Air quality changes in Shijiazhuang during COVID-19 outbreak

Background The coronavirus disease 2019 (COVID-19) was first detected in December 2019. To combat the disease, a series of strict measures were adopted across the country, which led of improved air quality. This provides an opportunity to discuss the impact of human activities on air quality.

Objective This study investigates the air quality changes in Shijiazhuang, and analyzes the impacts of epidemic prevention and control measures on air quality, so as to provide reference and ideas for further improving air quality and prevention and control measures.

Methods The air quality data were collected online from https://www.zq12369.com/ and https://aqicn.org/city/shijiazhuang/cn/. Comparisons in air quality index (AQI) and the concentrations of air pollutants (PM_2.5, PM₁₀, SO₂, CO, NO₂, and O₃) were made between the period from December 2019 to June 2020 (reference) and the same period from 2016 to 2019 by t-test and chi-square test.

Results The daily average AQI dropped by 25.38% in Shijiazhuang during the COVID-19 prevention and control compared with the some period from 2016 to 2019 (t=6.28, P < 0.05). The proportions of pollution days during the COVID-19 outbreak in Shijiazhuang were PM_2.5 (44.56%), O₃ (31.09%), PM₁₀ (23.83%), and NO₂ (2.59%) successively, the pollution days of PM₁₀ decreased significantly (χ²=3.86, P < 0.05) compared with 2016-2019, but during traffic lockdown the numbers of pollution days of PM_2.5 and in the mid stage of prevention the number of pollution days of O₃ increased (P < 0.05). Compared with the control period, the concentrations of the six air pollutants decreased to varying degrees (P < 0.05), especially SO₂ dropped by 55.36%.

Conclusion The measures taken for COVID-19 control and prevention have reduced the pollution sources and emissions, which resulted in better general air quality of Shijiazhuang City, but have aggravated the pollution of O₃ and other pollutants. It is necessary to further explore the causes for the aggravation of O₃ pollution in order to formulate reasonable air quality control strategies.