Can Infrared Spectra Functional Group Measurements Improve Organic Aerosol Characterization from Time of Flight-Aerosol Chemical Speciation Monitor (TOF-ACSM)?

NA MAO, Manjula Canagaratna, Nga Lee Ng, Satoshi Takahama, Ann Dillner, University of California, Davis

     Abstract Number: 128
     Working Group: Instrumentation and Methods

Abstract
Aerosols affect climate, ecosystems, and human health. Characterizing organic matter (OM) in aerosols is crucial in understanding atmospheric processes in different locations, such as urban and remote areas. The Aerodyne Time of Flight Aerosol Chemical Speciation Monitor (ToF-ACSM) has been used to quantify inorganic and organic aerosols with high time resolution for a decade. However, the significant fragmentation of organic molecules by the electron impact ionization source creates uncertainties in analyzing organic aerosol compositions. Fourier transform- infrared (FT-IR) spectra measure functional groups in bulk aerosols but are limited by their low temporal resolution compared to ToF-ACSM. Using multivariate techniques, this study systematically explores the relationships between fragment ions from several individual compounds representative of carboxylic acids and alcohols, and multi-functional compounds and their measured functional groups. The fragment ions and functional groups are obtained using ToF-ACSM and FTIR, respectively. First, a PTFE filter-based OM functional group calibration was established using a wide range of chemicals with multiple functional groups such as carbonyl (CO), non-acid carbonyl (naCO), carboxylic acid (COOH), alcohol OH (aOH), alkane (CH), and unsaturated hydrocarbon (UnsCH), using partial least square (PLS) regression. Second, mass spectra of fragment ions are collected for the same chemical species. Third, the correlations of ACSM fragment ions with functional groups and spectral features are explored to assess how FT-IR spectroscopy can enhance the ToF-ACSM organic characterization.