A modelling study of the formation of volatile particles in a combustor exhaust has been carried out in the frame of the PartEmis European project. A kinetic model has been used in order to investigate nucleation efficiency of the H2O-H2SO4 binary mixture in the sampling system. A value for the fraction e of the fuel sulphur S(IV) converted into S(VI) has been indirectly deduced from comparisons between model results and measurements. In the present study, e ranges between roughly 2.5% and 6%, depending on the combustor settings and on the microphysical approach used. Soot particles hygroscopicity has also been investigated as their activation is a key parameter for contrail formation. Growth factors of monodisperse particles exposed to high relative humidity (95%) have been calculated and compared with experimental results. The modelling study confirms that the growth factor increases as the soot particle size decreases.
Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling
Authors: Reichardt J. , Dörnbrack A. , Reichardt S. , Yang P. , McGee T. J.
Published: April 2010

Abstract. The exceptional day-long observation of a polar stratospheric cloud (PSC) by two ground-based lidars at the Swedish research facility Esrange (67.9° N, 21.1° E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale meteorological modeling is utilized to resolve the time-space ambiguity of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC consisted of irregular-shaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 μm, and a number density from 8 to 12 cm−3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 μm, a refractive index of 1.39 and a number density from 7 to 11 cm−3. NAT activation was probably substantial (~53%) which appears to be the effect of the high cooling rates (>100 K/h) in the stratospheric mountain wave. The total amount of condensed HNO3 was in the range of 57–90% of the HNO3 gas reservoir. By early afternoon the mountain wave-induced ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 4.3 to 1.9 μm with time, possibly due to a diminishing growth rate. Later on, following the cessation of particle nucleation upwind wave-processed LTA was observed only. Our study demonstrates that ground-based lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.
Analysis of a jet stream induced gravity wave associated with an observed ice cloud over Greenland
Authors: Buss S. , Hertzog A. , Hostettler C. , Bui T. P. , Lüthi T. , Wernli H.
Published: April 2010

Abstract. A polar stratospheric ice cloud (PSC type II) was observed by airborne lidar above Greenland on 14 January 2000. Is was the unique observation of an ice cloud over Greenland during the SOLVE/THESEO 2000 campaign. Mesoscale simulations with the hydrostatic HRM model are presented which, in contrast to global analyses, are capable to produce a vertically propagating gravity wave that induces the low temperatures at the level of the PSC afforded for the ice formation. The simulated minimum temperature is ~8 K below the driving analyses and ~3 K below the frost point, exactly coinciding with the location of the observed ice cloud. Despite the high elevations of the Greenland orography the simulated gravity wave is not a mountain wave. Analyses of the horizontal wind divergence, of the background wind profiles, of backward gravity wave ray-tracing trajectories, of HRM experiments with reduced Greenland topography and of several instability diagnostics near the tropopause level provide consistent evidence that the wave is emitted by the geostrophic adjustment of a jet instability associated with an intense, rapidly evolving, anticyclonically curved jet stream. In order to evaluate the potential frequency of such non-orographic polar stratospheric cloud events, an approximate jet instability diagnostic is performed for the winter 1999/2000. It indicates that ice-PSCs are only occasionally generated by gravity waves emanating from an unstable jet.
Heterogeneous conversion of NO2 on secondary organic aerosol surfaces: A possible source of nitrous acid (HONO) in the atmosphere?
Authors: Bröske R. , Kleffmann J. , Wiesen P.
Published: April 2010

Abstract. The heterogeneous conversion of NO2 on different secondary organic aerosols (SOA) was investigated with the focus on a possible formation of nitrous acid (HONO). In one set of experiments different organic aerosols were produced in the reactions of O3 with α-pinene, limonene or catechol and OH radicals with toluene or limonene, respectively. The aerosols were sampled on filters and exposed to humidified NO2 mixtures under atmospheric conditions. The estimated upper limits for the uptake coefficients of NO2 and the reactive uptake coefficients NO2 →HONO are in the range of 10−6 and 10−7, respectively. The integrated HONO formation for 1 h reaction time was <1013 cm−2 geometrical surface and <1017 g−1 particle mass. In a second set of experiments the conversion of NO2 into HONO in the presence of organic particles was carried out in an aerosol flow tube under atmospheric conditions. In this case the aerosols were produced in the reaction of O3 with β-pinene, limonene or catechol, respectively. The upper limits for the reactive uptake coefficients NO2 \\rightarrow HONO were in the range of 7×10−7 −9×10−6. The results from the present study show that heterogeneous formation of nitrous acid on secondary organic aerosols (SOA) is unimportant for the atmosphere.
On the influence of fuel sulfur induced stable negative ion formation on the total concentration of ions emitted by an aircraft gas turbine engine: comparison of model and experiment
Authors: Sorokin A. , Arnold F. , Mirabel P.
Published: April 2010

Abstract. A model which considers the formation and evolution of combustion ions in a combustor of an aircraft engine in dependence on the electron detachment efficiency from negative ions is presented. It is a further development of the model reported by (Sorokin et al., 2003). The model allows to consider the effect of the transformation of primary negative ions to more stable secondary negative ions with a much higher electron affinity and as a consequence a greater stability with respect to electron thermal detachment. The formed stable negative ions most probably are sulfur-bearing ions. This effect slows down the charged particle neutralization rate leading to an increase of the concentration of positive and negative ions at the combustor exit. The results of the simulation and their comparison with the ground-based experimental data obtained within the framework of the project PartEmis (Particle emission, measurements and predictions of emission of aerosols and gaseous precursors from gas turbine engines; coordinator: C. Wilson) at the QinetiQ test facility at Pyestock, UK (Wilson et al., 2003) support the above hypothesis, i.e. the increase of the fuel sulfur content leads to an increase of the ion concentration at the combustor exit.
Commentary on “Improving the seasonal cycle and interannual variations of biomass burning aerosol sources" by Generoso et al.
Authors: Giglio L. , Kendall J. D.
Published: April 2010

Abstract. In a recent published paper, Generoso et al. (2003), describe a method for improving the spatial and temporal distribution of pyrogenic aerosol emission inventories. In the course of their analysis, the authors note several significant discrepancies in the seasonality of burning as observed by the Visible and Infrared Scanner (VIRS) and four other biomass burning data sets derived from satellite observations. In this commentary we explain the source of these discrepancies and clarify the origin of the VIRS observations that were used by Generoso et al.
A new feedback mechanism linking forests, aerosols, and climate
Authors: Kulmala M. , Suni T. , Lehtinen K. E. J. , Dal Maso M. , Boy M. , Reissell A. , Rannik Ü. , Aalto P. , Keronen P. , Hakola H. , Bäck J. , Hoffmann T. , Vesala T. , Hari P.
Published: April 2010

Abstract. Among significant issues in climate change studies are the possible connections between the carbon balance of ecosystems and aerosol-cloud-climate interactions. Carbon dioxide is a greenhouse gas, whereas the net effect of atmospheric aerosols is to cool the climate. Here, we investigated the connection between forest-atmosphere carbon exchange and aerosol dynamics in the continental boundary layer by means of multiannual data sets of particle formation and growth rates, of CO2 fluxes, and of monoterpene concentrations in a Scots pine forest in southern Finland. We suggest a new, interesting link and a potentially important feedback among forest ecosystem functioning, aerosols, and climate: Considering that globally increasing temperatures and CO2 fertilization are likely to lead to increased photosynthesis and forest growth, an increase in forest biomass would increase emissions of non-methane biogenic volatile organic compounds and thereby enhance organic aerosol production. This feedback mechanism couples the climate effect of CO2 with that of aerosols in a novel way.