Local and Regional-Scale Racial and Ethnic Disparities in Air Pollution Determined by Long-Term Mobile Monitoring

Disparity in air pollution exposure arises from variation at multiple spatial scales: along urban-to-rural gradients, between individual cities within a metropolitan region, within individual neighborhoods, and between city blocks. Here, we improve on existing capabilities to systematically compare urban variation at several scales, from hyperlocal (<100m) to regional (>10km), and to assess consequences for the outdoor air pollution experienced by residents of different races and ethnicities, by creating a set of uniquely extensive and high-resolution observations of spatially-variable pollutants: NO, NO₂, black carbon (BC), and ultrafine particles (UFP). We conducted full coverage monitoring of a wide sample of urban and suburban neighborhoods (93 km², 450,000 residents) in four counties of the San Francisco Bay Area using Google Street View cars. Comparing scales of variation across the sampled population, greater differences arise from localized pollution gradients for BC and NO (pollutants dominated by primary sources) and from regional gradients for UFP and NO₂ (pollutants dominated by secondary contributions). Median concentrations of UFP, NO, and NO₂ are, for Hispanic and Black populations, 8%-30% higher than the population average; for white populations, average exposures to the same pollutants are 9%-14% lower than the population average. Systematic racial/ethnic disparities are strongly affected by regional differences in background concentrations due to sharp contrasts in demographic composition among cities and urban districts, while within-group extremes arise from local peaks. Our results illustrate how detailed and extensive fine-scale pollution observations can add new insights about differences and disparities in air pollution exposures at the population scale.