Depicting Photochemical Behaviour of Gaseous Secondary Pollutants: Environment-Specific Insights and Control Strategies from Near-Explicit Chemical Mechanism Modelling

Gaseous secondary pollutants, such as ozone (O3), peroxyacetyl nitrate (PAN), and aldehydes (e.g., formaldehyde), are air pollutants that form in the atmosphere through photochemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOCs) as their precursors. These pollutants can adversely affect human health, ecosystems, and the environment. Due to the non-linear relationship between secondary pollutants and their precursors in various environments and the complexity of ten-thousands of photochemical reactions, the development of effective control measures for regional secondary pollution is challenging. This is particularly true for China, which has experienced a significant increase in O3-related problems in recent years.

To address the responsible in-situ photochemistry and combat regional secondary pollution, measurements of air pollutants were conducted at multiple sites, particularly in southern China, encompassing urban, industrial, rural, mountainous and coastal environments. Additionally, photochemical box models, integrated with the near-explicit Master Chemical Mechanism, were employed to characterize the photochemical behavior of O3, PAN, and aldehydes. This included an analysis of their chemical sources, impacts on radical chemistry, and photochemical formation in various atmospheric conditions. Moreover, potential reduction measures were assessed from a chemical formation perspective. These studies have enhanced our understanding of gaseous secondary pollutants and contributed valuable insights into control strategies.