10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
SOA Formation from Toluene Oxidation in the Presence of Nox: The Importance of Relative Humidity
DAO HUANG, Yunle Chen, Masayuki Takeuchi, Taekyu Joo, Steve Kim, Gamze Eris, Nga Lee Ng, Zhejiang University
Abstract Number: 1045 Working Group: Aerosol Chemistry
Abstract Toluene is one of the most important anthropogenic volatile organic compounds (VOCs) considering its high concentration in urban and some rural areas and high secondary organic aerosol (SOA) yields. However, in the past decade, knowledge about toluene SOA in the presence of NOx is limited to SOA yield curve under dry conditions and a few scattered yields under humid conditions. Little is known about toluene SOA composition and the effects of relative humidity (RH) on toluene SOA yields and composition. In the present work, a series of toluene photooxidation experiments under dry and humid conditions were performed in the Georgia Tech Environmental Chamber facility (GTEC) to investigate the toluene SOA composition and RH effects. In situ photolysis of HONO was used as an OH radical and NOx sources. Ammonium sulfate was used as aerosol seeds. Particles were chemically characterized using a high-resolution time-of- flight aerosol mass spectrometer (HR-ToF-AMS) and a high-resolution chemical ionization time-of-flight mass spectrometer coupled with a filter inlet for gas and aerosol (FIGAERO-CIMS). Simultaneously, gas-phase compounds were determined by CIMS. Based on experimental results, we obtain different SOA yield curves as a function of organic aerosol (ΔMo) at various RH and compare the particle composition under dry and humid conditions. Generally, the molecular weights of SOA compounds generated under humid conditions is much smaller than that under dry conditions. Under humid conditions, oxygenated organic compounds containing 6 or fewer carbons are the major components of SOA. Under dry conditions, organic nitrates containing 7 or more carbons are the main components of SOA. Further, the evolution of SOA composition over time is also different under dry and humid conditions. We also investigate SOA formation mechanisms under humid conditions by comparing experimental results with MCM modeling. Studying toluene SOA composition and the role of water in SOA formation is important for understanding SOA and haze formation in the real atmosphere.