French network on ultrafine particles monitoring : first results
Résumé
Context : Since 2012, various projects have been dedicated to airborne ultrafine particles by French air quality monitoring networks in Rhône-Alpes, Aquitaine, and PACA, constituting the first French UFP “Observatory”. These projects were carried out with the French reference laboratory for air quality monitoring (LCSQA), leading to the building up of a national Working Group on UFP. Several questions are addressed, including the identification and quantification of local industrial sources, the assessment of the impact of industrial, traffic and residential heating emissions on total particle number, as well as the investigation of phenomena’s influencing UFP concentrations. Method : 7 granulometers UFP3031(*) have been acquired by all the partners. This instrument measures the size distribution and number concentration within 6 particle size classes between 20 and 800 nm. Both short term campaigns and long term monitoring programs have been considered, in mobile or fixed air monitoring stations. The implementation concerns various typologies of stations, close to industry or to traffic, background urban sites (cf. Table 1). Other pollutants were monitored, such as SO2, NOx, PM2.5, PM10 and also PMff, PMwb (fossil fuel and wood burning part of combustion measured with AE33). Results : In a metallurgical complex, investigated through the implementation of a UFP3031 at various places around a steel mill, UFP based wind roses appear to be largely more specific than PM based for identifying the sources. Close to a chemistry area, a strong correlation between UFP <70 nm and SO2 has been observed. Close to heavy traffic roads, UFP size distribution and concentration appeared to be mainly leaded by traffic variations, regardless of seasonal or meteorological conditions. UFP < 50nm roughly represent 50% of the total number concentration. At urban background sites, UFP characteristics are primarily influenced by meteorological parameters. During winter, PMwb (wood burning part) presents a very good correlation with UFP > 70nm (especially 100-200nm). A quite good correlation is also observed with UFP >70nm and pollutants indicators of traffic such as PMff (fossil fuel part) or NO2. During summer season, the UFP monitoring allows also to show the formation of new particles (<50nm) in the afternoon, due to photochemical reactions.