Wildfires and the Changing Landscape of Air Pollution-related Health Burden in California

Abstract

Rationale: Wildfires are a growing source of pollution including particulate matter ⩽2.5 μm in aerodynamic diameter (PM_2.5), but associated trends in health burden are not well characterized. Objectives: We investigated trends and disparities in PM_2.5-related cardiorespiratory health burden (asthma, chronic obstructive pulmonary disease, and all-cause respiratory and cardiovascular emergency department [ED] visits and hospital admissions) for all days and wildfire smoke-affected days across California from 2008 to 2016. Methods: Using residential Zone Improvement Plan code and daily PM_2.5 exposures, we estimated overall and subgroup-specific (age, gender, race and ethnicity) associations with cardiorespiratory outcomes. Health burden trends and disparities were evaluated on the basis of relative risk, attributable number, and attributable fraction by demographic and geographic factors and over time. Measurements and Main Results: PM_2.5-attributed burden steadily decreased, whereas the fraction attributed to wildfire smoke varied by fire season intensity, constituting up to 15% of the annual PM_2.5-burden. The highest relative risk and PM_2.5-attributed burden (92 per 100,000 people) was observed for respiratory ED visits, accounting for 2.2% of the respiratory annual burden. Disparities in overall morbidity in the oldest age, Black, and "other" race groups were also reflected in PM_2.5-attributed burden, whereas Asian populations had the highest risk rate in respiratory outcomes and thus the largest fraction of the total burden attributed to the exposure. In contrast, high wildfire PM_2.5-attributed burden rates in rural, central, and northern California populations occurred because of differential exposure. Conclusions: In California, wildfires' impact on air quality offset the public health gains achieved through reductions in nonsmoke PM_2.5. Disproportionate effects could be attributed to differences in subpopulation susceptibility, relative risk, and differential exposure.

Keywords: burden of disease; respiratory outcomes; wildfire smoke exposure.

Figure 1.

Daily mean fine particulate matter (PM_2.5) concentrations on days where smoke was not detected (A), and the cumulative number of days on which smoke was detected (B), between 2008 and 2016. ZIP codes level maps are color coded by the quintiles of respective distributions and black boundaries denote counties.

Figure 2.

Percent change in risk of emergency department visits and hospital admissions related to asthma and respiratory disease (A) and chronic obstructive pulmonary disease (COPD) and cardiovascular disease (B) per 10 μg/m³ increase in fine particulate matter (PM_2.5), California, 2008–2016. ^aRace/Ethnicity: White, Black, Asian, Native American, and Other categories are exclusive of Hispanic or Latino

Figure 2.

Percent change in risk of emergency department visits and hospital admissions related to asthma and respiratory disease (A) and chronic obstructive pulmonary disease (COPD) and cardiovascular disease (B) per 10 μg/m³ increase in fine particulate matter (PM_2.5), California, 2008–2016. ^aRace/Ethnicity: White, Black, Asian, Native American, and Other categories are exclusive of Hispanic or Latino

Figure 3.

Annual PM_2.5 attributable fraction (A) and percent of PM_2.5 burden on days with wildfire smoke (B), for emergency department visits related to asthma, chronic obstructive pulmonary disease (COPD), respiratory disease, and cardiovascular disease, California, 2008–2016.

Figure 4.

PM_2.5 attributable rate of cardiorespiratory-related emergency department visits per 100,000 people on days affected by smoke, cumulatively over 2008–2016, at ZIP code resolution, for (A) asthma, (B) chronic obstructive pulmonary disease (COPD), (C) respiratory disease, and (D) cardiovascular disease. Color gradient is determined by the following percentile ranges of the ZIP code-level rates: 0–50, 50–75, 75–95, 95–99, and 99–100. Black boundaries denote counties.