Impact of COVID-19 lockdowns on air pollution in Tbilisi

The COVID-19 pandemic lockdown provided a unique opportunity to assess the effects of mobility restrictions on urban air pollution. Prior studies have shown that scale and impact of these reductions varied by location and time. This study assessed how daily concentrations of PM₂.₅ and PM₁₀ changed during 2020 lockdown compared to the same period in 2019 and 2021, and evaluated how these levels aligned with the updated WHO Air Quality Guidelines and Georgia's national standards. Daily average concentrations of PM₂.₅ and PM₁₀ were analyzed over a 63-day period (March 21 to May 22) for 2019, 2020, and 2021. Descriptive statistics, ANOVA, and pairwise post-hoc tests were used to assess changes. Exceedance rates for WHO guidelines and Georgian standards were also calculated to evaluate compliance. Average daily concentrations of PM₂.₅ and PM₁₀ declined modestly during the 2020 lockdown compared to pre-lockdown 2019, but increased significantly post-lockdown in 2021. PM₂.₅ increased from 11.7 µg/m3 in 2020 to 14.6 µg/m3 in 2021 (p = 0.010); PM₁₀ increased from 23.2 µg/m3 to 32.3 µg/m3 (p = 0.001). The proportion of days exceeding WHO values was lowest in 2020 for both PM₂.₅ (23.3%) and PM₁₀ (5.0%) but increased in 2021. Exceedances of Georgian standards remained minimal across all years. The lockdown was associated with a temporary decline in PM₂.₅ and PM₁₀ in Tbilisi, however, levels increased again in 2021, with more frequent exceedances of WHO guidelines. The consistently low exceedance under Georgia's national standards highlights the urgency of revising thresholds and strengthening long-term air quality policies.