Evolution of source attributed organic aerosols and gases in a megacity of central China

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The secondary production of the oxygenated organic aerosol (OOA) impacts air quality, climate and human health. The importance of various sources in contributing to the OOA loading and associated different aging mechanisms remains to be elucidated. Here we present concurrent observation and factorization analysis on the mass spectra of organic aerosol (OA) by a high-resolution aerosol mass spectrometer and volatile organic compounds (VOCs) by a proton-transfer-reaction mass spectrometer in Wuhan, a megacity in central China during autumntime. The full mass spectra of organics with two principle anthropogenic sources were identified as the traffic and cooking sources, for their primary emission profiles in aerosol and gas phases, the evolutions, and their respective roles in producing OOA and secondary VOCs. Primary emissions in gas and aerosol phases both contributed to the production of OOA. The photooxidation of traffic sources from morning rush-hour caused 2.5-folds increase of OOA mass in a higher oxidation state (O / C = 0.72), coproducing gas-phase carboxylic acids; while at night, cooking aerosols and VOCs (particularly acrolein and hexanal) importantly caused the nocturnal formation of oxygenated intermediate VOCs, increasing OOA mass by a factor of 1.7 (O / C = 0.42). The daytime and nighttime formation of secondary aerosols as contributed by different sources, was found to be modulated by solar radiation and air moisture respectively. The environmental policy should therefore consider the primary emissions and their respective ageing mechanisms influenced by meteorological conditions.