Comparative analysis of the impact of weather conditions and human activities on air quality in the Dongting and Poyang Lake Region during the COVID-19 pandemic

During the COVID-19 lockdown, only the most basic and necessary production activities were retained in China. Such strict measures have caused many inconveniences to the people and the economy, but also provided the research community with a rare opportunity to compare the effects of weather conditions and human activities on air quality in the region. Here, a comparative analysis of the impact of weather conditions and human activities on air quality in the Dongting and Poyang Lake Region (DPLR) is proposed during the COVID-19 pandemic based on a circulation-to-environment approach. T-mode objective circulation classification method was applied to explore the effects of weather conditions on the concentration of two typical pollutants (PM2.5 and ozone) affecting the DPLR. PM2.5 and ozone concentrations under the nine identified circulation patterns are discussed. Under the control of circulation type CT1, CT3 and CT6, the PM2.5 concentrations in this area are high, while under the control of CT2 and CT9, the ozone concentrations are high. By comparing the variation in PM2.5 and ozone concentrations in three important cities in the region (Wuhan, Changsha, and Nanchang) during the three stages (Before Controlling, During Controlling and After Controlling) of COVID-19 from January to April 2020 and the corresponding months of a reference period (2015-2019), it is found that after controlling the human activities, the PM2.5 concentration dropped by 37.45%, while the ozone concentration increased by 111.83%. Ozone concentration was mainly affected by the synoptic circulation pattern, while the PM2.5 concentration was more affected by human activities.