Yields ofβ-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates formed from OH radical-initiated reactions of 2-methyl-1-alkenes

Abstract

Yields of β-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates, in particles formed from OH radical-initiated reactions of C 9 -C 15 2-methyl-1-alkenes in the presence of NO x were measured by using a thermal desorption particle beam mass spectrometer coupled to a high-performance liquid chromatograph with a UVvisible (UV-vis) detector. Yields of β-hydroxynitrates and dihydroxynitrates increased with carbon number primarily due to enhanced gas-to-particle partitioning before reaching plateaus at ≈C 14 -C 15 , where the compounds were essentially entirely in the particle phase. Plateau yields of β-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates were 0.183 AE 0.005, 0.045 AE 0.005, and 0.034AE 0.005, and, after normalization for OH radical addition to the C ¼ C double bond, were 0.225 AE 0.007, 0.055 AE 0.006, and 0.042 AE 0.006. The fractions of 1-hydroxy and 2-hydroxy β-hydroxynitrate isomers were 0.90∕0.10. Yields measured here and in our previous study of reactions of linear internal alkenes and linear 1-alkenes indicate that, for these alkene classes, the relative branching ratios for forming tertiary, secondary, and primary β-hydroxyalkyl radicals by OH radical addition to the C ¼ C double bond are 4.3∕1.9∕1.0, and the branching ratios for forming β-hydroxynitrates from reactions of tertiary, secondary, and primary β-hydroxyperoxy radicals with NO are 0.25, 0.15, and 0.12. The effects of H 2 O vapor and NH 3 on yields were also explored.aerosol | atmospheric chemistry | organice nitrate | particles H ydrocarbons are emitted to the atmosphere from anthropogenic and biogenic sources. Globally, more than half are biogenic alkenes including isoprene (C 5 ), monoterpenes (C 10 ), and sesquiterpenes (C 15 ) (1). These compounds have a variety of linear, branched, and cyclic structures containing one or more C ¼ C double bonds and in the atmosphere react with OH radicals, O 3 , and NO 3 radicals to form oxidized products (2, 3). In urban and polluted rural areas where peroxy radical intermediates react primarily with NO (4), one important class of products is organic nitrates (2, 3). For example, hydroxynitrates formed from OH radical-initiated reactions of isoprene have been identified in urban air (5) and impact O 3 formation and NO x removal (6) as well as secondary organic aerosol (SOA) formation (7). It has been estimated that, globally, about two-thirds of hydroxyperoxy radicals formed from isoprene oxidation react with NO (8), a value that probably applies to other terpenes.In spite of their atmospheric importance, little is known about the chemistry of hydroxynitrates. This is primarily because of a lack of analytical methods and reference compounds (5, 9). In a recent study, Paulot et al. (10) employed chemical ionization mass spectrometry to monitor hydroxynitrates formed during isoprene photooxidation, and then used this information to help constrain a detailed chemical mechanism. Even here, however, significant uncertainties exist because many hydroxynitrate isomers could not be disti...

Thermodynamics and kinetics of the hydrolysis of atmospherically relevant organonitrates and organosulfates

“…The hydrolysis of tertiary organonitrates was again found to be highly efficient even at neutral conditions. Similarly, a previous laboratory study on the formation of organonitrates from 2-methyl-1-alkenes found that SOA filter samples containing tertiary organonitrates were much less stable than secondary organonitrates (Matsunaga and Ziemann, 2010). Thus, it is likely that all tertiary organonitrates are unstable on SOA under typical ambient conditions and this result rationalizes previous observations of efficient organonitrate hydrolysis on aerosols (Nguyen et al, 2011;Day et al, 2010).…”

Chemical Mechanisms of Aging of Aerosol Formed from the Reaction ofn-Pentadecane with OH Radicals in the Presence of NOx

“…DHF then evaporate from particles and react with OH radicals via addition to the C C double bond, followed by reactions similar to those of alkyl radicals to form second-generation cyclic hemiacetal nitrates (CHAN) or cyclic hydroxyalkoxy radicals that decompose and then react with O 2 to form carbonylesters (CE) (Martin et al 2002;Lim and Ziemann 2009a). Martin et al (2002) measured a CE molar yield of 0.72 from the reaction of a C 5 DHF and also observed smaller decomposition products, but for a C 15 DHF the major product other than CE should be CHAN because the nitrate yield increases significantly with increasing carbon number (Matsunaga and Ziemann 2010a). Based on results presented here we propose that, in addition to dehydration, CHA and CHAN can react with 1,4HC to form hemiacetals (HA), which can convert to acetals via cyclization-dehydration, a reaction that is favored over bimolecular acetal formation because of the negligible decrease in entropy (Bruckner 2002).…”

“…Note that none of the monomer products shown in Figure 1 contain more than one hydroxyl group, since it is expected that compounds such as 1,4HN, 1,4HC, and CHA will be primarily in the SOA and so not available for significant further reactions with OH radicals. The rapid reaction of DHF with OH radicals should form ∼80% CE and ∼20% CHAN (Matsunaga and Ziemann 2010a), thus regenerating a large fraction of carbonyl groups lost by CHA dehydration, but a much smaller fraction of hydroxyl groups. CHAN formed in this reaction also contribute to the increase in nitrate groups, as do low volatility multigeneration products formed from reactions of volatile AN.…”

“…A blank filter was analyzed similarly. Carbonyl, hydroxyl, carboxyl, and ester groups were quantified using derivatization/spectrophotometric methods we recently adapted from the chemistry literature (Aimanant and Ziemann 2013), peroxide was analyzed as described in Docherty et al (2005), and the method used for nitrate analysis is based on the chromatographic method of Matsunaga and Ziemann (2010a). Briefly, UV-Vis absorption was measured at selected wavelengths using an Ocean Optics spectrophotometer for compounds reacted as follows: carbonyl groups derivatized with 2,4-dinitrophenylhydrazine -480 nm; hydroxyl groups derivatized with 4-nitrobenzoyl chloride -253 nm; carboxyl groups derivatized with 2-nitrophenylhydrazine hydrochloride -550 nm; esters reacted with hydroxylamine hydrochloride and then ferric iron to form ferric hydroxamate -540 nm; peroxides reacted with KI to form I 3 − -470 nm; and underivatized nitrates -210 nm.…”

Particulate organic nitrates observed in an oil and natural gas production region during wintertime

“…For long-chain aliphatics, laboratory experiments and simulations have demonstrated substantial contribution of organic nitrates in the resulting particulate matter (Jordan et al, 2008;Lim and Ziemann, 2009;Matsunaga and Ziemann, 2010), but there exist few field observations capable of assessing whether these mechanisms are representative of the ambient processes. Here we describe observations of organic nitrate aerosol observed in the Uintah Basin, Utah, during winter 2012.…”