bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional characteristics of spring Asian dust and its impact on aerosol chemistry over northern China
Authors: Sun Y. L. , Zhuang G. S. , Wang Z. F. , Wang Y. , Zhang W. J. , Tang A. H. , Zhao X. J. , Jia L.
Published: April 2010

Abstract. TSP and PM2.5 aerosol samples were synchronously collected at six sites along the transport pathway of dust storm from desert regions to coastal areas in the spring of 2004. The aerosol concentration and composition were measured to investigate the regional characteristics of spring Asian dust and its impact on aerosol chemistry over northern China. Based on the daily PM10 concentrations in 13 cities, the northern China could be divided into five regions, i.e., Northern Dust Region, Northeastern Dust Region, Western Dust Region, Inland Passing Region, and Coastal Region. Northern Dust Region was characterized by high content of Ca and Northeastern Dust Region was characterized by low one instead. Northeastern Dust Region was a relatively clean area with the lowest concentrations of pollutants and secondary ions among all sites. Inland Passing Region and Coastal Region showed high concentrations of pollutants, of which As and Pb in Inland Passing Region, and Na+, SO42− and NO3− in Coastal Region were the highest, respectively. The impact of dust on air quality was the greatest in the cities near source regions, and this impact decreased in the order of Yulin/Duolun > Beijing > Qingdao/Shanghai as the increase of transport distance. The spring Asian dust was inclined to affect the chemical components in coarse particles near source regions and those in fine particles in the cities far from source regions. Dust storm could mix significant quantities of pollutants on the pathway and carry them to the downwind cities or dilute the pollutants in the cities over northern China. Each dust episode corresponded to a low ratio of NO3−/SO42− with the lowest value appearing after the peak of dust storm. Asian dust played an important role in buffering and neutralizing the acidity of atmosphere in the cities over northern China, which could lead to the pH in the aerosols increase ~1 in spring.
ENSO surface longwave radiation forcing over the tropical Pacific
Authors: Pavlakis K. G. , Hatzidimitriou D. , Drakakis E. , Matsoukas C. , Fotiadi A. , Hatzianastassiou N. , Vardavas I.
Published: April 2010

Abstract. We have studied the spatial and temporal variation of the surface longwave radiation (downwelling and net) over a 21-year period in the tropical and subtropical Pacific Ocean (40 S–40 N, 90 E–75 W). The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite data from the ISCCP-D2 database and reanalysis data from NCEP/NCAR (acronyms explained in main text), for the key atmospheric and surface input parameters. An excellent correlation was found between the downwelling longwave radiation (DLR) anomaly and the Niño-3.4 index time-series, over the Niño-3.4 region located in the central Pacific. A high anti-correlation was also found over the western Pacific (15–0 S, 105–130 E). There is convincing evidence that the time series of the mean downwelling longwave radiation anomaly in the western Pacific precedes that in the Niño-3.4 region by 3–4 months. Thus, the downwelling longwave radiation anomaly is a complementary index to the SST anomaly for the study of ENSO events and can be used to asses whether or not El Niño or La Niña conditions prevail. Over the Niño-3.4 region, the mean DLR anomaly values range from +20 Wm−2 during El Niño episodes to –20 Wm−2 during La Niña events, while over the western Pacific (15–0 S, 105–130 E) these values range from –15 Wm−2 to +10 Wm−2, respectively. The long- term average (1984–2004) distribution of the net surface longwave radiation to the surface over the tropical and subtropical Pacific for the three month period November-December-January shows a net thermal cooling of the ocean surface. When El Niño conditions prevail, the thermal radiative cooling in the central and south-eastern tropical Pacific becomes weaker by 10 Wm−2 south of the equator in the central Pacific (7–0 S, 160–120 W) for the three-month period of NDJ, because the DLR increase is larger than the increase in surface thermal emission. In contrast, the thermal radiative cooling over Indonesia is enhanced by 10 Wm−2 during the early (August–September–October) El Niño phase.
Radiation budget estimates over Africa and surrounding oceans: inter-annual comparisons
Authors: Ben Rehouma A. , Viollier M. , Desbois M.
Published: April 2010

Abstract. Three independent datasets of Radiation Budget at the top of the atmosphere (TOA) spanning two decades are compared: the Scanner Narrow Field of View data (from ERBE, ScaRaB, and CERES instruments, 1985–2005), the ERBS Nonscanner Wide Field of View data (1985–1998) and the simulated broadband fluxes from the International Satellite Cloud Climatology Project (ISCCP-FD, 1983–2004). The analysis concerns the shortwave (SW) reflected flux, the longwave (LW) emitted flux and the net flux at the Top Of the Atmosphere (TOA) over Africa and the surrounding oceans (45° S–45° N/60° W–60° E), a region particularly impacted by climate variability. For each month, local anomalies are computed with reference to the average over this large region, and their differences between the 2002–2005 and 1985–1989 periods are analysed. These anomalies are relative values and are mostly independent on the absolute observed trends (about 2.5 Wm−2 per decade) which may be affected by possible calibration drifts. Large inter-annual variations are observed locally. Over a part of the South East Atlantic (35°–10° S/10° W–10° E), including the marine low cloud area off Angola, there is a decrease of the yearly means of net flux estimated to 2.2, 3 and 6 Wm−2 respectively for the Scanner, Nonscanner and ISCPP-FD data. Over a narrow strip of the Sahel Zone, the net flux increases by about 5 Wm−2.
A parameterization of size resolved below cloud scavenging of aerosols by rain
Authors: Henzing J. S. , Olivié D. J. L. , Van Velthoven P. F. J.
Published: April 2010

Abstract. A size dependent parameterization for the removal of aerosol particles by falling rain droplets is developed. Scavenging coefficients are calculated explicitly as a function of aerosol particle size and precipitation intensity including the full interaction of rain droplet size distribution and aerosol particles. The actual parameterization is a simple and accurate three-parameter fit through these pre-calculated scavenging coefficients. The parameterization is applied in the global chemistry transport model TM4 and the importance of below-cloud scavenging relative to other removal mechanisms is investigated for sea salt aerosol. For a full year run (year 2000), we find that below-cloud scavenging accounts for 12% of the total removal of super-micron aerosol. At mid-latitudes of both hemispheres the fractional contribution of below-cloud scavenging to the total removal of super-micron sea salt is about 30% with regional maxima exceeding 50%. Below-cloud scavenging reduces the global average super-micron aerosol lifetime from 2.47 to 2.16 days in our simulations. Despite large uncertainties in precipitation, relative humidity, and water uptake by aerosol particles, we conclude that below cloud scavenging is likely an important sink for super-micron sized sea salt aerosol particles that needs to be included in size-resolved aerosol models.
Integrated systems for forecasting urban meteorology, air pollution and population exposure
Authors: Baklanov A. , Hänninen O. , Slørdal L. H. , Kukkonen J. , Bjergene N. , Fay B. , Finardi S. , Hoe S. C. , Jantunen M. , Karppinen A. , Rasmussen A. , Skouloudis A. , Sokhi R. S. , Sørensen J. H.
Published: April 2010

Abstract. Urban air pollution is associated with significant adverse health effects. Model-based abatement strategies are required and developed for the growing urban populations. In the initial development stage, these are focussed on exceedances of air quality standards caused by high short-term pollutant concentrations. Prediction of health effects and implementation of urban air quality information and abatement systems require accurate forecasting of air pollution episodes and population exposure, including modelling of emissions, meteorology, atmospheric dispersion and chemical reaction of pollutants, population mobility, and indoor-outdoor relationship of the pollutants. In the past, these different areas have been treated separately by different models and even institutions. Progress in computer resources and ensuing improvements in numerical weather prediction, air chemistry, and exposure modelling recently allow a unification and integration of the disjunctive models and approaches. The current work presents a novel approach that integrates the latest developments in meteorological, air quality, and population exposure modelling into Urban Air Quality Information and Forecasting Systems (UAQIFS) in the context of the European Union FUMAPEX project. The suggested integrated strategy is demonstrated for examples of the systems in three Nordic cities: Helsinki and Oslo for assessment and forecasting of urban air pollution and Copenhagen for urban emergency preparedness.
Retrieval of cloud spherical albedo from top-of-atmosphere reflectance measurements performed at a single observation angle
Authors: Kokhanovsky A. , Mayer B. , von Hoyningen-Huene W.
Published: April 2010

Abstract. The paper is devoted to the derivation of the simple analytical relationship between the cloud spherical albedo and the cloud reflection function. The relationship obtained can be used for the derivation of the spherical albedo from backscattered solar light measurements performed by radiometers on geostationary and polar orbiting satellites. The example of the application of the technique to MODIS data is shown.
Remote sensing of cirrus clouds and aerosols by a sun photometer in Tunisia
Authors: Chtioui H. , Mansour F. B. , Elouragini S. , Flamant P. H.
Published: April 2010

Abstract. Some ground based measurements of solar radiation by using a sun photometer, have been conducted in Tunisia during the period of November 2000–February 2002. Five key measurement sites were selected: Three Sites (Tunis, Sousse, Gabes) are located on the Mediterranean coast and Two sites (Gafsa, Tozeur) on the boarder of Sahara. Over a total of 149 measurement days, 21 days are identified as clear sky, 114 days as Cirrus clouds and 14 days as aerosols. Aerosols and Cirrus clouds Optical Thickness (AOT) are derived from photometric measurements at 532 nm wavelength. Spatial and temporal variabilities of AOT are presented and discussed in this paper. Cirrus clouds were frequently observed at Gafsa and Tozeur where saharan aerosol events are expected to be more frequent than cirrus clouds. The mediterranean sea and saharan aerosols are suspected to have the main role in cirrus clouds formation, by providing water vapor and high concentrations of cloud condensation and ice forming nuclei.
Vehicular fuel composition and atmospheric emissions in South China: Hong Kong, Macau, Guangzhou, and Zhuhai
Authors: Tsai W. Y. , Chan L. Y. , Blake D. R. , Chu K. W.
Published: April 2010

Abstract. Vehicular emission is an important source of air pollutants in urban cities in the Pearl River Delta (PRD) region of South China. In order to study the impact of vehicular fuel on air quality, several commonly used fuel samples were collected in four main cities in the PRD region – Hong Kong, Guangzhou, Macau and Zhuhai, and analyzed for their volatile organic compounds (VOCs) composition. Source profiles of the vehicular fuels used in these cities were constructed and are believed to be the first reported for the PRD region. The C8–C10 hydrocarbons were the main constituents of diesel. Different from diesel, gasoline used in the PRD region was mainly comprised of lighter C4–C7 hydrocarbons, with toluene and i-pentane being the two most abundant species. The benzene content in the Guangzhou and Zhuhai gasoline samples were higher than that in Hong Kong and Macau and exceeded the maximum benzene levels for Mainland China unleaded gasoline. Liquefied Petroleum Gas (LPG) samples were collected only in Hong Kong and were comprised mainly of n-butane, propane and i-butane. Traffic samples indicated that evaporative loss and vehicular combustion were the primary contributors to elevated VOC levels in roadside atmospheres. Significant i-pentane and toluene concentrations were observed in roadside atmospheres in all four cities. Ratio of i-pentane in gasoline samples to that in roadside samples were calculated and this showed that the degree of evaporative loss was higher in Guangzhou and Zhuhai than that in Hong Kong and Macau. We suggest the difference is due to the better maintenance and more new cars in Hong Kong and Macau. From tunnel samples collected in Hong Kong in two different years, we found that the relative amount of propane, i-butane, and n-butane increased between 2001 to 2003, consistent with the 40% increase in LPG fueled vehicles. Propane to butanes ratios were calculated for LPG and tunnels samples, and the comparable ratios illustrated the LPG leakages from LPG fueled vehicles crossing the tunnel.
Aerosol composition and source apportionment in the Mexico City Metropolitan Area with PIXE/PESA/STIM and multivariate analysis
Authors: Johnson K. S. , de Foy B. , Zuberi B. , Molina L. T. , Molina M. J. , Xie Y. , Laskin A. , Shutthanandan V.
Published: April 2010

Abstract. Aerosols play an important role in the atmosphere but are poorly characterized, particularly in urban areas like the Mexico City Metropolitan Area (MCMA). The chemical composition of urban particles must be known to assess their effects on the environment, and specific particulate emissions sources should be identified to establish effective pollution control standards. For these reasons, samples of particulate matter ≤2.5 μm (PM2.5) were collected during the MCMA-2003 Field Campaign for elemental and multivariate analyses. Proton-Induced X-ray Emission (PIXE), Proton-Elastic Scattering Analysis (PESA) and Scanning Transmission Ion Microscopy (STIM) techniques were done to determine concentrations of 19 elements from Na to Pb, hydrogen, and total mass, respectively. The most abundant elements from PIXE analysis were S, Si, K, Fe, Ca, and Al, while the major emissions sources associated with these elements were industry, wind-blown soil, and biomass burning. Wind trajectories suggest that metals associated with industrial emissions came from northern areas of the city whereas soil aerosols came from the southwest and increased in concentration during dry conditions. Elemental markers for fuel oil combustion V and Ni correlated with a large SO2 plume to suggest an anthropogenic, rather than volcanic, emissions source. By subtracting major components of soil and sulfate determined by PIXE analysis from STIM total mass measurements, we estimate that approximately 50% of non-volatile PM2.5 consisted of carbonaceous material.
The effect of sensor resolution on the number of cloud-free observations from space
Authors: Krijger J. M. , van Weele M. , Aben I. , Frey R.
Published: April 2010

Abstract. Air quality and surface emission inversions are likely to be focal points for future satellite missions on atmospheric composition. Most important for these applications is sensitivity to the atmospheric composition in the lowest few kilometers of the troposphere. Reduced sensitivity by clouds needs to be minimized. In this study we have quantified the increase in number of useful footprints, i.e. footprints which are sufficient cloud-free, as a function of sensor resolution (footprint area). High resolution (1 km×1 km) MODIS TERRA cloud mask observations are aggregated to lower resolutions. Statistics for different thresholds on cloudiness are applied. For each month in 2004 two days of MODIS data are analyzed. Globally the fraction of cloud-free observations drops from 16% at 100 km2 resolution to only 3% at 10 000 km2 if not a single MODIS observation within a footprint is allowed to be cloudy. If up to 5% or 20% of a footprint is allowed to be cloudy, the fraction of cloud-free observations is 9% or 17%, respectively, at 10 000 km2 resolution. The probability of finding cloud-free observations for different sensor resolutions is also quantified as a function of geolocation and season, showing examples over Europe and northern South America.
Variability of organic and elemental carbon, water soluble organic carbon, and isotopes in Hong Kong
Authors: Ho K. F. , Lee S. C. , Cao J. J. , Li Y. S. , Chow J. C. , Watson J. G. , Fung K.
Published: April 2010

Abstract. To determine the levels and variations of carbonaceous aerosol in Hong Kong, PM2.5 and PM10 samples were collected by high volume (Hi-vol) samplers at three monitoring stations (representing middle-scale roadside, urban-, and regional-scale environments) during winter (November 2000 to February 2001) and summer (June 2001 to August 2001) periods. The highest concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were found at the middle-scale roadside site with the lowest at the regional-scale site. The percentages of WSOC in total carbon at these sites were inversely correlated with their concentrations (i.e., the highest percentages of WSOC were observed at the regional-scale site). A high WSOC fraction may be associated with aged aerosol because of the secondary formation by photochemical oxidation of organic precursors of anthropogenic pollutants during transport. The annual average of isotope abundances (δ13C) of OC and EC were –26.9±0.5 and –25.6±0.1, respectively. There were no notable differences for seasonal distributions of carbon isotopic composition, consistent with motor vehicle emissions being the main source contributors of carbonaceous aerosol in Hong Kong. OC 13C abundances at the regional-scale site were higher than those at the middle-scale roadside and urban sites, consistent with secondary organic aerosols of biogenic origin.
Some experimental constraints for spectral parameters used in the Warner and McIntyre gravity wave parameterization scheme
Authors: Ern M. , Preusse P. , Warner C. D.
Published: April 2010

Abstract. In order to incorporate the effect of gravity waves (GWs) on the atmospheric circulation most global circulation models (GCMs) employ gravity wave parameterization schemes. To date, GW parameterization schemes in GCMs are used without experimental validation of the set of global parameters assumed for the GW launch spectrum. This paper focuses on the Warner and McIntyre GW parameterization scheme. Ranges of parameters compatible with absolute values of gravity wave momentum flux (GW-MF) derived from CRISTA-1 and CRISTA-2 satellite measurements are deduced for several of the parameters and the limitations of both model and measurements are discussed. The findings presented in this paper show that the initial guess of spectral parameters provided by Warner and McIntyre (2001) are some kind of compromise with respect to agreement of absolute values and agreement of the horizontal structures found in both measurements and model results. Better agreement can be achieved by using a vertical wavenumber launch spectrum with a wider saturated spectral range and reduced spectral power in the unsaturated part. Still, even global features of the measurements remain unmatched, and it is inevitable to provide a globally varying source distribution in future.
Measurement-based modeling of bromine chemistry in the boundary layer: 1. Bromine chemistry at the Dead Sea
Authors: Tas E. , Peleg M. , Pedersen D. U. , Matveev V. , Pour Biazar A. , Luria M.
Published: April 2010

Abstract. The Dead Sea is an excellent natural laboratory for the investigation of Reactive Bromine Species (RBS) chemistry, due to the high RBS levels observed in this area, combined with anthropogenic air pollutants up to several ppb. The present study investigated the chemical mechanism of RBS at the Dead Sea using a numerical one-dimensional chemical model. Simulations were based on data obtained from comprehensive measurements performed at sites along the Dead Sea. The simulations showed that the high BrO levels measured frequently at the Dead Sea could only partially be attributed to the highly concentrated Br− present in the Dead Sea water. Further, the RBS activity at the Dead Sea cannot solely be explained by a pure gas phase mechanism. This paper presents a chemical mechanism which can account for the observed chemical activity at the Dead Sea, with the addition of only two heterogeneous processes: the "Bromine Explosion" mechanism and the heterogeneous decomposition of BrONO2. Ozone frequently dropped below a threshold value of ~1 to 2 ppbv at the Dead Sea evaporation ponds, and in such cases, O3 became a limiting factor for the production of BrOx (BrO+Br). The entrainment of O3 fluxes into the evaporation ponds was found to be essential for the continuation of RBS activity, and to be the main reason for the positive correlation observed between BrO and O3 at low O3 concentrations, and for the jagged diurnal pattern of BrO observed in the Dead Sea area. The present study has shown that the heterogeneous decomposition of BrONO2 has the potential to greatly affect the RBS activity in areas under anthropogenic influence, mainly due to the positive correlation between the rate of this process and the levels of NO2. Further investigation of the influence of the decomposition of BrONO2 may be especially important in understanding the RBS activity at mid-latitudes.
Validation of remotely sensed profiles of atmospheric state variables: strategies and terminology
Authors: von Clarmann T.
Published: April 2010

Abstract. This technical note summarizes and classifies the various approaches to validation of remote measurements of atmospheric state variables, and tries to recommend a clear and unambiguous terminology. The following approaches have been identified: Intercomparison of single profiles for accuracy validation; statistical comparison of matched pairs of measurements with respect to bias determination and precision validation; statistical intercomparison of randomly sampled measurements by two instruments, and comparison of a single measurement to an ensemble of measurements. Applicable statistics are shortly reviewed, and recipes for evaluation of the co-incidence error due to less than perfect co-incidences are presented. A rigorous approach is suggested to quantitatively validate profile measurements when full covariance matrices are unavailable. We distinguish between ''necessary validation'' which is rejection of the null hypothesis that a difference between two measurements is significant, and ''sufficient validation'' which means to provide evidence that the probability that there is a significant difference is definitely small.
Photochemical modelling in the Po basin with focus on formaldehyde and ozone
Authors: Liu L. , Flatøy F. , Ordóñez C. , Braathen G. O. , Hak C. , Junkermann W. , Andreani-Aksoyoglu S. , Mellqvist J. , Galle B. , Prévôt A. S. H. , Isaksen I. S. A.
Published: April 2010

Abstract. As part of the EU project FORMAT (Formaldehyde as a Tracer of Oxidation in the Troposphere), a field campaign was carried out in the vicinity of Milan during the summer of 2002. Results from a 3-D regional chemical transport model (NILU RCTM) were used to interpret the observations focusing primarily on HCHO and ozone. The performance of the model was assessed by comparing model results with ground based and aircraft measurements. The model results show good agreement with surface measurements, and the model is able to reproduce the photochemical episodes during fair weather days. The comparison indicates that the model can represent well the HCHO concentrations as well as their temporal and spatial variability. The relationship between HCHO and (O3×H2O) was used to validate the model ability to predict the HCHO concentrations. Further analysis revealed the importance of the representativity of different instruments: in-situ concentrations might be locally enhanced by emissions, while long path measurements over a forest can be influenced by rapid formation of HCHO from isoprene. The model is able to capture the plume from the city of Milan and the modelled levels agree generally well with the aircraft measurements, although the wind fields used in the model can lead to a displacement of the ozone plume. During the campaign period, O3 levels were seldom higher than 80 ppbv, the peak surface ozone maxima reached 90 ppbv. Those relatively low values can be explained by low emissions during the August vacation and unstable weather conditions in this period. The modelled ΔO3/ΔNOz slope at Alzate of 5.1 agrees well with the measured slope of 4.9.
Comparisons between SCIAMACHY atmospheric CO2 retrieved using (FSI) WFM-DOAS to ground based FTIR data and the TM3 chemistry transport model
Authors: Barkley M. P. , Monks P. S. , Frieß U. , Mittermeier R. L. , Fast H. , Körner S. , Heimann M.
Published: April 2010

Abstract. Atmospheric CO2 concentrations, retrieved from spectral measurements made in the near infrared (NIR) by the SCIAMACHY instrument, using Full Spectral Initiation Weighting Function Modified Differential Optical Absorption Spectroscopy (FSI WFM-DOAS), are compared to ground based Fourier Transform Infrared (FTIR) data and to the output from a global chemistry-transport model. Analysis of the FSI WFM-DOAS retrievals with respect to the ground based FTIR instrument, located at Egbert, Canada, show good agreement with an average negative bias of approximately −4.0% with a standard deviation of ~3.0%. This bias which exhibits an apparent seasonal trend, is of unknown origin, though slight differences between the averaging kernels of the instruments and the limited temporal coverage of the FTIR data may be the cause. The relative scatter of the retrieved vertical column densities is comparable to the spread of the FTIR measurements themselves. Normalizing the CO2 columns using the surface pressure does not affect the magnitude of this bias although it slightly increases the scatter of the FSI data. Comparisons of the FSI retrievals to the TM3 global chemistry-transport model, performed over four selected Northern Hemisphere scenes show good agreement. The correlation, between the time series of the SCIAMACHY and model monthly scene averages, are ~0.7 or greater, demonstrating the ability of SCIAMACHY to detect seasonal changes in the CO2 distribution. The amplitude of the seasonal cycle, peak to peak, observed by SCIAMACHY however, is overestimated by a factor of 2–3, which cannot be explained. The yearly means detected by SCIAMACHY are within 2% of those of the model with the mean difference between the CO2 distributions also approximately 2.0%. Additionally, analysis of the retrieved CO2 distributions reveals structure not evident in the model fields which correlates well with land classification type. From these comparisons, the overall precision and bias of the CO2 columns retrieved by the FSI algorithm are estimated to be close to 1.0% and <4.0% respectively.
Size distributions of non-volatile particle residuals (Dp<800 nm) at a rural site in Germany and relation to air mass origin
Authors: Engler C. , Rose D. , Wehner B. , Wiedensohler A. , Brüggemann E. , Gnauk T. , Spindler G. , Tuch T. , Birmili W.
Published: April 2010

Abstract. Atmospheric aerosol particle size distributions at a continental background site in Eastern Germany were examined for a one-year period. Particles were classified using a twin differential mobility particle sizer in a size range between 3 and 800 nm. As a novelty, every second measurement of this experiment involved the removal of volatile chemical compounds in a thermodenuder at 300°C. This concept allowed to quantify the number size distribution of non-volatile particle cores – primarily associated with elemental carbon, and to compare this to the original ambient size distribution. A general result was that practically every ambient particle in continental background air contained a non-volatile core. The volume fraction of non-volatile particulate matter (ambient Dp<800 nm) varied between 10 and 30% and was largely consistent with the experimentally determined mass fraction of elemental carbon. The average size of the non-volatile particle cores was estimated as a function of original ambient size using a summation method, which showed that larger particles (>200 nm) contained more non-volatile compounds than smaller particles (<50 nm), thus indicating a significantly different chemical composition. Two alternative air mass classification schemes based on either, synoptic chart analysis (Berliner Wetterkarte) or back trajectories showed, that the volume and number fractions of non-volatile cores were less dependent on air mass than the absolute concentrations in the particle size distributions. In all air masses, the non-volatile size distributions showed a more and a less volatile ("soot") mode, which is located in the size range of about 50 nm. During unstable conditions and in maritime air masses, smaller values were observed compared to continental or stable conditions. This reflects the significant emissions of non-volatile material over the continent and, depending on atmospheric stratification, increased concentrations at ground level.
Implementation of a Markov Chain Monte Carlo Method to inorganic aerosol modeling of observations from the MCMA-2003 Campaign. Part I: Model description and application to the La Merced Site
Authors: San Martini F. M. , Dunlea E. J. , Grutter M. , Onasch T. B. , Jayne J. T. , Canagaratna M. R. , Worsnop D. R. , Kolb C. E. , Shorter J. H. , Herndon S. C. , Zahniser M. S. , Ortega J. M. , McRae G. J. , Molina L. T. , Molina M. J.
Published: April 2010

Abstract. The equilibrium inorganic aerosol model ISORROPIA was embedded in a Markov Chain Monte Carlo algorithm to produce a powerful tool to analyze aerosol data and predict gas phase concentrations where these are unavailable. The method directly incorporates measurement uncertainty, prior knowledge, and provides for a formal framework to combine measurements of different quality. The method was applied to aerosol- and gas-phase precursor observations taken at La Merced during the Mexico City Metropolitan Area (MCMA) 2003 Field Campaign and served to discriminate between diverging gas-phase observations of ammonia. The model reproduced observations of particle-phase ammonium, nitrate, and sulfate well. The most likely concentrations of ammonia were found to vary between 4 and 26 ppbv, while the range for nitric acid was 0.1 to 55 ppbv. During periods where the aerosol chloride observations were consistently above the detection limit, the model was able to reproduce the aerosol chloride observations well and predicted the most likely gas-phase hydrochloric acid concentration varied between 0.4 and 5 ppbv. Despite the high ammonia concentrations observed and predicted by the model, when the aerosols were assumed to be in the efflorescence branch they are predicted to be acidic (pH~3).
Characterization of aerosol pollution events in France using ground-based and POLDER-2 satellite data
Authors: Kacenelenbogen M. , Léon J.-F. , Chiapello I. , Tanré D.
Published: April 2010

Abstract. We analyze the relationship between daily fine particle mass concentration (PM2.5) and columnar aerosol optical thickness derived from the Polarization and Directionality of Earth's Reflectances (POLDER) satellite sensor. The study is focused over France during the POLDER-2 lifetime between April and October 2003. We have first compared the POLDER derived aerosol optical thickness (AOT) with integrated volume size distribution derived from ground-based Sun Photometer observations. The good correlation (R=0.72) with sub-micron volume fraction indicates that POLDER derived AOT is sensitive to the fine aerosol mass concentration. Considering 1974 match-up data points over 28 fine particle monitoring sites, the POLDER-2 derived AOT is fairly well correlated with collocated PM2.5 measurements, with a correlation coefficient of 0.55. The correlation coefficient reaches a maximum of 0.80 for particular sites. We have analyzed the probability to find an appropriate air quality category (AQC) as defined by the U.S. Environmental Protection Agency (EPA) from POLDER-2 AOT measurements. The probability can be up to 88.8% (±3.7%) for the "Good'' AQC and 89.1% (±3.6%) for the "Moderate'' AQC.
Variability and trends in total and vertically resolved stratospheric ozone
Authors: Brunner D. , Staehelin J. , Maeder J. A. , Wohltmann I. , Bodeker G. E.
Published: April 2010

Abstract. Trends in ozone columns and vertical distributions were calculated for the period 1979–2004 based on the three-dimensional ozone data set CATO (Candidoz Assimilated Three-dimensional Ozone) using a multiple linear regression model. CATO has been reconstructed from TOMS, GOME and SBUV total column ozone observations in an equivalent latitude and potential temperature framework and offers a pole to pole coverage of the stratosphere on 15 potential temperature levels. The regression model includes explanatory variables describing the influence of the quasi-biennial oscillation, volcanic eruptions, the solar cycle, the Brewer-Dobson circulation, Arctic ozone depletion, and the increase in stratospheric chlorine. The effects of displacements of the polar vortex and jet streams due to planetary waves, which may significantly affect trends at a given geographical latitude, are eliminated in the equivalent latitude framework. Ozone variability is largely explained by the QBO and stratospheric aerosol loading and the spatial structure of their influence is in good agreement with previous studies. The solar cycle signal peaks at about 30 to 35 km altitude which is lower than reported previously, and no negative signal is found in the tropical lower stratosphere. The Brewer-Dobson circulation shows a dominant contribution to interannual variability at both high and low latitudes and accounts for some of the ozone increase seen in the northern hemisphere since the mid-1990s. Arctic ozone depletion significantly affects the high northern latitudes between January and March and extends its influence to the mid-latitudes during later months. The vertical distribution of the ozone trend shows distinct negative trends at about 18 km in the lower stratosphere with largest declines over the poles, and above 35 km in the upper stratosphere. A narrow band of large negative trends extends into the tropical lower stratosphere. Assuming that the observed negative trend before 1995 continued to 2004 cannot explain the ozone changes since 1996. A model accounting for recent changes in EESC, aerosols and Eliassen-Palm flux, on the other hand, closely tracks ozone changes since 1995.
Direct measurement of particle formation and growth from the oxidation of biogenic emissions
Authors: VanReken T. M. , Greenberg J. P. , Harley P. C. , Guenther A. B. , Smith J. N.
Published: April 2010

Abstract. A new facility has been developed to investigate the formation of new particles from the oxidation of volatile organic compounds emitted from vegetation. The facility consists of a biogenic emissions enclosure, an aerosol growth chamber, and the associated instrumentation. Using the facility, new particle formation events have been induced through the reaction of ozone with three different precursor gas mixtures: an α-pinene test mixture and the emissions of Holm oak (Quercus ilex) and loblolly pine (Pinus taeda). The results demonstrate the variability between species in their potential to form new aerosol products. The emissions of Q. ilex resulted in fewer particles than did α-pinene, although the concentration of monoterpenes was roughly equal in both experiments before the addition of ozone. Conversely, the oxidation of P. taeda emissions led to the formation of more particles than either of the other two gas mixtures, despite a lower initial terpenoid concentration. These variations can be attributed to differences in the speciation of the vegetative emissions with respect to the α-pinene mixture and to each other. Specifically, the presence of β-pinene and other slower-reacting monoterpenes inhibited particle formation in the Q. ilex experiment, while the presence of sesquiterpenes, including β-caryophyllene, in the emissions of P. taeda were the likely cause of the more intense particle formation events observed during that experiment.
Spectral characteristics of atmospheric pressure and electric field variations under severe weather conditions at high latitudes
Authors: Kasatkina E. A. , Shumilov O. I. , Vinogradov Y. A. , Vasilyev A. N.
Published: April 2010

Abstract. The time-dependent relationships between atmospheric parameters (electric field, positive and negative conductivity, variations of atmospheric pressure) and different meteorological phenomena (rain, fogs, snowstorms, thunderstorms) were investigated through spectral analysis. These parameters were measured with help of a high-latitude computer-aided complex installed at Apatity (66.5 N, 33.4 E). The complex consists of three spaced microbarographs for measurements of atmospheric pressure variations in the range of periods from 1 s to 40 min, an instrument measuring the vertical component of the electric field, and instrument used for measurements of air conductivity and surface ozone. A computer-aided data-gathering system makes it possible to obtain information in the frequency range between 1 and 0.0001 Hz. The time-dependent frequency analysis showed that the spectral characteristics of both electric field and atmospheric pressure variations changed synchronously during severe weather conditions.
Carbonate precipitation in brine – the trigger for tropospheric ozone depletion events
Authors: Sander R. , Burrows J. , Kaleschke L.
Published: April 2010

Abstract. Tropospheric ozone depletion events (ODEs) at high latitudes were discovered 20 years ago and are attributed to bromine explosions. However, an outstanding and unresolved issue is the explanation of how the acid-catalyzed reaction cycle is triggered in atmospheric particles derived from alkaline sea water. By simulating the chemistry occuring in polar regions over recently formed sea ice, we can model successfully the transformation of inert sea-salt bromide to reactive bromine monoxide (BrO) and the subsequent ODE when precipitation of calcium carbonate from freezing sea water is taken into account. In addition, we found the temperature dependence of the equilibrium BrCl+Br⇌Br2Cl− to be important.
Annual variation and global distribution of strato-mesospheric carbon monoxide measured by ground-based Fourier Transform Infrared spectrometry
Authors: Velazco V. , Wood S. W. , Sinnhuber M. , Kramer I. , Jones N. B. , Kasai Y. , Notholt J. , Warneke T. , Blumenstock T. , Hase F. , Murcray F. J. , Schrems O.
Published: April 2010

Abstract. We present long-term time-series of strato-mesospheric CO vertical columns measured from stations located in Antarctica, mid-latitudes and the Arctic, covering the period from 1997–2005. The instrument and the measurement technique allows the separation of tropospheric and strato-mesospheric contributions to the CO column, therefore providing information on the chemistry and dynamics both at low and high altitudes. Data from polar stations show a similar annual variability of strato-mesospheric CO with a strong maximum in late winter and spring and a small enhancement in late summer for some stations, which we call the "summer bulge''. Generally, the mid-latitude stations show no significant annual variability of strato-mesospheric CO columns. Measurements were compared with a two-dimensional chemistry-transport model of the middle atmosphere. The annual and latitudinal variations of CO are reproduced very well by a model run including thermospheric CO. Comparison with different model scenarios show that the polar winter maximum is due solely to downward transport of thermospheric CO, while the summer maximum is due to CHOx chemistry in the stratosphere.
Observations of sulfur dioxide uptake and new particle formation in a midlatitude cumulus cloud
Authors: Peter J. R. , Siems S. T. , Jensen J. B. , Gras J. L. , Ishizaka Y. , Hacker J. M.
Published: April 2010

Abstract. Airborne measurements, obtained during the Asian Aerosol Characterisation Experiment (ACE-Asia), of SO2 and condensation nuclei (CN) concentrations were made in the local environment of a cumulus cloud band. Conserved quantities, wet equivalent potential temperature θq, and total water content Q, were used to identify the sources of air detrained on the downwind side of the cumulus band. It was found that ~65% of the detrained air originated from below cloud base and the remainder was air that had been entrained from the free troposphere upwind of the cloud and subsequently been detrained. Calculation of the sources of the detrained air parcels enabled a prediction of the concentration of SO2 and CN, assuming that SO2 and CN experienced no processing within cloud. A comparison of the predicted concentration of SO2 and CN was made with those observed. The concentration of SO2 observed was less than predicted and the amount of SO2 scavenged within cloud was calculated. The CN concentration observed was also less than predicted and, moreover, inclusion of the loss of CN to cloud droplets due to Brownian scavenging resulted in an enhanced decrease of the number concentration of CN predicted. Clear air regions around the cloud exhibited no indication of being a major source of new particles. It was concluded that new particles were formed within cloud.
Stratospheric variability and trends in IPCC model simulations
Authors: Cordero E. C. , de F. Forster P. M.
Published: April 2010

Abstract. Atmosphere and Ocean General Circulation Model (AOGCM) experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report are analyzed using both 20th and 21st century model output to better understand model variability and assess the importance of various forcing mechanisms on stratospheric trends. While models represent the climatology of the stratosphere reasonably well in comparison with NCEP reanalysis, there are biases and large variability among models. In general, AOGCMs are cooler than NCEP throughout the stratosphere, with the largest differences in the tropics. Around half the AOGCMs have a top level beneath ~2 hPa and show a significant cold bias in their upper levels (~10 hPa) compared to NCEP, suggesting that these models may have compromised simulations near 10 hPa due to a low model top or insufficient stratospheric levels. In the lower stratosphere (50 hPa), the temperature variability associated with large volcanic eruptions is either absent (in about half of the models) or the warming is overestimated in the models that do include volcanic aerosols. There is general agreement on the vertical structure of temperature trends over the last few decades, differences between models are explained by the inclusion of different forcing mechanisms, such as stratospheric ozone depletion and volcanic aerosols. However, even when human and natural forcing agents are included in the simulations, significant differences remain between observations and model trends, particularly in the upper tropical troposphere (200 hPa–100 hPa), where, since 1979, models show a warming trend and the observations a cooling trend.
The effects of convection on the summertime mid-latitude overworld
Authors: Dessler A. E.
Published: April 2010

Abstract. Halogen Occultation Experiment measurements of H2O are used to investigate the influence of mid-latitude convection on the summertime overworld between 30° N and 40° N. We find that most of the convective influence over this latitude range occurs over the Asian monsoon and over North America. Over North America, the effects of convection extend to ~410 K (17.5 km). Over Asia, the effects of convection extend to ~460 K (19 km), about 50 K (1.5 km) higher than over North America.
Using discriminant analysis as a nucleation event classification method
Authors: Mikkonen S. , Lehtinen K. E. J. , Hamed A. , Joutsensaari J. , Facchini M. C. , Laaksonen A.
Published: April 2010

Abstract. More than three years of measurements of aerosol size-distribution and different gas and meteorological parameters made in Po Valley, Italy were analysed for this study to examine which of the meteorological and trace gas variables effect on the emergence of nucleation events. As the analysis method, we used discriminant analysis with non-parametric Epanechnikov kernel, included in non-parametric density estimation method. The best classification result in our data was reached with the combination of relative humidity, ozone concentration and a third degree polynomial of radiation. RH appeared to have a preventing effect on the new particle formation whereas the effects of O3 and radiation were more conductive. The concentration of SO2 and NO2 also appeared to have significant effect on the emergence of nucleation events but because of the great amount of missing observations, we had to exclude them from the final analysis.
Cn to ccn relationships and cloud microphysical properties in different air masses at a free tropospheric site
Authors: Dupuy R. , Laj P. , Sellegri K.
Published: April 2010

Abstract. The fraction of aerosol particles activated to droplets (CCN) is often derived from semi-empirical relationships that commonly tend to overestimate droplet number concentration leading to major uncertainties in global climate models. One of the difficulties in relating aerosol concentration to cloud microphysics and cloud albedo lies in the necessity of working at a constant liquid water path (LWP), which is very difficult to control. In this study we observed the relationships between aerosol number concentration (NCN), cloud droplet concentration (Nd) and effective radius (Reff), at the Puy de Dôme (France). A total of 20 cloud events were sampled representing a period of more than 250 h of cloud sampling. Samples are classified first according to air mass origins (Modified Marine, Continental and Polluted) and then according to their liquid water content (Thin, Medium and Thick clouds). The CCN fraction of aerosols appears to vary significantly according to the air mass origin. It is maximum for Continental air masses and minimum for Polluted air masses. Surprisingly, the CCN fraction of Modified Marine air masses fraction is lower than the continental air mass and from expected from previous studies. The limited number of activated particles in Modified Marine air masses is most likely the result of the presence of hydrophobic organic compounds. The limited activation effect leads to a 0.5 to 1 μm increase in Reff with respect to an ideal Marine case. This is significant and implies that the dReff/dNCN of low-continental clouds is higher than expected.