Evolution of open air quality of urbanized territories under Covid-19 pandemic conditions

Current state of world affairs in 2020 during quarantine enforced due to COVID-19 pandemic is characterized, on the one hand, with economic recession, but on the other hand, also with improvement of ecological state of environment. Thus a unique opportunity came up to study processes of open air conditions formation in settlements in circumstances of restricted economic activity and limitations imposed on all kinds of transportation. This article presents results of research of trends of formation of open air quality of urbanized territories (using city of Rivne as an example) during quarantine enforced due to COVID-19 pandemic. It is determined that due to introduction of quarantine measures air quality has improved. So, during the quarantine as well as after relaxation of quarantine measures only concentration of formaldehyde in open air of Rivne city did exceed average daily MAC. Primary source of open air pollution in Rivne city is motor vehicles which comprise 79% of total amount of pollutant emissions. Main pollutants which influence formation of open air quality in the city are: dust, sulfur dioxide, nitrogen dioxide, hydrogen fluoride and formaldehyde. They exceeded average daily MAC by factor of 1.3 to 32. Complex air pollution index (CAPI) was equal to 5.4 during quarantine restrictions but grew to 5.7 when the restrictions were partially loosened. Thus, air pollution level was evaluated as "mild pollution". During the corresponding periods of 2019 this index was changing from 6.9 ("mild air pollution") to 7.7 ("polluted air") respectively. Open air pollution level is determined by a complex of constituents including pollutant emission amounts, their specifics and dependency on meteorological factors. Due to this aspect we have performed statistical examinations to determine dependency of open air pollutant concentrations on meteorological conditions using multiple correlation coefficients. Strong correlation was exhibited for nitrogen oxide, hydrogen chloride and ammonia: multiple correlation coefficients fall within 0.76-0.80 range; moderate correlation was seen for dust, sulfur dioxide, nitrogen dioxide, hydrogen disulphide, phenol and formaldehyde with multiple correlation coefficients varying in 0.51-0.70 range.