Top panel: SARS-CoV-2 test positivity rate from 15 May 2020 to 20 Oct 2020. Expected positivity rates were estimated by the model which included the 7-day average of daily mean PM2.5 as a predictor. The black line indicates the 7-day moving average of the positivity rate (each day averaged with the 3 days prior and the 3 days following). The blue line indicates the expected positivity rate if the concentration of 7-day average PM2.5 during the period 16 Aug 2020 to 10 Oct 2020 had remained at the average level of the same period in 2019 (4.5 µg/m3). The red-shaded region indicates the expected positivity rate based on the actual PM2.5, which is indicated by the red line. For this figure, weekday effects were removed from the model estimates for clarity. Middle panel: Daily number of patients with SARS-CoV-2 NAA tests at Renown is indicated by the thin line, while the 7-day average is indicated by the bold line. Bottom panel: daily mean temperature (°C) is indicated by the thin line, while the 7-day average is indicated by the bold line.