key: cord-0884952-bkwvyiut
authors: Naqvi, Hasan Raja; Mutreja, Guneet; Shakeel, Adnan; Singh, Karan; Abbas, Kumail; Naqvi, Darakhsha Fatma; Chaudhary, Anis Ahmad; Siddiqui, Masood Ahsan; Gautam, Alok Sagar; Gautam, Sneha; Naqvi, Afsar Raza
title: Wildfire-Induced Pollution and its Short-Term Impact on COVID-19 Cases and Mortality in California
date: 2022-05-04
journal: Gondwana Res
DOI: 10.1016/j.gr.2022.04.016
sha: 620c0b06f394fb87e10808a1dd98321d5d4c796e
doc_id: 884952
cord_uid: bkwvyiut

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 PM2.5, 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 PM2.5, and CO for the cities examined clearly suggesting wildfire-induced surge in air pollution. Fresno and Sacramento showed increment in the ground PM2.5, 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.

In the past decades, the world has witnessed widespread impact of anthropogenic activities on climate pattern changes in the form of extreme, unprecedented and detrimental weather conditions that are considered a threat to human existence (Abatzoglu and Williams, 2016; Fazel-Rastgar, 2020) . Prolonged warm and dry weather is becoming a global phenomenon and has contributed to numerous record-breaking wildfires in the recent years destroying wildlife habitat, vegetation, livestock, displacing millions of residents and above all costs thousands of human lives (Westerling, 2016) .

In addition, historic heat waves and sudden outpouring of atmospheric pollutants to local environment are secondary effects of wildfires that further complicate their containment and amplify their adverse health effects well beyond the local geographic region (Holm et al., 2021) . Understanding the spatiotemporal effects of wildfires on tropospheric and ground air pollutants and their impact on the human health is critical to inform local environmental policies to mitigate human cost of natural disasters (Davis et al., 2017; Tomshin and Solovyev, 2021) . Numerous studies have reported global increase in wildfire frequency and extended duration in the recent years (North et al., 2015; Doerr and Santín, 2016) . Approximately 30-46 million km 2 , ~4% of the total land surface, burned every year signifying its profound impact of greenhouse gas release (Johnston et al., 2012) . Wildfires release substantial amount of pollutants into the atmosphere each year, influencing weather, climate, and air quality, which attributed to an average of 339,000 deaths annually (Johnston et al., 2012) . Global economic damage from wildfires over the period of 1984-2014 amounted to an average of US $2677 million annually (Doerr and Santin, 2016) . While direct impact of wildfires is detrimental yet short-term, its secondary and long-term effects such as accelerated flooding, soil erosion, mass movement and pollution of water bodies further adds to the global economic burden (Santin and Martin, 2016) .

Wildfires generate various pollutants including particulate matter (PM) and gases (including CO, NO 2 and O 3 ) that enters into atmosphere and pose a great risk to human health. PM 2.5 is the major component of wildfire smoke that affects public health (Gupta et al., 2018; Liu et al., 2015) and a short-term exposure to PM 2.5 leads to severe health outcomes (Deryugina et al., 2019) . By virtue of its small size compared with other coarse particulate matter, PM 2.5 can reach deeper into the respiratory system to cause long-term health problems (Kim et al., 2015) . Burke et al., (2021) showed that 25% of the PM 2.5 is contributed by wildfires alone and at some places up to 50%. The CORINAIR-1990 inventory reveals that 0.2% of the NO 2 emissions, 0.5% of the nonmethane volatile organic compounds, 0.4% of the NH 4 emissions and 1.9% of the CO emissions are contributed by wildfires, which in turn, adversely affect the human health (EMEP-CORINAIR, 2002) .

Patients with chronic respiratory disease are susceptible to COVID-19 infection and exhibit severe clinical manifestations that may lead to death (O'Horo, 2021; Beltramo et al., 2021) . Recent studies have shown association between increased air pollution and severe COVID-19 illness, health outcomes and mortality. A study by Pozzer et al., (2020) shows the relationship between particle pollution and COVID-19 mortality worldwide which concludes that 15% of the deaths throughout the world due to COVID-19 may be associated to long-term exposure to air pollution. The particulate matters like PM 2.5 and PM 10 have direct association with the increasing number of respiratory diseases (pneumonia) and hospital admissions (Lelieveld et al., 2015; Wonjun et al., 2017; Zanobetti, 2010; Cheng et al., 2019; Sun and Sung, 2020) .

Nitrogen dioxide (NO 2 ) is an important air pollutant and its higher atmospheric concentrations may cause increased toxicity to respiratory systems and mortality (Faustini et al., 2014) . NO 2 is also linked with several other diseases such as diabetes, hypertension and heart related diseases (Maawa et al., 2020) . Similarly, short-term exposure to ozone (O 3 ) in combination with other atmospheric factors could be linked with the initiation and transmission of COVID-19 (Adhikari and Yin, 2020) .

In the recent decades, the US has seen surge in wildfires days and size (NIFC, 2021) . National Interagency Fire Center data shows that 2.83 million hectares of land burns in the US every year and 4.09 million hectares of land was under wildfire during (NIFC, 2021 . The area under wildfires in the US during the last ten years has increased by 195% (NIFC, 2021). The US witnessed worst wildfire season on record from February 15 − December 31, 2020 during which 9917 fire spots were reported.

These wildfires burnt 1.77 million hectares of land, which accounted for almost 4% of the total land area and on August 18, 2020, it was declared a national disaster (Cal Fire, 2020) . The wildfires were at their peak during the month of August releasing large amount of pollution into the atmosphere, which coincided with the surge in COVID-19 cases and mortalities (Meo et al., 2020) .

We and others have shown the impact of COVID-19 lockdown on air pollutants and the association with virus infection and mortality globally (Naqvi et al., 2020; Naqvi et al., 2021a; Naqvi et al., 2021b; Gautam, 2021c; Cole et al., 2020; Travaglio et al., 2021) . Numerous studies have reported decreased air pollution during COVID-19 lockdown period when people stayed at home due to reduced anthropogenic activities (Gautam et al., 2020a; Chelani and Gautam, 2021; Ambade et al., 2021; Gautam et al., 2021a; Gautam, 2020c; Naqvi et al., 2020; Naqvi et al., 2021a; Gautam et al., 2021d) .

Respiratory manifestations of COVID-19 are further complicated by natural disasterinduced air pollution (Copat et al., 2021; Villeneuve & Goldberg, 2020) . Increasing range and intensity of wildfires across the globe has further complicated global response to contain virus. However, the association between wildfire-induced pollution and COVID-19 is poorly studied. Whether the local wildfires contribute to the air pollution and exacerbate COVID-19 infection and mortalities remain understudied. Here, we assessed the impact of California wildfires on tropospheric and ground air pollutants during July − October 2020 and its correlation with COVID-19 cases and mortalities in five cities viz., Fresno, Los Angeles, Sacramento, San Diego and San Francisco with largest wildfire area.

The remote sensing data product Sentinel 5P Tropospheric Monitoring Instrument (TROPOMI) is widely used for air quality applications (Veefkind et al., 2012) . Satellite datasets are becoming easier to extract through Google Earth Engine platform to monitor the changes in tropospheric pollutants. Accordingly, we extracted the Absorbing Aerosol Index (AAI), column number density of carbon monoxide (CO), nitrogen dioxide (NO 2 ) and Ozone (O 3 ) in mol/m 2 for July 16 -October 15, 2019 and 2020 from the United States Geological Survey portal (USGS: https://lpdaac.usgs.gov/produ cts/mcd19a2v006/). A series of wildfires burned during February 15 -December 31, 2020 in California. However, it was important to find out the peak period of wildfire and its association with COVID-19. Based on the California wildfire information, we decided to classify the wildfire periods in three categories viz., (i) onset: July 16 -August 15, (ii) peak: August 16 -September 15 (Sannigrahi et al., 2020) 

Next, we identified the Californian cities severely affected by wildfires and with the highest COVID-19 morbidity and mortalities rates in the state. After careful assessment of the wildfire and COVID-19 datasets, we selected Fresno, Los Angeles, Sacramento, San Diego and San Francisco cities, where both the crisis were ongoing. The daily median of ground air pollutants viz., PM 2.5 , O 3 , NO 2 (in µg/m 3 ) and CO (in ppm) were obtained from different websites (California Air Pollution: Air Quality Index-AQI, 2020

and Environmental Protection Agency -EPA, USA, 2020). A few data points of some pollutants were missing from the datasets used in this study. We addressed this issue by using median values one-week before and after the missing point, a widely accepted approach (Cokluk and Kayri, 2011; Gopal et al., 2019) . Later, we assessed the trends and patterns along with their association with daily COVID-19 cases and deaths (Worldometer, 2020; COVID-19 Live Tracker Johns Hopkins, 2020) in each city under the classified periods of wildfire.

California wildfires were catastrophic and created environmental disaster in the midst of the ongoing pandemic. We asked whether wildfires burned during August to October 2020 in California, the most populated state in US, contributed to temporal changes in air pollutants. To this end, average values of various tropospheric pollutants viz., aerosols, carbon monoxide (CO), NO 2 , and O 3 were examined during three phases of wildfires: onset (July 16 -August 15), peak (August 16-September 15) and slowdown (September 16 -October 15, 2020) Wildfires contribute to the increase in aerosol concentrations (Burke et al., 2021) .

The report of NASA on California wildfire 2020 revealed that the CO concentrations were >10 times compared to the normal days (Science Daily, 2020) . Another study on California wildfire also highlighted that CO concentration highly increased in the initial days of wildfire (Schneising et al., 2020) . Sannigrahi et al., (2020) observed that the variations in tropospheric NO 2 was nominal compared to aerosol and CO pollutant and interestingly, negative changes were observed in satellite derived O 3 pollutants. Our results show a sudden spike in tropospheric aerosol index, CO and NO 2 that corroborate with the previous findings (Meo et al., 2020 (Meo et al., , 2021 Preisler et al. 2015) .

Next, we asked whether wildfires influenced ground pollutant levels during the study period. To this end, five cities viz., Fresno, Los Angeles, Sacramento, San Diego and San Francisco from California that were severely affected by the wildfires were selected to assess the impact of wildfires on the ground pollutant (including PM 2.5 , CO, NO 2 and The CO concentrations (in ppm) and trends in all the stations during the study period of 2019 were similar. CO values ranged within 0.1 to 0.7 ppm and rarely crossed 1.0 ppm, except at Fresno after October 10, 2019 (Fig 6c) . CO levels showed a pattern and trend similar to PM 2.5 (Fig. 6b, d) . Three different CO spikes overlapped with PM 2.5 clearly suggesting contribution of an external event that induced local pollutant levels (Fig 6d) . Sacramento and Fresno stations showed higher CO levels in all three peaks in 2020, whereas, these stations recorded lowest CO (<0.5 ppm) concentrations in 2019 (Fig 6d) further supporting our hypothesis of wildfire induced pollutant outburst.

In 2019, NO 2 levels were recorded at <10 µg/m 3 at all the stations except the Los Angeles, where this pollutant was two-folds higher than other places throughout the study period (fig 6e) . Intriguingly, unlike other pollutants (PM 2.5 and CO), NO 2 concentration and temporal pattern did not exhibit any noticeable changes in 2020. Los Angeles ground NO 2 levels (~40 µg/m 3 ) were markedly higher compared to other cities; however, some small peaks were noticed for Fresno and San Francisco stations (Fig   6f) . Los Angeles is the largest urban regions of USA where the anthropogenic factors, predominantly fuel burning, and industrial facilities contribute towards NO 2 emission (U.S. EPA, 2008; Kerr et al., 2021) . Our findings also supported that NO 2 levels in Los Angeles were consistently high compared to other places during the study period.

In case of O 3 , the maximum concentration was recorded at the Fresno station (~30 µg/m 3 ), while other places recorded between 10-30 µg/m 3 , whereas the lowest value was recorded in Los Angeles (Fig. 6g) . Sacramento, San Diego and San Francisco stations showed some minor peaks corresponding to a higher O 3 levels (~40 µg/m 3 ) during August 16 -September 15, 2020 (Fig. 6h) . We observed cyclic pattern of air pollutant levels after August 15, 2020 at most of the stations since the wildfires started and their containment. Our findings of PM 2.5 and CO levels and their pattern of daily median indicates that most of the wildfires occurred between August 16 − September 15, 2020 and gradually suppressed at the end of September 2020 (Sannigrahi et al., 2020; California wildfires, 2020) .

Further, we calculated the percentage change in each pollutant in 2020 compared to the corresponding periods in 2019. Our analysis revealed that Sacramento and Fresno showed most remarkable increase ~400% and 200%, respectively, in PM 2.5 during the peak compared to the corresponding time period of 2019 (fig 7a) . For CO, we noticed marked increase in Fresno (220%), Sacramento (94%) and San Francisco (50%) stations, while Los Angeles and San Diego showed minimal change (fig 7b) . It is interesting to note that except PM 2.5 other pollutants exhibit unique pattern and variation during the study period. Similar analysis for NO 2 revealed wildfires had relatively less impact on annual changes in this ground pollutant; however, Fresno (50%) and Los Angeles (28%) still showed increase during the peak, while San Diego showed 66% higher NO 2 levels during the slowdown period (Fig 7c) . Finally, we analyzed changes in O 3 levels but did not observe any significant impact. Only Fresno or Sacramento stations showed approximately 5% increase during the peak period (fig 7d) . We observed that among all the ground air pollutants, PM 2.5 was highly induced by the wildfires, followed by CO and O 3 . Our results corroborate with the findings of Zhou et al., (2021) that showed drastic increase in the PM 2.5 levels due to wildfire in different counties of California between August 15 -October 5, . Meo et al., (2021 analyzed the changes in air pollutants viz., PM 2.5 , CO, and O 3 during California wildfires in 2020 and respectively noticed 220%, 151% and 19% increase lending support to our findings.

Since we noticed marked increase in multiple air pollutants, the impact of adverse air pollution on COVID-19 cases and mortalities was examined. To this end, daily COVID-19 cases and mortality data was procured for Fresno, Los Angeles, Sacramento, San Diego and San Francisco during the study period (July 16 -October 15, 2020) ( fig. 7ah) . A linear trend line was added to highlight the time points with spike in COVID-19 cases and deaths. In general, we noticed increment in both COVID-19 cases and mortalities in all the cities, albeit to a varying extent ( fig. 7a-h) . Sacramento and Fresno showed spike in COVID-19 cases that overlaps with the peak period (August 15 -August 30, 2020) and multiple spikes in the infections are evident ( fig. 7c, d) . In both of these cities, average daily infections ranged around 300-400, but these numbers increased to ~600-650 during the initial days of peak period. However, compared to Fresno, multiple spikes in COVID-19 cases can be noticed suggesting more profound impact of wildfire-induced virus spread. Subtle increments in COVID-19 infections were observed in Los Angeles and San Francisco during July, 2020 where wildfires started from mid-June to July (Calfire, 2021). In San Diego multiple small peaks of infections was noticed across the study period.

Assessment of COVID-19 mortality revealed higher rates in all the cities (fig 7e- h). Intriguingly, we noticed that COVID-19 mortalities were relatively higher after August 15, 2020 except Los Angeles. In particular, San Diego showed ~300% increase in COVID-19 mortalities around September 17-24, 2020 which correlates with active wildfires (September 5-24, 2020) . While COVID-19 infections showed more pronounced increase during the onset of wildfires, more consistent increment in COVID-19 mortalities was apparent after the peak period. Previous studies have shown that wildfire-induced pollution levels in ten affected counties in California was attributed to an increase in COVID-19 cases (56.9%) and mortalities (148.2%) (Meo et al., 2021) . A study conducted in San Francisco also revealed that wildfire associated pollutants such as PM 2.5 and CO had a positive relationship with an increased number of SARS-COV-2 daily cases, cumulative cases and cumulative deaths (Meo et al., 2020) . A logical justification is the natural progression of COVID-19, which can take weeks and months; however, severe air pollution can exacerbate the clinical manifestations of disease.

Increased air pollution and its effect on COVID-19 infections is the most heated, debated and deliberated topic among the academicians, researchers, policymakers, stakeholders, etc. Fine particulate matter and other harmful gases are responsible for millions of death annually. Studies have shown that long-term exposure to air pollution leads to higher frequency of respiratory diseases (Brauer, 2010; Guan et. al., 2016; Bloemsma et al., 2016; Schiavoni et al., 2017) . Higher levels of PM 2.5 , PM 10 , NO 2 , SO 2 , and O 3 show strong association with COVID-19 infection and mortalities (Naqvi et al., 2021(a) ; Naqvi et al., 2021(b) ; Wu et al., 2020; Naqvi et al., 2020) . In the North America, increased exposure to pollution due to particulate matter was attributed to 17% increase in COVID-19 mortality (Pozzer et al., 2020) . In a study by Liang et al. (2020) , it was argued that long-term exposure to fine particulate matter pollution, O 3 , and specifically NO 2 is associated with rising rate of deaths due to COVID-19. Li et al., (2020) assessed the relationship between air quality indexes (AQI) and the rate of occurrence of COVID-19 in Wuhan. Of the four major air pollutants (PM 2.5 , PM 10 , NO 2 , and CO) examined, NO 2 and PM 2.5 levels strongly correlated with the prevalence of COVID-19. Wu et al., (2020) noticed a positive relationship between increased COVID-19 mortality and exposure to PM 2.5 in the United States. In most of the investigated cities, we noticed that the daily COVID-19 cases and deaths overlap with spike in PM 2.5 and CO levels, as observed by three different peaks during the wildfire period. These findings indicate that COVID-19 cases and mortalities could be directly impacted by wildfires and other natural disasters due to prolonged stay in shelters, often with minimal social distancing to avoid viral spread and demands further investigation.

In this study, we examined wildfire-induced short-term changes in the tropospheric and ground air pollutants in five major cities in California, US. Our results show that wildfires contribute to a rapid surge in PM 2.5 and CO levels during the peak wildfire period (August 16-September 15, 2020). Interestingly, increase in air pollution overlaps with the spike in COVID-19 cases and mortalities in Fresno, Sacramento suggesting that in addition to wildfire generates air pollution, other factors may contribute to the adverse increment in viral spread. Our results highlight the crosstalk between wildfire-induced air pollution, and human health in the wake of a highly transmissible pandemic. 

California wildfires, 2021. Wikipedia, Wikimedia Foundation

Impact of anthropogenic climate change on wildfire across western US forests

Short-term effects of ambient ozone, PM2.5, and meteorological factors on COVID-19 confirmed cases and deaths in Queens

COVID-19 lockdowns reduce the Black carbon and polycyclic aromatic hydrocarbons of the Asian atmosphere: source apportionment and health hazard evaluation

Chronic respiratory diseases are predictors of severe outcome in COVID-19 hospitalised patients: a nationwide study

Panel studies of air pollution in patients with COPD: systematic review and meta-analysis

How much, how long, what, and where: air pollution exposure assessment for epidemiologic studies of respiratory disease

The changing risk and burden of wildfire in the United States

Lockdown during COVID-19 pandemic: A case study from Indian cities shows insignificant effects on persistent property of urban air quality

Association between Particulate Matter Air Pollution and Hospital Emergency Room Visits for Pneumonia with Septicemia: A Retrospective Analysis

The Effects of Methods of Imputation for Missing Values on the Validity and Reliability of Scales

Air Pollution Exposure and COVID-19. DISCUSSION PAPER SERIESIZA DP No. 13367. IZA -Institute of Labor Economics

The role of air pollution (PM and NO 2 ) in COVID-19 spread and lethality: A systematic review

COVID-19 Live Tracker Johns Hopkins

The normal fire environment-Modeling environmental suitability for large forest wildfires using past, present, and future climate normals. Forest Eco. and Mang

The mortality and medical costs of air pollution: Evidence from changes in wind direction

Global trends in wildfire and its impacts: perceptions versus realities in a changing world

Prepared by the EMEP Task force on Emission Inventories

Nitrogen dioxide and mortality: review and meta-analysis of long-term studies

Extreme weather events related to climate change: widespread flooding in Iran

Temporary reduction in air pollution due to anthropogenic activity switch-of during COVID-19 lockdown in northern parts of India

Pandemic induced lockdown as a boon to the Environment: trends in air pollution concentration across India

The influence of COVID -19 on air quality in India: A boon or inutile

COVID -19: Air pollution remains low as people stay at home

Strong link between coronavirus count and bad air: A case study of India

Comparative Analysis Of Different Imputation Techniques For Handling Missing Dataset

Impact of air pollution on the burden of chronic respiratory diseases in China: time for urgent action

Impact of California fires on local and regional air quality: the role of a low-cost sensor network and satellite observations

Health effects of wildfire smoke in children and public health tools: a narrative review

Estimated global mortality attributable to smoke from landscape fires

COVID-19 pandemic reveals persistent disparities in nitrogen dioxide pollution

A review on the human health impact of airborne particulate matter

The contribution of outdoor air pollution sources to premature mortality on a global scale

Air pollution and temperature are associated with increased COVID-19 incidence: a time series study

Urban Air Pollution May Enhance COVID-19 Case-Fatality and Mortality Rates in the United States

A systematic review of the physical health impacts from non-occupational exposure to wildfire smoke

Performance, combustion, and emission characteristics of a CI engine fueled with emulsified diesel-biodiesel blends at different water contents

At the nexus of fire, water and society

Effect of Environmental Pollutants PM-2.5, Carbon Monoxide, and Ozone on the Incidence and Mortality of SARS-COV-2 Infection in Wildfire Affected Ten Counties in California

Wildfire and COVID-19 pandemic: effect of environmental pollution PM-2.5 and carbon monoxide on the dynamics of daily cases and deaths due to SARS-COV-2 infection in

Improved air quality and associated mortalities in India under COVID-19 lockdown

Global assessment of tropospheric and ground air pollutants and its correlation with COVID-19

Spatio-temporal analysis of air quality and its relationship with major COVID-19 hotspot places in India

ENVIRONMENTAL SCIENCE. Reform forest fire management

Outcomes of COVID-19 with the Mayo Clinic Model of Care and Research

Regional and global contributions of air pollution to risk of death from COVID-19

A statistical model for determining impact of wildland fires on Particulate Matter (PM2.5) in Central California aided by satellite imagery of smoke

Effects of West Coast forest fire emissions on atmospheric environment: A coupled satellite and groundbased assessment. Pre-print in Arxiv

Fire effects on soils: the human dimension

The dangerous liaison between pollens and pollution in respiratory allergy

Severe Californian wildfires in November 2018 observed from space: the carbon monoxide perspective

NASA monitors carbon monoxide from California wildfires

Particulate-Matter Related Respiratory Diseases

Spatio-temporal patterns of wildfires in Siberia during

Links between air pollution and COVID-19 in England

Risk and Exposure Assessment to Support the Review of the NO2 Primary National Ambient Air Quality Standard

TROPOMI on the ESA Sentinel-5 Precursor: a GMES mission for global observations of the atmospheric composition for climate, air quality and ozone layer applications

Methodological considerations for epidemiological studies of air pollution and the SARS and COVID-19 coronavirus outbreaks

Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring

Prolonged effect of air pollution on pneumonia: a nationwide cohort study

Air pollution and COVID-19 mortality in the United States: Strengths and limitations of an ecological regression analysis

Air Pollution and Pneumonia The "Old Man" Has a New "Friend

Excess of COVID-19 cases and deaths due to fine particulate matter exposure during the 2020 wildfires in the United States

Temporal impact of California wildfires was examined on air pollution and COVID-19

Higher levels of ground PM 2.5 , CO, and NO 2 detected in five major cities in California

Pattern of wildfire-induced PM 2.5 and CO spikes overlap with COVID-19 cases and mortalities