Air pollution during COVID-19 pandemic: Exploration in the Bulgarian city of Stara Zagora using interrupted time series ARMA model

The COVID-19 global pandemic has likely affected air quality due to extreme changes in human behavior. The aim of this paper is to explore the consequence of the COVID-19 pandemic on the air quality improvement in the Bulgarian city of Stara Zagora using Interrupted Time Series ARMA Model. After adjusting by meteorology and Sunday effect, the results confirm positive and significant effect immediately after the announcement of COVID-19 pandemic in Bulgaria and negative and significant trend in the levels for PM2.5 and O-3. For the remaining CO and NO series of data, the estimate of the time series slope, i.e. the expected change in the concentration associated with a time unit increase is positive and significant. The temporal dynamics for each time series are reported by the ARMA coefficients: an A RMA (2,3) structure is estimated for 03 and NO, and an ARMA(1,1) is the best choice for CO while AR(5) for PM2.5. Understanding how air pollution is affected during COVID-19 pandemic will contribute to future air quality management policies and human health.