Post Date: 15 August 2022

Development of an enhanced method to characterize atmospheric carbonyl compounds and their roles in photochemistry in subtropical Hong Kong

Abstract

Carbonyl compounds are ubiquitous atmosphere pollutants and greatly affect atmospheric chemistry via playing an important role in the cycling of radicals and formation of ozone and secondary organic aerosols (SOA). Increasing studies have revealed significant abundance and species of carbonyls compounds in different environments, of critical significance in the tropospheric photochemistry. Identifying and quantifying the complex carbonyl compounds with various structural groups and better understanding their atmospheric behavior is essential to assess their contributions in photochemical pollution and to develop more pollution control measures. In this study, we developed an enhanced method using ultra-performance liquid chromatography and electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) to determine and quantify 39 carbonyl compounds with different structures simultaneously and with high sensitivity. Using the new method, 21 aliphatic mono-carbonyls, 7 aromatic mono-carbonyls, 4 other unsaturated mono-carbonyls, and 3 di-carbonyls were quantified in the subtropical coastal atmosphere in Hong Kong. The total concentration of investigated carbonyls was in the range of 9.1~33ppb, and besides the simple species (C≤4), nonanaldehyde (C9), benzaldehyde (BZA), 2,5-dimethylbenzaldehyde (2,5-DB), and di-carbonyls showed significant contribution to the total carbonyls in coastal atmosphere. Higher carbonyl concentrations were observed in the harbor and over the sea with intensive shipping and navigation activities than that in coastal suburban area and rural waters. Ship emissions seem play important role in the long-chain aldehydes (C≥6) in the coastal atmosphere. Moreover, more carbonyl species, such as long-chain aldehydes and di-carbonyls, which are beyond of the species measured by the conventional method, exhibited high concentrations and photochemical reactivities, and had significant formation potentials in ozone and SOA in the coastal environment in Hong Kong. This study highlights the importance of various carbonyls, especially those highly reactive species have not been well understood, in the atmospheric chemistry in urban and coastal regions, and the newly develop method will be useful to better characterize the carbonyl compounds in a more complete manner and advance our understanding of their roles in photochemical air pollution.