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Impact of COVID-19 on air quality in the Yangtze River Delta, China.

ABSTRACT: To investigate the effect of nationwide restrictions due to COVID-19 on air quality in the Yangtze River Delta (YRD), China, we defined four periods named period I (January 1 to 23, 2020), period II (January 24 to February 23), period III (February 24 to April 7), and period IV (April 8 to May 31), which indicated normal period, lockdown period, regional work resumption period, and nationwide work resumption period, respectively. Hourly PM_2.5, PM₁₀, NO₂, SO₂, CO, and O₃ in 41 cities in the YRD region were analyzed. Compared to period I, NO₂ decreased by 58% during period II and increased in periods III and IV. SO₂ remained constant during the four periods (7-8 μg/m³). Higher PM_2.5 concentration was monitored during period II (41 μg/m³) when compared to period III (35 μg/m³), which was resulted from the enhanced secondary formation. Spatial distribution analysis further indicated that PM_2.5 in the northern YRD during period II was higher than that during period III, whereas PM_2.5 in the southern YRD in the period II was similar to that in period III. The results demonstrated that PM_2.5 shows a nonlinear response to the reduction of its precursors, and this phenomenon varies in different areas. Compared to periods I (36 μg/m³) and III (64 μg/m³), relatively higher O₃ during period II (64 μg/m³) was probably resulted from less NO emission and hence weakened NO titration effect. The study suggested that coordinated and balanced measures are needed to improve air quality.

SUBMITTER: Yao L

PROVIDER: S-EPMC8315727 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The outbreak of COVID-19 has spreaded rapidly across the world. To control the rapid dispersion of the virus, China has imposed national lockdown policies to practise social distancing. This has led to reduced human activities and hence primary air pollutant emissions, which caused improvement of air quality as a side-product. To investigate the air quality changes during the COVID-19 lockdown over the YRD Region, we apply the WRF-CAMx modelling system together with monitoring data to investigate the impact of human activity pattern changes on air quality. Results show that human activities were lowered significantly during the period: industrial operations, VKT, constructions in operation, etc. were significantly reduced, leading to lowered SO2, NOx, PM2.5 and VOCs emissions by approximately 16-26%, 29-47%, 27-46% and 37-57% during the Level I and Level II response periods respectively. These emission reduction has played a significant role in the improvement of air quality. Concentrations of PM2.5, NO2 and SO2 decreased by 31.8%, 45.1% and 20.4% during the Level I period; and 33.2%, 27.2% and 7.6% during the Level II period compared with 2019. However, ozone did not show any reduction and increased greatly. Our results also show that even during the lockdown, with primary emissions reduction of 15%-61%, the daily average PM2.5 concentrations range between 15 and 79 ?g m-3, which shows that background and residual pollutions are still high. Source apportionment results indicate that the residual pollution of PM2.5 comes from industry (32.2-61.1%), mobile (3.9-8.1%), dust (2.6-7.7%), residential sources (2.1-28.5%) in YRD and 14.0-28.6% contribution from long-range transport coming from northern China. This indicates that in spite of the extreme reductions in primary emissions, it cannot fully tackle the current air pollution. Re-organisation of the energy and industrial strategy together with trans-regional joint-control for a full long-term air pollution plan need to be further taken into account.

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Impact of COVID-19 on air quality in the Yangtze River Delta, China.

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