Multihazard exposure and environmental injustice: The correlation between air pollution and heat drives socioeconomic inequities

Research on environmental justice has revealed that various hazards can be created by deleterious planning decisions. Multihazard exposure , or the co-location of two or more hazards in a neighborhood, has been little studied to date. We examine heat and air pollution across the census block groups (CBGs) of 55 US cities to evaluate the distribution and sources of inequities in multihazard exposure. The study combines measures of temperature from a volunteer science campaign; air pollution from remote sensing; street density and tree canopy as hazard-driving infrastructure; and demographics. On average, heat and air pollution were moderately correlated across the CBGs of a city ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mi>r</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>=</mml:mo> <mml:mo>.</mml:mo> <mml:mn>34</mml:mn> </mml:mrow> </mml:math> ), but this measure of multihazard exposure varied substantially. Multihazard exposure was greatest in cities where neighborhoods with high street density often lacked tree canopy. In those same cities, low-income communities tended to live in neighborhoods with greater hazard-driving infrastructure. Cities with less coincidence between high street density and low canopy coverage, however, had less multihazard exposure and, in turn, fewer inequities. Consequently, multihazard exposure was inequitably concentrated in low-income communities in most, but not all, cities. The results implicate a two-step process for how multihazard exposure emerges in a city. First, discrete decisions begin to create exposures in certain neighborhoods. These then create the basis for circumstances and decisions that further concentrate hazards in communities inhabited by marginalized populations.