Empirical model of global soil‐biogenic NOχemissions

We construct a global, temperature and precipitation dependent, empirical model of soil‐biogenic NO x emissions using 6‐hour general circulation model forcing. New features of this source relative to the latest published ones by Dignon et al. 1992 and Muller 1992 include synoptic‐scale modeling of “pulsing” (the emissions burst following the wetting of a dry soil), a biome dependent scheme to estimate canopy recapture of NO χ , and an explicit linear dependence of emission on N fertilizer rate for agricultural soils. Our best estimate for annual above‐canopy emissions is 5.5 Tg N (NO χ ) with a range of 3.3–7.7 Tg N. Globally, the strongest emitters are agriculture, grasslands, and tropical rain forests, accounting for 41%, 35%, and 16% of the annual budget, respectively. “Pulsing” contributes 1.3 Tg N annually. In temperate regions, agriculture dominates emission, and in tropical regions, grassland dominates. Canopy recapture is significant, consuming, on average, possibly 50% of soil emissions. In temperate regions, periodic temperature changes associated with synoptic‐scale disturbances can cause emission fluctuations of up to 20 ng N m −2 s −1 , indicating a close correlation between emission and warm weather events favorable to O 3 /smog formation. By the year 2025, increasing use of nitrogen fertilizer may raise total annual emissions to 6.9 Tg N with agriculture accounting for more than 50% of the global source. Finally, biomass burning may add up to an additional 0.6 Tg N globally by stimulating emissions for a short period after the burn.