Whats the role of night time chemistry in the sequestration of Nox? At the completion of the isotopic analysis project, we will expand our research focus to include the night time reaction between the nitrate radical (NO3) and isoprene. This project will focus on determining speciated isoprene nitrates produced from nighttime NO3 + isoprene chemistry in ambient air. To date only laboratory studies have been conducted, but results and calculations have shown that the production of RONO2 in the UMBS environment from NO3 radical chemistry can be important for the typical NOx and ozone (O3) conditions (Brown et al., 2009; Kwok et al., 1996; Perring et al., 2009; Rollins et al., 2009; Werner et al., 1999; Levi Mielke thesis, 2009). Data collected during the 2008 PROHET campaign indicates that a significant fraction of the total (24 hr.) RONO2 production occurs due to NO3 chemistry. It is calculated that the nighttime NO3 production rate could be as high as 1.1x106 molecules/cm3s. When compared to the day time OH production rate of 1.9x106 molecules/cm3s it is clear that many total RONO2 studies have missed a significant production term (Levi Mielke thesis, 2009). Quantification and speciation of these isoprene nitrates is important as reported yields ranging between 65 - 80% are large enough that it is a significant sink for NOx (Perring et al., 2009; Rollins et al., 2009). Furthermore, it could be a significant contributing factor in the nocturnal production of secondary organic aerosols (SOA) as organic nitrates have been shown to be precursors (Rollins et al., 2009), and to be present in ambient aerosol. Brown et al. (2009) calculated that the isoprene SOA mass derived from NO3 was approximately 50% larger than that of OH.