Wildfire-induced pollution and its short-term impact on COVID-19 cases and mortality in California

Abstract

Globally, wildfires have seen remarkable increase in duration and size and have become a health hazard. In addition to vegetation and habitat destruction, rapid release of smoke, dust and gaseous pollutants in the atmosphere contributes to its short and long-term detrimental effects. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has emerged as a public health concern worldwide that primarily target lungs and respiratory tract, akin to air pollutants. Studies from our lab and others have demonstrated association between air pollution and COVID-19 infection and mortality rates. However, current knowledge on the impact of wildfire-mediated sudden outburst of air pollutants on COVID-19 is limited. In this study, we examined the association of air pollutants and COVID-19 during wildfires burned during August-October 2020 in California, United States. We observed an increase in the tropospheric pollutants including aerosols (particulate matter [PM]), carbon monoxide (CO) and nitrogen dioxide (NO₂) by approximately 150%, 100% and 20%, respectively, in 2020 compared to the 2019. Except ozone (O₃), similar proportion of increment was noticed during the peak wildfire period (August 16 - September 15, 2020) in the ground PM_2.5, CO, and NO₂ levels at Fresno, Los Angeles, Sacramento, San Diego and San Francisco, cities with largest active wildfire area. We identified three different spikes in the concentrations of PM_2.5, and CO for the cities examined clearly suggesting wildfire-induced surge in air pollution. Fresno and Sacramento showed increment in the ground PM_2.5, CO and NO₂ levels, while San Diego recorded highest change rate in NO₂ levels. Interestingly, we observed a similar pattern of higher COVID-19 cases and mortalities in the cities with adverse air pollution caused by wildfires. These findings provide a logical rationale to strategize public health policies for future impact of COVID-19 on humans residing in geographic locations susceptible to sudden increase in local air pollution.

Keywords: Air quality; COVID-19 pandemic; California; Respiratory diseases; Wildfires.

Graphical abstract

Fig. 1

California wildfire impact on tropospheric aerosols index. Maps showing satellite-derived average absorbing aerosol index (AAI) concentrations during (a, and e) 16 July – 15 Aug ust, (b, and f) 16 August − 15 September and, (c, and g) 16 September – 15 October and (d, and h) average values for each time period in 2019 and 2020.

Fig. 2

Variations in CO concentrations during California wildfires. Maps showing satellite-derived average CO concentrations (mol/m²) during (a, and e) 16 July −15 August, (b, and f) 16 August − 15 September and, (c, and g) 16 September −15 October and (d, and h) average values for each time period in 2019 and 2020.

Fig. 3

Spatiotemporal changes in Tropospheric NO₂. Maps showing satellite-derived average NO₂ concentrations (mol/m²) during (a, and e) 16 July – 15 August, (b, and f) 16 August – 15 September and, (c, and g) 16 September – 15 October and (d, and h) average values for each time period in 2019 and 2020.

Fig. 4

Tropospheric O₃ levels did not fluctuate during study period. Maps showing satellite-derived average O₃ concentrations (mol/m²) during (a, and e) 16 July −15 August, (b, and f) 16 August- 15 September and, (c, and g) 16 September −15 October and (d, and h) average values for each time period in 2019 and 2020.

Fig. 5

Tropospheric pollutant levels change during 2020 compared to 2019. Marked increment in aerosol index and CO, as well as subtle increase in NO₂ were observed during peak (16 August −15 September) of 2020 compared to onset (16 July –15 August), slowdown period (16September –15 October) and corresponding periods of 2019.

Fig. 6

Ground air pollutants level analysis in 2019 and 2020. Daily median of PM_2.5 levels in (a) 2019 and (b) 2020. Panel P1, P2, P3 (peaks) showed surge in PM_2.5 levels during wildfire in 2020. CO levels in (c) 2019 and (d) 2020 shows tremendous growth in CO levels under same coded panels defined above. NO₂ levels in (e) 2019 and (f) 2020 shows nominal NO₂ variations. O₃ levels in (g) 2019 and (h) 2020.

Fig. 7

Change rate of ground air pollutants. A marked increase in (a) PM_2.5, (b) CO, and (c) NO₂ levels was noticed in all stations during peak period (August 16–15 September) compared to other periods of 2020 and corresponding periods of 2019, while (d) O₃ levels do not exhibit any discernable change.

Fig. 8

Daily COVID-19 cases and mortalities. Bar graphs depicts daily COVID-19 cases from 16 July – 15 October 2020 in (a) Fresno, (b) Los Angeles, (c) Sacramento, (d) San Diego and (e) San Francisco. Similarly, daily COVID-19 deaths are plotted in (f) Fresno, (g) Los Angeles, (h) Sacramento, (i) San Diego and (j) San Francisco during the same time period as referred for cases. Dotted red line indicates the average value and value above this line reflect surge in COVID-19 cases and mortalities. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)