title: Yields of beta-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates formed from OH radical-initiated reactions of 2-methyl-1-alkenes.
abstract: Yields of beta-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 UV-visible (UV-vis) detector. Yields of beta-hydroxynitrates and dihydroxynitrates increased with carbon number primarily due to enhanced gas-to-particle partitioning before reaching plateaus at approximately C(14)-C(15), where the compounds were essentially entirely in the particle phase. Plateau yields of beta-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates were 0.183 +/- 0.005, 0.045 +/- 0.005, and 0.034 +/- 0.005, and, after normalization for OH radical addition to the C = C double bond, were 0.225 +/- 0.007, 0.055 +/- 0.006, and 0.042 +/- 0.006. The fractions of 1-hydroxy and 2-hydroxy beta-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 beta-hydroxyalkyl radicals by OH radical addition to the C=C double bond are 4.3/1.9/1.0, and the branching ratios for forming beta-hydroxynitrates from reactions of tertiary, secondary, and primary beta-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.
authors.affiliation: Air Pollution Research Center, Department of Chemistry, University of California, Riverside, CA 92521, USA.
authors.forename: Aiko
authors.initials: A
authors.lastname: Matsunaga
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Ziemann
mesh_terms: D000336:Aerosols / Q000737:chemistry; D000475:Alkenes / Q000737:chemistry*; D000641:Ammonia / Q000737:chemistry; D001272:Atmosphere; D002244:Carbon / Q000737:chemistry; D002625:Chemistry, Organic / Q000379:methods; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004784:Environmental Monitoring / Q000379:methods; D017665:Hydroxyl Radical; D013058:Mass Spectrometry / Q000379:methods; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry*; D010316:Particle Size; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D000336:Aerosols; D000475:Alkenes; D009566:Nitrates; D014867:Water; D017665:Hydroxyl Radical; D002244:Carbon; D000641:Ammonia