Search

A large population in China has been exposed to both severe ozone (O3) pollution and extreme heat under global warming. Here, the spatiotemporal characteristics of coupled extremes in surface O3 and heat (OPCs) over China are investigated using surface observations, a process-based chemical transport model (GEOS-Chem), and multi-model simulations from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). North China Plain (NCP; 37–41∘ N; 114–120∘ E) is identified as a hot spot of OPCs, where more than half of the O3 pollution days are accompanied by high temperature extremes. OPCs over NCP exceeded 40 d during 2014–2019, exhibiting an increasing trend. Both O3 concentrations and temperatures are elevated during OPCs compared with O3 pollution days occurring individually (OPIs). Therefore, OPCs impose more severe health impacts to humans than OPIs, but the stronger health effects are mainly driven by the higher temperatures. GEOS-Chem simulations further reveal that enhanced chemical production resulting from hot and stable atmospheric conditions under anomalous weather patterns primarily contributes to the exacerbated O3 levels during OPCs. In the future, CMIP6 projections suggest increased occurrences of OPCs over NCP in the middle of this century, but by the end of this century, OPCs may decrease or increase depending on the pollutant emission scenarios. However, for all future scenarios, extreme high temperatures will play an increasingly important role in modulating O3 pollution in a warming climate.

We applied the global 3-D chemical transport model GEOS-Chem to examine the anthropogenic and meteorological contributions in driving summertime (JJA) surface ozone (O3) trend in China during the Clean Air Action period 2012–2017. The model captures the observed spatial distribution of summertime O3 concentrations in China (R = 0.78) and reproduces the observed increasing trends in two most populated city clusters: North China Plain (NCP) and Yangtze River Delta (YRD). Trend of simulated maximum daily 8-h average (MDA8) O3 concentration is 0.58 ppbv yr−1 in NCP and 1.74 ppbv yr−1 in YRD in JJA 2012–2017. Sensitivity studies show that both changes in anthropogenic emissions and meteorology favored the MDA8 O3 increases in these two regions with respective contributions of 39% and 49% in NCP, and 13% and 84% in YRD. In NCP, the 49% meteorology impact includes a considerable contribution from natural emissions (19%). Changes in biogenic VOCs, soil NOx, and lightning NOx emissions are estimated to enhance MDA8 O3 in NCP with a rate of 0.14, 0.10, and 0.14 ppbv yr−1, respectively. In YRD, natural emissions made small contributions to the MDA8 O3 trend. Statistical analysis shows that higher temperatures and anomalous southerlies at 850 hPa in 2017 relative to 2012 are the two major meteorological drivers in NCP that favored the O3 increases, while weaker wind speed and lower relative humidity are those for YRD. We further examined the trend of fourth highest daily maximum 8-h average (4MDA8) O3 among a specific month that linked with extreme pollution episodes. Trends of simulated 4MDA8 O3 in NCP and YRD are 34–46% higher than those of MDA8 O3 and are found more meteorology-induced. Our results suggest an important role of meteorology in driving summertime O3 increases in China in recent years.

The health impact of changes in particulate matter with an aerodynamic diameter, Graphical abstract Image 1

Summertime ozone (O3) concentrations over China continue to increase although the governmental Clear Air Actions have been carried out since 2013. The worst O3 pollution is confronted over North China Plain. Ozone polluted days (with observed regionally-averaged maximum daily 8-h average (MDA8) O3 concentrations exceeding 80 ppbv) in May–July in North China increased from 35 days in year 2014 to 56 days in year 2018, and persistent O3 pollution episodes that lasted for 5 days or longer (OPEs5) contributed 14.3% and 66.1% to those O3 polluted days in 2014 and 2018, respectively. Model simulations suggest that O3 transport from central eastern China (including Shandong, Henan, Jiangsu and Anhui Provinces) contributes 36% of the enhanced O3 concentrations in North China during OPEs5 relative to the seasonal mean. We find that emission control of volatile organic compounds in central eastern China is most effective to alleviate intensity of OPEs5 in North China.

Accurate identification of key parameters for data assimilation is important in simulating the planetary boundary layer height (PBLH) and structure evolution in numerical weather prediction models. In this study, surface observational data and lidar-derived PBLH on 42 cloudless days from June 2007 to May 2008 are used to quantify the statistical relationships between surface parameters and the PBLH at a semiarid climate observational site in Northwest China. The results indicate that surface upward long wave radiation, surface temperature, and surface sensible heat fluxes show strong correlations with the PBLH with correlation coefficients at a range of 0.63–0.72. But these parameters show varying correlation response time to the different stages of PBL development. Furthermore, the air temperature shows the highest correlation with the PBLH near the surface and the correlation decreases with increasing height.