title: Atmospheric chemistry of nonanal.
abstract: During the Southern Oxidants Study 1999 field campaign at Dickson, TN, we conducted measurements of the n-aldehydes propanal, pentanal, hexanal, heptanal, octanal, and nonanal. Propanal and nonanal tended to have the largest concentrations, with afternoon maxima of approximately 0.3 ppb. These aldehydes typically represented a significant fraction of the VOC reactivity defined as k(OH)[VOC]. However, this information is misleading with regard to the impact of these aldehydes on ozone formation, as their oxidation can represent a significant NOx sink. Motivated by the relatively large nonanal concentrations, we conducted a laboratory study of the products of the nonanal + OH reaction. The OH + nonanal reaction rate constant was determined via the relative rate technique and found to be 3.6 (+/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). Under conditions of high [NO2]/[NO], we determined that 50 +/- 6% of OH-nonanal reaction occurs via abstraction of the aldehydic H-atom through measurement of the peroxynonanyl nitrate yield. We also studied the production of organic nitrates from OH reaction with nonanal in the presence of NO. As expected, a major product (20% at large [NO]/[NO2]) of this reaction was 1-nitrooxy octane. We calculate that the branching ratio for 1-nitrooxy octane formation from peroxyoctyl radicals is 0.40 +/- 0.05. On the basis of these measurements, we find that for more than 50% of the time OH reacts with nonanal (for midday summer conditions) an organic nitrate or PAN compound is formed, making this important atmospheric aldehyde an effective NOx sink.
authors.affiliation: Department of Chemistry, Purdue University, 1393 Brown Building, West Lafayette, Indiana 47907, USA.
authors.forename: Julia Hurst
authors.initials: JH
authors.lastname: Bowman
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Barket
authors.forename: Paul B
authors.initials: PB
authors.lastname: Shepson
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000447:Aldehydes / Q000032:analysis*; D001272:Atmosphere / Q000737:chemistry*; D004784:Environmental Monitoring; D009566:Nitrates / Q000737:chemistry; D010084:Oxidation-Reduction; D013714:Tennessee
chemical_list: D000393:Air Pollutants; D000447:Aldehydes; D009566:Nitrates; C008664:nonanal