Compound Risk of Air Pollution and Heat Days and the Influence of Wildfire by SES across California, 2018-2020: Implications for Environmental Justice in the Context of Climate Change

Co-occurring climate events and environmental justice in California, 2018-2019

Climate change will increase the frequency of extreme weather events. This means climate-driven events like wildfires and power outages will likely co-occur more often, potentially magnifying their health risks. We characterized three types of climate-driven events-anomalously warm temperatures, wildfire burn zone disasters, and long power outages-in 58 California counties during 2018-2019. We defined county-day anomalously warm temperatures when daily average temperatures exceeded 24 °C and the 85th percentile of the long-term county average. We defined county-day wildfire burn zone disasters when an active wildfire burn zone intersected a county, burned 1+ structures, killed a civilian, or received a Federal Emergency Management Agency Fire Management Declaration, and overlapped with a community. For a subset of the 38 counties (66%), long power outage county days were identified using PowerOutage.us data when an outage affected >0.5% of county customers for 8+ h. Co-occurring events were when 2+ of these events occurred on the same county day. Using the CDC/ATSDR Social Vulnerability Index (SVI), we determined whether co-occurring events disproportionately affected vulnerable populations. Nearly every county (97%) experienced at least one day of anomalously warm temperatures, 57% had at least one wildfire burn zone disaster day, and 63% (24/38 counties with available data) had at least one long power outage day. The most common co-occurring events (anomalously warm temperatures and wildfire burn zone disasters) impacted 24 (41%) counties for 144 total county-days. We did not find a clear connection between co-occurring events and social vulnerability. We observed an inverse correlation between co-occurring wildfire burn zone disasters and long power outage days with SVI, and a positive correlation between co-occurring anomalously warm and long power outage days with SVI. This analysis can inform regional resource allocation and other state-wide planning and policy objectives to reduce the adverse effects of climate-driven events.

Coexposure to extreme heat, wildfire burn zones, and wildfire smoke in the Western US from 2006 to 2020

Climate change drives three heat-related hazards: extreme heat (EH), wildfire burn zones (WFBZs), and wildfire smoke (WFS). Using daily census tract-level data from 2006 to 2020, we investigated when, where, and whom these hazards coexposed in 11 Western US states. Among 18,106 tracts, at least one hazard occurred an average of 32 days (581,867 tract-days) annually. EH-WFS coexposure increased over the study period and was the most frequent coexposure (annual average of 38,218 tract-days). EH-WFS-affected regions varied year to year. WFBZ-involved coexposures were spatially confined and did not increase over time. On average, the most tract-days of EH-WFBZ-WFS coexposure took place in California, Arizona, and Oregon. Among census tracts most exposed to EH-WFBZ-WFS, populations disproportionately consisted of people of older age, with disabilities, and living in poverty. American Indian and Alaska Native individuals disproportionately faced all coexposures. As climate change accelerates, tracking coexposure to multiple hazards can help target resources to protect health.

Unveiling the Impact of Wildfires on Nanoparticle Characteristics and Exposure Disparities through Mobile and Fixed-Site Monitoring in Toronto, Canada

This study investigates the impacts of wildfires on nanoparticle characteristics and exposure disparities in Toronto, integrating data from a large-scale mobile monitoring campaign and fixed-site measurements during the unprecedented 2023 wildfire season. Our results reveal changes in particle characteristics during wildfire days, with particle number concentrations decreasing by 60% and particle diameter increasing by 30% compared to nonwildfire days. Moreover, the median lung deposited surface area (LDSA) levels rose by 31% during wildfire events. We employed gradient boosting models to estimate near-road LDSA levels on both wildfire and nonwildfire days. The LDSA ratio (wildfire/nonwildfire) exceeded 2.0 in certain areas along highways and in downtown Toronto. Furthermore, our findings show that marginalized communities faced greater LDSA increases than less marginalized ones. Under wildfire conditions, the LDSA ratio difference between the most and least marginalized groups was 16% for recent immigrants and visible minorities and 7% for seniors and children, both statistically significant. This study delivers critical insights into the spatiotemporal variations of nanoparticle characteristics during wildfire and nonwildfire periods, demonstrating the substantial health risks posed by increased LDSA levels and the inequitable distribution of these risks among Toronto's diverse population.

Racial and Economic Disparities in High-Temperature Exposure in Brazil

Primary studies analyzing the distribution of exposure to the consequences of climate change among different vulnerable groups are scarce. This study addresses this gap by investigating racial and economic disparities in high-temperature exposure in Brazil, focusing on the impact on vulnerable subpopulations. We utilized georeferenced temperature data from the Global High-Resolution Estimates of Extreme Heat (GEHE) and population data from the 2010 Census. The disparity analyses included (i) estimating the exposure rate to temperatures exceeding 28 °C, expressed as population-weighted heat exposure (PHE¯); (ii) determining the difference in exposure between the most and least exposed groups; and (iii) calculating weighted Gini coefficients. The findings reveal that low-income and black, brown, and indigenous populations are predominantly the most exposed to PHE¯ exceeding 28 °C. Nationally, the indigenous population is the most exposed racial group, with a PHE¯ 47% higher than that of the white population. Stratified analyses indicate that, despite varying climatic and environmental conditions across regions, the black-brown-indigenous population consistently faces the highest heat exposure in Brazil. Income disparity analyses show that the lowest per capita income groups are the most exposed to high temperatures across the country. The study highlights the impact of climate change on economic inequality and the deepening of within-country inequalities, particularly affecting socioeconomically disadvantaged groups. These findings underscore the urgent need for evidence-informed public policies to address racial and economic disparities in high-temperature exposure, mitigate health risks associated with climate change, and emphasize the importance of context-sensitive analyses for a comprehensive understanding of heat-related risks and public health.

The association of short-term increases in ambient PM2.5 and temperature exposures with stillbirth: racial/ethnic disparities among Medicaid recipients

Racial/ethnic disparities in the association between short-term (eg, days, weeks), ambient fine particulate matter (PM2.5) and temperature exposures and stillbirth in the United States have been understudied. A time-stratified, case-crossover design using a distributed lag nonlinear model (0- to 6-day lag) was used to estimate stillbirth odds due to short-term increases in average daily PM2.5 and temperature exposures among 118 632 Medicaid recipients from 2000 to 2014. Disparities by maternal race/ethnicity (Black, White, Hispanic, Asian, American Indian) and zip code-level socioeconomic status (SES) were assessed. In the temperature-adjusted model, a 10 μg m-3 increase in PM2.5 concentration was marginally associated with increased stillbirth odds at lag 1 (0.68%; 95% CI, -0.04% to 1.40%) and lag 2 (0.52%; 95% CI, -0.03 to 1.06) but not lag 0-6 (2.80%; 95% CI, -0.81 to 6.45). An association between daily PM2.5 concentrations and stillbirth odds was found among Black individuals at the cumulative lag (0-6 days: 9.26% 95% CI, 3.12%-15.77%) but not among other races or ethnicities. A stronger association between PM2.5 concentrations and stillbirth odds existed among Black individuals living in zip codes with the lowest median household income (lag 0-6: 14.13%; 95% CI, 4.64%-25.79%). Short-term temperature increases were not associated with stillbirth risk among any race/ethnicity. Black Medicaid enrollees, and especially those living in lower SES areas, may be more vulnerable to stillbirth due to short-term increases in PM2.5 exposure. This article is part of a Special Collection on Environmental Epidemiology.

Physicochemical Characterization of the Particulate Matter in New Jersey/New York City Area, Resulting from the Canadian Quebec Wildfires in June 2023

The global increase in wildfires, primarily driven by climate change, significantly affects air quality and health. Wildfire-emitted particulate matter (WFPM) is linked to adverse health effects, yet the toxicological mechanisms are not fully understood given its physicochemical complexity and the lack of spatiotemporal exposure data. This study focuses on the physicochemical characterization of WFPM from a Canadian wildfire in June 2023, which affected over 100 million people in the US Northeast, particularly around New Jersey/New York. Aerosol systems were deployed to characterize WFPM during the 3 day event, revealing unprecedented mass concentrations mainly in the WFPM0.1 and WFPM0.1-2.5 size fractions. Peak WFPM2.5 concentrations reached 317 μg/m3, nearly 10 times the National Ambient Air Quality Standard (NAAQS) 24 h average limit. Chemical analysis showed a high organic-to-total carbon ratio (96%), consistent with brown carbon wildfires nanoparticles. Large concentrations of high-molecular-weight PAHs were found predominantly bound to WFPM0.1, with retene, a molecular marker of biomass burning and a known teratogen, being the most abundant (>70%). Computational modeling estimated a total lung deposition of 9.15 mg over 72 h, highlighting the health risks of WFPM, particularly due to its long-distance travel capability and impact on densely populated areas.

Climate change and health: rethinking public health messaging for wildfire smoke and extreme heat co-exposures

With the growing climate change crisis, public health agencies and practitioners must increasingly develop guidance documents addressing the public health risks and protective measures associated with multi-hazard events. Our Policy and Practice Review aims to assess current public health guidance and related messaging about co-exposure to wildfire smoke and extreme heat and recommend strengthened messaging to better protect people from these climate-sensitive hazards. We reviewed public health messaging published by governmental agencies between January 2013 and May 2023 in Canada and the United States. Publicly available resources were eligible if they discussed the co-occurrence of wildfire smoke and extreme heat and mentioned personal interventions (protective measures) to prevent exposure to either hazard. We reviewed local, regional, and national governmental agency messaging resources, such as online fact sheets and guidance documents. We assessed these resources according to four public health messaging themes, including (1) discussions around vulnerable groups and risk factors, (2) symptoms associated with these exposures, (3) health risks of each exposure individually, and (4) health risks from combined exposure. Additionally, we conducted a detailed assessment of current messaging about measures to mitigate exposure. We found 15 online public-facing resources that provided health messaging about co-exposure; however, only one discussed all four themes. We identified 21 distinct protective measures mentioned across the 15 resources. There is considerable variability and inconsistency regarding the types and level of detail across described protective measures. Of the identified 21 protective measures, nine may protect against both hazards simultaneously, suggesting opportunities to emphasize these particular messages to address both hazards together. More precise, complete, and coordinated public health messaging would protect against climate-sensitive health outcomes attributable to wildfire smoke and extreme heat co-exposures.

Measuring long-term exposure to wildfire PM2.5 in California: Time-varying inequities in environmental burden

Wildfires have become more frequent and intense due to climate change and outdoor wildfire fine particulate matter (PM2.5) concentrations differ from relatively smoothly varying total PM2.5. Thus, we introduced a conceptual model for computing long-term wildfire PM2.5 and assessed disproportionate exposures among marginalized communities. We used monitoring data and statistical techniques to characterize annual wildfire PM2.5 exposure based on intermittent and extreme daily wildfire PM2.5 concentrations in California census tracts (2006 to 2020). Metrics included: 1) weeks with wildfire PM2.5 < 5 μg/m3; 2) days with non-zero wildfire PM2.5; 3) mean wildfire PM2.5 during peak exposure week; 4) smoke waves (≥2 consecutive days with <15 μg/m3 wildfire PM2.5); and 5) mean annual wildfire PM2.5 concentration. We classified tracts by their racial/ethnic composition and CalEnviroScreen (CES) score, an environmental and social vulnerability composite measure. We examined associations of CES and racial/ethnic composition with the wildfire PM2.5 metrics using mixed-effects models. Averaged 2006 to 2020, we detected little difference in exposure by CES score or racial/ethnic composition, except for non-Hispanic American Indian and Alaska Native populations, where a 1-SD increase was associated with higher exposure for 4/5 metrics. CES or racial/ethnic × year interaction term models revealed exposure disparities in some years. Compared to their California-wide representation, the exposed populations of non-Hispanic American Indian and Alaska Native (1.68×, 95% CI: 1.01 to 2.81), white (1.13×, 95% CI: 0.99 to 1.32), and multiracial (1.06×, 95% CI: 0.97 to 1.23) people were over-represented from 2006 to 2020. In conclusion, during our study period in California, we detected disproportionate long-term wildfire PM2.5 exposure for several racial/ethnic groups.