Summertime carbonyl compounds in an urban area in the North China Plain: Identification of sources, key precursors and their contribution to O formation.

Carbonyl compounds are critical components of volatile organic compounds, which significantly participate in the photochemical formation of atmospheric ozone and thus threaten human health. Here we measured 15 C-C carbonyl compounds at an urban site in Linyi, a typically industrialised city in the North China Plain (NCP). Formaldehyde (3.89 ppbv), acetaldehyde (1.66 ppbv) and acetone (2.03 ppbv) were found to be the top three carbonyl compounds, accounting for 76.11% of the total concentration of carbonyl compounds. Anthropogenic secondary formation was recognised as the main source of the top five carbonyl compounds, which included formaldehyde, acetaldehyde, acetone, butyraldehyde and benzaldehyde, and accounted for 46-54% of all sources. Alkenes were the most important precursors of formaldehyde and acetaldehyde, suggesting that reducing the emission of alkenes from anthropogenic sources is an effective way to control carbonyl compound pollution in Linyi. Furthermore, the photolysis of carbonyl compounds played a significant role (68-75%) as sources of HO• and RO• and thus made a significant contribution (14.6%) to the photochemical formation of O. This study highlights the importance of anthropogenic secondary formation as a source of carbonyl compounds and provides a scientific basis for O pollution control in carbonyl compound-enriched cities in the NCP.