A Global Assessment of Dissolved Organic Carbon in Precipitation

Abstract

Precipitation is the largest physical removal pathway of atmospheric reactive organic carbon in the form of dissolved organic carbon (DOC). We present the first global DOC distribution simulated with a global model. A total of 85 and 188 Tg C yr⁻¹ are deposited to the ocean and the land, respectively, with DOC ranging between 0.1 and 10 mg C L⁻¹ in this GEOS‐Chem simulation. We compare the 2010 simulated DOC to a 30 year synthesis of measurements. Despite limited measurements and imperfect temporal matching, the model is able to reproduce much of the spatial variability of DOC (r = 0.63), with a low bias of 35%. We present the global average carbon oxidation state (OS[overline][subscript c]) as a simple metric for describing the chemical composition. In the atmosphere, -1.8 ≤ OS[overline][subscript c] ≤ -0.6, and the increase in solubility upon oxidation leads to a global increase in (OS[overline][subscript c]) in precipitation with -0.6 ≤OS[overline][subscript c] ≤ 0. Keywords: dissolved organic carbon; average carbon oxidation state; GEOS-Chem