Response of ozone to current and future emission scenarios and the resultant human health impact in Southeast Asia

Recent evidence has shown the increasing trend of tropospheric ozone (O₃) in Southeast Asia. Mitigating O₃ pollution in Southeast Asia has become important and urgent. While the nonlinear O₃ chemistry makes policy-making complicated, the O₃ formation regime and O₃ response to different emissions have rarely been assessed in Southeast Asia. Furthermore, the O₃-attributable health impacts in Southeast Asia under future emission scenarios have yet to be quantified. Herein, we applied the regional chemical transport model with the High-order Decoupled Direct Method (HDDM) to simulate the O₃ sensitivity to precursor emissions in Southeast Asia, and then projected the health benefits under future Shared Socioeconomic Pathways (SSP) emission scenarios, providing policy suggestions for mitigating O₃ pollution and its health impacts. Our results show O₃ in urban areas (i.e., Singapore, Jakarta, Kuala Lumpur, Bangkok, and Ho Chi Minh City) was sensitive to both nitrogen oxides (NO_x) and volatile organic compounds (VOCs) emissions, and synergistic NO_x and VOCs control is thus essential. Suburban, rural, and sea areas were under a NO_x-limited regime, suggesting the high effectiveness of controlling NO_x over these areas. Compared with the health impacts in baseline year (2019), the annual total O₃-attributed premature mortality under the business-as-usual emission scenario (SSP245) is projected to reduce by 22 k (47 %) by 2050 due to the future NO_x emission reductions in power generation, industrial process, and transportation. Most of the health benefits will happen in Indonesia, Philippines, Vietnam, and Thailand. The sustainable emission scenario (SSP126) is projected to avoid 36 k annual O₃-attributed premature mortalities by 2050 due to its more stringent NO_x reductions in shipping, transportation, and industrial process. SSP370 and SSP585 are projected to increase the O₃-attributable premature mortality by up to 33 k because of the rising NO_x emissions.