8Increasing the complexity of the chemistry scheme in the global chemistry transport model STOCHEM to STOCHEMCRI (Utembe et al., 2010) leads to an increase in NOx as well as ozone resulting in higher NO3 production overforested regions and regions impacted by anthropogenic emission. Peak NO3 is located over the continents nearNOx emission sources. NO3 is formed in the main by the reaction of NO2 with O3, and the significant losses of NO3are due to the photolysis and the reactions with NO and VOCs. Isoprene is an important biogenic VOC, and thepossibility of HOx recycling via isoprene chemistry and other mechanisms such as the reaction of RO2 with HO2has been investigated previously (Archibald et al., 2010a). The importance of including HOx recycling processeson the global budget of NO3 for present and pre-industrial scenarios has been studied using STOCHEM-CRI, andthe results are compared. The large increase (up to 60% for present and up to 80% for pre-industrial) in NO3 is drivenby the reduced lifetime of emitted VOCs because of the increase in the HOx concentration. Themaximum concentrationchanges (up to 15 ppt) for NO3 from pre-industrial to present day are found at the surface between 30oN and60oN because of the increase in NOx concentrations in the present day integrations.