This study provides an empirical test of two mechanisms (social capital and exposure to air pollution) that are theorized to mediate the effect of neighborhood on health and contribute to racial disparities in health outcomes. To this end, we utilize the Social Capital Benchmark Study, a national survey of individuals nested within communities in the United States, to estimate how multiple dimensions of social capital and exposure to air pollution, explain racial disparities in self-rated health. Our main findings show that when controlling for individual-confounders, and nesting within communities, our indicator of cognitive bridging, generalized trust, decreases the gap in self-rated health between African Americans and Whites by 84%, and the gap between Hispanics and Whites by 54%. Our other indicator of cognitive social capital, cognitive linking as represented by engagement in politics, decreases the gap in health between Hispanics and Whites by 32%, but has little impact on African Americans. We also assessed whether the gap in health was explained by respondents’ estimated exposure to toxicity-weighted air pollutants from large industrial facilities over the previous year. Our results show that accounting for exposure to these toxins has no effect on the racial gap in self-rated health in these data. This paper contributes to the neighborhood effects literature by examining the impact that estimated annual industrial air pollution, and multiple measures of social capital, have on explaining the racial gap in health in a sample of individuals nested within communities across the United States.

Biochar has been heralded for improving soil quality, sequestering C, and converting organic residues into value‐added amendments. Biochar research in agricultural settings has been primarily conducted on acidic soils, with few studies evaluating biochar effects on alkaline soils. Given the rise of small‐scale, sustainable farmers experimenting with biochar in South Florida's alkaline, carbonaceous soil, this study sought to assess biochar use in South Florida using an invasive plant species as a feedstock. Melaleuca quinquenervia (Cav.) S.T. Blake biomass was converted into biochar to measure how application at two rates, 2 and 5% (w/w), affects plant growth, soil macro‐ and micronutrients, and microbial gas flux (CO2) in a potted greenhouse experiment using Phaseolus vulgaris L. Plant growth was inhibited with biochar addition at the 2 and 5% rates. Dry shoot, pod weight, and pod length decreased significantly between treatments (P < 0.001). Significant reductions in plant‐available P, Ca, Mg, Cu, and Zn were observed in the 5% biochar soil postharvest (P < 0.05). Compared with the control, addition of biochar at 2 and 5% rates significantly reduced CO2 flux during the growing season, but not at harvest (P < 0.01). Our results indicate that those considering biochar application in South Florida's alkaline soil should be cautious in selecting feedstock and temperature for biochar production. Biochar can be produced at lower temperatures to decrease pH, but the concomitant increase in volatile matter (VM) is of concern. Although CO2 flux may have decreased, the deleterious impacts of M. quinquenervia biochar (pH = 8.12, VM = 26.5%) on P. vulgaris production should not be dismissed. Core Ideas South Florida invasive Melaleuca quinquenervia was used to make biochar. Increasing rates of M. quinquenervia biochar reduced bean growth in calcareous soil. A 5% (w/w) rate of M. quinquenervia biochar reduced available nutrients in soil. Melaleuca quinquenervia biochar addition reduced soil respiration compared with the control.

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