Size distribution of EC and OC in the aerosol of Alpine valleys during summer and winter

International audienceCollections of samples were conducted for the determination of the size distributions of EC and OC during the intensive sampling campaigns of the POVA program, in two Alpine valleys of the French Alps, in summer and in winter. The comparison of concentrations obtained for samples collected in parallel with impactor- and filter-based methods indicates that the correction of pyrolysis seems to work for the impactor samples despite non even deposits. The size distributions of the concentrations of EC and OC present large evolutions between winter and summer, and between a suburban and a rural site. In winter, an overwhelming proportion of the mass fraction of both species is found in the droplet and accumulation modes, often (but not always) in association with sulfate and other chemical species resulting from secondary formation processes. Some indications of gas/particles exchanges can be found for the other parts of the size spectrum (the Aitken and super micron modes) in the case of the rural site. In summer, the changes are more drastic with, according to the case, a dominant droplet or accumulation mode. Particularly at the rural site, the large extent of processing of the aerosol due to gas/particles exchanges is evident for the Aitken and super micron modes, with increasing of the OC mass fractions in these size ranges. All of these observations give indications on the degree of internal vs. external mixing of the species investigated in the different modes

Size distribution of EC and OC in the aerosol of Alpine valleys during summer and winter

Collections of samples were conducted for the determination of the size distributions of EC and OC during the intensive sampling campaigns of the POVA program, in two Alpine valleys of the French Alps, in summer and in winter. The comparison of concentrations obtained for samples collected in parallel with impactor- and filter-based methods is rather positive with slopes of 0.95 and 0.76 for OC and EC, respectively and correlations close to 1 (0.92 and 0.90 for OC and EC, respectively, n=26). This is an indication that the correction of pyrolysis seems to work for the impactor samples despite non even deposits. The size distributions of the concentrations of EC and OC present large evolutions between winter and summer, and between a suburban and a rural site. In winter, an overwhelming proportion of the mass fraction of both species is found in the droplet and accumulation modes, often (but not always) in association with sulfate and other chemical species resulting from secondary formation processes. Some indications of gas/particles exchanges can be found for the other parts of the size spectrum (the Aitken and super micron modes) in the case of the rural site. In summer, the changes are more drastic with, according to the case, a dominant droplet or accumulation mode. Particularly at the rural site, the large extent of processing of the aerosol due to gas/particles exchanges is evident for the Aitken and super micron modes, with increasing of the OC mass fractions in these size ranges. All of these observations give indications on the degree of internal vs. external mixing of the species investigated in the different modes

Polycyclic aromatic hydrocarbons (PAHs) in the atmospheres of two French alpine valleys: sources and temporal patterns

International audienceAlpine valleys represent some of the most important crossroads for international heavy-duty traffic in Europe, but the full impact of this traffic on air quality is not known due to a lack of data concerning these complex systems. As part of the program "Pollution des Vallées Alpines" (POVA), we performed two sampling surveys of polycyclic aromatic hydrocarbons (PAHs) in two sensitive valleys: the Chamonix and Maurienne Valleys, between France and Italy. Sampling campaigns were performed during the summer of 2000 and the winter of 2001, with both periods taking place during the closure of the "Tunnel du Mont-Blanc". The first objective of this paper is to describe the relations between PAH concentrations, external parameters (sampling site localization, meteorological parameters, sources), and aerosol characteristics, including its carbonaceous fraction (OC and EC). The second objective is to study the capacity of PAH profiles to accurately distinguish the different emission sources. Temporal evolution of the relative concentration of an individual PAH (CHR) and the PAH groups BghiP+COR and BbF+BkF is studied in order to differentiate wood combustion, gasoline, and diesel emissions, respectively. The results show that the total particulate PAH concentrations were higher in the Chamonix valley during both seasons, despite the cessation of international traffic. Seasonal cycles, with higher concentrations in winter, are also stronger in this valley. During winter, particulate PAH concentration can reach very high levels (up to 155 ng.m-3) in this valley during cold anticyclonic periods. The examination of sources shows the impact during summer of heavy-duty traffic in the Maurienne valley and of gasoline vehicles in the Chamonix valley. During winter, Chamonix is characterized by the strong influence of wood combustion in residential fireplaces, even if the temporal evolution of specific PAH ratios are difficult to interpret. Information on sources given by PAH profiles can only be considered in qualitative terms

Yearly chemical profiles of aerosol in 2 Alpine valleys

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VOCS EVOLUTION DURING A SAHARAN DUST EPISODE IN AN ALPINE VALLEY IN AUGUST 2000

International audienceAs part of a regional project of the study of pollution in two alpine valleys (POVA), an intensive campaign of measurements for VOCs, carbonyl compounds, PM 10 , particles and major ionic species was performed in Maurienne Valley (French Alps) during one week in August 2000. In summer, under anticyclonic conditions, the dispersion of air pollutants in deep valleys is mainly dependent on an usual characteristic cycle: up-valley wind for the day, down-valley wind for the night. During the sampling campaign, the diurnal variation west-east wind was changed by a South wind for two days. A saharan dust episode occurred, characterized by large increases of PM 10 , large particles, and Ca 2+. This dust episode was followed by an increase of fine particles (0.3 µm) and of SO 4 2-. , indicating the intrusion of an anthropogenic air mass. The evolution of VOCs have been influenced by these events and the concentration levels were higher during this period. The ratio benzene/ toluene was low (0.7) during the episode, which indicates an urban pollution

VOCS EVOLUTION DURING A SAHARAN DUST EPISODE IN AN ALPINE VALLEY IN AUGUST 2000

International audienceAs part of a regional project of the study of pollution in two alpine valleys (POVA), an intensive campaign of measurements for VOCs, carbonyl compounds, PM 10 , particles and major ionic species was performed in Maurienne Valley (French Alps) during one week in August 2000. In summer, under anticyclonic conditions, the dispersion of air pollutants in deep valleys is mainly dependent on an usual characteristic cycle: up-valley wind for the day, down-valley wind for the night. During the sampling campaign, the diurnal variation west-east wind was changed by a South wind for two days. A saharan dust episode occurred, characterized by large increases of PM 10 , large particles, and Ca 2+. This dust episode was followed by an increase of fine particles (0.3 µm) and of SO 4 2-. , indicating the intrusion of an anthropogenic air mass. The evolution of VOCs have been influenced by these events and the concentration levels were higher during this period. The ratio benzene/ toluene was low (0.7) during the episode, which indicates an urban pollution

VOCS EVOLUTION DURING A SAHARAN DUST EPISODE IN AN ALPINE VALLEY IN AUGUST 2000

International audienceAs part of a regional project of the study of pollution in two alpine valleys (POVA), an intensive campaign of measurements for VOCs, carbonyl compounds, PM 10 , particles and major ionic species was performed in Maurienne Valley (French Alps) during one week in August 2000. In summer, under anticyclonic conditions, the dispersion of air pollutants in deep valleys is mainly dependent on an usual characteristic cycle: up-valley wind for the day, down-valley wind for the night. During the sampling campaign, the diurnal variation west-east wind was changed by a South wind for two days. A saharan dust episode occurred, characterized by large increases of PM 10 , large particles, and Ca 2+. This dust episode was followed by an increase of fine particles (0.3 µm) and of SO 4 2-. , indicating the intrusion of an anthropogenic air mass. The evolution of VOCs have been influenced by these events and the concentration levels were higher during this period. The ratio benzene/ toluene was low (0.7) during the episode, which indicates an urban pollution

Seasonal variation of PM10 main constituents in two valleys of the French Alps, I : EC/OC fractions

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