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

Abstract

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. We estimate average total residential long-term NO2 exposure across the United States to be ∼10 ppbv for people who own a gas stove (∼18 ppbv or more for households in the top 5% of gas burned while cooking) and ∼8 ppbv from total outdoor exposure for those with electric stoves, which cause no additional NO2 exposure. Across the United States, the NO2 exposure of ∼22 million people would fall below the World Health Organization (WHO)'s long-term exposure guideline (10 µg/m3 or 5.2 ppbv) if they reduced or stopped cooking with gas or propane. Gas and propane stoves are also responsible for virtually all (>99%) of the residential exceedances of the WHO's 1-h-averaged air quality guideline across the United States. Gas and propane stoves are a substantial source of residential NO2 exposure even when compared with all outdoor sources combined.