Variations in the chemical composition of the submicron aerosol and in the sources of the organic fraction at a regional background site of the Po Valley (Italy)

摘要

pstrongAbstract./strong Fine particulate matter (PM) levels and resulting impacts on human health are in the Po Valley (Italy) among the highest in Europe. To build effective PM abatement strategies, it is necessary to characterize fine PM chemical composition, sources and atmospheric processes on long timescales (&span class="thinspace"/spanmonths), with short time resolution (&span class="thinspace"/spanday), and with particular emphasis on the predominant organic fraction. Although previous studies have been conducted in this region, none of them addressed all these aspects together. For the first time in the Po Valley, we investigate the chemical composition of nonrefractory submicron PM (NR-PMsub1/sub) with a time resolution of 30span class="thinspace"/spanmin at the regional background site of Ispra during 1 full year, using the Aerodyne Aerosol Chemical Speciation Monitor (ACSM) under the most up-to-date and stringent quality assurance protocol. The identification of the main components of the organic fraction is made using the Multilinear-Engine 2 algorithm implemented within the latest version of the SoFi toolkit. In addition, with the aim of a potential implementation of ACSM measurements in European air quality networks as a replacement of traditional filter-based techniques, parallel multiple offline analyses were carried out to assess the performance of the ACSM in the determination of PM chemical species regulated by air quality directives. The annual NR-PMsub1/sub level monitored at the study site (14.2span class="thinspace"/span?μgspan class="thinspace"/spanmsupa??3/sup) is among the highest in Europe and is even comparable to levels reported in urban areas like New York City and Tokyo. On the annual basis, submicron particles are primarily composed of organic aerosol (OA, 58span class="thinspace"/span% of NR-PMsub1/sub). This fraction was apportioned into oxygenated OA (OOA, 66span class="thinspace"/span%), hydrocarbon-like OA (HOA, 11span class="thinspace"/span% of OA) and biomass burning OA (BBOA, 23span class="thinspace"/span%). Among the primary sources of OA, biomass burning (23span class="thinspace"/span%) is thus bigger than fossil fuel combustion (11span class="thinspace"/span%). Significant contributions of aged secondary organic aerosol (OOA) are observed throughout the year. The unexpectedly high degree of oxygenation estimated during wintertime is probably due to the contribution of secondary BBOA and the enhancement of aqueous-phase production of OOA during cold months. BBOA and nitrate are the only components of which contributions increase with the NR-PMsub1/sub levels. Therefore, biomass burning and NOsubix/i/sub emission reductions would be particularly efficient in limiting submicron aerosol pollution events. Abatement strategies conducted during cold seasons appear to be more efficient than annual-based policies. In a broader context, further studies using high-time-resolution analytical techniques on a long-term basis for the characterization of fine aerosol should help better shape our future air quality policies, which constantly need refinement./p.