Alkyl Nitrate Formation from the Reactions of C₈–C₁₄n-Alkanes with OH Radicals in the Presence of NO_x: Measured Yields with Essential Corrections for Gas–Wall Partitioning

Abstract

In this study, C8-C14 n-alkanes were reacted with OH radicals in the presence of NO(x) in a Teflon film environmental chamber and isomer-specific yields of alkyl nitrates were determined using gas chromatography. Because results indicated significant losses of alkyl nitrates to chamber walls, gas-wall partitioning was investigated by monitoring the concentrations of a suite of synthesized alkyl nitrates added to the chamber. Gas-to-wall partitioning increased with increasing carbon number and with proximity of the nitrooxy group to the terminal carbon, with losses as high as 86%. The results were used to develop a structure-activity model to predict the effects of carbon number and isomer structure on gas-wall partitioning, which was used to correct the measured yields of alkyl nitrate isomers formed in chamber reactions. The resulting branching ratios for formation of secondary alkyl nitrates were similar for all isomers of a particular carbon number, and average values, which were almost identical to alkyl nitrate yields, were 0.219, 0.206, 0.254, 0.291, and 0.315 for reactions of n-octane, n-decane, n-dodecane, n-tridecane, and n-tetradecane, respectively. The increase in average branching ratios and alkyl nitrate yields with increasing carbon number to a plateau value of ∼0.30 at about C13-C14 is consistent with predictions of a previously developed model, indicating that the model is valid for alkane carbon numbers ≥C3.

A two-dimensional volatility basis set – Part 3: Prognostic modeling and NO<sub><i>x</i></sub> dependence

“…The first is the probability (1 − β) that RO 2 will react with NO; the second is the yield, η, of organonitrates from RO 2 + NO. The nitrate yield η rises with increasing carbon number (Arey et al, 2001;Yeh and Ziemann, 2014) and depends on the functionality of the RO 2 (Lim and Ziemann, 2009;Elrod, 2011); however, for organics large enough to partition to the condensed phase, η is at an asymptotic limit, and we assume a homogeneous distribution of RO 2 structures within any given VBS cell. We thus assume that η = 0.30 in all cases.…”

Large Enhancement in the Heterogeneous Oxidation Rate of Organic Aerosols by Hydroxyl Radicals in the Presence of Nitric Oxide

“…In the condensed phase for large hydrocarbons, we would expect that the formation of organic nitrates to be in fact favored due to the solvent cage efficiently removing energy from the RO 2 NO* intermediate. 24 However, it is possible that RO 2 NO* in the condensed organic phase is stabilized but then decomposes into RO and NO 2 . This reaction would be analogous to peroxynitrous acid (HOONO), which has a lifetime of seconds in water and decomposes to form NO 2 and OH.…”

Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning

“…Second, it is likely that previous estimates of SOA yields from wellknown VOC precursors (e.g., toluene, xylene, alkanes, isoprene, terpenes) derived from smog chamber experiments were biased by unaccounted loss of semivolatile organic vapors to the chamber walls (Hildebrandt et al, 2009;Mat-B. N. Murphy et al: Comprehensive evaluation of CMAQ semivolatile POA sunaga and Ziemann, 2010; Loza et al, 2010;Yeh and Ziemann, 2014;Zhang et al, 2014Zhang et al, , 2015Cappa et al, 2016;Nah et al, 2016;Krechmer et al, 2016;Saha and Grieshop, 2016;Ma et al, 2017;Nah et al, 2017). The magnitude of this bias likely varies substantially among experimental systems (i.e., precursor and oxidant identity) and experimental conditions (e.g., seed concentration, relative humidity, temperature; Krechmer et al, 2016;Nah et al, 2016).…”