Integrating Satellite Observations, Chemical Transport Modeling, and Population Data to Estimate Decadal Trends in Ground-Level NO2 Exposure Worldwide.

Abstract:

Nitrogen dioxide (NO₂) is a common component of air pollution and can act as a tracer for other constituents associated with combustion emissions. An approach to unify observations of NO₂ tropospheric vertical column densities from three separate satellite instruments (GOME, SCIAMACHY, GOME-2) was used in combination with chemical transport modeling (GEOS-Chem) to produce a global 17-year record of ground-level NO₂ at 0.1° x 0.1° resolution. This data set was combined with maps of population density at the same temporal and spatial resolution, allowing a novel exploration of changing human exposure to air pollution worldwide. Population-weighted mean concentrations (PWMC) were calculated by region, and cumulative distribution plots were used to illustrate the changing spatial allocation of NO₂ extremes. The most significant decrease in PWMC occurred in North America, with a decline of 60% between 1996 and 2012. This is 1.5 times greater than the rate of decrease in reported total anthropogenic NO_x emissions. PWMC have also decreased by 32% in Western Europe, but have increased by 128% in East Asia. Historically, the highest PWMC occurred in Asia Pacific, although levels have decreased by 36% since 1996. However, exposure to the most extreme concentrations has varied by region over time, moving from North America in 1996 to East Asia in 2012. This unique merging of satellite observations, modeled vertical profiles, and population data offers an innovative approach to investigating pollution trends globally and by region that could relate more directly to health cost expectations over other observational datasets alone.