Increases in surface ozone pollution in China from 2013 to 2019: anthropogenic and meteorological influences

Abstract

Abstract. Surface ozone data from the Chinese Ministry of Ecology and Environment (MEE) network show sustained increases across the country over the 2013–2019 period. Despite Phase 2 of the Clean Air Action Plan targeting ozone pollution, ozone was higher in 2018–2019 than in previous years. The mean summer 2013–2019 trend in maximum 8 h average (MDA8) ozone was 1.9 ppb a−1 (p<0.01) across China and 3.3 ppb a−1 (p<0.01) over the North China Plain (NCP). Fitting ozone to meteorological variables with a multiple linear regression model shows that meteorology played a significant but not dominant role in the 2013–2019 ozone trend, contributing 0.70 ppb a−1 (p<0.01) across China and 1.4 ppb a−1 (p=0.02) over the NCP. Rising June–July temperatures over the NCP were the main meteorological driver, particularly in recent years (2017–2019), and were associated with increased foehn winds. NCP data for 2017–2019 show a 15 % decrease in fine particulate matter (PM2.5) that may be driving the continued anthropogenic increase in ozone, as well as unmitigated emissions of volatile organic compounds (VOCs). VOC emission reductions, as targeted by Phase 2 of the Chinese Clean Air Action Plan, are needed to reverse the increase in ozone.

Ozone pollution in the North China Plain spreading into the late-winter haze season

“…We conducted GEOS-Chem simulations with 2013 and 2019 emissions to understand the effect of changes in anthropogenic emissions on the seasonality of ozone increase in the North China Plain ( Materials and Methods ). NO x emissions in the MEIC inventory for the North China Plain decreased by 30% from 2013 to 2019, VOC emissions stayed flat, and observed PM 2.5 concentrations decreased by about 50% in all seasons ( 8 , 9 , 36 ). Model results shown in Fig.…”

“…The experience of the COVID-19 lockdown dramatically illustrates how the continuing decrease of NO x emissions in China under the Clean Air Action may lead to high-ozone episodes during the winter haze season. National NO x emissions have decreased by 30% over the 2013 to 2019 period ( 9 , 36 , 46 , 47 ). Fig.…”

“…Fig. 4 A shows the seasonality of observed 2013 to 2019 ozone trends in the North China Plain after filtering of interannual meteorological variability with a stepwise multiple regression model ( Materials and Methods ) to better resolve the effect of anthropogenic emission changes ( 6 , 8 , 9 ). Trends in the original unfiltered data are shown in SI Appendix , Fig.…”

“…We converted concentrations to ppb following ref. 9 . We also used PAN concentrations measured by researchers from the China Meteorological Administration at a site on the campus of Minzu University of China (39.95°N, 116.32°E) in urban Beijing.…”

“…The worst conditions are in the North China Plain, home to over 300 million residents, where wintertime PM 2.5 (particulate matter smaller than 2.5 µm in diameter) and summertime ozone concentrations routinely exceed air quality standards ( 3 – 6 ). Vigorous emission controls implemented by the Chinese government through the Clean Air Action ( 7 ) have reduced PM 2.5 concentrations in the North China Plain by 40 to 50% since 2013 for all seasons ( 8 ), but summertime ozone concentrations have been increasing ( 9 ). Ozone is generally viewed as a summertime problem, with very low concentrations in winter ( 4 , 10 ).…”