The impact of COVID-19 preventive policies and pandemic states on ambient sulfur dioxide pollution in various industrial areas of Taiwan

Abstract The pandemic and lockdown policies of COVID-19 significantly reduced industrial activities worldwide. This reduction might lead to a decline in air pollutant concentrations, particularly sulfur dioxide (SO 2 ). This study aimed to explore the changes in SO 2 concentrations under lockdown policy and various pandemic states of COVID-19 for different industrial areas in Taiwan. We collected SO 2 and meteorological data from the air quality monitoring stations in the vicinity of six industrial areas, including high-tech, petrochemical, and traditional industries, from 2015 to 2023. We compared the SO 2 concentrations in different alert periods in 2021 and different pandemic states from 2019 to 2023. Polar plots were used to observe short-term changes in SO 2 pollution sources and concentrations during different alert periods. The Theil-Sen estimator was applied to predict the SO 2 concentrations during the COVID-19 pandemic. It was found that the SO 2 concentrations in selected air monitoring stations were representative of the industrial areas. The emission of SO 2 from high-tech industries was slightly affected by lockdown policies, and the SO 2 concentrations showed an annual increasing, even exceeding the predicted values, as the pandemic worsened. In contrast, the SO 2 emissions from petrochemical industries were significantly impacted by lockdown policies and pandemic states, resulting in a substantial decline even below the predicted values. With varying development of traditional industries, the emission of SO 2 was influenced to different levels by lockdown policies and pandemic states. Given these findings, various industries were affected by the COVID epidemic in different degrees, resulting in differences in the surrounding SO 2 concentrations.