Background: Air quality in California ranks among the worst in the United States (US), with many areas failing to meet National Ambient Air Quality Standards for fine particulate matter (PM2.5) and ozone (O3). Exposure contributes to substantial morbidity and mortality and disproportionately affects communities of color. On the other hand, ethnic enclaves, areas where an ethnic group is densely concentrated and socially distinct, have been shown to be favorable for many health endpoints through social support mechanisms. However, evidence on whether ambient pollutant concentration within enclaves are different from other areas is limited.

Objective: To examine associations between Latino ethnic enclaves and ambient air pollution concentrations.

Methods: This ecological study consists of 2,590 California ZIP code tabulation areas (ZCTAs). Enclaves were defined using the American Community Survey 5-year estimates (2009–2013; 2014–2018): population density, dissimilarity index, and isolation index. Each metric was classified into tertiles and ZCTAs in the highest tertile for all three metrics were considered enclaves. Daily PM2.5 and O3 concentrations, derived from US Environmental Protection Agency monitoring data, were linked to ZCTAs and aggregated to weekly averages. Generalized linear mixed models estimated percent differences in pollutant concentrations between enclave and non-enclave and 95% confidence intervals (CI) while adjusting for temporal autocorrelation and confounders.

Results: Compared with non-enclaves, ZCTAs classified as Latino enclaves and Mexican enclaves were associated with 3.50% (95% CI: 2.37, 4.65) and 7.16% (95% CI: 4.54, 9.85) higher weekly PM2.5 concentration, respectively. No significant associations were observed for O3.

Conclusion: Latino and Mexican enclaves in California experience higher PM2.5 concentrations than non-enclaves, highlighting the need for equity-focused air pollution exposure mitigation efforts.