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 m−3) comprise a large fraction of organic aerosol, while
intermediate-volatility organic compounds (IVOCs) (C* of
103–106 µg m−3) and volatile organic compounds (VOCs)
(C* ≥ 106 µg m−3) are gas-phase precursors to SOA and
ozone. The Comprehensive Thermal Desorption Aerosol Gas Chromatograph (cTAG) is the
first single instrument simultaneously quantitative for a broad range of
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–C32 SVOCs on the
other coupled to a single high-resolution time-of-flight mass spectrometer,
achieving consistent quantification across 15 orders of magnitude of vapor
pressure. cTAG obtains concentrations hourly and gas–particle partitioning
for SVOCs every other hour, enabling observation of the evolution of these species
through oxidation and partitioning into the particle phase. Online
derivatization for the SVOC channel enables detection of more polar and
oxidized species. In this work we present design details and data evaluating key parameters of
instrument performance such as I/VOC collector design optimization,
linearity and reproducibility of calibration curves obtained using a custom
liquid evaporation system for I/VOCs and the effect of an ozone removal
filter on instrument performance. Example timelines of precursors with
secondary products are shown, and analysis of a subset of compounds
detectable by cTAG demonstrates some of the analytical possibilities with
this instrument.
Dermal absorption of semivolatile organic compounds from the gas phase: Sensitivity of exposure assessment by steady state modeling to key parameters
