We observe a 2.6% (95%CrI: 2.4%, 2.7%) increase in the COVID-19 mortality risk for every 1 μg/m3 increase in the long-term exposure to NO2, based on model 1 (Fig. 3 & Supplemental Material Table S4). There is still evidence of an effect, albeit smaller, once we adjust for spatial autocorrelation or confounders, with increases in the long-term exposure to NO2 of, respectively, 1.3% (95% CrI: 0.8%, 1.8%), 1.8% (95% CrI: 1.5%, 2.1%) for every 1 μg/m3. When we adjust for both autocorrelation and confounders the evidence is less strong, with estimates of 0.5% (95% CrI: −0.2%, 1.2%) for every 1 μg/m3 (Fig. 3 & Supplemental Material Table S4) and posterior probability of a positive effect reaching 0.93. The spatial relative risk in England varies from 0.24 (95% CrI: 0.08, 0.69) to 2.09 (95% CrI: 1.30, 3.11) in model 2 and from 0.30 (95% CrI: 0.10, 0.84) to 1.87 (95% CrI: 1.18, 2.93) in model 4, implying that the confounders explain very little of the observed variation (Fig. 3). The variation is more pronounced in the cities and suburban areas (with posterior probability higher than 1; Fig. 3).
Fig. 3 Density strips for the posterior of COVID-19 mortality relative risk with 1 μg/m3 increase in NO2 (top panel) and PM2.5 (bottom panel) averaged long-term exposure.