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Continuous measurements of physical and chemical properties at the Mt. Cimone GAW-WMO Global Station (2165ma.s.l.) allowed the detection of the volcanic aerosol plume resulting from the Eyjafjallajökull eruption of spring 2010. The event affected the site after a transport over a distance of more than 3000 km. Two main transport episodes were detected during the eruption period, showing a volcanic fingerprint discernible against the free tropospheric background conditions typical of the site, the first from 19 to 21 April and the second from 18 to 20 May 2010. The paper reports the modification of aerosol characteristics observed during the two episodes, both characterized by an abrupt increase in fine and, especially, coarse mode particle number. Analysis of major, minor and trace elements by different analytical techniques (Ionic Chromatography, PIXE-PIGE and ICP-MS) were performed on aerosols collected by ground level discrete sampling. The resulting database allows the characterization of aerosol chemical composition during the volcanic plume transport and in background conditions. During the passage of the volcanic plume, the fine fraction was dominated by sulphates, denoting the secondary origin of this mode, mainly resulting from inplume oxidation of volcanic SO2. By contrast, the coarse fraction was characterized by increased concentration of numerous elements of crustal origin, such as Fe, Ti, Mn, Ca, Na, and Mg, which enter the composition of silicate minerals. Data analysis of selected elements (Ti, Al, Fe, Mn) allowed the estimation of the volcanic plume's contribution to total PM10, resulting in a local enhancement of up to 9.5 µgm-3, i.e. 40% of total PM10, on 18 May, which was the most intense of the two episodes. These results appear significant, especially in the light of the huge distance of Mt. Cimone from the source, confirming the widespread diffusion of the Eyjafjallajokull ashes over Europe. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols have been sampled and characterised at the Mace Head North East (N.E.) Atlantic atmospheric research station since 1958, with many interesting phenomena being discovered. However, with the range of new discoveries and scientific advances, there has been a range of concomitant criticisms challenging the representativeness of aerosol sampled at the station to that of aerosol over the open ocean. Two recurring criticisms relate to the lack of representativeness due to enhanced coastal sources, thereby leading to artificially high values to aerosol parameters, and to the influence of long-range transport of anthropogenic aerosol and its potential dominance over, or drowning-out of, a natural marine aerosol signal. Here we review the results of previous experimental studies into marine aerosols over the N.E. Atlantic and at Mace Head with the aim of evaluating their representativeness relative to that of an open ocean aerosol with negligible anthropogenic influence. Particular focus is given to organic matter (OM) aerosol. In summary, no correlation was found between OM and black carbon (BC) either at BC levels of 0-15 or 15-50 ngm-3, suggesting that OM concentrations up to peak values of 3.8 μgm-3 are predominantly natural in origin. Sophisticated carbon isotope analysis and aerosol mass spectral finger printing corroborate the natural source of OM with 80% biogenic source apportionment being observed for general clean air conditions, rising to 98% during specific primary marine organic plumes when peak concentrations >3 μgm-3 are observed. A range of other experiments are discussed which corroborate the dominance of a marine signal under Mace Head clean air criteria along. Further, analysis of a series of experiments conducted at Mace Head conclude that negligible coastal, surf zone, or tidal effects are discernible in the submicron size range for sampling heights of 7m and above. The Mace Head clean air criteria ensures anthropogenic and coastal effects are sufficiently minimised so as to guarantee a dominant, if not at times, an overwhelming natural marine aerosol signal. [ABSTRACT FROM AUTHOR]

Measurements of aerosol chemical composition made on the island of Lampedusa, south of the Sicily channel, during years 2004-2008, are used to identify the in- fluence of heavy fuel oil (HFO) combustion emissions on aerosol particles in the Central Mediterranean. Aerosol samples influenced by HFO are characterized by elevated Ni and V soluble fraction (about 80% for aerosol from HFO combustion, versus about 40% for crustal particles), high V and Ni to Si ratios, and values of Vsol > 6 ng m-3. Evidence of HFO combustion influence is found in 17% of the daily samples. Back trajectories analysis on the selected events show that air masses prevalently come from the Sicily channel region, where an intense ship traffic occurs. This behavior suggests that single fixed sources like refineries are not the main responsible for the elevated V and Ni events, which are probably mainly due to ships emissions. Vsol, Nisol, and non-sea salt Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. show a marked seasonal behaviour, with an evident summer maximum. Such a pattern can be explained by several processes: (i) increased photochemical activity in summer, leading to a faster production of secondary aerosols, mainly Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. , from the oxidation of SO2 (ii) stronger marine boundary layer (MBL) stability in summer, leading to higher concentration of emitted compounds in the lowest atmospheric layers. A very intense event in spring 2008 was studied in detail, also using size segregated chemical measurements. These data show that elements arising from heavy oil combustion (V, Ni, Al, Fe) are distributed in the sub-micrometric fraction of the aerosol, and the metals are present as free metals, carbonates, oxides hydrates or labile complex with organic ligands, so that they are dissolved in mild condition (HNO3, pH1.5). Data suggest a characteristic Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. ratio in the range 200-400 for HFO combustion aerosols in summer at Lampedusa. By using the value of 200 a lower limit for the HFO contribution to total sulphates is estimated. HFO combustion emissions account, as a summer average, at least for 1.2 µgm-3, representing about 30% of the total Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. , 3.9% of PM10, 8% of PM2.5, and 11% of PM1. Within the used dataset, sulphate from HFO combustion emissions reached the peak value of 6.1 µgm-3 on 26 June 2008, when it contributed by 47% to Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. , and by 15% to PM10. [ABSTRACT FROM AUTHOR]

The number concentration of cloud droplets determines several climatically relevant cloud properties. A major cause for the high uncertainty in the indirect aerosol forcing is the availability of cloud condensation nuclei (CCN), which in turn is highly sensitive to atmospheric new particle formation. Here we present the effect of new particle formation on anthropogenic aerosol forcing in present-day (year 2000) and future (year 2100) conditions. The present-day total aerosol forcing is increased from -1.0Wm-2 to -1.6Wm-2 when nucleation is introduced into the model. Nucleation doubles the change in aerosol forcing between years 2000 and 2100, from +0.6Wm-2 to +1.4Wm-2. Two climate feedbacks are studied, resulting in additional negative forcings of -0.1Wm-2 (+10% DMS emissions in year 2100) and -0.5Wm-2 (+50% BVOC emissions in year 2100). With the total aerosol forcing diminishing in response to air pollution control measures taking effect, warming from increased greenhouse gas concentrations can potentially increase at a very rapid rate. [ABSTRACT FROM AUTHOR]

The new global anthropogenic emission inventory (EDGAR-CIRCE) of gas and aerosol pollutants has been incorporated in the chemistry general circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry). A relatively high horizontal resolution simulation is performed for the years 2005-2008 to evaluate the capability of the model and the emissions to reproduce observed aerosol concentrations and aerosol optical depth (AOD) values. Model output is compared with observations from different measurement networks (CASTNET, EMEP and EANET) and AODs from remote sensing instruments (MODIS and MISR). A good spatial agreement of the distribution of sulfate and ammonium aerosol is found when compared to observations, while calculated nitrate aerosol concentrations show some discrepancies. The simulated temporal development of the inorganic aerosols is in line with measurements of sulfate and nitrate aerosol, while for ammonium aerosol some deviations from observations occur over the USA, due to the wrong temporal distribution of ammonia gas emissions. The calculated AODs agree well with the satellite observations in most regions, while negative biases are found for the equatorial area and in the dust outflow regions (i.e. Central Atlantic and Northern Indian Ocean), due to an underestimation of biomass burning and aeolian dust emissions, respectively. Aerosols and precursors budgets for five different regions (North America, Europe, East Asia, Central Africa and South America) are calculated. Over East-Asia most of the emitted aerosols (precursors) are also deposited within the region, while in North America and Europe transport plays a larger role. Further, it is shown that a simulation with monthly varying anthropogenic emissions typically improves the temporal correlation by 5-10% compared to one with constant annual emissions. [ABSTRACT FROM AUTHOR]

We discuss the use of a two-dimensional volatility-oxidation space (2-D-VBS) to describe organicaerosol chemical evolution. The space is built around two coordinates, volatility and the degree of oxidation, both of which can be constrained observationally or specified for known molecules. Earlier work presented the thermodynamics of organics forming the foundation of this 2-D-VBS, allowing us to define the average composition (C, H, and O) of organics, including organic aerosol (OA) based on volatility and oxidation state. Here we discuss how we can analyze experimental data, using the 2-D-VBS to gain fundamental insight into organic-aerosol chemistry. We first present a well-understood "traditional" secondary organic aerosol (SOA) system -- SOA from α-pinene + ozone, and then turn to two examples of "non-traditional" SOA formation -- SOA from wood smoke and dilute diesel-engine emissions. Finally, we discuss the broader implications of this analysis. [ABSTRACT FROM AUTHOR]

In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies. [ABSTRACT FROM AUTHOR]

Dual carbon isotope analysis of marine aerosol samples has been performed for the first time demonstrating a potential in organic matter apportionment between three principal sources: marine, terrestrial (non-fossil) and fossil fuel due to unique isotopic signatures. The results presented here, utilising combinations of dual carbon isotope analysis, provides conclusive evidence of a dominant biogenic organic fraction to organic aerosol over biologically active oceans. In particular, the NE Atlantic, which is also subjected to notable anthropogenic influences via pollution transport processes, was found to contain 80% organic aerosol matter of biogenic origin directly linked to plankton emissions. The remaining carbonaceous aerosol was of terrestrial origin. By contrast, for polluted air advected out from Europe into the NE Atlantic, the source apportionment is 30% marine biogenic, 40% fossil fuel, and 30% continental non-fossil fuel. The dominant marine organic aerosol source in the atmosphere has significant implications for climate change feedback processes. [ABSTRACT FROM AUTHOR]

The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements including both filter sampling (PM1) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure online air mass concentrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic functional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed separately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrometer organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group compositions. The NMR results supported the AMS speciation of oxidized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organics. The more oxidized component was characterized by a mass spectrum dominated by the m/z 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic backbones highly substituted with oxygenated functional groups (carbonyls/ carboxyls and hydroxyls). Such component, contributing on average 50% of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component showed features consistent with less oxygenated aerosols and was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investigations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated to the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral profiles obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources originating biogenic organic aerosols in Hyytiälä by oxidation and condensation mechanisms: reactive terpenes emitted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably be exploited to complement aerosol mass spectrometric measurements in organic source apportionment studies. [ABSTRACT FROM AUTHOR]

3 For oceans to become a significant source of primary organic aerosol (POA), sea spray must be highly enriched with organics relative to the bulk seawater. We propose that organic enrichment at the air-sea interface, chemical composition of seawater, and the aerosol size are three main parameters controlling the organic mass fraction of sea spray aerosol (OM ). To test this hypothesis, we developed a new marine POA emissssion function based on a conceptual relationship between the organic enrichment at the air-sea interface and surface wind speed. The resulting parameterization is explored using aerosol chemical composition and surface wind speed from Atlantic and Pacific coastal stations, and satellite-derived ocean concentrations of chlorophyll-a, dissolved organic carbon, and particulate organic carbon. Of all the parameters examined, a multi-variable logistic regression revealed that the combination of 10m wind speed and surface chlorophyll-a concentration ([Chl-a]) are the most consistent predictors of OMss. This relationship, combined the published aerosol size dependence of OMss , resulted in a new parameterization for the organic carbon fraction of sea spray. Global marine primary organic emission is investigated here by applying this newly-developed relationship to existing sea spray emission functions, satellite-derived [Chl-a], and modeled 10 meter winds. Analysis of model simulations show that global annual submicron marine organic emission associated with sea spray is estimated to be from 2.8 to 5.6 TgCyr-1. This study provides additional evidence that marine primary organic aerosols are a globally significant source of organics in the atmosphere. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the number concentration of atmospheric Aitken particles by a combination of in-situ meteorological and gas phase parameters. The study uses a Global Model of Aerosol Processes (GLOMAP) to describe the factors which affect the growth of newly formed aerosol particles. It concludes that such model indicate that the parameterization can be utilized a part of a larger atmospheric model to forecast the concentration of climatically active particles.

Dual carbon isotope analysis has been performed for the first time demonstrating a potential in organic matter apportionment between three principal sources: marine, terrestrial (non-fossil) and fossil fuel due to unique isotopic signatures. The results presented here, utilising combinations of dual carbon isotope analysis, provides a conclusive evidence of a dominant biogenic organic fraction to organic aerosol over biologically active oceans. In particular, the NE Atlantic, which is also subjected to notable anthropogenic influences via pollution transport processes, was found to contain 80% organic aerosol matter of biogenic origin directly linked to plankton emissions. The remaining carbonaceous aerosol was of fossil-fuel origin. By contrast, for polluted air advecting out from Europe into the NE Atlantic, the source apportionment is 30% marine biogenic, 40% fossil fuel, and 30% continental non-fossil fuel. The dominant marine organic aerosol source in the atmosphere has significant implications for climate change feedback processes. [ABSTRACT FROM AUTHOR]

This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory-Pyramid (NCO-P) located at 5079ma.s.l. on the southern foothills of Mt. Everest, in the framework of ABC-UNEP and SHARE-Ev-K2-CNR projects. The work presents a characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity. The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa, -3.0 °C, 4.7ms-1, respectively. The highest seasonal values of temperature (1.7 °C) and relative humidity (94%) were registered during the monsoon season, which was also characterized by thick clouds, present in about 80% of the afternoon hours, and by a frequency of cloud-free sky of less than 10%. The lowest temperature and relative humidity seasonal values were registered during winter, -6.3 °C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rare thick clouds. The summer monsoon influenced rain precipitation (seasonal mean: 237 mm), while wind was dominated by flows from the bottom of the valley (S-SW) and upper mountain (N-NE). The atmospheric composition at NCO-P has been studied thanks to measurements of black carbon (BC), aerosol scattering coefficient, PM1, coarse particles and ozone. The annual behaviour of the measured parameters shows the highest seasonal values during the premonsoon (BC: 316.9 ngm-3, PM1: 3.9 μgm-3, scattering coefficient: 11.9Mm-1, coarse particles: 0.37 cm-3 and O3: 60.9 ppbv), while the lowest concentrations occurred during the monsoon (BC: 49.6 ngm-3, PM1: 0.6 μgm-3, scattering coefficient: 2.2Mm-1, and O3: 38.9 ppbv) and, for coarse particles, during the post-monsoon (0.07 cm-3). At NCO-P, the synoptic-scale circulation regimes present three principal contributions: Westerly, South-Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories. The influence of the brown cloud (AOD>0.4) extending over Indo-Gangetic Plains up to the Himalayan foothills has been evaluated by analysing the in-situ concentrations of the ABC constituents. This analysis revealed that brown cloud hot spots mainly influence the South Himalayas during the pre-monsoon, in the presence of very high levels of atmospheric compounds (BC: 1974.1 ngm-3, PM1: 23.5 μgm-3, scattering coefficient: 57.7Mm-1, coarse particles: 0.64 cm-3, O3: 69.2 ppbv, respectively). During this season 20% of the days were characterised by a strong brown cloud influence during the afternoon, leading to a 5-fold increased in the BC and PM1 values, in comparison with seasonal means. Our investigations provide clear evidence that, especially during the pre-monsoon, the southern side of the high Himalayan valleys represent a "direct channel" able to transport brown cloud pollutants up to 5000ma.s.l., where the pristine atmospheric composition can be strongly influenced. [ABSTRACT FROM AUTHOR]

The article discusses a study which aims to forecast the number concentration of 50 nanometer (nm) atmospheric aerosol particles. The study has used a combination of in-situ gas phase and meteorological parameters. Results revealed that the parameters used in the study are effective in predicting the concentration of climatically active particles.

We report chemical composition data for PM10 and PM1 from the Nepal Climate Observatory-Pyramid (NCO-P), the world's highest aerosol observatory, located at 5079m a.s.l. at the foothills of Mt. Everest. Despite its high altitude, the average PM10 mass apportioned by the chemical analyses is of the order of 6 μgm-3 (i.e., 10 μg/scm), with almost a half of this mass accounted for by organic matter, elemental carbon (EC) and inorganic ions, the rest being mineral dust. Organic matter, in particular, accounted for by 2.0 μgm-3 (i.e., 3.6 μg/scm) on a yearly basis, and it is by far the major PM10 component beside mineral oxides. Non-negligible concentrations of EC were also observed (0.36 μg/scm), confirming that light-absorbing aerosol produced from combustion sources can be efficiently transported up the altitudes of Himalayan glaciers. The concentrations of carbonaceous and ionic aerosols follow a common time trend with a maximum in the premonsoon season, a minimum during the monsoon and a slow recovery during the postmonsoon and dry seasons, which is the same phenomenology observed for other Nepalese Himalayan sites in previous studies. Such seasonal cycle can be explained by the seasonal variations of dry and moist convection and of wet scavenging processes characterizing the climate of north Indian subcontinent. We document the effect of orographic transport of carbonaceous and sulphate particles upslope the Himalayas, showing that the valley breeze circulation, which is almost permanently active during the out-of-monsoon season, greatly impacts the chemical composition of PM10 and PM1 in the high Himalayas and provides an efficient mechanism for bringing anthropogenic aerosols into the Asian upper troposphere (>5000m a.s.l.). The concentrations of mineral dust are impacted to a smaller extent by valley breezes and follow a unique seasonal cycle which suggest multiple source areas in central and south-west Asia. Our findings, based on two years of observations of the aerosol chemical composition, provide clear evidence that the southern side of the high Himalayas is impacted by transport of anthropogenic aerosols which constitute the Asian brown cloud. [ABSTRACT FROM AUTHOR]

South Asia is strongly influenced by the so-called Atmospheric Brown Cloud (ABC), a wide polluted layer extending from the Indian Ocean to the Himalayas during the winter and pre-monsoon seasons (November to April). This thick, grey-brown haze blanket substantially interacts with the incoming solar radiation, causing a cooling of the Earth's surface and a warming of the atmosphere, thus influencing the monsoon system and climate. In this area, the Himalayan region, particularly sensitive to climate change, offers a unique opportunity to detect global change processes and to analyse the influence of anthropogenic pollution on background atmospheric conditions through continuous monitoring activities. This paper provides a detailed description of the atmospheric conditions characterizing the high Himalayas, thanks to continuous observations begun in March 2006 at the Nepal Climate Observatory - Pyramid (NCO-P) located at 5079m a.s.l. on the southern foothills of Mt. Everest, in the framework of ABC-UNEP and SHARE-Ev-K2-CNR projects. Besides giving an overview of the measurement site and experimental activities, the work presents an in-depth characterization of meteorological conditions and air-mass circulation at NCO-P during the first two years of activity (March 2006-February 2008). The mean values of atmospheric pressure, temperature and wind speed recorded at the site were: 551 hPa, -3.0 °C, 4.7ms-1, respectively. The highest seasonal values of temperature (1.7 °C) and relative humidity (94%) were registered during the monsoon season, which was also characterized by thick clouds present in about 80% of the afternoon hours and by a frequency of cloud-free sky less than 10%. The lowest temperature and relative humidity values were registered during winter, -6.3 °C and 22%, respectively, the season being characterised by mainly cloud-free sky conditions and rare thick clouds. The summer monsoon influenced the rain precipitation (seasonal mean 237 mm), while wind was dominated by flows from the bottom of the valley (S-SW) and upper mountain (N-NE). In relation to seasonal weather conditions, the time series variability of black carbon and dust particles (optical active aerosols) and ozone (regional greenhouse gas) were analysed, as they are significant constituents of the Atmospheric Brown Cloud and strongly influence the atmospheric radiative forcing. The highest seasonal values of black carbon (BC), ozone (O3) and dust particles were observed during the pre-monsoon season (316.9 ngm-3, 60.9 ppbv, 0.37 cm-3, respectively), while the lowest concentrations occurred during the monsoon for BC and O3 (49.6 ngm-3 and 33.6 ppbv, respectively) and postmonsoon for dust particles (0.07 cm-3). The seasonal cycles of these compounds are influenced both by the local mountain wind system and by the three principal largescale circulation regimes: Westerly, South-Westerly and Regional, as shown by the analysis of in-situ meteorological parameters and 5-day LAGRANTO back-trajectories.… [ABSTRACT FROM AUTHOR]

HUmic-LIke Substances (HULIS) have been identified as major contributors to the organic carbon in atmospheric aerosol. The term HULIS is used to describe the organic material found in aerosol particles which resembles the humic organic material in river and sea water and in soils. In this study two sets of filter samples from atmospheric aerosols were collected at different sites. One sample was collected at the K-puszta rural site in Hungary, about 80 km SE of Budapest, and a second set of samples was collected at a site in Rondônia, Amazonia, Brazil, during the LBA-SMOCC biomass burning season experiment. HULIS were extracted from the samples, and their hygroscopic properties were studied using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) at relative humidity (RH) <100%, and a cloud condensation nucleus counter (CCNC) at RH >100%. The H-TDMA measurements were carried out at a dry diameter of 100 nm and for RH ranging from 30 to 98%. At 90% RH the HULIS samples showed diameter growth factors between 1.04 and 1.07, reaching values of 1.4 at 98% RH. The cloud nucleating properties of the two sets of aerosol samples were analyzed using two types of thermal static cloud condensation nucleus counters (CCNC). Two different parameterization models were used to investigate the potential effect of HULIS surface activity, both yielding similar results. For the K-puszta winter HULIS sample, the surface tension at the point of activation was estimated to be lowered by between 34% (47.7 m N/m) and 31% (50.3 m N/m) for dry sizes between 50 and 120 nm in comparison to pure water. A moderate lowering was also observed for the entire water soluble aerosol sample, including both organic and inorganic compounds, where the surface tension was decreased by between 2% (71.2 mN/m) and 13% (63.3 mN/m). [ABSTRACT FROM AUTHOR]

We report chemical composition data for PM10 and PM1 from the Nepal Climate Observatory-Pyramid (NCO-P), the world's highest aerosol observatory, located at 5079 m a.s.l. at the foothills of Mt. Everest. Despite its high altitude, the average PM10 mass apportioned by the chemical analyses is of the order of 6 μgm-3 (i.e., 10 μg/scm), with almost a half of this mass accounted for by organic matter, elemental carbon (EC) and inorganic ions, the rest being mineral dust. Organic matter, in particular, accounted for by 2.0 μgm-3 (i.e., 3.6 μg/scm) on a yearly basis, and it is by far the major PM10 component beside mineral oxides. Non-negligible concentrations of EC were also observed (0.36 μg/scm), confirming that optically-active aerosol produced from combustion sources can be efficiently transported up the altitudes of Himalayan glaciers. The concentrations of carbonaceous and ionic aerosols follow a common time trend with a maximum in the premonsoon season, a minimum during the monsoon and a slow "ramp-up" period in the postmonsoon and dry seasons, which is the same phenomenology observed for other Nepalese Himalayan sites in previous studies. Such seasonal cycle can be explained by the seasonal variations of dry and moist convection and of wet scavenging processes characterizing the climate of north Indian subcontinent. We document the effect of orographic transport of carbonaceous and sulphate particles upslope the Himalayas, showing that the valley breeze circulation, which is almost permanently active during the out-of-monsoon season, greatly impacts the chemical composition of PM10 and PM1 in the high Himalayas and provides an efficient mechanism for bringing anthropogenic optically-active aerosols into the Asian upper troposphere (>5000 m a.s.l.). The concentrations of mineral dust are impacted to a smaller extent by valley breezes and follow a unique seasonal cycle which suggest multiple source areas in central and south-west Asia. Our findings, based on two years of observations of the aerosol chemical composition, provide clear evidence that the southern side of the high Himalayas are impacted by transport of anthropogenic aerosols which constitute the Asian brown cloud. [ABSTRACT FROM AUTHOR]

In the present study, ambient aerosol (PM10) concentrations of elemental carbon (EC), organic carbon (OC), and total carbon (TC) are reported for 12 European rural background sites and two urban background sites following a one-year (1 July 2002-1 July 2003) sampling campaign within the European Monitoring and Evaluation Programme, EMEP (http://www.emep.int/). The purpose of the campaign was to assess the feasibility of performing EC and OC monitoring on a regular basis and to obtain an overview of the spatial and seasonal variability on a regional scale in Europe. Analyses were performed using the thermal-optical transmission (TOT) instrument from Sunset Lab Inc., operating according to a NIOSH derived temperature program. The annual mean mass concentration of EC ranged from 0.17±0.19µgm-3 (mean ± SD) at Birkenes (Norway) to 1.83±1.32µgm-3 at Ispra (Italy). The corresponding range for OC was 1.20±1.29µgm-3 at Mace Head (Ireland) to 7.79±6.80µgm-3 at Ispra. On average, annual concentrations of EC, OC, and TC were three times higher for rural background sites in Central, Eastern and Southern Europe compared to those situated in the Northern and Western parts of Europe. Wintertime concentrations of EC and OC were higher than those recorded during summer for the majority of the sites. Moderate to high Pearson correlation coefficients (rp) (0.50-0.94) were observed for EC versus OC for the sites investigated. The lowest correlation coefficients were noted for the three Scandinavian sites: Aspvreten (SE), Birkenes (NO), and Virolahti (FI), and the Slovakian site Stara Lesna, and are suggested to reflect biogenic sources, wild and prescribed fires. This suggestion is supported by the fact that higher concentrations of OC are observed for summer compared to winter for these sites. For the rural background sites, total carbonaceous material accounted for 30±9% of PM10, of which 27±9% could be attributed to organic matter (OM) and 3.4±1.0% to elemental matter (EM). OM was found to be more abundant than SO42- for sites reporting both parameters. [ABSTRACT FROM AUTHOR]

In this paper, we study the transport of air mass to San Pietro Capofiume (SPC) in Po Valley, Italy, by means of back trajectory analysis. Our main aim is to investigate whether air masses originate from different regions on nucleation event days and on nonevent days, during three years when nucleation events have been continuously recorded at SPC. The results indicate that nucleation events occur frequently in air masses arriving form Central Europe, whereas event frequency is much lower in air transported from southern directions and from the Atlantic Ocean. We also analyzed the behaviour of meteorological parameters during 96 h transport to SPC, and found that on average, event trajectories undergo stronger subsidence during the last 12 h before the arrival at SPC than nonevent trajectories. This causes a reversal in the temperature and relative humidity (RH) differences between event and nonevent trajectories: between 96 and 12 h back time, temperatures are lower and RH's higher for event than nonevent trajectories and between 12 and 0 h vice versa. Boundary layer mixing is stronger along the event trajectories compared to nonevent trajectories. The absolute humidity (AH) is similar for the event and nonevent trajectories between about 96 h and about 60 h back time, but after that, the event trajectories AH becomes lower due to stronger rain. We also studied transport of SO2 to SPC, and conclude that although sources in Po Valley most probably dominate the measured concentrations, certain Central and Eastern European sources can also have a non-negligible contribution. [ABSTRACT FROM AUTHOR]

Water soluble organic compounds (WSOC) in aerosol samples collected in the Amazon Basin in a period encompassing the middle/late dry season and the beginning of the wet season, were investigated by H NMR spectroscopy. HiVol filter samples (PM2.5 and PM>2.5) and size-segregated samples from multistage impactor were subjected 5 to H NMR characterization. The H NMR methodology, recently developed for the analysis of organic aerosol samples, has been improved exploiting chemical methylation of carboxylic groups with diazomethane, which allows the direct determination of the carboxylic acid content of WSOC. The content of carboxylic carbons for the different periods and sizes ranged from 12% to 20% of total measured carbon depending on the season and aerosol size, with higher contents for the fine particles in the transition and wet periods with respect to the dry period. A comprehensive picture is presented of WSOC functional groups in aerosol samples representative of the biomass burning period, as well as of transition and semi-clean atmospheric conditions. A difference in composition between fine (PM2.5) and coarse (PM>2.5) size fractions emerged from the NMR data, the former showing higher alkylic content, the latter being largely dominated by R-O-H (or R-O-R') functional groups, likely coming from polyols. Very small particles (<0.14 µm), however, present higher alkyl-chain content and less oxygenated carbons than larger fine particles (0.42-1.2 µm). More limited variations were found between the average compositions in the different periods of the campaign. [ABSTRACT FROM AUTHOR]

Size-segregated aerosol samples were collected during the QUEST field campaign at Hyyti¨al¨a, a boreal forest site in Southern Finland, during spring 2003. Aerosol samples were selectively collected during both particle formation events and periods in which no particle formation occurred. A comprehensive characterisation of the aerosol chemical properties (water-soluble inorganic and organic fraction) and an analysis of the relevant meteorological parameters revealed how aerosol chemistry and meteorology combine to determine a favorable "environment" for new particle formation. The results indicated that all events, typically favored during northerly air mass advection, were background aerosols (total mass concentrations range between 1.97 and 4.31 µgm-3), with an increasingly pronounced marine character as the northerly air flow arrived progressively from the west and, in contrast, with a moderate SO2-pollution influence as the air arrived from more easterly directions. Conversely, the non-event aerosol, transported from the south, exhibited the chemical features of European continental sites, with a marked increase in the concentrations of all major anthropogenic aerosol constituents. The higher non-event mass concentration (total mass concentrations range between 6.88 and 16.30 µgm-3) and, thus, a larger surface area, tended to suppress new particle formation, more efficiently depleting potential gaseous precursors for nucleation. The analysis of water-soluble organic compounds showed that clean nucleation episodes were dominated by aliphatic biogenic species, while non-events were characterised by a large abundance of anthropogenic oxygenated species. Interestingly, a significant content of α-pinene photo-oxidation products was observed in the events aerosol, accounting for, on average, 72% of their WSOC; while only moderate amounts of these species were found in the non-event aerosol. If the organic vapors condensing onto accumulation mode particles are responsible also for the growth of newly formed thermodynamically stable clusters, our finding allows one to postulate that, at the site, α-pinene photo-oxidation products (and probably also photo-oxidation products from other terpenes) are the most likely species to contribute to the growth of nanometersized particles. [ABSTRACT FROM AUTHOR]

The effects of atmospheric aerosol on climate forcing may be very substantial but are quantified poorly at present; in particular, the effects of aerosols on cloud radiative properties, or the "indirect effects" are credited with the greatest range of uncertainty amongst the known causes of radiative forcing. This manuscript explores the effects that the composition and properties of atmospheric aerosol can have on the activation of droplets in warm clouds, so potentially influencing the magnitude of the indirect effect. The effects of size, composition, mixing state and various derived properties are assessed and a range of these properties provided by atmospheric measurements in a variety of locations is briefly reviewed. The suitability of a range of process-level descriptions to capture these aerosol effects is investigated by assessment of their sensitivities to uncertainties in aerosol properties and by their performance in closure studies. The treatment of these effects within global models is reviewed and suggestions for future investigations are made. [ABSTRACT FROM AUTHOR]

The chemical composition of carbonaceous aerosols collected during the LBA-SMOCC field experiment, conducted in Rondônia, Brazil, in 2002 during the transition from the dry to the wet season, was investigated by a suite of advanced analytical techniques. The period of most intense biomass burning was characterized by high concentrations of submicron particles rich in carbonaceous material and water-soluble organic compounds (WSOC). At the onset of the rainy period, submicron total carbon (TC) concentrations had decreased by about 20 times. In contrast, the concentration of supermicron TC was fairly constant throughout the experiment, pointing to a constant emission of coarse particles from the natural background. About 6-8% of TC (9-11% of WSOC) was speciated at the molecular level by GC-MS and liquid chromatography. Poly-hydroxylated compounds, aliphatic and aromatic acids were the main classes of compounds accounted for by individual compound analysis. Functional group analysis by proton NMR and chromatographic separation on ion-exchange columns allowed characterization of ca. 50-90% of WSOC into broad chemical classes (neutral species/light acids/humic-like substances). In spite of the significant change in the chemical composition of tracer compounds from the dry to the wet period, the functional groups and the general chemical classes of WSOC changed only to a lesser extent. Model compounds representing size-resolved WSOC chemical composition for the different periods of the campaign are then proposed in this paper, based on the chemical characterization by both individual compound analysis and functional group analysis deployed during the LBA-SMOCC experiment. Model compounds reproduce quantitatively the average chemical structure of WSOC and can be used as best-guess surrogates in microphysical models involving organic aerosol particles over tropical areas affected by biomass burning. [ABSTRACT FROM AUTHOR]

The organic fraction of atmospheric aerosols contains a multitude of compounds and usually only a small fraction can be identified and quantified. However, a limited number of representative organic compounds can be used to describe the water-soluble organic fraction. In this work, initiated within the EU 5FP project SMOCC, four mixtures containing various amounts of inorganic salts (ammonium sulfate, ammonium nitrate, and sodium chloride) and three model organic compounds (levoglucosan, succinic acid and fulvic acid) were studied. The interaction between water vapor and aerosol particles was studied at different relative humidities: at subsaturation using a hygroscopic tandem differential mobility analyzer (H-TDMA) and at supersaturation using a cloud condensation nuclei spectrometer (CCN spectrometer). Surface tensions as a function of carbon concentrations were measured using a bubble tensiometer. Parameterizations of water activity as a function of molality, based on hygroscopic growth, are given for the pure organic compounds and for the mixtures, indicating van't Hoff factors around 1 for the organics. The Zdanovskii-Stokes-Robinson (ZSR) mixing rule was tested on the hygroscopic growth of the mixtures and it was found to adequately explain the hygroscopic growth for 3 out of 4 mixtures, when the limited solubility of succinic acid is taken into account. One mixture containing sodium chloride was studied and showed a pronounced deviation from the ZSR mixing rule. Critical supersaturations calculated using the parameterizations of water activity and the measured surface tensions were compared with those determined experimentally. [ABSTRACT FROM AUTHOR]

A number of field observations employing aerosol mass spectrometers (AMS) have demonstrated that organic matter rich in monocarboxylic acids and aliphatic carbonyls originating from cooking activities (the COA factor) contributes significantly to ambient organic matter (OM) in urban environments. Little is known about the contribution and nature of COA in rural localities. We studied the correlation of COA with chemical tracers at a rural site in the Po Valley, Italy. Our statistical approach, based on positive matrix factorization (PMF) shows that the COA factor was clearly linked to local emissions of chloride and methanesulfonic acid (MSA), chemical tracers not associated with cooking emissions, or with combustion sources. While the association with Cl is not understood at this stage, the emission of reduced sulfur compounds, aliphatic carbonyls and monocarboxylic acids is consistent with several agricultural practices (e.g., manure storage) and waste disposal systems (e.g., landfills) which characterize the suburban and rural areas of the Po Valley and of other many populated environments. It is concluded that the nature and origins of the AMS COA factor measured at a rural site are complex and include far more than the emissions from food cooking. [ABSTRACT FROM AUTHOR]