Effect of historical redlining and current-day segregation on air pollution disparities across 143 cities in the USA

Abstract

BACKGROUND AND AIM: Systematic racial/ethnic segregation via historical redlining has been identified as a potential contributor to environmental injustices in the US today, particularly air pollution. However, no studies have examined how the effect of current-day racial/ethnic segregation has modified this association. This study examined this hypothesized effect modification on current levels of air pollution (i.e., PM2.5 and diesel PM) across the USA. METHODS: Current-day demographics and air pollution levels were estimated for USA census tracts using the EPA EJSCREEN. Census-tract-level HOLC grade was assessed using 2010 Historical Redlining Scores, and current-day segregation from the dissimilarity index. We examined differences in air pollution by HOLC grades using city-adjusted, intra-urban air pollution levels from mixed-effects linear regression models using cities as a random intercept to account for city-to-city differences in air pollution levels. We examined our hypothesized effect by investigating the joint effects of redlining (comparing A- and D-grade census tracts) and current-day segregation (comparing low and moderate/high levels of dissimilarity) on log-transformed, population-weighted average diesel PM and PM2.5 levels. RESULTS: Overall, D-grade air pollution levels are 28% (95% CI: 25% to 31%) and 1.2% (1% to 1.4%) higher than A-grade census tracts for diesel PM and PM2.5, respectively. Moderately/highly segregated, D-grade census tracts have 70% (49% to 95%) times higher diesel PM levels and 5% (0%, 11%) times higher PM2.5 levels compared to lowly segregated, A-grade census tracts. Estimates indicate significant departures from additive (RERI: 24%; 14% to 34%) and multiplicative joint effects (percent change of interaction term: 10%; 3% to 17%) for diesel PM, and similarly for PM2.5 (RERI: 1%, 1% to 2%; percent change of interaction term: 1%, 1% to 2%). CONCLUSIONS: Current-day segregation modifies the association between historical redlining and air pollution in the USA. KEYWORDS: environmental justice; redlining; air pollution; effect modification; RERI