Spatiotemporal characterization of aerosols and trace gases over the Yangtze River Delta region, China: impact of trans-boundary pollution and meteorology

Abstract

Background The spatiotemporal variation of observed trace gases (NO2, SO2, O3) and particulate matter (PM2.5, PM10) were investigated over cities of Yangtze River Delta (YRD) region including Nanjing, Hefei, Shanghai and Hangzhou. Furthermore, the characteristics of different pollution episodes, i.e., haze events (visibility < 7 km, relative humidity < 80%, and PM2.5 > 40 µg/m3) and complex pollution episodes (PM2.5 > 35 µg/m3 and O3 > 160 µg/m3) were studied over the cities of the YRD region. The impact of China clean air action plan on concentration of aerosols and trace gases is examined. The impacts of trans-boundary pollution and different meteorological conditions were also examined. Results The highest annual mean concentrations of PM2.5, PM10, NO2 and O3 were found for 2019 over all the cities. The annual mean concentrations of PM2.5, PM10, and NO2 showed continuous declines from 2019 to 2021 due to emission control measures and implementation of the Clean Air Action plan over all the cities of the YRD region. The annual mean O3 levels showed a decline in 2020 over all the cities of YRD region, which is unprecedented since the beginning of the China’s National environmental monitoring program since 2013. However, a slight increase in annual O3 was observed in 2021. The highest overall means of PM2.5, PM10, SO2, and NO2 were observed over Hefei, whereas the highest O3 levels were found in Nanjing. Despite the strict control measures, PM2.5 and PM10 concentrations exceeded the Grade-1 National Ambient Air Quality Standards (NAAQS) and WHO (World Health Organization) guidelines over all the cities of the YRD region. The number of haze days was higher in Hefei and Nanjing, whereas the complex pollution episodes or concurrent occurrence of O3 and PM2.5 pollution days were higher in Hangzhou and Shanghai. The in situ data for SO2 and NO2 showed strong correlation with Tropospheric Monitoring Instrument (TROPOMI) satellite data. Conclusions Despite the observed reductions in primary pollutants concentrations, the secondary pollutants formation is still a concern for major metropolises. The increase in temperature and lower relative humidity favors the accumulation of O3, while low temperature, low wind speeds and lower relative humidity favor the accumulation of primary pollutants. This study depicts different air pollution problems for different cities inside a region. Therefore, there is a dire need to continuous monitoring and analysis of air quality parameters and design city-specific policies and action plans to effectively deal with the metropolitan pollution.

Analysis of Air Pollutants and Their Potential Sources in Eastern Xinjiang, Northwestern Inland China, from 2018 to 2022

“…These results indicate that air pollution control measures in eastern Xinjiang have achieved some effectiveness in recent years, but the PM concentrations in eastern Xinjiang remain at high levels, possibly due to its unique geographic location, frequent dust storms, and the influence of regional transport. [41,42]. Therefore, coarse particles from dust emissions are the main cause of PM pollution in eastern Xinjiang [43].…”

“…Some studies have shown that the atmospheric boundary layer height in the Xinjiang region exhibits a distinct unimodal variation, gradually increasing during the daytime and decreasing during the nighttime [48,49]. Therefore, these variations are [41,42]. Therefore, coarse particles from dust emissions are the main cause of PM pollution in eastern Xinjiang [43].…”

“…The average concentrations of NO 2 in 2020 (Hami, 25.1 µg•m −3 ; Turpan, 30.6 µg•m −3 ) were significantly (p < 0.05) lower than those in 2019 (28.6 µg•m −3 ; 34.4 µg•m −3 ) and 2021 (27.5 µg•m −3 ; 32.9 µg•m −3 ), which was likely ascribed to the sharp decrease in urban traffic as a result of the COVID-19 control [40]. PM 2.5 /PM 10 ratios at Hami and Turpan ranged from 0.23 to 0.38, and were much lower than those at BTH (0.53) and YRD (0.60)[41,42]. Therefore, coarse particles from dust emissions are the main cause of PM pollution in eastern Xinjiang[43].…”

Patterns and Influencing Factors of Air Pollution at a Southeast Chinese City

“…In addition, weather conditions could be different in different locations within one city. Limited studies in Hangzhou using official or remote sensing data could not accurately obtain such data for the monitoring sites [3,23,24]. Hence, first-hand monitoring data near the emission source, including meteorological factors, is necessary.…”

Examining Current Research Trends in Ozone Formation Sensitivity: A Bibliometric Analysis

“…Tropospheric O 3 formation is a complex process that depends on precursor species and several other factors. The COVID-19 pandemic and subsequent lockdown measures resulted in emission reductions of VOCs and NO x , but O 3 concentrations still increased in many regions [14][15][16]. Recent studies suggest this is due to the various factors (e.g., aerosols, meteorology and pollution source distribution) that govern atmospheric O 3 formation [12,17].…”