bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical-chemical relationships for carbonaceous aerosols observed at Jeju Island, Korea with a 3-laser photoacoustic spectrometer
Authors: Flowers B. A. , Dubey M. K. , Mazzoleni C. , Stone E. A. , Schauer J. J.. , Kim S.-W.
Published: April 2010

Abstract. Transport of aerosols in pollution plumes from the mainland Asian continent was observed in situ at Jeju, South Korea during the Cheju Asian Brown Cloud Plume-Asian Monsoon Experiment (CAPMEX) field campaign throughout August and September 2008 using a 3-laser photoacoustic spectrometer. Transport of mixed sulfate, carbonaceous, and nitrate aerosols from various Asian pollution plumes to Jeju accounted for 76% of the deployment days, showing large variations in their measured chemical and optical properties. Our analysis of eight distinct episodes, spanning a wide range of chemical composition, optical properties, and source regions, reveals that at episodes with higher OC/SO2−4 and NO−3/SO2−4 composition ratios exhibit lower single scatter albedo at shorter wavelengths (ω405); significantly lower [ω405meas = 0.79±0.06, ω405calc = 0.86±0.01] than predicted by an optical model that assumes constant complex index of refraction with wavelength (an optical model of soot). We attribute this discrepancy to enhanced absorption by organic material. Organic carbon absorption accounts for up to 50% of the measured aerosol absorption at 405 nm for the high OC/SO2−4 episode. Coatings of elemental carbon aerosol cores are hypothesized to increase absorption by factors up to 6 at visible wavelengths. Carbonaceous aerosol absorption can alter global radiative forcing estimates substantially, underscoring the need to understand and predict chemical composition effects on optical properties.
Synergetic use of millimeter and centimeter wavelength radars for retrievals of cloud and rainfall parameters
Authors: Matrosov S. Y.
Published: April 2010

Abstract. A remote sensing approach for simultaneous retrievals of cloud and rainfall parameters in the vertical column above the US Department of Energy's (DOE) Climate Research Facility at the Tropical Western Pacific (TWP) Darwin site in Australia is described. This approach uses vertically pointing measurements from a DOE Ka-band radar and scanning measurements from a nearby C-band radar pointing toward the TWP Darwin site. Rainfall retrieval constraints are provided by data from a surface impact disdrometer. The approach is applicable to stratiform precipitating cloud systems when a separation between the liquid hydrometeor layer, which contains rainfall and liquid water clouds, and the ice hydrometeor layer is provided by the radar bright band. Absolute C-band reflectivities and Ka-band vertical reflectivity gradients in the liquid layer are used for retrievals of the mean layer rain rate and cloud liquid water path (CLWP). C-band radar reflectivities are also used to estimate ice water path (IWP) in regions above the melting layer. The retrieval uncertainties of CLWP and IWP for typical stratiform precipitation systems are about 500–800 g m−2 (for CLWP) and a factor of 2 (for IWP). The CLWP retrieval uncertainties increase with rain rate, so retrievals for higher rain rates may be impractical. The expected uncertainties of layer mean rain rate retrievals are around 20%, which, in part, is due to constraints available from the disdrometer data. The applicability of the suggested approach is illustrated for two characteristic events observed at the TWP Darwin site during the wet season of 2007. A future deployment of W-band radars at the DOE tropical Climate Research Facilities can improve CLWP estimate accuracies and provide retrievals for a wider range of stratiform precipitating cloud events.
Heterogeneous freezing of water droplets containing kaolinite and montmorillonite particles
Authors: Murray B. J. , Wilson T. W. , Broadley S. L. , Wills R. H.
Published: April 2010

Abstract. Clouds composed of both ice particles and supercooled liquid water droplets exist at temperatures above ~236 K. These mixed phase clouds, which strongly impact climate, are very sensitive to the presence of solid particles that can catalyse freezing. In this paper we describe experiments to determine the rate at which kaolinite and montmorillonite nucleate ice when immersed within water droplets. These are the first immersion mode experiments in which the ice nucleating ability of individual minerals has been determined quantitatively. Water droplets containing a known amount of clay mineral were supported on a hydrophobic surface and cooled at a rate of 10 K min−1. The temperatures at which individual 10–40 μm diameter droplets froze were determined by optical microscopy. As the concentration of kaolinite in the droplets was increased from 0.005 wt% to 1 wt% the median nucleation temperature increased from close to the homogeneous nucleation limit (236 K) to 240.8±0.6 K. We go onto show that the probability of freezing scales with surface area of the kaolinite inclusions rather than, as is often assumed, the volume of the droplet. When droplets contained montmorillonite ice always nucleated at 245.8±0.6 K, independent of the mineral concentration. We report temperature dependent nucleation rates and present parameterisations for nucleation by these minerals which capture the surface area and cooling rate dependence of the nucleation rate. We show that our parameterisations produce significantly different results to parameterisations employed in global models. These results also highlight the importance of understanding the ice nucleating properties of individual minerals rather than complex mixtures of minerals found in natural dusts and so-called test dusts.
The spatial distribution of mineral dust and its shortwave radiative forcing over North Africa: modeling sensitivities to dust emissions and aerosol size treatments
Authors: Zhao C. , Liu X. , Leung L. R. , Johnson B. , McFarlane S. A. , Gustafson W. I. , Fast J. D. , Easter R.
Published: April 2010

Abstract. A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate mineral dust and its shortwave (SW) radiative forcing over North Africa. Two dust emission schemes (GOCART and DUSTRAN) and two aerosol models (MADE/SORGAM and MOSAIC) are adopted in simulations to investigate the modeling sensitivities to dust emissions and aerosol size treatments. The modeled size distribution and spatial variability of mineral dust and its radiative properties are evaluated using measurements (ground-based, aircraft, and satellites) during the AMMA SOP0 campaign from 6 January to 3 February of 2006 (the SOP0 period) over North Africa. Two dust emission schemes generally simulate similar spatial distributions and temporal evolutions of dust emissions. Simulations using the GOCART scheme with different initial (emitted) dust size distributions show that the difference of initial dust size distributions can result in significant difference (up to ~50%) in simulating SW dust heating and SW dust radiative forcing at the surface over the Sahel region. The modal approach of MADE/SORGAM retains 25% more fine dust particles (radius <1.25 μm) but 8% less coarse dust particles (radius >1.25 μm) than the sectional approach of MOSAIC in simulations using the same size-resolved dust emissions. Consequently, MADE/SORGAM simulates 11% higher AOD, up to 13% lower SW dust heating rate, and 15% larger (more negative) SW dust radiative forcing at the surface than MOSAIC over the Sahel region. In the daytime of the SOP0 period, the model simulations show that mineral dust heats the lower atmosphere (1–3 km) with a maximum rate of 0.8±0.5 K day−1 below 1 km and reduces the downwelling SW radiation at the surface by up to 58 W m−2 over the Sahel region. This highlights the importance of including dust radiative impact in understanding the regional climate of North Africa. When compared to the available measurements, the WRF-Chem simulations can generally capture the measured features of mineral dust and its radiative properties over North Africa, suggesting that the model is suitable for more extensive simulations of dust impact on regional climate over North Africa.
Observations of elevated formaldehyde over a forest canopy suggest missing sources from rapid oxidation of arboreal hydrocarbons
Authors: Choi W. , Faloona I. C. , Bouvier-Brown N. C. , McKay M. , Goldstein A. H. , Mao J. , Brune W. H. , LaFranchi B. W. , Cohen R. C. , Wolfe G. M. , Thornton J. A. , Sonnenfroh D. M. , Millet D. B.
Published: April 2010

Abstract. To better understand the processing of biogenic VOCs (BVOCs) in the pine forests of the U.S. Sierra Nevada, we measured HCHO at Blodgett Research Station using Quantum Cascade Laser Spectroscopy (QCLS) during the Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX) of late summer 2007. Four days of the experiment exhibited particularly copious HCHO, with midday peaks between 15–20 ppbv, while the other days developed delayed maxima between 8–14 ppbv in the early evening. From the expansive photochemical data set, we attempt to explain the observed HCHO concentrations by quantifying the various known photochemical production and loss terms in its chemical budget. Overall, known chemistry predicts a factor of 3–5 times less HCHO than observed. By examining diurnal patterns of the various budget terms we conclude that, during the high HCHO period, local, highly reactive oxidation chemistry produces an abundance of formaldehyde at the site. The results support the hypothesis of previous work at Blodgett Forest suggesting that large quantities of BVOC oxidation products, observed directly above the ponderosa pine canopy, are evidence of profuse emissions of very reactive volatile organic compounds (VR-VOCs) from the forest. However, on the majority of days, under generally cooler and more moist conditions, lower levels of HCHO develop primarily influenced by the influx of precursors transported into the region along with the Sacramento plume.
Sensitivity study of dimethylsulphide (DMS) atmospheric concentrations and sulphate aerosol indirect radiative forcing to the DMS source representation and oxidation
Authors: Boucher O. , Moulin C. , Belviso S. , Aumont O. , Bopp L. , Cosme E. , von Kuhlmann R. , Lawrence M. G. , Pham M. , Reddy M. S. , Sciare J. , Venkataraman C.
Published: April 2010

Abstract. The global sulphur cycle has been simulated using a general circulation model with a focus on the source and oxidation of atmospheric dimethylsulphide (DMS). The sensitivity of atmospheric DMS to the oceanic DMS climatology, the parameterisation of the sea-air transfer and to the oxidant fields have been studied. The importance of additional oxidation pathways (by O3 in the gas- and aqueous-phases and by BrO in the gas phase) not incorporated in global models has also been evaluated. While the global DMS flux is well constrained at 24-27 Tg S yr -1, there are large differences in the spatial and seasonal distribution of the atmospheric DMS flux generated from the three climatologies of oceanic DMS considered here. The relative contributions of OH and NO3 radicals to DMS oxidation depends critically on which oxidant fields are prescribed in the model. Oxidation by O3 appears to be significant at high latitudes in both hemispheres. Oxidation by BrO could be significant even for BrO concentrations at sub-pptv levels in the marine boundary layer.
Aerosol sources and their contribution to the chemical composition of aerosols in the Eastern Mediterranean Sea during summertime
Authors: Sciare J. , Bardouki H. , Moulin C. , Mihalopoulos N.
Published: April 2010

Abstract. A detailed study on the temporal variability of compounds important in controlling aerosol chemical composition was performed during a one-month experiment conducted during summer 2000 at a background site on Crete, in the Eastern Mediterranean Sea. Contribution of different aerosol sources in the Eastern Mediterranean Basin could be investigated at this location since the site is influenced by a wide range of air masses originating mainly in Europe and Africa. Chemical apportionment was performed for various air mass origins and showed a strong impact of anthropogenic emissions in the Turkey and Central Europe sectors, with black carbon (BC) and non-sea-salt sulfate (nss-SO4) concentrations being almost a factor of two higher than observed in the Eastern and Western Europe sectors. High levels of non-sea-salt calcium (nss-Ca) were associated with air masses from Africa but also from Central Turkey. Evidence was found that BC calculation based on light absorbance during dust events was biased. A source-oriented model was applied for these compounds as well as for sulfur dioxide (SO2), in order to examine the source-receptor relationships responsible for the observed levels in Crete. Among the results obtained from this model, the major contribution of Turkey and Central Europe was confirmed in terms of anthropogenic emissions. Comparisons with remote optical properties obtained from Satellite observations (SEAWIFS) north of Crete indicates that our ground based aerosol characterization was suitable for describing aerosol properties in the atmospheric column for most of the time during the campaign.
An exploration of ozone changes and their radiative forcing prior to the chlorofluorocarbon era
Authors: Shindell D. T. , Faluvegi G.
Published: April 2010

Abstract. Using historical observations and model simulations, we investigate ozone trends prior to the mid-1970s onset of halogen-induced ozone depletion. Though measurements are quite limited, an analysis based on multiple, independent data sets (direct and indirect) provides better constraints than any individual set of observations. We find that three data sets support an apparent long-term stratospheric ozone trend of -7.2 ± 2.3 DU during 1957-1975, which modeling attributes primarily to water vapor increases. The results suggest that stratospheric ozone depletion may have been roughly 50% more than is generally supposed. Similarly, three data sets support tropospheric ozone increases over polluted Northern Hemisphere continental regions of 8.2 ± 2.1 DU during this period, which are mutually consistent with the stratospheric trends. As with paleoclimate data, which is also based on indirect proxies and/or limited spatial coverage, these results must be interpreted with caution. However, they provide the most thorough estimates presently available of ozone changes prior to the coincident onset of satellite data and halogen dominated ozone changes. If these apparent trends were real, the radiative forcing by stratospheric ozone since the 1950s would then have been -0.15 ± 0.05 W/m2, and -0.2 W/m2 since the preindustrial. For tropospheric ozone, it would have been 0.38 ±  0.10 W/m2 since the 1950s, larger than current estimates since 1850 which are derived from models that are even less well constrained. Going back to the preindustrial, the radiative forcing would have been +0.7 W/m2, roughly double what is generally assumed, although even more uncertain than the late twentieth century trends. These calculations demonstrate the importance of gaining a better understanding of historical ozone changes.
The impact of multiphase reactions of NO2 with aromatics: a modelling approach
Authors: Lahoutifard N. , Ammann M. , Gutzwiller L. , Ervens B. , George Ch.
Published: April 2010

Abstract. The impact of multiphase reactions involving nitrogen dioxide (NO2) and aromatic compounds was simulated in this study. A mechanism (CAPRAM 2.4, MODAC Mechanism), was applied for the aqueous phase reactions whereas RACM was applied for the gas phase chemistry. Liquid droplets were considered as monodispersed with a mean radius of 0.1 mm and a liquid water content (LWC) of 50mg m-3. The multiphase mechanism has been further extended to the chemistry of aromatics, i.e. reactions involving benzene, toluene, xylene, phenol and cresol have been added. In addition, reaction of NO2 with dissociated hydroxyl substituted aromatic compounds has also been implemented. These reactions proceed through charge exchange leading to nitrite ions and therefore to nitrous acid formation. The strength of this source was explored under urban polluted conditions. It was shown that it may significantly increase gas phase HONO levels. About one order of magnitude change of HONO concentration was observed with finally, a minor effect on subsequent gas phase daytime photochemistry because of the limited aerosol life time considered.
Modelling studies of wind field on urban environment
Authors: Radics K. , Bartholy J. , Pongrácz R.
Published: April 2010

Abstract. Increasing load of air pollution in urban environment emphasises the need for detailed evaluation of wind characteristics that significantly affect the air quality of urban areas, especially, in large agglomerations. This paper includes analysis of urban wind climatology and estimation of wind profiles based on measurements of the new urban climate station located at the Eötvös University, observations of the meteorological station network of the Budapest agglomeration area, and multi-level wind measurements near Hegyhátsál. Furthermore, wind field modelling (using the WAsP linear spectral wind flow model) is presented over selected representative complex areas that demonstrates strong dependence between wind, height, topography, and roughness.
Strategies for measuring canonical tracer relationships in the stratosphere
Authors: Morgenstern O. , Pyle J. A.
Published: April 2010

Abstract. A high-resolution simulation of stratospheric long-lived trace gases is subsampled in ways resembling various commonly used measurement platforms. The resulting measurements are analyzed with respect to whether they allow an accurate determination of stratospheric tracer relationships, as a prerequisite for a quantification of mixing processes from them. By varying the simulated locations, frequencies, and, in the case of satellite data, accuracies of the measurements we determine minimal requirements that the measurements need to satisfy in order to be suitable for a derivation of tracer relationships.
Atmospheric measurements of gas-phase HNO3 and SO2 using chemical ionization mass spectrometry during the MINATROC field campaign 2000 on Monte Cimone
Authors: Hanke M. , Umann B. , Uecker J. , Arnold F. , Bunz B.
Published: April 2010

Abstract. The EU-project MINATROC (MINeral dust And TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust, a major, but to date largely ignored component of tropospheric aerosol, on tropospheric oxidant cycles. Within the scope of this project continuous atmospheric measurements of gas-phase HNO3 and SO2 were conducted in June and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC) (44° 11' N -- 10° 42' E, 2165 m asl), Italy. African air transporting dust is occasionally advected over the Mediterranean Sea to the site, thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO3 and SO2 were measured with an improved CIMS (chemical ionization mass spectrometry) system for ground-based measurements that was developed and built at MPI-K Heidelberg. Since HNO3 is a very sticky compound special care was paid for the air-sampling and background-measurement system. Complete data sets could be obtained before, during and after major dust intrusions. For the first time these measurements might provide a strong observational indication of efficient uptake of gas-phase HNO3 by atmospheric mineral-dust aerosol particles.
A novel model to predict the physical state of atmospheric H2SO4/NH3/H2O aerosol particles
Authors: Colberg C. A. , Luo B. P. , Wernli H. , Koop T. , Peter Th.
Published: April 2010

Abstract. The physical state of tropospheric aerosol particles is largely unknown despite its importance for cloud formation and for the aerosols' radiative properties. Here we show the first systematic global modelling study of the physical state of the H2SO4/NH3/H2O aerosol, which constitutes an important class of aerosols in the free troposphere. The Aerosol Physical State Model (APSM) developed here is based on Lagrangian trajectories computed from ECMWF (European Centre for Medium Range Weather Forecasts) analyses, taking full account of the deliquescence/efflorescence hysteresis. As input APSM requires three data sets: (i) deliquescence and efflorescence relative humidities from laboratory measurements, (ii) ammonia-to-sulfate ratios (ASR) calculated by a global circulation model, and (iii) relative humidities determined from the ECMWF analyses. APSM results indicate that globally averaged a significant fraction (17-57%) of the ammoniated sulfate aerosol particles contain solids with the ratio of solid-containing to purely liquid particles increasing with altitude (between 2 and 10 km). In our calculations the most abundant solid is letovicite, (NH4)3H(SO4)2, while there is only little ammonium sulfate, (NH4)2SO4. Since ammonium bisulfate, NH4HSO4, does not nucleate homogeneously, it can only form via heterogeneous crystallization. As the ammonia-to-sulfate ratios of the atmospheric aerosol usually do not correspond to the stoichiometries of known crystalline substances, all solids are expected to occur in mixed-phase aerosol particles. This work highlights the global importance of letovicite, whose role as cloud condensation nucleus (CCN) and as scatterer of solar radiation remains to be scrutinized.
Trends and inter-annual variability of methane emissions derived from 1979-1993 global CTM simulations
Authors: Dentener F. , van Weele M. , Krol M. , Houweling S. , van Velthoven P.
Published: April 2010

Abstract. The trend and interannual variability of methane sources are derived from multi-annual simulations of tropospheric photochemistry using a 3D global chemistry-transport model. Our semi-inverse analysis uses the fifteen years (1979 -1993) re-analysis of ECMWF meteorological data and annually varying including photo-chemistry, in conjunction with observed CH4 concentration distributions and trends derived from the NOAA-CMDL surface stations. Dividing the world in four zonal regions, (45-90 N, 0-45 N, 0-45 S; 45-90 S) we find good agreement in each region between (top-down) calculated emission trends from model simulations and (bottom-up) estimated anthropogenic emission trends based on the EDGAR global anthropogenic emission database, which amounts for the period 1979 -1993 2.7 Tg CH4 yr -1. Also the top-down determined total global methane emission compares well with the total of the bottom-up estimates. We use the difference between the bottom-up and top-down determined emission trends to calculate residual emissions. These residual emissions represent the inter-annual variability of the methane emissions. Simulations have been performed in which the year-to-year meteorology, the emissions of ozone precursor gases, and the stratospheric ozone column distribution are either varied, or kept constant. The analyses reveals that the variability of the emissions is of the order of 8 Tg CH4 yr -1, and most likely related to mid- and low-latitude wetland emissions and/or biomass burning. Indeed, a weak correlation is found between the residual emissions and regional scale temperatures.
NAT-rock formation by mother clouds: a microphysical model study
Authors: Fueglistaler S. , Luo B. P. , Voigt C. , Carslaw K. S. , Peter Th.
Published: April 2010

Abstract. Polar stratospheric clouds (PSCs) of type 1a or 1a-enh containing high number densities of nitric acid trihydrate (NAT) particles, can act as mother clouds for extremely large NAT particles, termed NAT-rocks, provided the air below the clouds is supersaturated with respect to NAT. Individual NAT particles at the cloud base fall into undepleted gas phase and rapidly accelerate due to a positive feedback between their growth and sedimentation. The resulting reduction in number density is further enhanced by the strong HNO3 depletion within a thin layer below the mother cloud, which delays subsequent particles. This paper introduces the basic microphysical principles behind this mother cloud/NAT-rock mechanism, which produces 10-4 cm-3 NAT-rocks with radii around 10mm some kilometers below the mother cloud. The mechanism requires neither selective nucleation nor additional atmospheric dilution and works even for a monodisperse particle size distribution in the mother cloud.
Application of the variability-size relationship to atmospheric aerosol studies: estimating aerosol lifetimes and ages
Authors: Williams J. , de Reus M. , Krejci R. , Fischer H. , Ström J.
Published: April 2010

Abstract. Aerosol variability is examined as function of particle size for data collected over the Northern Indian Ocean in February 1999 as part of the INDOEX experiment. It was found that for particles believed to be of terrestrial or oceanic origin, the variability correlated with the average number concentration. For particles that are thought to be formed and grow in the atmosphere through coagulation and condensation an anticorrelation was observed, the minimum in variability coinciding with the maximum in the number concentration. Three altitude ranges were examined (0 --1, 4 -- 8 and 8 --13 km) and the minimum in variability was found to occur at lower particle sizes in the free troposphere (0.065 mm) than in the boundary layer (0.165 mm). The observed variability has been compared to that generated by a numerical model in order to determine the relative importance of the physical processes. Modelled variability of 0.02 mm particles caused by nucleation was not observed in the measurements. A previously derived empirical relationship for aerosol residence time was compared with the measured variability as a function of bin size. The aerosol variability / residence time relationship was characterised by a coefficient (b) at all altitudes and for both correlating and anticorrelating regimes. By combining the derived coefficient with the model predicted lifetime for 0.020 mm particles we estimated residence times and ages as a function of particle size and altitude. General agreement was found with previous estimates of aerosol residence time. In the upper atmosphere aerosols of 0.065 mm in size have residence times of approximately 1 month and can be transported on a hemispheric scale. The same size aerosol has a lifetime one order of magnitude less in the boundary layer and therefore will not be transported far from the source regions.
Redistribution of trace gases by convective clouds – mixed-phase processes
Authors: Yin Y. , Carslaw K. S. , Parker D. J.
Published: April 2010

Abstract. The efficiency of gas transport to the free and upper troposphere in convective clouds is investigated in an axisymmetric dynamic cloud model with detailed microphysics. In particular, we examine the sensitivity of gas transport to the treatment of gas uptake by different ice hydrometeors. Two parameters are used to describe this uptake. The gas retention coefficient defines the fraction of dissolved gas that is retained in an ice particle upon freezing, which includes also the riming process. We also define a gas burial efficiency defining the amount of gas entrapped in ice crystals growing by vapour diffusion. Model calculations are performed for continental and maritime clouds using a complete range of gas solubilities, retention coefficients and burial efficiencies. The results show that the magnitude of the gas retention coefficient is much more important for gas transport in maritime clouds than in continental clouds. The cause of this difference lies in the different microphysical processes dominating the formation and evolution of hydrometeors in the two cloud types. For highly soluble gases, the amount of gas transported to the free troposphere in maritime clouds falls approximately linearly by a factor of 12 as the retention coefficient is varied between 0 and 1. Gas transport is relatively insensitive to the magnitude of the gas burial efficiency. However, the burial efficiency strongly controls the concentration of trace gases inside anvil ice crystals, which subsequently form cirrus clouds.
Dynamics and chemistry of vortex remnants in late Arctic spring 1997 and 2000: Simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS)
Authors: Konopka P. , Grooß J.-U. , Bausch S. , Müller R. , McKenna D. S. , Morgenstern O. , Orsolini Y.
Published: April 2010

Abstract. High resolution simulations of the chemical composition of the Arctic stratosphere during late spring 1997 and 2000 have been conducted with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations were performed for the entire northern hemisphere on two isentropic levels 450 K (~18 km) and 585 K (~24 km). The spatial distribution and the lifetime of the vortex remnants formed after the vortex breakup in May 1997 show a completely different behavior above and below 20 km. Above 20 km, vortex remnants effectively propagate southward (up to 40° N) and are "frozen'' in the summer circulation without significant mixing. Below 20 km the southward propagation of the remnants is bounded by the subtropical jet near 55° N. Their lifetime is shorter by a factor of 2 than above 20 km, owing to significant stirring below this altitude. The behavior of vortex remnants formed in March 2000 is similar but, due to an earlier vortex breakup, dominated until mid of May by westerly winds, even above 20 km. Vortex remnants formed in May 1997 are characterized by large mixing ratios of HCl indicating a negligible contribution of the halogen-induced ozone loss. In contrast, mid-latitude ozone loss in late boreal spring 2000 is dominated by an irreversible transport of the ozone-depleted polar air masses (dilution) and, until mid of April, by halogen-induced ozone destruction within the vortex remnants. By varying the effective diffusivity of CLaMS, the impact of mixing on the formation of ClONO2 and ozone depletion is considered. In particular, the photochemical decomposition of HNO3 and not mixing with NOx-rich mid-latitude air is the main source of NOx within the vortex remnants in March and April 2000. Ozone depletion in the remnants is driven by ClOx photolytically formed from ClONO2 and can be properly resolved for CLaMS spatial resolution better then 100\\,km. At 450 K, ozone loss in the vortex remnants contributes by ~2% to the ozone deficit poleward of 30° N.
Chemical characteristics assigned to trajectory clusters during the MINOS campaign
Authors: Traub M. , Fischer H. , de Reus M. , Kormann R. , Heland J. , Ziereis H. , Schlager H. , Holzinger R. , Williams J. , Warneke C. , de Gouw J. , Lelieveld J.
Published: April 2010

Abstract. During the Mediterranean Intensive Oxidant Study (MINOS) in August 2001 a total of 14 measurement flights were performed with the DLR Falcon aircraft from Heraklion, Crete. One objective of this campaign was to investigate the role of long-range transport of pollutants into the Mediterranean area. An analysis of 5-day back trajectories indicates that in the lower troposphere (0–4 km) air masses originated from eastern and western Europe, in the mid-troposphere (4–8 km) from the Atlantic Ocean region and in the upper troposphere (8–14 km) from North Artlantic Ocean/North America  (NAONA) as well as South Asia. We allocated all back trajectories to clusters based on their ending height and source region. The mixing ratios of ozone, nitrogen oxide, total reactive oxidized nitrogen (NOy), formaldehyde, methanol, acetonitrile, acetone, peroxyacetyl nitrate (PAN), carbon dioxide, carbon monoxide and methane measured along the flight tracks are examined in relation to the different cluster trajectories. In the lower troposphere the mean gas mixing ratios of the eastern Europe cluster trajectories were significantly higher than that from western Europe. Considering 2-day instead of 5-day trajectories the relative differences between the concentrations of these two clusters increased. In the upper troposphere relatively high concentrations of  O3 and NOy, combined with low CO of the NAONA trajectories indicate mixing with stratospheric air masses.
GC×&GC measurements of C7–C11 aromatic and n-alkane hydrocarbons on Crete, in air from Eastern Europe during the MINOS campaign
Authors: Xu X. , Williams J. , Plass-Dülmer C. , Berresheim H. , Salisbury G. , Lange L. , Lelieveld J.
Published: April 2010

Abstract. During the Mediterranean Intensive Oxidant Study (MINOS) campaign in August 2001 gas-phase organic compounds were measured using comprehensive two-dimensional gas chromatography (GC×GC) at the Finokalia ground station, Crete. In this paper, C7–C11 aromatic and n-alkane measurements are presented and interpreted. The mean mixing ratios of the hydrocarbons varied from 1+/−1 pptv (i-propylbenzene) to 43+/−36 pptv (toluene). The observed mixing ratios showed strong day-to-day variations and generally higher levels during the first half of the campaign. Mean diel profiles showed maxima at local midnight and late morning, and minima in the early morning and evening. Results from analysis using a simplified box model suggest that both the chemical sink (i.e. reaction with OH) and the variability of source strengths were the causes of the observed variations in hydrocarbon mixing ratios. The logarithms of hydrocarbon concentrations were negatively correlated with the OH concentrations integral over a day prior to the hydrocarbon measurements. Slopes of the regression lines derived from these correlations for different compounds are compared with literature rate constants for their reactions with OH. The slopes for most compounds agree reasonably well with the literature rate constants. A sequential reaction model has been applied to the interpretation of the relationship between ethylbenzene and two of its potential products, i.e. acetophenone and benzeneacetaldehyde. The model can explain the good correlation observed between [acetophenone]/[ethylbenzene] and [benzeneacetaldehyde]/[ethylbenzene]. The model results and field measurements suggest that the reactivity of benzeneacetaldehyde may lie between those of acetophenone and ethylbenzene and that the ratio between yields of acetophenone and benzeneacetaldehyde may be up to 28:1. Photochemical ages of trace gases sampled at Finokalia during the campaign are estimated using the sequential reaction model and related data. They lie in the range of about 0.5–2.5 days.
Ultrathin Tropical Tropopause Clouds (UTTCs): I. Cloud morphology and occurrence
Authors: Peter T. , Luo B. P. , Wernli H. , Wirth M. , Kiemle C. , Flentje H. , Yushkov V. A. , Khattatov V. , Rudakov V. , Thomas A. , Borrmann S. , Toci G. , Mazzinghi P. , Beuermann J. , Schiller C. , Cairo F. , Di Don-francesco G. , Mazzinghi P. , Beuermann J. , Schiller C. , Cairo F. , Di Don-francesco G. , Adriani A. , Volk C. M. , Strom J. , Noone K. , Mitev V. , MacKenzie R. A. , Carslaw K. S. , Trautmann T. , Santacesaria V. , Stefanutti L.
Published: April 2010

Abstract. Subvisible cirrus clouds (SVCs) may contribute to dehydration close to the tropical tropopause. The higher and colder SVCs and the larger their ice crystals, the more likely they represent the last efficient point of contact of the gas phase with the ice phase and, hence, the last dehydrating step, before the air enters the stratosphere. The first simultaneous in situ and remote sensing measurements of SVCs were taken during the APE-THESEO campaign in the western Indian ocean in February/March 1999. The observed clouds, termed Ultrathin Tropical Tropopause Clouds (UTTCs), belong to the geometrically and optically thinnest large-scale clouds in the Earth's atmosphere. Individual UTTCs may exist for many hours as an only 200–300 m thick cloud layer just a few hundred meters below the tropical cold point tropopause, covering up to 105 km2. With temperatures as low as 181 K these clouds are prime representatives for defining the water mixing ratio of air entering the lower stratosphere.
Origin of anthropogenic hydrocarbons and halocarbons measured in the summertime European outflow (on Crete in 2001)
Authors: Gros V. , Williams J. , van Aardenne J. A. , Salisbury G. , Hofmann R. , Lawrence M. G. , von Kuhlmann R. , Lelieveld J. , Krol M. , Berresheim H. , Lobert J. M. , Atlas E.
Published: April 2010

Abstract. During the Mediterranean Intensive Oxidant Study MINOS in August 2001, 87 air samples were collected at the ground-based station Finokalia (35° 19' N, 25° 40' E) on the north coast of Crete and subsequently analysed by GC-MS. The analysis includes various hydrocarbons, organo-halogens, HCFCs and CFCs. These compounds have a wide variety of sources and sinks and a large range of atmospheric lifetimes. By plotting the measured variability of these species against lifetime, we found that the compounds describe a linear relationship. It is shown, based on air mass origin analysis and chemical ratios, that several distinct anthropogenic sources influenced the atmospheric composition in Crete. Propane observations are compared to a global model to assess the fossil fuel related emission inventory. Although the model reproduces the general pattern of the propane variations, the model mixing ratios are systematically too low by a factor of 1.5 to 3, probably due to an underestimation of the propane emissions from east European countries in the underlying global database EDGAR. Another important finding was that methyl chloroform, a compound banned under the Montreal protocol, showed significant enhancements from background, which were well correlated with CFC-113. This suggests continued use and emission of methyl chloroform by one or more European countries. We also discuss the observed variations of bromomethane and suggest that the significant peak observed on 12 August 2001 reflects heavy agricultural use as a soil fumigant in Italy.
Climatological aspects of aerosol optical properties in Northern Greece
Authors: Gerasopoulos E. , Andreae M. O. , Zerefos C. S. , Andreae T. W. , Balis D. , Formenti P. , Merlet P. , Amiridis V. , Papastefanou C.
Published: April 2010

Abstract. Measurements of aerosol optical properties (aerosol optical depth, scattering and backscattering coefficients) have been conducted at two ground-based sites in Northern Greece, Ouranoupolis (40° 23' N, 23° 57 E, 170 m a.s.l.) and Thessaloniki (40° 38' N, 22° 57 E, 80 m a.s.l.), between 1999 and 2002. Their frequency distributions have revealed the presence of individual modes of high and low values, indicating the influence from different sources. At both sites, the mean aerosol optical depth at 500 nm was 0.23. Values increase considerably during summer when they remain persistently between 0.3 and 0.5, going up to 0.7–0.8 during specific cases. The mean value of 65±40 Mm−1 of the particle scattering coefficient at 550 nm reflects the impact of continental pollution in the regional boundary layer. Trajectory analysis has shown that higher values of aerosol optical depth and the scattering coefficient are found in the east sector (former Soviet Union countries, eastern Balkan countries), whereas cleaner conditions are found for the NW direction. The influence of Sahara dust events is clearly reflected in the Angström exponents. About 45–60% of the observed diurnal variation of the optical properties was attributed to the growth of aerosols with humidity, while the rest of the variability is in phase with the evolution of the sea-breeze cell. Local pollution is estimated to contribute 35±10% to the average aerosol optical depth at the Thessaloniki site during summer. Finally, the aerosol scale height was found to be related to the height of the boundary layer with values between 0.5–1 km during winter and up to 2.5–3 km during summer.
Trace elements in South America aerosol during 20th century inferred from a Nevado Illimani ice core, Eastern Bolivian Andes (6350 m a.s.l.)
Authors: Correia A. , Freydier R. , Delmas R. J. , Simões J. C. , Taupin J.-D. , Dupré B. , Artaxo P.
Published: April 2010

Abstract. A 137 m ice core drilled in 1999 from Eastern Bolivian Andes at the summit of Nevado Illimani (16° 37' S, 67° 46' W, 6350 m a.s.l.) was analyzed at high temporal resolution, allowing a characterization of trace elements in Andean aerosol trapped in the ice during the 20th century. The upper 50 m of the ice core were dated by multi-proxy analysis of stable isotopes (d18O and d2H), 137Cs and Ca+2 content, electrical conductivity, and insoluble microparticle content, together with reference historical horizons from atmospheric nuclear tests and known volcanic eruptions. This 50 m section corresponds to a record of environmental variations spanning about 80 years from 1919 to 1999. It was cut in 744 sub-samples under laminar flow in a clean bench, which were analyzed by Ion Chromatography for major ionic concentration, by a particle counter for insoluble aerosol content, and by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for the concentration of 45 chemical species from Li to U. This paper focuses on results of trace element concentrations measured by ICP-MS. The high temporal resolution used in the analyses allowed classifying samples as belonging to dry or wet seasons. During wet season elemental concentrations are low and samples show high crustal enrichment factors. During dry seasons the situation is opposite, with high elemental concentrations and low crustal enrichments. For example, with salt lakes as main sources in the region, average Li concentration during the 20th century is 0.035 and 0.90 ng g−1 for wet and dry seasons, respectively. Illimani average seasonal concentration ranges cover the spectrum of elemental concentration measurements at another Andean ice core site (Sajama) for most soil-related elements. Regional crustal dust load in the deposits was found to be overwhelming during dry season, obfuscating the contribution of biomass burning material. Marked temporal trends from the onset of 20th century to more recent years were identified for the concentrations of several trace species of anthropic origin, especially for Cu, As, Zn, Cd, Co, Ni and Cr. Among these elements, Cu shows average wet season crustal enrichment factors above 103, while the others range between 102 to about 5×102. P and K show moderate average wet season enrichment factors, suggesting an impact of natural biogenic emissions from the Amazon Basin. Pb has multiple anthropic sources in the region, from mining activities in the beginning of 20th century to automotive fuel after 1950's. From the large number of samples analyzed from Illimani, it was possible to derive an effective chemical characterization of the deposited background Andean soil dust aerosol during 20th century.
Detailed modeling of mountain wave PSCs
Authors: Fueglistaler S. , Buss S. , Luo B. P. , Wernli H. , Flentje H. , Hostetler C. A. , Poole L. R. , Carslaw K. S. , Peter T.
Published: April 2010

Abstract. Polar stratospheric clouds (PSCs) play a key role in polar ozone depletion. In the Arctic, PSCs can occur on the mesoscale due to orographically induced gravity waves. Here we present a detailed study of a mountain wave PSC event on 25–27 January 2000 over Scandinavia. The mountain wave PSCs were intensively observed by in-situ and remote-sensing techniques during the second phase of the SOLVE/THESEO-2000 Arctic campaign. We use these excellent data of PSC observations on 3 successive days to analyze the PSCs and to perform a detailed comparison with modeled clouds. We simulated the 3-dimensional PSC structure on all 3 days with a mesoscale numerical weather prediction (NWP) model and a microphysical box model (using state-of-the-art nucleation rates for ice and nitric acid trihydrate particles). We show that the combined mesoscale/microphysical model is capable to reproduce the PSC measurements within the uncertainty of data interpretation with respect to spatial dimensions, temporal development and microphysical properties, without manipulating temperatures or using other tuning parameters. In contrast, microphysical modeling based upon coarser scale global NWP data, e.g. current ECMWF analysis data, cannot reproduce observations, in particular the occurrence of ice and nitric acid trihydrate clouds. Combined mesoscale/microphysical modeling may be used for detailed a posteriori PSC analysis and for future Arctic campaign flight and mission planning. The fact that remote sensing alone cannot further constrain model results due to uncertainities in the interpretation of measurements, underlines the need for synchronous in-situ PSC observations in campaigns.
Size resolved mass concentration and elemental composition of atmospheric aerosols over the eastern Mediterranean area
Authors: Smolik J. , Ždimal V. , Schwarz J. , Lazaridis M. , Havránek V. , Eleftheriadis K. , Mihalopoulos N. , Bryant C. , Colbeck I.
Published: April 2010

Abstract. A Berner low pressure impactor was used to collect size-segregated aerosol samples at Finokalia, located on the north-eastern coast of Crete, Greece during July 2000 and January 2001. Several samples were also collected during the summer campaign aboard the research vessel "AEGAIEO" in the Aegean Sea. Gravimetric analysis and inversion techniques yielded daily PM1 and PM10 mass concentrations. Further, the samples were analysed by PIXE giving elemental size distributions of Al, Si, K, Ca, Ti, Mn, Fe, Sr, S, Cl, Ni, V, Cu, Cr, Zn, and Pb. The crustal elements and sea-salt had a unimodal supermicron size distribution. Sulphur was found predominantly in submicron fractions. K, V, and Ni exhibited bimodal distribution with a submicron mode produced by forest fires and oil combustion. The anthropogenic elements had broad and not well-defined distributions. The time series for PM1 and PM10 mass and elemental concentrations showed both daily and seasonal variation. Higher mass concentrations were observed during two incursions of Saharan dust. Higher concentrations of S, Cu, Zn, and Pb were encountered in samples collected in air masses arriving from northern Greece or the western coast of Turkey. Higher concentrations of chlorine were found in samples with air masses either originating above the Atlantic Ocean and arriving at Finokalia via western Europe or recirculating over the western coast of the Black Sea.
Validation of a 3-D hemispheric nested air pollution model
Authors: Frohn L. M. , Christensen J. H. , Brandt J. , Geels C. , Hansen K. M.
Published: April 2010

Abstract. Several air pollution transport models have been developed at the National Environmental Research Institute in Denmark over the last decade (DREAM, DEHM, ACDEP and DEOM). A new 3-D nested Eulerian transport-chemistry model: REGIonal high resolutioN Air pollution model (REGINA) is based on modules and parameterisations from these models as well as new methods. The model covers the majority of the Northern Hemisphere with currently one nest implemented. The horizontal resolution in the mother domain is 150 km × 150 km, and the nesting factor is three. A chemical scheme (originally 51 species) has been extended with a detailed description of the ammonia chemistry and implemented in the model. The mesoscale numerical weather prediction model MM5v2 is used as meteorological driver for the model. The concentrations of air pollutants, such as sulphur and nitrogen in various forms, have been calculated, applying zero nesting and one nest. The model setup is currently being validated by comparing calculated values of concentrations to measurements from approximately 100 stations included in the European Monitoring and Evalutation Programme (EMEP). The present paper describes the physical processes and parameterisations of the model together with the modifications of the chemical scheme. Validation of the model calculations by comparison to EMEP measurements for a summer and a winter month is shown and discussed. Furthermore, results from a sensitivity study of the model performance with respect to resolution in emission and meteorology input data is presented. Finally the future prospects of the model are discussed. The overall validation shows that the model performs well with respect to correlation for both monthly and daily mean values.