Investigation of urban air quality affected by the pandemic of COVID-19: case studies in Iran

In recent decades, climate change and its direct impact on the lives of living organisms and ecosystems worldwide have been noticeable. In addition, to environmental crises and climate change, the COVID-19 virus pandemic has become a considerable human concern. This observational study collected climatic factors such as local temperature, wind speed, and humidity as input data from meteorological stations. Pollutants, like NOx, NO2, CO, NO, SO2, O3, and PM2.5, are considered output data. This local information has been obtained adequately for Tehran, Shiraz as residential and megacities, Arak as an industrial city, and Birjand as a sample of the rural area from 2019 to 2020. Artificial neural network (ANN) has been used as a possible model to accurately simulate air quality forecasting before and after quarantine in Iran. SO2 has been little change (about 10%) in Tehran and Shiraz, and in Arak, in early 2020, firstly has been had an upward trend (about 90%) and then has remained stable. In Shiraz, NOx has increased (about 20%), while in three other cities has remained constant. NO, in Arak, has a gradual increase in the first month (0 ppb) and then has remained consistent. In Shiraz, it has decreased (about 35%), and in Tehran and Birjand, it has been unchanged. NO2 concentration in Shiraz has been reduced (about 25%). In Shiraz, the amount of CO has leaped (about 13%), and in Birjand, it has decreased by about 33%. PM2.5 in Arak has gradually increased by about 52%, and the concentration of O3 has had a continuous change. According to the study, in megacities, the cause of air pollution is most traffic, which has been eliminated by lockdown and air quality has increased. No significant change has been achieved in other cities.