Source apportionment of PM10 in a North-Western Europe regional urban background site (Lens, France) : interest of the use of organic tracers in a positive matrix factorization methodology
Résumé
The sources of ambient particulate matter (PM10) collected over a one year period at an urban background site in Lens (France) were determined with Positive Matrix Factorization (US EPA PMF v3.0). Components measured and used in the PMF include the conventional species (soluble ionic species, trace elements, levoglucosan, elemental carbon (EC) and organic carbon (OC)) and also a wide range of organic tracers (sugars alcohols, hopanes, alkanes, sulfur containing PAH, PAH and methylPAH). A selective iteration process was followed for the qualification of the more robust and meaningful PMF solution. The contribution made by organic tracers on the PMF output increases the ability to identify and define some PM sources like primary biogenic emission and combustion source. By using this data set, PMF outputs showed that the main emission sources were (in a decreasing order of contribution): secondary inorganic aerosols, biomass burning, aged marine emissions, with probably predominant contribution of shipping activities, mineral dust, fresh sea salts, primary biogenic emissions, traffic emissions, and coal combustion. Significant temporal variations were observed for most of the identified sources. Biomass burning emissions were weak in summer but responsible for a much larger fraction of total OC in wintertime. In addition, the factor "coal combustion" also presents a very marked seasonal variability since it is negligible in summer and increases in winter. This factor has been identified and quantified using organic markers such as PAHs and sulfur containing PAHs. Conversely, primary biogenic emissions were negligible in winter but represent large fraction in summer. The latter result calls for more investigations of primary biogenic aerosols using source apportionment studies, which quite usually disregards this type of sources.