The global nonmethane reactive organic carbon budget: A modeling perspective

Abstract

The cycling of reactive organic carbon (ROC) is central to tropospheric chemistry. We characterize the global tropospheric ROC budget as simulated with the GEOS-Chem model. We expand the standard simulation by including new emissions and gas-phase chemistry, an expansion of dry and wet removal, and a mass tracking of all ROC species to achieve carbon closure. The resulting global annual mean ROC burden is 16 Tg C, with sources from methane oxidation and direct emissions contributing 415 and 935 Tg C yr⁻¹. ROC is lost from the atmosphere via physical deposition (460 Tg C yr⁻¹), and oxidation to CO/CO2 (875 Tg C yr⁻¹). Ketones, alkanes, alkenes, and aromatic hydrocarbons dominate the ROC burden, whereas aldehydes and isoprene dominate the ROC global mean surface OH reactivity. Simulated OH reactivities are between 0.8–1 s⁻¹, 3–14 s⁻¹, and 12–34 s⁻¹ over selected regions in the remote ocean, continental midlatitudes, and the tropics, respectively, and are consistent with observational constraints.