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

Rationale: Wildfires are a growing source of pollution including particulate matter ⩽2.5 microm 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.