Tropospheric Ozone Changes And Source Analysis In Southeast Asia From 1990 To 201

Observations indicate that tropospheric O₃concentrations over Southeast Asia have been increasing since the 1990s.This study quantifies source contributions from geographical regions and emission sectors of the two distinct types of O₃precursors,i.e.,nitrogen oxides（NO_x）and volatile organic compounds（VOCs）,to the increase in tropospheric O₃in Southeast Asia during 1990–2019 using an O₃source tagging technique implemented in a global chemistry-climate model CESM（Community Earth System Model）.The results show that O₃variations in Southeast Asia from 1990-2019 are mainly influenced by anthropogenic emissions rather than atmospheric circulation.The annual mean total surface O₃concentrations in Southeast Asia are dominated by anthropogenic NO_xemissions from regions outside Southeast Asia as well as natural sources,while local anthropogenic NO_xemissions in Southeast Asia contribute only 18%of the annual mean surface O₃.The contribution of local NO_xemissions to the average surface O₃increasing trend in Southeast Asia（1.07 ppb/decade）is 107%due to the significant increase in local anthropogenic NO_xemissions over the period 1990-2019.Increases in NO_xemissions from East Asia and South Asia explain 29%of the increasing trend,but 13%is offset by the emission reduction in North America and Europe.In terms of different emission sectors,ground transportation is responsible for 79%of the rapid O₃increase,followed by39%contribution from international shipping.The reduction of NO_xfrom biomass burning reduces the O₃trend by 31%.The increasing trend of tropospheric O₃column burden in Southeast Asia is 1-3 DU/decade.Anthropogenic emissions of NMVOCs（Non-Methane Volatile Organic Compounds）account for only 10%of the annual average surface O₃concentrations in Southeast Asia,with CH₄（Methane）and BVOCs（Biogenic Volatile Organic Compounds）accounting for37%and 31%,respectively.The increase in anthropogenic NO_xemissions increases the O₃production efficiency of VOCs,with CH₄and BVOCs being the largest contributors to the increase of surface O₃concentrations in Southeast Asia,accounting for 54%and 31%of the rapid O₃increase,respectively.Anthropogenic NMVOCs emissions in Southeast Asia,East Asia,Africa and South Asia contribute 16%,8%,6%and 5%respectively to the O₃increasing trend during 1990-2019,while NMVOCs emission reductions in North America and Europe offset the increasing trend by 9% and 6%.