AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Comprehensive Thermal Desorption Aerosol Gas Chromatograph (cTAG) for Consistent Quantification of VOCs, IVOCs and SVOCs
REBECCA WERNIS, Nathan Kreisberg, Robert Weber, Susanne Hering, Allen Goldstein, University of California, Berkeley
Abstract Number: 748 Working Group: Instrumentation and Methods
Abstract Aerosols are a source of great uncertainty in radiative forcing predictions and have poorly understood health impacts. Most aerosol mass is formed in the atmosphere from reactive gas phase organic precursors, forming secondary organic aerosol (SOA). Semivolatile organic compounds (SVOCs) (effective saturation concentration, C*, of 10-1 - 103 μg/m3) comprise a large fraction of organic aerosol, while intermediate volatility organic compounds (IVOCs) (C* of 103 - 106 μg/m3) are abundant and efficiently react to form SOA. VOCs (C*≥106 μg/m3) are precursors to SOA with high reactivity, abundance, and impacts on ozone formation.
The Comprehensive Thermal Desorption Aerosol Gas Chromatograph (cTAG) is the first single instrument sensitive to compound-specific VOCs, IVOCs and SVOCs. cTAG is a two channel instrument which measures concentrations of C5 – C16 alkane equivalent volatility VOCs and IVOCs on one channel and C14 – C30 IVOCs and SVOCs on the other coupled to a single High-Resolution Time-of-Flight Mass Spectrometer, achieving consistent quantification across 14 orders of magnitude of vapor pressure. cTAG obtains concentrations hourly and gas-particle partitioning for SVOCs bihourly, enabling observation of the evolution of these species through oxidation and partitioning into the particle phase. Online derivatization for SVOCs enables detection of polar and oxidized species.
In this work we present design details and data evaluating key parameters of instrument performance such as detection limits, measurement uncertainties, and linearity and reproducibility of calibration curves obtained using a custom liquid evaporation system for I/VOCs. VOC measurements are compared with a collocated GC-FID system performing routine VOC monitoring. Example timelines of precursors with secondary products are shown. Based on known chemical tracers and temporal correlations between measured compounds, we present the initial findings to elucidate the relative contributions of pollution sources to PM2.5 in Livermore, CA during spring 2018.