Long-Term Trends Worldwide in Ambient NO(2) Concentrations Inferred from Satellite Observations

BACKGROUND: Air pollution is associated with morbidity and premature mortality. Satellite remote sensing provides globally consistent decadal-scale observations of ambient nitrogen dioxide (NO(2)) pollution. OBJECTIVE: We determined global population-weighted annual mean NO(2) concentrations from 1996 through 2012. METHODS: We used observations of NO(2) tropospheric column densities from three satellite instruments in combination with chemical transport modeling to produce a global 17-year record of ground-level NO(2) at 0.1° × 0.1° resolution. We calculated linear trends in population-weighted annual mean NO(2) (PWM(NO2)) concentrations in different regions around the world. RESULTS: We found that PWM(NO2) in high-income North America (Canada and the United States) decreased more steeply than in any other region, having declined at a rate of –4.7%/year [95% confidence interval (CI): –5.3, –4.1]. PWM(NO2) decreased in western Europe at a rate of –2.5%/year (95% CI: –3.0, –2.1). The highest PWM(NO2) occurred in high-income Asia Pacific (predominantly Japan and South Korea) in 1996, with a subsequent decrease of –2.1%/year (95% CI: –2.7, –1.5). In contrast, PWM(NO2) almost tripled in East Asia (China, North Korea, and Taiwan) at a rate of 6.7%/year (95% CI: 6.0, 7.3). The satellite-derived estimates of trends in ground-level NO(2) were consistent with regional trends inferred from data obtained from ground-station monitoring networks in North America (within 0.7%/year) and Europe (within 0.3%/year). Our rankings of regional average NO(2) and long-term trends differed from the satellite-derived estimates of fine particulate matter reported elsewhere, demonstrating the utility of both indicators to describe changing pollutant mixtures. CONCLUSIONS: Long-term trends in satellite-derived ambient NO(2) provide new information about changing global exposure to ambient air pollution. Our estimates are publicly available at http://fizz.phys.dal.ca/~atmos/martin/?page_id=232. CITATION: Geddes JA, Martin RV, Boys BL, van Donkelaar A. 2016. Long-term trends worldwide in ambient NO(2) concentrations inferred from satellite observations. Environ Health Perspect 124:281–289; http://dx.doi.org/10.1289/ehp.1409567