Relationships are analysed between advection pathways and atmospheric composition at the high-mountain station of Mt. Cimone (Italy), between 1998 and 2011. Back-trajectory cluster analysis identifies eight main advection pathways. A connection is demonstrated between the seasonality of airmass transport and atmospheric composition. Temporal trends and correlation of variables, flow types and teleconnection indices show, among other, decreasing trends of Pb-210 (a radionuclide of crustal origin; -0.008 mBq m(-3) year as well as PM10 (-0.15 mu g m(-3) year(-1)), indicating that previously observed downward PM10 trends in Europe may actually be attributable to a combination of meteorological factors and decreasing anthropogenic emissions. The detection of a positive (negative) correlation of these tracers with Western (Arctic) air masses, showing significant downward (upward) trends at the study site, further confirms our findings. Lastly, relationships between teleconnection indices and atmospheric transport types/atmospheric variables are further analysed, focusing on large-scale atmospheric circulation indices and regional low-frequency atmospheric circulation pathways, the Mediterranean Oscillation and the Western Mediterranean Oscillation. The analysis reveals the important influence of such regional indices on the advection pathways.

Aerosols of biogenic and anthropogenic origin affect the total radiative forcing of global climate. Poor knowledge of the pre-industrial aerosol concentration and composition, in particular of particles formed directly in the atmosphere from gaseous precursors, constitutes a large uncertainty in the anthropogenic radiative forcing. Investigations of new particle formation at pre-industrial-like conditions can contribute to the reduction of this uncertainty. Here we present observations taken at the remote Nepal Climate Observatory Pyramid station at 5,079 m above sea level, a few kilometres from the summit of Everest. We show that up-valley winds funnel gaseous aerosol precursors to higher altitudes. During this transport, these are oxidized into compounds of very low volatility, which rapidly form a large number of aerosol particles. These are then transported into the free troposphere, which suggests that the whole Himalayan region may act as an ‘aerosol factory’ and contribute substantially to the free tropospheric aerosol population. Aerosol production in this region occurs mainly via organic precursors of biogenic origin with little evidence of the involvement of anthropogenic pollutants. This process is therefore likely to be essentially unchanged since the pre-industrial period, and may have been one of the major sources that contributes to the upper tropospheric aerosol population during that time. Newly formed biogenic particles in the Himalaya increase free-tropospheric background aerosol concentration by a factor of up to two.

CNR-ISAC, National Research Council of Italy, Institute of Atmospheric Sciences and Climate, Bologna, Italy ENEA, Roma, Italy University "G. d'Annunzio" of Chieti-Pescara, Department of Psychological, Health & Territorial Sciences, Chieti, Italy National Research Council of Italy, Institute of Atmospheric Pollution, Rende, Italy National Research Council of Italy, Institute of Dynamics for Environmental Processess, Venezia, Italy University of Urbino, Department of Pure and Applied Sciences, Urbino, Italy

Organic (OC) and Elemental Carbon (EC) are important components of atmospheric aerosol particles, playing a key role in climate system and potentially affecting human health. There is a lack of data reported for Southern Italy and this work aims to fill this gap, focusing the attention on the long-term trends of OC and EC concentrations in PM2.5 and PM10, and on atmospheric processes and sources influencing seasonal variability. Measurements were taken at the Environmental-Climate Observatory of Lecce (SE Italy, 40°20′8″N-18°07′28″E, 37ma.s.l.), regional station of the Global Atmosphere Watch program (GAW-WMO). Daily PM10 and PM2.5 samples were collected between July 2013 and July 2016. In addition, starting in December 2014, simultaneous equivalent Black Carbon (eBC) concentrations in PM10 were measured using a Multi Angle Absorption Photometer. A subset of 722PM samples (361 for each size fraction) was analysed by using a thermo-optical method with a Sunset Laboratory OC/EC analyser, to determine elemental and organic carbon concentrations. The average PM10 and PM2.5 concentrations were 28.8μg/m3 and 17.5μg/m3. The average OC and EC concentrations in PM10 were 5.4μg/m3 and 0.8μg/m3, in PM2.5 these were 4.7μg/m3 and 0.6μg/m3. Carbonaceous content was larger during cold season with respect to warm season as well as secondary organic carbon (SOC) that was evaluated using the OC/EC minimum ratio method. SOC was mainly segregated in PM2.5 and represented 53% - 75% of the total OC. A subset of EC data was compared with eBC measurements, showing a good correlation (R2=0.80), however, eBC concentrations were higher than EC concentrations of an average factor of 1.95 (+/− 0.55 standard deviation). This could be explained by the presence of a contribution of Brown Carbon (BrC), for example from biomass burning, in eBC measurements. Weekly patterns showed a slight decrease of carbon content during weekends with respect to weekdays especially visible on eBC concentration due to the decrease of road traffic emissions. The daily patterns of hourly eBC concentrations showed a decrease in central diurnal hours, due to the cycle of planetary boundary-layer height, and concentrations peaks during rush hours due to road traffic emissions.

Comparison of fine and coarse fractions in terms of sources and dynamics is scarce in southeast Mediterranean countries; differences are relevant because of the importance of natural sources like sea spray and Saharan dust advection, because most of the monitoring networks are limited to PM10. In this work, the main seasonal variabilities of sources and processes involving fine and coarse PM (particulate matter) were studied at the Environmental-Climate Observatory of Lecce (Southern Italy). Simultaneous PM2.5 and PM10 samples were collected between July 2013 and July 2014 and chemically analysed to determine concentrations of several species: OC (organic carbon) and EC (elemental carbon) via thermo-optical analysis, 9 major ions via IC, and 23 metals via ICP-MS. Data was processed through mass closure analysis and Positive Matrix Factorization (PMF) receptor model characterizing seasonal variabilities of nine sources contributions. Organic and inorganic secondary aerosol accounts for 43% of PM2.5 and 12% of PM2.5–10 with small seasonal changes. SIA (secondary inorganic aerosol) seasonal pattern is opposite to that of SOC (secondary organic carbon). SOC is larger during the cold period, sulphate (the major contributor to SIA) is larger during summer. Two forms of nitrate were identified: NaNO3, correlated with chloride depletion and aging of sea-spray, mainly present in PM2.5–10; NH4NO3 more abundant in PM2.5. Biomass burning is a relevant source with larger contribution during autumn and winter because of the influence of domestic heating, however, is not negligible in spring and summer, because of the contributions of fires and agricultural practices. Mass closure analysis and PMF results identify two soil sources: crustal associated to long range transport and carbonates associated to local resuspended dust. Both sources contributes to the coarse fraction and have different dynamics with crustal source contributing mainly in high winds from SE conditions and carbonates during high winds from North direction.

Measurement campaigns at the high mountain Observatory Mt. Cimone (CMN; 2165 m a.s.l.) were performed during May 2014 and October 2015. The concentration of Ice Nucleating Particles (INPs) were measured offline with a dynamic filter processing chamber (DFPC), in the deposition and condensation mode, after collecting PM1. and PM10 aerosol samples. Presented INP data are the first ever published for a high mountain site in the Mediterranean basin. During the May campaign, parallel INP measurements were also carried out at San Pietro Capofiume (SPC), a low altitude rural background area within the Po Valley basin, by the same offline technique. The average INPPM10 concentration at CMN was 86 m(-3) (saturation ratio S-W = 1.01; T =-18 degrees C) during the May 2014 campaign, while it was 171 m(-3) at SPC, in the same period. A lower average INPPM10 concentration was observed at CMN during October 2015 (43 m(-3)). A significantly higher activated fraction (AF) characterized the October 2015 campaign, suggesting that the seasonal changes in the aerosol sources have an impact on the INP efficiency of the aerosol at CMN. Super-micrometer INP contributed for similar to 30% of total INP in the May 2014 campaign, at both sites, and for similar to 70% in the October 2015 campaign, showing the importance of coarse particles in the INP population. The analysis of meteorological parameters, gaseous tracers concentrations and backwards trajectories suggests that the INP population at CMN is contributed by transport processes occurring at diverse spatial scales, from the local to the synoptic scale. During the Saharan Dust transport Event observed in May 2014, a reduction of the AF was observed, suggesting, for this case, a limited ice nucleating activity for Saharan dust particles. This may be due to physico-chemical aging of the Saharan dust particles during transport or to the relatively high activation temperature at which the experiments were performed in this study.

In this work, we analysed reactive gases (O-3, CO, NOx) and aerosol properties (eqBC, sigma(s) and particle number concentration) collected at the WMO/GAW Mt. Cimone station (2165 m a.s.l., Italy) during the summer of 2012 in the framework of PEGASOS project. The major aim of this experiment is providing a characterization of the variability of summer atmospheric composition over the central Mediterranean basin, which is considered as a global "hot-spot" for atmospheric pollution and climate change.The atmospheric tracers have been analysed as a function of (i) meteorological parameters, (ii) synoptic-scale circulation and (iii) anthropogenic emission source proximity as estimated by O-3/NOx ratio variability. In particular, we identified three O-3/NOx regimes which tagged the distance of anthropogenic sources: near outflow (23% of hourly data), far-outflow (38% of data) and background (39% of data). The highest levels of anthropogenic pollutants (e.g. O-3, CO, eqBC, accumulation particles) were concomitant with fresh emissions from northern Italy under near-outflow conditions: once injected to the free troposphere, these air-masses, rich in pollutants and climate-forcers (i.e. O-3, eqBC) and soil dust, can be spread over a large region, thus significantly affecting regional climate. Moreover, based on the anthropogenic source proximity, atmospheric tracer variability and synoptic-scale atmospheric circulation, we categorized and characterised four types of atmospheric regimes associated with (1) air-mass transport from the free troposphere, (2) transport of fresh emitted pollutants from the PBL, (3) transport at regional/continental scale of aged anthropogenic (4) transport of air-mass rich in mineral dust from northern Africa (i.e. coming from more than 1000 km).Lastly, by analysing the probability density functions (PDFs) of trace gases and aerosol properties, "fingerprints" of the mentioned atmospheric regimes were pointed out. Such information is useful for the implementation of early-warning services, for the timely detection of event occurrence as well as for the definition of observation-based diagnostic for model verifications. (C) 2016 Elsevier Ltd. All rights reserved.

Black carbon (BC) in snow in the Himalayas has recently attracted considerable interest due to its impact on snow albedo, snow and glacier melting, regional climate and water resources. A single particle soot photometer (SP2) instrument was used to measure refractory BC (rBC) in a series of surface snow samples collected in the upper Khumbu Valley, Nepal between November 2009 and February 2012. The obtained time series indicates annual cycles with maximum rBC concentrations before the onset of the monsoon season and fast decreases during the monsoon period. Detected concentrations ranged from a few up to 70 ppb with rather large uncertainties due to the handling of the samples. Detailed modeling of the snowpack, including the detected range and an estimated upper limit of BC concentrations, was performed to study the role of BC in the seasonal snowpack. Simulations were performed for three winter seasons with the snowpack model Crocus, including a detailed description of the radiative transfer inside the snowpack. While the standard Crocus model strongly overestimates the height and the duration of the seasonal snowpack, a better calculation of the snow albedo with the new radiative transfer scheme enhanced the representation of the snow. However, the period with snow on the ground without BC in the snow was still overestimated between 37 and 66 days, which was further diminished by 8 to 15 % and more than 40 % in the presence of 100 or 300 ppb of BC. Compared to snow without BC, the albedo is reduced on average by 0.027 and 0.060 in the presence of 100 and 300 ppb BC. While the impact of increasing BC in the snow on the albedo was largest for clean snow, the impact on the local radiative forcing is the opposite. Here, increasing BC caused an even larger impact at higher BC concentrations. This effect is related to an accelerated melting of the snowpack caused by a more efficient metamorphism of the snow due to an increasing size of the snow grains with increasing BC concentrations. The melting of the winter snowpack was shifted by 3 to 10 and 17 to 27 days during the three winter seasons in the presence of 100 and 300 ppb BC compared to clean snow, while the simulated annual local radiative forcing corresponds to 3 to 4.5 and 10.5 to 13.0 W m−2. An increased sublimation or evaporation of the snow reduces the simulated radiative forcing, leading to a net forcing that is lower by 0.5 to 1.5 W m−2, while the addition of 10 ppm dust causes an increase of the radiative forcing between 2.5 and 3 W m−2. According to the simulations, 7.5 ppm of dust has an effect equivalent to 100 ppb of BC concerning the impact on the melting of the snowpack and the local radiative forcing.

The Mediterranean basin represents a hot spot area for short-term O-3 distribution and anthropogenic contributions to it. This is why we analysed in this work the surface O-3 variability observed at Mt. Cimone WMO/GAW global station (CMN, 44 degrees 12' N, 10 degrees 42' E, 2165 m a.s.l., Italy) from 1991 to 2011. The measurements performed at this mountain observatory represent the longest surface O-3 record at a baseline site in the Mediterranean basin.Monthly O-3 averages at CMN show a typical seasonal cycle characterised by a winter minimum and a spring - summer maxima. The shape of the mean annual variation of O-3 is well comparable with those observed at other four baseline sites in the Alps and in the Mediterranean region: Jungfraujoch - Swiss Alps, Sonnblick - Austrian Alps, Mt Krvavec- Slovenia and Giordan Lightouse - Island of Gozo, Malta. In general, O-3 levels at CMN show higher values during warm months, which is likely to be related both to vertical transport of polluted air-masses at regional and continental scales and to enhanced photochemistry.Here, we also investigate the influence of specific atmospheric processes (i.e. the occurrence of heat-waves, North Atlantic Oscillation, thermal transport of air-masses from the regional PBL and strato-spheric intrusions) in affecting O-3 variability at CMN.Overall, a significant positive (95% confidence level) linear trend in monthly O-3 mole fraction was observed over the period 1991-2011 (0.21 +/- 0.10 nmol/mol yr(-1)) while no trend (-0.02 +/- 0.12 nmol/ mol yr(-1)) was detected for the 1996-2011, when measurements were carried out by an homogeneous set-up. On a seasonal basis, a positive trend has been observed for 1996-2011 (0.34 +/- 032 nmol/mol yr(-1)) only for spring. Significant decreases of the seasonal O-3 growth-rates have been detected at CMN during 1991-2011 from winter to spring and only for summer during 1996-2011. (C) 2014 The Authors. Published by Elsevier Ltd.

High-resolution aerosol mass spectrometer measurements were performed, for the first time, at the Mt. Cimone Global Atmosphere Watch (GAW) station between June and July 2012, within the EU project PEGASOS and the ARPA–Emilia-Romagna project SUPERSITO. Submicron aerosol was dominated by organics (63 %), with sulfate, ammonium and nitrate contributing the remaining 20, 9 and 7 %, respectively. Organic aerosol (OA) was in general highly oxygenated, consistent with the remote character of the site; our observations suggest that oxidation and secondary organic aerosol (SOA) formation processes occurred during aerosol transport to high altitudes. All of the aerosol component concentrations as well as the OA elemental ratios showed a clear daily trend, driven by the evolution of the planetary boundary layer (PBL) and by the mountain wind regime. Higher loadings and lower OA oxidation levels were observed during the day, when the site was within the PBL, and therefore affected by relatively fresh aerosol transported from lower altitudes. Conversely, lower loadings and higher OA oxidation levels were observed at night, when the top of Mt. Cimone resided in the free troposphere although affected by the transport of residual layers on several days of the campaign. Analysis of the elemental ratios in a Van Krevelen space shows that OA oxidation follows a slope comprised between −0.5 and −1, consistent with addition of carboxylic groups, with or without fragmentation of the parent molecules. The increase of carboxylic groups during OA ageing is confirmed by the increased contribution of organic fragments containing more than one oxygen atom in the free troposphere night-time mass spectra. Finally, positive matrix factorization was able to deconvolve the contributions of relatively fresh OA (OOAa) originating from the PBL, more aged OA (OOAb) present at high altitudes during periods of atmospheric stagnation, and very aged aerosols (OOAc) transported over long distances in the free troposphere.

The Kathmandu Valley in south Asia is considered as one of the global "hot spots" in terms of urban air pollution. It is facing severe air quality problems as a result of rapid urbanization and land use change, socioeconomic transformation, and high population growth. In this paper, we present the first full year (February 2013–January 2014) analysis of simultaneous measurements of two short-lived climate forcers/pollutants (SLCF/P), i.e., ozone (O3) and equivalent black carbon (hereinafter noted as BC) and aerosol number concentration at Paknajol, in the city center of Kathmandu. The diurnal behavior of equivalent BC and aerosol number concentration indicated that local pollution sources represent the major contributions to air pollution in this city. In addition to photochemistry, the planetary boundary layer (PBL) and wind play important roles in determining O3 variability, as suggested by the analysis of seasonal changes of the diurnal cycles and the correlation with meteorological parameters and aerosol properties. Especially during pre-monsoon, high values of O3 were found during the afternoon/evening. This could be related to mixing and entrainment processes between upper residual layers and the PBL. The high O3 concentrations, in particular during pre-monsoon, appeared well related to the impact of major open vegetation fires occurring at the regional scale. On a synoptic-scale perspective, westerly and regional atmospheric circulations appeared to be especially conducive for the occurrence of the high BC and O3 values. The very high values of SLCF/P, detected during the whole measurement period, indicated persisting adverse air quality conditions, dangerous for the health of over 3 million residents of the Kathmandu Valley, and the environment. Consequently, all of this information may be useful for implementing control measures to mitigate the occurrence of acute pollution levels in the Kathmandu Valley and surrounding area.

Continuous measurements of physical and chemical properties at the Mt. Cimone (Italy) GAW-WMO (Global Atmosphere Watch, World Meteorological Organization) Global Station (2165 m a.s.l.) have allowed the detection of the volcanic aerosol plume resulting from the Eyjafjallajökull (Iceland) eruption of spring 2010. The event affected the Mt. Cimone 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 April 19 to 21 and the second from 18 to 20 May 2010. This paper reports the modification of aerosol characteristics observed during the two episodes, both characterised 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, particle induced X-ray emission–particle induced gamma-ray emission (PIXE–PIGE) and inductively coupled plasma mass spectrometry (ICP-MS)) were performed on aerosols collected by ground-level discrete sampling. The resulting database allows the characterisation 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 in-plume oxidation of volcanic SO2. By contrast, the coarse fraction was characterised 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 μg m−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 light of the huge distance of Mt. Cimone from the source, confirming the widespread diffusion of the Eyjafjallajökull ashes over Europe.

A shallow ice core was extracted at the summit of Mera Peak at 6376 m a.s.l. in the southern flank of the Nepalese Himalaya range. From this core, we reconstructed the seasonal deposition fluxes of dust and refractory black carbon (rBC) since 1999. This archive presents well preserved seasonal cycles based on a monsoonal precipitation pattern. According to the seasonal precipitation regime in which 80% of annual precipitation falls between June and September, we estimated changes in the concentrations of these aerosols in surface snow. The analyses revealed that mass fluxes are a few orders of magnitude higher for dust (10.4 ± 2.8 g m−2 yr−1 than for rBC (7.9 ± 2.8 mg m−2 yr−1). The relative lack of seasonality in the dust record may reflect a high background level of dust inputs, whether from local or regional sources. Over the 10-year record, no deposition flux trends were detected for any of the species of interest. The data were then used to simulate changes in the surface snow albedo over time and the potential melting caused by these impurities. Mean potential melting caused by dust and rBC combined was 713 kg m−2 yr−1, and for rBC alone, 342 kg m−2 yr−1 for rBC under certain assumptions. Compared to the melting rate measured using the mass and energy balance at 5360 m a.s.l. on Mera Glacier between November 2009 and October 2010, i.e. 3000 kg m−2 yr−1 and 3690 kg m−2 yr−1 respectively, the impact of rBC represents less than 16% of annual potential melting while the contribution of dust and rBC combined to surface melting represents a maximum of 26%. Over the 10-year period, rBC variability in the ice core signal primarily reflected variability of the monsoon signal rather than variations in the intensity of emissions.

Long-term monitoring of the chemical composition of clouds (73 cloud events representing 199 individual samples) sampled at the puy de Dôme (pdD) station (France) was performed between 2001 and 2011. Physicochemical parameters, as well as the concentrations of the major organic and inorganic constituents, were measured and analyzed by multicomponent statistical analysis. Along with the corresponding back-trajectory plots, this allowed for distinguishing four different categories of air masses reaching the summit of the pdD: polluted, continental, marine and highly marine. The statistical analysis led to the determination of criteria (concentrations of inorganic compounds, pH) that differentiate each category of air masses. Highly marine clouds exhibited high concentrations of Na+ and Cl−; the marine category presented lower concentration of ions but more elevated pH. Finally, the two remaining clusters were classified as "continental" and "polluted"; these clusters had the second-highest and highest levels of NH4+, NO3−, and SO24−, respectively. This unique data set of cloud chemical composition is then discussed as a function of this classification. Total organic carbon (TOC) is significantly higher in polluted air masses than in the other categories, which suggests additional anthropogenic sources. Concentrations of carboxylic acids and carbonyls represent around 10% of the organic matter in all categories of air masses and are studied for their relative importance. Iron concentrations are significantly higher for polluted air masses and iron is mainly present in its oxidation state (+II) in all categories of air masses. Finally, H2O2 concentrations are much more varied in marine and highly marine clouds than in polluted clouds, which are characterized by the lowest average concentration of H2O2. This data set provides concentration ranges of main inorganic and organic compounds for modeling purposes on multiphase cloud chemistry.

Cluster~analysis of particle number size distributions from~background sites across Europe~is presented. This generated a total of nine clusters of particle size distributions which could be further combined into two main groups, namely: a south-to-north category (four clusters) and a west-to-east category (five clusters). The first group was identified as most frequently being detected inside and around northern Germany and neighbouring countries, showing clear evidence of local afternoon nucleation and growth events that could be linked to movement of air masses from south to north arriving ultimately at the Arctic contributing to Arctic haze.~The second group of particle size spectra proved to have narrower size distributions and collectively showed a dependence of modal diameter upon the longitude of the site (west to east) at which they were most frequently detected.~These clusters indicated regional nucleation (at the coastal sites) growing to larger modes further inland. The apparent growth rate of the modal diameter was around 0.6–0.9 nm h−1. Four specific air mass back-trajectories were successively taken as case studies to examine in real time the evolution of aerosol size distributions across Europe. ~While aerosol growth processes can be observed as aerosol traverses Europe, the processes are often obscured by the addition of aerosol by emissions en route. This study revealed that some of the 24 stations exhibit more complex behaviour than others, especially when impacted by local sources or a variety of different air masses. Overall, the aerosol size distribution clustering analysis greatly simplifies the complex data set and allows a description of aerosol aging processes, which reflects the longer-term average development of particle number size distributions as air masses advect across Europe.

We applied a climate-chemistry global model to evaluate the impact of black carbon (BC) deposition on the Himalayan snow cover from 1998 to 2008. Using a stretched grid with a resolution of 50 km over this complex topography, the model reproduces reasonably well the remotely sensed observations of the snow cover duration. Similar to observations, modelled atmospheric BC concentrations in the central Himalayas reach a minimum during the monsoon and a maximum during the post- and pre-monsoon periods. Comparing the simulated BC concentrations in the snow with observations is more challenging because of their high spatial variability and complex vertical distribution. We simulated spring BC concentrations in surface snow varying from tens to hundreds of μg kg−1, higher by one to two orders of magnitude than those observed in ice cores extracted from central Himalayan glaciers at high elevations (>6000 m a.s.l.), but typical for seasonal snow cover sampled in middle elevation regions (<6000 m a.s.l.). In these areas, we estimate that both wet and dry BC depositions affect the Himalayan snow cover reducing its annual duration by 1 to 8 days. In our simulations, the effect of anthropogenic BC deposition on snow is quite low over the Tibetan Plateau because this area is only sparsely snow covered. However, the impact becomes larger along the entire Hindu-Kush, Karakorum and Himalayan mountain ranges. In these regions, BC in snow induces an increase of the net short-wave radiation at the surface with an annual mean of 1 to 3 W m−2 leading to a localised warming between 0.05 and 0.3 °C.