Atmospheric carbonyl compounds are crucial in regional ozone heavy pollution: insights from the Chengdu Plain Urban Agglomeration, China

Abstract

Gaseous carbonyl compounds serve as crucial precursors and intermediates in atmospheric photochemical reactions, significantly contributing to ambient ozone formation. To determine whether the impact of carbonyl compounds on regional ozone pollution is driven by their abundance or by specific secondary chemical processes, simultaneous field observations and observation-based modeling of ambient carbonyls were conducted at nine sites within the Chengdu Plain Urban Agglomeration (CPUA), China, during 4-18 August 2019, when three episodes of regional heavy ozone pollution occurred across eight cities within CPUA. Throughout the study, the total mixing ratios of 15 carbonyls ranged from 10.7 ± 4.2 to 35.2 ± 13.4 ppbv. The spatial distribution reveals that regions with higher concentrations of carbonyl compounds, such as around Chengdu, are also areas with more severe ozone pollution. Both the abundance and the chemical reactivity of carbonyl compounds, especially formaldehyde and acetaldehyde, play crucial roles in ozone formation in the CPUA. On ozone pollution days, carbonyl concentrations significantly increased by 22.8 % to 66.2 %. While the abundance of carbonyls is an important factor, their significant role in heavy ozone pollution within the CPUA is primarily driven by secondary chemical processes, particularly those involving alkenes and biogenic volatile organic compounds (BVOCs). Sites with higher average ozone concentrations during observations were mainly in the VOC-limited regime, while others were in the transitional regime. Additionally, the mutual transport of carbonyl compounds between cities in the CPUA suggests that regional collaboration is essential to address ozone pollution effectively. These findings offer valuable insights for developing effective strategies to control regional ozone pollution.