*2.2. Situations of Pandemic Prevention and Control*

On 22 January 2020, the National Health Commission of the People's Republic of China confirmed a positive case of COVID-19 in Suzhou, which was the first case in Jiangsu Province. In order to control the spread of COVID-19, Jiangsu activated the first-level public health emergency response at 0000 CST (China Standard Time, the same below) on 25 January 2020. The interventions included travel restrictions, restrictions on public gatherings, and temporary closures of businesses and facilities. At 0000 CST on 25 February 2020, the response level was adjusted to the second level, which meant that all businesses could reopen scientifically and reasonably. That is, it was suggested that production and life could be recovered, while gathering and group activities were still restricted. As of 27 March 2020, there had been no newly confirmed local patients for 38 consecutive days. Therefore, since 0000 CST on 28 March, the level of PPC measures was adjusted to the third level, and the normal production and living of people gradually recovered, entering the stage of regular PPC. The same emergency response was implemented to the whole province at the same time by the Jiangsu provincial government, making it possible to study the impact of PPC measures of different levels on air pollution in the whole province, which is what this paper concerns.
