AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Effect of Temperature and Dilution on Secondary Organic Aerosol (SOA) Formed from NO3 Oxidation of Monoterpenes: A Case Study for Aerosol Evaporation during the Night-to-Day Transition
CHRISTOPHER BOYD, Theodora Nah, Lu Xu, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 414 Working Group: Aerosol Chemistry
Abstract Oxidation of biogenic volatile organic compounds (BVOCs) by nitrate radical (NO3) is an important pathway in producing secondary organic aerosol (SOA) at night. Since NO3 is produced by the reaction of ozone with anthropogenic NO2, reaction of BVOCs with NO3 represents a direct link between anthropogenic pollution enhancing aerosol produced by biogenic emissions. During the night-to-day transition, SOA produced at night can undergo physical changes that lead to aerosol evaporation. These changes include dilution induced by the increase in ambient boundary layer height as well as rising ambient temperatures. Limonene and β-pinene are important biogenic precursors due to their high abundance at night and high aerosol mass yields when oxidized by NO3. In this study, chamber experiments focusing on limonene+NO3 and β-pinene+NO3 chemistry are performed at the Georgia Tech Environmental Chamber (GTEC) facility. Reactions are carried out under dry conditions in the presence of ammonium sulfate seed at either 25 °C or 40 °C. O3 and NO2 are pre-reacted in a flow tube to generate N2O5, which is then injected into the chamber to initiate oxidation of BVOCs. A few hours following peak aerosol growth for each reaction, aerosol evaporation is promoted either by isothermal dilution or by increasing the temperature from 25 °C to 40 °C. The mass of aerosol evaporation is determined using a Scanning Mobility Particle Sizer (SMPS) while changes in bulk aerosol composition are determined using a High Resolution-Time of Flight-Aerosol Mass Spectrometer (HR-ToF-AMS). From this study, we calculate an effective enthalpy of vaporization for the products formed by monoterpene+NO3 reactions. Additionally, preliminary results indicate that aerosol produced at 25 °C and subsequently heated to 40 °C have different mass and composition compared to aerosol produced at 40 °C. Possible reasons for this observation as well as its atmospheric implications will be discussed.