Evaluating the Effectiveness of COVID-19 Lockdown Measures Through Air Pollution Trends in the Republic of Georgia (March–June 2019–2022): An Interrupted Time-Series Analysis

The COVID-19 pandemic created a unique natural experiment to evaluate the impact of reduced human activity on urban air quality. This study assessed the effects of lockdown measures on major air pollutants across three Georgian cities with contrasting emission profiles: traffic-dominated Tbilisi, coastal Batumi, and industrial Rustavi. Daily concentrations of NO2, SO2, PM2.5, PM10, and O3 were obtained from the National Environmental Agency’s automated monitoring network for March–June 2019–2022. Following systematic missing value imputation, meteorologically adjusted interrupted time-series (segmented regression) models, incorporating daily temperature and wind speed as covariates, were used as the primary analysis; Mann–Kendall trend analysis was retained as a secondary, descriptive measure. Results were evaluated against WHO 2021 Air Quality Guidelines. Tbilisi showed the strongest lockdown response: NO2 declined by 47.9% in 2020 (vs. 2019), before rebounding fully in 2022. PM2.5 and PM10 showed attenuated reductions, reflecting continued heating combustion and dust sources. Ground-level O3 increased in Tbilisi in 2020 (+25.0% vs. 2019). Rustavi exhibited no NO2 response and an O3 decrease of 43.2% in 2020, with partial recovery in 2021–2022. Batumi showed intermediate responses, with PM2.5 and PM10 increases in 2020. Meteorologically adjusted interrupted time-series models confirmed 11 of 30 city–pollutant effect estimates after false discovery rate correction, most robustly for NO2; several borderline ozone and SO2 findings did not survive correction and are reported as suggestive only. Lockdown measures were associated with source-specific and temporary air quality improvements, after accounting for meteorological conditions. Sustained reductions require structural interventions targeting traffic, residential combustion, and industrial emissions simultaneously.