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Regional PM

In recent years, ozone pollution becomes a serious environmental issue in China. A good understanding of source-receptor relationships of ozone transport from aboard and inside China is beneficial to mitigating ozone pollution there. To date, these issues have not been comprehensively assessed, especially for highly polluted regions in the central and eastern China (CEC), including the North China Plain (NCP), Twain-Hu region (THR), Yangtze River Delta (YRD), Pearl River Delta (PRD), and Sichuan Basin (SCB). Here, based on simulations over 2013-2020 from a well-validated chemical transport model, GEOS-Chem, we show that foreign ozone accounts for a large portion of surface ozone over CEC, ranging from 25.0% in THR to 39.4% in NCP. Focusing on transport of domestic ozone between the five regions in CEC, we find that atmospheric transport can largely modulate regional interactions of ozone pollution in China. At the surface, THR receives the largest amount of ozone from the other four regions (54.2% of domestic ozone in the receptor region, the same in below), followed by PRD (32.3%), SCB (26.7%), YRD (21.1%), and NCP (18.0%). Meanwhile, YRD exports largest amount of ozone to the other regions, ranging from 8.9% in SCB to 28.4% in THR. Although SCB is relatively isolated and thus impacts NCP, YRD, and PRD weakly (2.2%), export of SCB ozone to THR reaches 9.3%. The regional ozone transport over CEC, occurring mostly in the lower troposphere, is mainly modulated by the East Asian monsoon circulations, proximity between source and receptor regions, seasonal changes of ozone production, and topography.

The terrain effect on atmospheric environment is poorly understood in particular for the polluted region with underlying complex topography. Therefore, this study targeted the Sichuan Basin (SCB), a deep basin with severe PM

The Sichuan Basin (SCB), to the east of the Tibetan Plateau (TP), experiences severe ozone (O

Surface radiation is crucial to atmospheric boundary layer development and air pollution formation. Several studies have revealed that surface radiation plays a vital role in developing the daytime convective boundary layer that controls the explosive growth of PM

Passages of strong cold airflow can quickly purge air pollutants over source region, e.g. North China Plain (NCP), while regional transport of air pollutants from source region would exacerbate air quality in the receptor region of Twain-Hu Basin (THB), due to the cold airflows modulated by atmospheric circulations over China. In this study, nine heavy pollution events (HPEs) in THB, Central China during the winters of 2015–2019 were identified for investigating the regional transport patterns of air pollutants from Central and Eastern China (CEC) to THB driven by strong cold airflows. Once regional transport of air pollutants from the CEC source regions was triggered by strong northerlies, PM2.5 pollution parcels then converged in the downwind THB receptor region through a dominant dynamic mechanism for most HPEs (66.7%) with downward airflow, which generally resulted in long durations of high PM2.5 concentrations and the impacted areas were modulated by synoptic patterns over the CEC. Non-dominant transport patterns were also observed with a cyclonic circulation of high wind speeds or a local stagnation of cold air over the THB, contributing to the highest and shortest PM2.5 peak or small impacted areas limited to the northern THB, respectively. It was estimated that the regional transport of PM2.5 from non-local regions accounted for 51.0%–85.7% of PM2.5 concentrations during the HPEs at Wuhan, revealing the dominance of regional transport of air pollutants from CEC to the THB with the meteorological drivers.

Compared with the 21-year climatological mean over the same period during 2000–2020, the aerosol optical depth (AOD) and Angstrom exponent (AE) during the COVID-19 lockdown (January 24–February 29, 2020) decreased and increased, respectively, in most regions of Central-Eastern China (CEC). The AOD (AE) values decreased (increased) by 39.2% (29.4%) and 31.0% (45.3%) in Hubei and Wuhan, respectively, because of the rigorous restrictions. These inverse changes reflected the reduction of total aerosols in the air and the contribution of the increase in fine-mode particles during the lockdown. The surface PM2.5 had a distinct spatial distribution over CEC during the lockdown, with high concentrations in North China and East China. In particular, relatively high PM2.5 concentrations were notable in the lower flatlands of Hubei Province in Central China, where six PM2.5 pollution events were identified during the lockdown. Using the observation data and model simulations, we found that 50% of the pollution episodes were associated with the long-range transport of air pollutants from upstream CEC source regions, which then converged in the downstream Hubei receptor region. However, local pollution was dominant for the remaining episodes because of stagnant meteorological conditions. The long-range transport of air pollutants substantially contributed to PM2.5 pollution in Hubei, reflecting the exceptional importance of meteorology in regional air quality in China., Graphical abstract Unlabelled Image, Highlights • Inverse changes in AOD and AE during lockdown were found over CEC. • Pollution events were frequently observed during the strictest lockdown over Hubei. • Air pollution was caused by regional transport of upstream air pollutants to Hubei. • Local pollution was accumulated despite of large reductions in air pollutant emissions.