Global modeling of the nitrate radical (NO3) for present and pre-industrial scenarios

Abstract Increasing the complexity of the chemistry scheme in the global chemistry transport model STOCHEM to STOCHEM-CRI (Utembe et al., 2010) leads to an increase in NO x as well as ozone resulting in higher NO 3 production over forested regions and regions impacted by anthropogenic emission. Peak NO 3 is located over the continents near NO x emission sources. NO 3 is formed in the main by the reaction of NO 2 with O 3 , and the significant losses of NO 3 are due to the photolysis and the reactions with NO and VOCs. Isoprene is an important biogenic VOC, and the possibility of HO x recycling via isoprene chemistry and other mechanisms such as the reaction of RO 2 with HO 2 has been investigated previously (Archibald et al., 2010a). The importance of including HO x recycling processes on the global budget of NO 3 for present and pre-industrial scenarios has been studied using STOCHEM-CRI, and the results are compared. The large increase (up to 60% for present and up to 80% for pre-industrial) in NO 3 is driven by the reduced lifetime of emitted VOCs because of the increase in the HO x concentration. The maximum concentration changes (up to 15 ppt) for NO 3 from pre-industrial to present day are found at the surface between 30 o N and 60 o N because of the increase in NO x concentrations in the present day integrations.