AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Volatility of Atmospheric Organic Nitrate Formed from Hydroxyl and Nitrate Radical Oxidation of α-Pinene and β-Pinene
MASAYUKI TAKEUCHI, Justin Min, Rodney J. Weber, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 443 Working Group: Aerosol Chemistry
Abstract Atmospheric organic nitrate (ON) plays a crucial role in the budget and cycling of NOx that affects ozone and secondary organic aerosol (SOA) formation. The effects of ON depend on its physical state (i.e., gas or aerosol phase) because the governing loss processes of ON could vary significantly. Further OH oxidation or photolysis for gaseous ON recycles NOx, whereas NOx is permanently removed from the atmosphere via hydrolysis or deposition of particulate ON. However, the physicochemical properties (e.g., volatility, solubility, etc) of atmospherically important ON are not well constrained by fundamental laboratory studies. We aim to systematically evaluate the volatility of ON formed from major biogenic volatile organic compounds via laboratory chamber experiments; the systems investigated include “α-pinene+OH+NO,” “β-pinene+OH+NO,” “α-pinene+NO3,” and “β-pinene+NO3.” The volatility of ON is determined by the yield-based approach using a High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), Scanning Mobility Particle Sizer (SMPS), and Particle-Into-Liquid Sampler coupled to Ion Chromatogram (PILS-IC), and by the thermogram-based approach using a Filter Inlet for Gases and AEROsols coupled to a High Resolution Time-of-Flight Iodide Chemical Ionization Mass Spectrometer (FIGAERO-HR-ToF-I-CIMS). Two methods are generally in a good agreement, though the yield-based method tends to measure a larger contribution of semi-volatile species than the thermogram-based approach. ON is found to be generally less volatile than previously measured for “α-pinene+OH+NO” and “β-pinene+NO3” systems. The discrepancy appears to stem from the limited range of organic mass loading conditions explored in past studies. Moreover, there are some fractions of low-volatility ON compounds that are essentially non-volatile in atmospherically relevant conditions (C* <0.1 µg m3); such low-volatility ON has not been reported in previous studies. Our estimated volatility values serve as the experimental constraints for parameterization of monoterpene ON in models, facilitating more accurate predictions regarding the role of ON in ozone and SOA formation.