Integrating indoor and outdoor nitrogen dioxide exposures in US homes nationally by ZIP code

Concentrations of nitrogen dioxide (NO₂) measured outdoors using satellites and ground-level stations across the United States are regularly used to estimate NO₂ exposures and disease burdens. In contrast, exposures attributable to sources of NO₂ indoors are neither systematically monitored nor estimated. Here, to our knowledge we produce the first nationwide, ZIP-code-level estimate of total residential NO₂ exposure that integrates both outdoor sources and the primary indoor source—gas- or propane-burning stoves. To estimate exposure by ZIP code, we combine our measurements of indoor NO₂ emissions and concentrations in more than 15 cities across seven regions with outdoor NO₂ concentrations and comprehensive housing stock data for 133 million residential dwellings and statistical samplings of occupant behavior. Gas and propane stoves are a substantial source of residential NO₂ exposure even when compared with all outdoor sources combined.