| Abstract
| - During the Southern Oxidants Study 1999 field campaignat Dickson, TN, we conducted measurements of then-aldehydes propanal, pentanal, hexanal, heptanal, octanal,and nonanal. Propanal and nonanal tended to have thelargest concentrations, with afternoon maxima of ∼0.3 ppb.These aldehydes typically represented a significantfraction of the VOC reactivity defined as kOH[VOC]. However,this information is misleading with regard to the impactof these aldehydes on ozone formation, as their oxidationcan represent a significant NOx sink. Motivated by therelatively large nonanal concentrations, we conducted alaboratory study of the products of the nonanal + OH reaction.The OH + nonanal reaction rate constant was determinedvia the relative rate technique and found to be 3.6(±0.7) × 10-11 cm3 molecule-1 s-1. Under conditions ofhigh [NO2]/[NO], we determined that 50 ± 6% of OH-nonanalreaction occurs via abstraction of the aldehydic H-atomthrough measurement of the peroxynonanyl nitrate yield. Wealso studied the production of organic nitrates from OHreaction with nonanal in the presence of NO. As expected,a major product (20% at large [NO]/[NO2]) of this reactionwas 1-nitrooxy octane. We calculate that the branchingratio for 1-nitrooxy octane formation from peroxyoctyl radicalsis 0.40 ± 0.05. On the basis of these measurements, wefind that for more than 50% of the time OH reacts withnonanal (for midday summer conditions) an organic nitrateor PAN compound is formed, making this importantatmospheric aldehyde an effective NOx sink.
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