Observations of total peroxy nitrates and aldehydes: measurement interpretation and inference of OH radical concentrations

Abstract

Abstract. We describe measurements of total peroxy nitrates (ΣPNs), NO2, O3 and several aldehydes at Granite Bay, California, during the Chemistry and Transport of the Sacramento Urban Plume (CATSUP) campaign, from 19 July–16 September 2001. We observed a strong photochemically driven variation of ΣPNs during the day with the median of 1.2 ppb at noon. Acetaldehyde, pentanal, hexanal and methacrolein had median abundances in the daytime of 1.2 ppb, 0.093 ppb, 0.14 ppb, and 0.27 ppb, respectively. We compare a steady state and a time dependent calculations of the dependence of ΣPNs on aldehydes, OH, NO and NO2 showing that the steady state calculations of are be accurate to ±30% between 10:00 a.m. and 06:00. We use the steady state calculation to investigate the composition of ΣPNs and the concentration of OH at Granite Bay. We find that PN molecules that have never been observed before make up an unreasonably large fraction of the ΣPNs unless we assume that there exists a PAN source that is much larger than the acetaldehyde source. We calculate that OH at the site varied between 1 and 6×106 molecules cm−3 at noon during the 8 weeks of the experiment.