The sensitivity of ground-level ozone to precursor emissions and source contributions in Southeast Asia

Abstract. To mitigate the surface ozone (O₃) pollution in Southeast Asia, a full understanding of the processes and contributions of precursor emissions [i.e., volatile organic compounds (VOCs) and nitrogen oxides (NO_x)] to O₃ is required but remains unclear. This study applied an adjoint sensitivity model to evaluate the source-receptor (S-R) relationship between O₃ and the precursors, as well as the source contributions over different receptor regions in Southeast Asia. The process analysis was performed to further characterize O₃ formation. We found a predominant NO_x-limited O₃ formation regime across Southeast Asia due to substantial regional biogenic VOC emissions, with exceptions in areas where anthropogenic NO_x emissions were significant, such as Singapore, Jakarta, Bangkok, and the Malacca Straits. NO_x was identified as the primary contributor to the surface O₃, whereas VOCs contributed positively to VOC-limited regions but negatively to NO_x-limited areas. Additionally, regional and super-regional transboundary air pollution accounted for 56–98 % of surface O₃ concentration across Southeast Asian countries. The findings highlighted the need for differentiated O₃ mitigation strategies in Southeast Asia, combining coordinated regional NO_x emission reductions with targeted VOC controls in the VOC-limited urban areas.