Effect size of COVID-19 mobility restrictions intensity on air pollution: a natural experiment

To improve air quality, regulatory actions targeting road traffic and industrial emissions must be implemented. This study determined the effect size (ES, Cohen’s δ) and the significance of progressive quarantine restrictions levels national quarantine [NQ + ], smart quarantine [SQ ++ ], and focalized quarantine [FQ +++ ] on air pollution in Bogotá, Colombia, during the COVID-19 pandemic. A natural experiment showed that, during SQ and FQ phases, concentrations of [PM₁₀, 20.0 µg/m3; PM₂.₅, 8.03 µg/m3; SO 2 , 1.61 µg/m3] and [PM₁₀, 23.2 µg/m3, PM₂.₅, 8.84 µg/m3], respectively, were significantly lower than during equivalent pre-pandemic periods (year 2019; p < 0.001). Effect sizes were larger during FQ (PM₁₀: -1.220, PM₂.₅: -0.605) than during SQ (PM₁₀: -1.180, PM₂.₅: -0.252, SO 2 : -0.388). Although pollutant concentrations remained below regulatory thresholds (environmentally significance), the ES for [PM₁₀ µg/m 3 ; PM₂.₅ µg/m 3 ] were larger during SQ and FQ. These findings support public health strategies aimed at strengthening the control of emission sources that degrade air quality, particularly those increasing [PM₁₀, PM₂.₅], Moreover, the introduction of the concept of “environmentally significant” effects may further improve decision-making and address environmental problems that affect human well-being.