Formation of secondary organic aerosol in the Paris pollution plume and its impact on surrounding regions

• Published in: Atmospheric chemistry and physics 2015-12, Vol.15 (24), p.13973-13992
• Main Authors: Zhang, Q. J, Beekmann, M, Freney, E, Sellegri, K, Pichon, J. M, Schwarzenboeck, A, Colomb, A, Bourrianne, T, Michoud, V, Borbon, A
• Format: Article
• Language: English
• Subjects: Aerosols; Ageing; Agglomeration; Aging; Air pollution; Air quality; Airborne sensing; Aircraft; Anthropogenic factors; Atmospheric and Oceanic Physics; Atmospheric chemistry; Climate effects; Computer simulation; Configurations; Emission; Emission inventories; Emissions; Environmental aspects; Evaluation; Frameworks; Human influences; Megacities; Mitigation; Nitrogen compounds; Organic compounds; Oxidation; Oxides; Ozone; Photochemicals; Photochemistry; Physics; Plumes; Pollutants; Pollution; Precursors; Ratios; Regional analysis; Secondary aerosols; Silicon compounds; Slope; Slopes; VOCs; Volatile organic compounds; Volatility
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-15-13973-2015

Secondary pollutants such as ozone, secondary inorganic aerosol, and secondary organic aerosol formed in the plumes of megacities can affect regional air quality. In the framework of the FP7/EU MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) project, an intensive campaign was launched in the greater Paris region in July 2009. The major objective was to quantify different sources of organic aerosol (OA) within a megacity and in its plume. In this study, we use airborne measurements aboard the French ATR-42 aircraft to evaluate the regional chemistry-transport model CHIMERE within and downwind of the Paris region. Two mechanisms of secondary OA (SOA) formation are used, both including SOA formation from oxidation and chemical aging of primary semivolatile and intermediate volatility organic compounds (SI-SOA) in the volatility basis set (VBS) framework. As for SOA formed from traditional VOC (volatile organic compound) precursors (traditional SOA), one applies chemical aging in the VBS framework adopting different SOA yields for high- and low-NOx environments, while another applies a single-step oxidation scheme without chemical aging. Two emission inventories are used for discussion of emission uncertainties. The slopes of the airborne OA levels versus Ox (i.e., O3 + NO2) show SOA formation normalized with respect to photochemical activity and are used for specific evaluation of the OA scheme in the model. The simulated slopes were overestimated slightly by factors of 1.1, 1.7 and 1.3 with respect to those observed for the three airborne measurements, when the most realistic "high-NOx" yields for traditional SOA formation in the VBS scheme are used in the model. In addition, these slopes are relatively stable from one day to another, which suggests that they are characteristic for the given megacity plume environment. The configuration with increased primary organic aerosol (POA) emissions and with a single-step oxidation scheme of traditional SOA also agrees with the OA / Ox slopes (about ± 50 % with respect to the observed ones); however, it underestimates the background. Both configurations are coherent with observed OA plume buildup, but they show very different SI-SOA and traditional anthropogenic SOA (ASOA) contributions. It is hence concluded that available theoretical knowledge and available data in this study are not sufficient to discern the