Global dry deposition of nitrogen dioxide and sulfur dioxide inferred from space-based measurements

摘要

A method is developed to estimate global NO_2 and SO_2 dry deposition fluxes at high spatial resolution (0.1? × 0.1?) using satellite measurements from the Ozone Monitoring Instrument (OMI) on the Aura satellite, in combination with simulations from the Goddard Earth Observing System chemical transport model (GEOS-Chem). These global maps for 2005–2007 provide a data set for use in examining global and regional budgets of deposition. In order to properly assess SO_2 on a global scale, a method is developed to account for the geospatial character of background offsets in retrieved satellite columns. Globally, annual dry deposition to land estimated from OMI as NO_2 contributes 1.5 ± 0.5 Tg of nitrogen and as SO_2 contributes 13.7 ± 4.0 Tg of sulfur. Differences between OMI-inferred NO_2 dry deposition fluxes and those of other models and observations vary from excellent agreement to an order of magnitude difference, with OMI typically on the low end of estimates. SO_2 dry deposition fluxes compare well with in situ Clear Air Status and Trends Network-inferred flux over North America (slope = 0.98, r = 0.71). The most significant NO_2 dry deposition flux to land per area occurs in the Pearl River Delta, China, at 13.9 kg N ha~(?1) yr~(?1), while SO_2 dry deposition has a global maximum rate of 72.0 kg S ha~(?1) yr~(?1) to the east of Jinan in China’s Shandong province. Dry deposition fluxes are explored in several urban areas, where NO_2 contributes on average 9–36% and as much as 85% of total NO_y dry deposition.