AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Volatility and Particle-phase Hydrolysis of Alkyl Nitrates from Anthropogenic Alkanes and Alkenes
DONGYU WANG, Alexander Bui, Sahil Bhandari, Jeffrey Bean, Surya Dhulipala, Henry Wallace, Robert Griffin, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 140 Working Group: Aerosol Chemistry
Abstract Alkyl nitrates (AN) are formed in the presence of nitrogen oxides (NOx) during atmospheric oxidation chemistry. Gas-particle partitioning of AN has been suggested as a mechanism for NOx cycling and transport, contributing to the regional nature of pollution events. Recent field and laboratory studies point towards hydrolysis of particulate alkyl nitrates (pAN) as a potential NOy removal pathway. The gas-particle partitioning of AN and the pAN hydrolysis rate remain largely unknown.
We carried out environmental chamber experiments to generate AN and secondary organic aerosol (SOA) from reactions of OH + NOx or nitrate radical with anthropogenic volatile organic compounds (VOCs), including four C10 alkanes and alkenes (1-decene, n-decane, butylcyclohexane, and 2-methyl-1-nonene). A High Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS) and a thermodenuder (TD) were deployed to determine the SOA concentration, composition, and volatility. A High Resolution Time-of-Flight Chemical Ionization Mass Spectrometer coupled to a Filter Inlet for Gases and AEROsols (FIGAERO) was used for molecular identification of alkyl nitrates in the gas and particle phases.
Significant SOA formation was observed, with NO3-initiated oxidation producing higher pAN mass fractions than oxidation initiated by OH + NOx. The hydrolysis rate is determined based on the pAN decay rate under low and high relative humidity conditions. An aerosol evaporation kinetics model is used to estimate SOA and pAN volatility distributions based on TD-AMS data obtained at different desorption temperatures. The pAN volatility distribution and hydrolysis rates from this work can be used in air-quality models to more accurately represent NOx cycling and the formation of SOA and ozone.