One year monitoring of PAHs, nitro-PAHs and oxy-PAHs in Grenoble (France): seasonal variability, gas/particle partitioning, source and cancer risk estimation
Résumé
Polycyclic aromatic hydrocarbons (PAHs) are anthropogenic compounds emitted in the atmosphere into the gaseous and particulate phases via incomplete combustion processes such as residential heating, wood burning and vehicle exhaust (Ravindra et al., 2008). In the troposphere, PAHs may react with oxidants following both, homogeneous and heterogeneous processes, to form oxygenated and nitrated PAHs (OPAHs and NPAHs). Such by-products can also be directly issued from primary emissions concomitantly to PAHs. Ubiquitous presence of atmospheric PAHs is one of major concern, particularly for air quality and are therefore regulated in Europe and USA. OPAHs and NPAHs are recognized as carcinogenic compounds (IARC 2010, 2013) and are probably more mutagenic than their parent PAHs (Rozenkranz and Mermelstein, 1985). Polycyclic aromatics can also be precursors of secondary organic aerosols (SOA) in urban areas (Chan et al., 2009). The aim of this study was to evaluate the variability and the primary/secondary origin of atmospheric PAHs, OPAHs and NPAHs during a period of one year (2013) on an urban sampling site in Grenoble (France). This location is known to be strongly impacted by wood combustion (residential heating) during the winter period. Concentrations of 23 PAHs, 27 OPAHs and 32 NPAHs, including some specific SOA-PAH markers, were measured every 3 days by GC-NICI/MS, in both the gaseous and particulate phases. Measurements of O3, NOx, PM10, PM2.5 and PM10 chemical components (EC/OC, anions/cations, levoglucosan) were also performed. Results showed that the average annual total concentration (gaseous + particulate phases) of Σ23PAHs, Σ27OPAHs were about 10 ng m-3 while Σ32NPAHs concentrations were 50 to 100 times lower. The highest concentration values were observed in the winter period (residential heating and accumulation of pollutants) whereas lower concentration in the warmest season may be explained by prevailing photodegradation processes (Figure 1). Late winter and early spring periods appeared the most favorable period for the formation of secondary OPAH, NPAH and SOA from PAH photooxidation processes. Strong PM pollution events observed in these periods were characterized by a large nitrate and ammonium contribution, and has shown a major influence of primary emissions (residential heating) and limited dispersion of the pollutants.