AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Hydrolysis and Gas-particle Partitioning of Organic Nitrates Formed in Environmental Chamber Experiments
JEFFREY BEAN, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 63 Working Group: Aerosol Chemistry
Abstract Understanding the partitioning and hydrolysis of organic nitrates is important in understanding their role as NOx sinks and sources in the atmosphere. Organic nitrates are abundant, and thus important in predicting the formation of ozone and the eventual fate of NOx in the atmosphere. We report both the hydrolysis rate and the partitioning coefficient for alpha-pinene derived organic nitrates formed under varying conditions. Experiments were performed in a 12 m$^3 atmospheric chamber at the University of Texas at Austin with initial concentrations of alpha-pinene from 26 to 128 ppb and initial VOC/NOx ratios of ~1.
An Aerosol Chemical Speciation Monitor (ACSM) is used to determine aerosol composition with a Scanning Electron Mobility System (SEMS) used to find the total organic aerosol concentration throughout experiments. A High Resolution Chemical Ionization Time of Flight Mass Spectrometer (HR-ToF-CIMS) is used to identify specific organic nitrates formed from alpha-pinene oxidation in high NOx conditions. The SAPRC model is used to find HNO$_3 concentrations throughout experiments so that a mass balance can be used to estimate total gas-phase organic nitrate concentration. We find that the ratio of particulate nitrate to total SOA decreases with increasing relative humidity, consistent with an increased level of hydrolysis as particles contain more water. The gas/particle partitioning is dependent on total OA concentrations consistent with absorptive partitioning theory.