Spatial concentrations and seasonnal variations of gaseous and particulate polycyclic aromatic hydrocarbons (PAH) : cases of Chamonix and Maurienne valleys
Particle size distributions and concentrations of Polycyclic Aromatic Hydrocarbons (PAHs) and Oxygenated PAH (OPAHs) in gas and particle phases were obtained during the program 'POllution des Vallées Alpines' (POVA). The general objectives of this program are the comparative studies of atmospheric pollution and the modeling of atmospheric emissions and transport in two French alpine valleys: Chamonix and Maurienne. Results presented here come from 15 days intensive field campaigns performed in winter 2002-2003 and summer 2003 after the reopening of the 'Tunnel du Mont Blanc' to heavy-duty traffic (which was closed for 3 years). A modified high volume sampler was used to collect PAH and oxygenated PAH in both particulate and gas phases. Size fractionated aerosol samples were collected with a seven stage high volume cascade impactor. Concentrations of 17 PAHs and 4 OPAHs were determined by HPLC coupled with a fluorometric/UV detector. Relationships between evolution of atmospheric PAH concentrations, external parameters (sampling site, meteorological conditions, sources), gas pollutants concentrations (CO, NO, NO2, O3) and the aerosol characteristics (PM10, EC and OC) were also studied. The results obtained in this study suggest : an important anthropogenic contribution in collected aerosol in both valleys, for both seasons and more particularly in winter when important PAH concentrations were observed (maximum average for S16-PAHs about 35 ng.m-3 for the particulate phase and 95 ng.m-3 for the gas phase) ; significant differences in particle size distributions of PAH in relation with source contributions and proximity with a maximum PAH abundance on particles having an aerodynamic diameter less than 1.3 µm in winter and less than 0.39 µm in summer ; for PAHs and OPAHs with molecular weights less than 208, variable gas/particle partioning were observed. The gas phase contribution, ranged from 36 to 100 % for PAHs and from 0 to 100 % for OPAHs, generally decreased with increasing molecular weight and increased with decreasing temperature.