Methyl, Ethyl, and Propyl Nitrates: Global Distribution and Impacts on Reactive Nitrogen in Remote Marine Environments

Abstract

Abstract Alkyl nitrates (RONO 2 ) are important components of tropospheric reactive nitrogen that serve as reservoirs for nitrogen oxides (NO x ≡ NO + NO 2 ). Here we implement a new simulation of atmospheric methyl, ethyl, and propyl nitrate chemistry in a global chemical transport model (GEOS‐Chem). We show that the model can reproduce the spatial and seasonal variability seen in a 20‐year ensemble of airborne observations. Methyl nitrate accounts for 17 Gg N globally, with maxima over the tropical Pacific and Southern Ocean. Propyl nitrate is enhanced in continental boundary layers, but its global impact (6 Gg N) is limited by a short lifetime (8 days vs. 26 days for methyl nitrate and 14 days for ethyl nitrate) that inhibits long‐range transport. Ethyl nitrate has the smallest impact of the three species (4 Gg N). We find that methyl nitrate is the dominant form of reactive nitrogen (NO y ) in the Southern Ocean marine boundary layer, where its addition to the model corrects a large NO y underestimate in austral winter relative to recent aircraft data. RONO 2 serve as a small net NO x source to the marine troposphere, except in the northern midlatitudes where the continental outflow is enriched in precursors that promote NO x loss via RONO 2 formation. Recent growth in NO x emissions from East Asia has enhanced the role of RONO 2 as a source of NO x to the remote free troposphere. This relationship implies projected future NO x emissions growth across the southern hemisphere may further enhance the importance of RONO 2 as a NO x reservoir.