AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Yields of Alkyl Nitrates and Hydroxynitrates Formed from the Reactions of C8–C14 n-Alkanes with OH Radicals in the Presence of NOx
GEOFFREY YEH, Paul Ziemann, UC Riverside
Abstract Number: 71 Working Group: Aerosol Chemistry
Abstract Alkanes account for nearly one half of total anthropogenic non-methane hydrocarbon emissions and are precursors of secondary organic aerosol (SOA). In the atmosphere, alkanes react with OH radicals to produce a variety of oxygenated products including alkyl nitrates and hydroxynitrates. In the experiments described, C8–C14 n-alkanes were reacted with OH radicals in the presence of NOx in an environmental chamber, and yields of alkyl nitrates and hydroxynitrates were measured. Particle-phase hydroxynitrates were sampled on filters, extracted, and analyzed by liquid chromatography with ultraviolet absorbance detection (LC/UV). Particle- and gas-phase alkyl nitrates were sampled on Tenax adsorbent and analyzed by gas chromatography with flame ionization detection (GC/FID). Gaseous alkyl nitrates in the size range studied can also be lost to chamber walls, so gas-wall partitioning was investigated by adding synthesized alkyl nitrates to the chamber and monitoring their losses over time. Whereas C8 alkyl nitrate remained entirely in the gas phase, C10–C14 alkyl nitrates partitioned increasingly with carbon number and proximity of nitrate substitution to the terminal carbon, and exhibited losses up to 85%. Using these data, an isomer-specific group contribution approach to estimate gas-wall partitioning was developed and used to correct the measured alkyl nitrate yields for wall losses. These results can be used to develop more accurate models of SOA formation from the atmospheric oxidation of alkanes.