Atmospheric chemistry of nonanal.
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.
Bowman
Julia Hurst
JH
Department of Chemistry, Purdue University, 1393 Brown Building, West Lafayette, Indiana 47907, USA.
Barket
Dennis J
DJ
Shepson
Paul B
PB
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
D000393:Air Pollutants; D000447:Aldehydes; D009566:Nitrates; C008664:nonanal