Observations of total alkyl nitrates within the Sacramento Urban Plume

Abstract

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 (Ox=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 Ox 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 HOx catalytic cycle by ΣAN formation once every 24 cycles. Analysis of the HNO3 observations in combination with the ΣAN and O3 measurements suggests that NOx terminations limit the HOx chain length to between 4.7 and 6.3.