Observations of total alkyl nitrates within the Sacramento Urban Plume

Abstract. During the summer of 2001, NO₂, total peroxy nitrates (ΣPNs), total alkyl nitrates (ΣANs), HNO₃, volatile organic compounds (VOC), CO₂, O₃, and meteorological variables were measured at Granite Bay, CA. The diurnal variation in ΣPNs, ΣANs and HNO₃ were all strongly correlated with sunlight, indicating both that they are photochemically produced and that they have a lifetime of a few hours at this site. The mixing ratios of ΣANs ranged as high as 2 ppbv. Mixing ratios at night averaged 0.4 ppbv. Odd-oxygen (O_x=O₃+NO₂) and ΣANs were strongly correlated reflecting both the common chemical source terms and the similar lifetimes of both species. Several approaches to interpreting the simultaneous variations of O_x and ΣANs are described, and used to derive a best estimate of the ΣAN yield from the VOC mixture at this site of 4.2% and an estimate of the range that is consistent with the observations of 3.9–5.8%. A yield of 4.2% implies termination of the HO_x catalytic cycle by ΣAN formation once every 24 cycles. Analysis of the HNO₃ observations in combination with the ΣAN and O₃ measurements suggests that NO_x terminations limit the HO_x chain length to between 4.7 and 6.3.