1,4-Hydroxycarbonyl Products of the OH Radical Initiated Reactions of C₅−C₈n-Alkanes in the Presence of NO

Abstract

Ambient measurements of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs were carried out during August 2002 and January 2003 in Los Angeles, CA, a source site and in Riverside, CA, a downwind receptor site approximately 90 km to the east of Los Angeles. Atmospheric concentrations of PAHs and nitro-PAHs are of interest because both of these compound classes include potent mutagens and carcinogens. To augment our current understanding of atmospheric formation of nitro-PAHs, four sampling periods were employed to study the diurnal variations of these compounds. The PAH concentrations were highest in Los Angeles during January, as a result of traffic input at this source site undertightwintertime atmospheric inversions. In contrast, nitro-PAH levels were highest in Riverside during August, as a result of enhanced summertime photochemistry. Hydroxyl radical-initiated reactions produced nitro-PAHs in both seasons, while in winter little evidence for nitrate radical chemistry was seen. For the August samples, nitrate radical-initiated formation of nitro-PAHs is suggested by nitro-PAH isomer profiles not only at the downwind location as anticipated, but also atthe source site. In southern California, the contribution of atmospheric formation through gas-phase radical-initiated PAH reactions to the ambient burden of nitro-PAHs is dominant, with the semi-volatile nitro-PAHs being the most abundant and 2-nitrofluoranthene being the major particle-associated nitro-PAH.

Identifying organic aerosol sources by comparing functional group composition in chamber and atmospheric particles

“…However, this composition is explained by the products of alkane oxidation by OH (23,24,(31)(32)(33). In the NO x regime (>30 ppt NO, likely for combustion emissions), major firstgeneration products from reactions of linear alkanes larger than ∼C 10 -C 15 are ∼30% monoalkyl nitrates, ∼55% 1,4-hydroxycarbonyls, and ∼15% 1,4-hydroxynitrates.…”

Investigation of the Gas-Phase Photolysis and Temperature-Dependent OH Reaction Kinetics of 4-Hydroxy-2-butanone

“…first (8) where t is the delay time between the photolysis and the probe beams, k first is the pseudo first-order rate coefficient, and k is the second-order rate coefficient for the 4H2B + OH reaction. In order to avoid the accumulation of photolysis or reaction products, the experiments were carried out under flow conditions so that the gas mixture in the cell was renewed between two consecutive photolysis pulses.…”

Chemistry of Secondary Organic Aerosol Formation from OH Radical-Initiated Reactions of Linear, Branched, and Cyclic Alkanes in the Presence of NOx

“…The products are 1,4-hydroxynitrates (1,4HN) [5] and 1,4-hydroxyalkoxy radicals that primarily undergo a reverse isomerization and react with O 2 to form 1,4-hydroxycarbonyls (1,4HC) [6]. AN, 1,4HN, and 1,4HC have been measured in the gas-phase for reactions of C 7 -C 10 alkanes, with yields of approximately 0.2, 0.05, and 0.5 (Reisen et al 2005) and with no other observed products. AN and 1,4HN yields are probably closer to ∼0.3 (Arey et al 2001) and ∼0.15 (Lim and Ziemann 2005) for reactions of larger alkanes.…”

“…The only other known potential effect of NH 3 on the reaction mechanism shown in Figure 2 is that it can bind to hydroxyperoxy radicals and thereby increase the formation of hydroxyalkoxy radicals from the reaction with NO (Matsunaga and Ziemann 2009), in this case at the expense of 1,4HN, the reaction co-product. This would increase the yield of 1,4HC (by possibly 10-20% from ∼0.5 if no 1,4-HN were formed (Reisen et al 2005;Lim and Ziemann 2005)) and also enhance CHA formation. Although we cannot rule out the possibility that NH 3 altered the reaction of 1,4-hydroxyperoxy radicals with NO, any impact appears to have been minor.…”