Carbonyl compounds in the atmosphere: A review of abundance, source and their contributions to O3 and SOA formation

Volatile organic compounds (VOCs) are an important precursor of ozone (O3) and secondary organic aerosols (SOA), which play vital roles on affecting the climate and human health. A key type of the VOC is carbonyls, which have been shown to be a significant source of radicals that directly influenced the oxidative capacity and nitrogen reservoirs, production of O3 and SOA. Carbonyls are being directly emitted through different natural and anthropogenic sources, or formed via secondary oxidation processes, thereby the characteristics of carbonyls have been found to vary temporally and spatially. Here we review the essential features of degradation and secondary formation of carbonyls processes in the atmosphere, followed by the speciation of carbonyls, source apportionments and their abundances in different environments around the world. This review also focuses on the roles of carbonyls in O3 and SOA formation on the basis of different parameterization methods and model simulation. Finally, based on the above summarized scientific findings of carbonyls over the past two decades, the future perspectives of carbonyl studies are suggested.