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 (O) in Southeast Asia. Mitigating O pollution in Southeast Asia has become important and urgent. While the nonlinear O chemistry makes policy-making complicated, the O formation regime and O response to different emissions have rarely been assessed in Southeast Asia. Furthermore, the O-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 O 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 O pollution and its health impacts. Our results show O in urban areas (i.e., Singapore, Jakarta, Kuala Lumpur, Bangkok, and Ho Chi Minh City) was sensitive to both nitrogen oxides (NO) and volatile organic compounds (VOCs) emissions, and synergistic NO and VOCs control is thus essential. Suburban, rural, and sea areas were under a NO-limited regime, suggesting the high effectiveness of controlling NO over these areas. Compared with the health impacts in baseline year (2019), the annual total O-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 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 O-attributed premature mortalities by 2050 due to its more stringent NO reductions in shipping, transportation, and industrial process. SSP370 and SSP585 are projected to increase the O-attributable premature mortality by up to 33 k because of the rising NO emissions.