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Fine particulate matter (PM2.5) pollution is still one of China's most important environmental issues, especially in northern cities during wintertime. In this study, intensive real-time measurement campaigns were conducted in Xi’an, Shijiazhuang, and Beijing to investigate the chemical characteristics and source contributions of PM2.5 and explore the formation progress of heavy pollution for policy implications. The chemical compositions of PM2.5 in the three cities were all dominated by organic aerosol (OA) and nitrate (NO3-). Results of source apportionment analyzed by the hybrid environmental receptor model (HERM) showed that the secondary nitrate plus sulfate contributed higher to PM2.5 compared to other primary sources. Biomass burning was the dominant primary source in the three pilot cities. The contribution of coal combustion to PM2.5 is non-negligible in Xi’an and Shijiazhuang but is no longer the important contributor in the capital city of Beijing due to the execution of a strict coal-banning policy. The potential formation mechanisms of secondary aerosol in three cities were further explored by establishing the correlations between the secondary nitrate plus sulfate and aerosol liquid water content (ALWC), and Ox (O3 + NO2), respectively. The results showed that photochemical oxidation and aqueous-phase reaction were two important pathways of secondary aerosol formation. According to the source variations, air pollution events that occurred in campaigns were classified into three types: biomass combustion dominated, secondary nitrate plus sulfate dominated, and a combination of primary and secondary sources. Additionally, this study compared the changes in chemical composition and source contributions of PM2.5 in past decades. The results suggested that the clean energy replacements for the rural household should be urgently encouraged to reduce the primary source emissions in northern China, and collaborative control on ozone and particulate matter need to be continuously promoted to weaken the atmosphere oxidation capacity for the sake of reducing secondary aerosol formation.

We investigated the seasonal trends of OA sources affecting the air quality of Marseille (France) which is the largest harbor of the Mediterranean Sea. This was achieved by measurements of nebulized filter extracts using an aerosol mass spectrometer (offline-AMS). PM2.5 (particulate matter with an aerodynamic diameter

A detailed knowledge of the sources, transformation, and fate of organic aerosols (OA) in the atmosphere has become essential because of their major impacts on climate change and air quality. A complete understanding is still hindered by the immense chemical complexity of the organic fraction emitted from both anthropogenic and biogenic sources (primary organic aerosols, POA) or formed into the atmosphere via the photochemical oxidation of (semi-) volatile organic compounds (secondary organic aerosols, SOA). The chemical speciation of OA and the identification of their major sources are then necessary. So far, detailed information on the chemical components is generally only available for 10–30% of OA. In the present study, the source apportionment of OA is presented based on the characterization of the water-soluble organic fraction of ambient air particles, collected onto conventional filters using offline-AMS analysis. An intensive campaign was performed at SIRTA-LSCE, which illustrates the suburban background conditions of Paris (France). Every 4 hour filter measurements were conducted over a period from 6 to 24, March 2015, concomitantly with online measurements, carried out using ACSM, Aethalometer, TEOM-FDMS, NOx and O3 analyzers. Source apportionment was performed on offline- AMS data by multi-linear engine (ME-2), using the newly developed Source Finder (SoFi) package. External markers (i.e. organic species like MSA, levoglucosan, oxalate and SOA molecular compounds) are used to substantiate the presence of primary and secondary factors. SoFi outputs indicate that some factors highlight different contribution over the first and second half of the sampling campaign, advocating the role of different chemical processes during these periods. Data analysis also provides more information about the different factors, their contribution to OA and existing major OA sources in Paris. Finally, results clearly illustrate the benefit of combining different measurements and the use of external markers, in aerosol source apportionment studies.