Worsening urban ozone pollution in China from 2013 to 2017 - Part 2: The effects of emission changes and implications for multi-pollutant control

Yiming Liu, Tao Wang

Research output: Journal article publicationJournal articleAcademic researchpeer-review

16 Citations (Scopus)

Abstract

The Chinese government launched the Air Pollution Prevention and Control Action Plan in 2013, and various stringent measures have since been implemented, which have resulted in significant decreases in emissions and ambient concentrations of primary pollutants such as <span classCombining double low line"inline-formula">SO2</span>, <span classCombining double low line"inline-formula">NOx</span>, and particulate matter (PM). However, surface ozone (<span classCombining double low line"inline-formula">O3</span>) concentrations have still been increasing in urban areas across the country. In a previous analysis, we examined in detail the roles of meteorological variation during 2013-2017 in the summertime surface <span classCombining double low line"inline-formula">O3</span> trend in various regions of China. In this study, we evaluated the effect of changes in multi-pollutant emissions from anthropogenic activities on <span classCombining double low line"inline-formula">O3</span> levels during the same period by using an up-to-date regional chemical transport model (WRF-CMAQ) driven by an interannual anthropogenic emission inventory. The Community Multiscale Air Quality (CMAQ) model was improved with regard to heterogeneous reactions of reactive gases on aerosol surfaces, which led to better model performance in reproducing the ambient concentrations of those gases. The model simulations showed that the maximum daily 8&thinsp;<span classCombining double low line"inline-formula">h</span> average (MDA8) <span classCombining double low line"inline-formula">O3</span> mixing ratio in urban areas increased by 0.46&thinsp;ppbv per year (<span classCombining double low line"inline-formula">ppbv a-1</span>) (<span classCombining double low line"inline-formula">pCombining double low line0.001</span>) from 2013 to 2017. In contrast, a slight decrease in MDA8 <span classCombining double low line"inline-formula">O3</span> by 0.17&thinsp;<span classCombining double low line"inline-formula">ppbv a-1</span> (<span classCombining double low line"inline-formula">pCombining double low line0.005</span>) in rural areas was predicted, mainly attributable to the <span classCombining double low line"inline-formula">NOx</span> emission reduction. The effects of changes in individual pollutant emissions on <span classCombining double low line"inline-formula">O3</span> were also simulated. The reduction of <span classCombining double low line"inline-formula">NOx</span> emission increased the <span classCombining double low line"inline-formula">O3</span> levels in urban areas due to the nonlinear <span classCombining double low line"inline-formula">NOx</span> and volatile organic compound (VOC) chemistry and decreasing aerosol effects; the slight increase in VOC emissions enhanced the <span classCombining double low line"inline-formula">O3</span> levels; the reduction of PM emissions increased the <span classCombining double low line"inline-formula">O3</span> levels by enhancing the photolysis rates and reducing the loss of reactive gases on aerosol surfaces; and the reduction of <span classCombining double low line"inline-formula">SO2</span> emissions resulted in a drastic decrease in sulfate concentrations, which increased <span classCombining double low line"inline-formula">O3</span> through aerosol effects. In contrast to the unfavorable effect of the above changes in pollutant emissions on efforts to reduce surface <span classCombining double low line"inline-formula">O3</span>, the reduction of CO emissions did help to decrease the <span classCombining double low line"inline-formula">O3</span> level in recent years. The dominant cause of increasing <span classCombining double low line"inline-formula">O3</span> due to changes in anthropogenic emissions varied geographically. In Beijing, <span classCombining double low line"inline-formula">NOx</span> and PM emission reductions were the two largest causes of the <span classCombining double low line"inline-formula">O3</span> increase; in Shanghai, the reduction of <span classCombining double low line"inline-formula">NOx</span> and increase in VOC emissions were the two major causes; in Guangzhou, <span classCombining double low line"inline-formula">NOx</span> reduction was the primary cause; in Chengdu, the PM and <span classCombining double low line"inline-formula">SO2</span> emission decreases contributed most to the <span classCombining double low line"inline-formula">O3</span> increase. Regarding the effects of decreasing concentrations of aerosols, the drop in heterogeneous uptake of reactive gases - mainly <span classCombining double low line"inline-formula">HO2</span> and <span classCombining double low line"inline-formula">O3</span> - was found to be more important than the increase in photolysis rates. The adverse effect of the reductions of <span classCombining double low line"inline-formula">NOx</span>, <span classCombining double low line"inline-formula">SO2</span>, and PM emissions on <span classCombining double low line"inline-formula">O3</span> abatement in Beijing, Shanghai, Guangzhou, and Chengdu would have been avoided if the anthropogenic VOCs emission had been reduced by 24&thinsp;%, 23&thinsp;%, 20&thinsp;%, and 16&thinsp;%, respectively, from 2013 to 2017. Our analysis revealed that the <span classCombining double low line"inline-formula">NOx</span> reduction in recent years has helped to contain the total <span classCombining double low line"inline-formula">O3</span> production in China. However, to reduce <span classCombining double low line"inline-formula">O3</span> levels in major urban and industrial areas, VOC emission controls should be added to the current <span classCombining double low line"inline-formula">NOx</span>-<span classCombining double low line"inline-formula">SO2</span>-PM policy.

Original languageEnglish
Pages (from-to)6323-6337
Number of pages15
JournalAtmospheric Chemistry and Physics
Volume20
Issue number11
DOIs
Publication statusPublished - 3 Jun 2020

ASJC Scopus subject areas

  • Atmospheric Science

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