AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Investigation of Secondary Organic Aerosol Formation by a Filter-Based Thermal Desorption System (F-TDIS)
YUANLONG HUANG, Christopher Kenseth, John Seinfeld, California Institute of Technology
Abstract Number: 128 Working Group: Aerosol Chemistry
Abstract Determination of particle-phase composition at the molecular level remains a challenge. The combination of the filter-inlet for gases and aerosol (FIGAERO), which applies thermal-driven evaporation/decomposition of particle-phase compounds, and chemical ionization mass spectrometry (CIMS) is widely used to characterize gas- and particle-phase molecular constituents. We report here the development of a filter-based thermal desorption inlet system (F-TDIS) for the CF3O--CIMS, which is similar to FIGAERO but is designed for more facile filter exchange. The F-TDIS is able to reproduce FIGAERO-derived thermograms (CIMS signal vs. desorption temperature) for a wide variety of atmospherically relevant standards. The F-TDIS was applied to analysis of SOA derived from the ozonolysis of α- and β-pinene (w/, w/o OH scavenger and at different RH) in the Caltech PhotoOxidation flow Tube (CPOT). Filters for F-TDIS were collected in triplicate for each condition and treated as follows: thermal desorption by F-TDIS with ramping temperature followed by water extraction, isothermal evaporation by F-TDIS followed by water extraction, and direct extraction into water. By comparing the molecular composition of aqueous SOA extracts from filter residuals following thermal desorption or isothermal evaporation to those from “fresh” filter samples using UPLC/(-)ESI-Q-TOF-MS, together with CIMS thermograms, we evaluate the extent to which semi-volatile compounds and oligomers contribute to SOA derived from pinene ozonolysis and examine the influence of particle phase state and molecular volatility on the evolution of particle-phase composition.