Long-term trends worldwide in ambient NO2 concentrations inferred from satellite observations
Geddes, J.A.; Martin, R.V.; Boys, B.L.; van Donkelaar, A.
BACKGROUND: Air pollution is associated with morbidity and premature mortality. Satellite
remote sensing provides globally consistent decadal-scale observations of ambient nitrogen dioxide
(NO2) pollution.
OBJECTIVE: We determined global population-weighted annual mean NO2 concentrations from
1996 through 2012.
METHODS: We used observations of NO2 tropospheric column densities from three satellite instruments
in combination with chemical transport modeling to produce a global 17-year record of
ground-level NO2 at 0.1° × 0.1° resolution. We calculated linear trends in population-weighted
annual mean NO2 (PWMNO2) concentrations in different regions around the world.
RESULTS: We found that PWMNO2 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]. PWMNO2 decreased in western Europe at a rate of –2.5%/year
(95% CI: –3.0, –2.1). The highest PWMNO2 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, PWMNO2 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 NO2
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 NO2 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 NO2 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.
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