2 research outputs found
The First Combined Thermal Desorption Aerosol Gas Chromatograph—Aerosol Mass Spectrometer (TAG-AMS)
<div><p>To address the critical need for improving the chemical characterization of the organic composition of ambient particulate matter, we introduce a combined thermal desorption aerosol gas chromatograph—aerosol mass spectrometer (TAG-AMS). The TAG system provides <i>in-situ</i> speciation of organic chemicals in ambient aerosol particles with hourly time resolution for marker compounds indicative of sources and transformation processes. However, by itself the TAG cannot separate by particle size and it typically speciates and quantifies only a fraction of the organic aerosol (OA) mass. The AMS is a real-time, <i>in-situ</i> instrument that provides quantitative size distributions and mass loadings for ambient fine OA and major inorganic fractions; however, by itself the AMS has limited ability for identification of individual organic compounds due to the electron impact ionization detection scheme used without prior molecular separation.</p>
<p>The combined TAG-AMS system provides real-time detection by AMS followed by semicontinuous analysis of the TAG sample that was acquired during AMS operation, achieving simultaneous and complementary measurements of quantitative organic mass loading and detailed organic speciation. We have employed a high-resolution time-of-flight mass spectrometer (HR-ToF-MS) to enable elemental-level determination of OA oxidation state as measured on the AMS, and to allow improved compound identification and separation of unresolved complex mixtures (UCM) measured on the TAG. The TAG-AMS interface has been developed as an upgrade for existing AMS systems. Such measurements will improve the identification of organic constituents of ambient aerosol and contribute to the ability of atmospheric chemistry models to predict ambient aerosol composition and loadings.</p>
<p>Copyright 2014 American Association for Aerosol Research</p>
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Contribution of Nitrated Phenols to Wood Burning Brown Carbon Light Absorption in Detling, United Kingdom during Winter Time
We
show for the first time quantitative online measurements of
five nitrated phenol (NP) compounds in ambient air (nitrophenol C<sub>6</sub>H<sub>5</sub>NO<sub>3</sub>, methylnitrophenol C<sub>7</sub>H<sub>7</sub>NO<sub>3</sub>, nitrocatechol C<sub>6</sub>H<sub>5</sub>NO<sub>4</sub>, methylnitrocatechol C<sub>7</sub>H<sub>7</sub>NO<sub>4</sub>, and dinitrophenol C<sub>6</sub>H<sub>4</sub>N<sub>2</sub>O<sub>5</sub>) measured with a micro-orifice volatilization impactor
(MOVI) high-resolution chemical ionization mass spectrometer in Detling,
United Kingdom during January–February, 2012. NPs absorb radiation
in the near-ultraviolet (UV) range of the electromagnetic spectrum
and thus are potential components of poorly characterized light-absorbing
organic matter (“brown carbon”) which can affect the
climate and air quality. Total NP concentrations varied between less
than 1 and 98 ng m<sup>–3</sup>, with a mean value of 20 ng
m<sup>–3</sup>. We conclude that NPs measured in Detling have
a significant contribution from biomass burning with an estimated
emission factor of 0.2 ng (ppb CO)<sup>−1</sup>. Particle light
absorption measurements by a seven-wavelength aethalometer in the
near-UV (370 nm) and literature values of molecular absorption cross
sections are used to estimate the contribution of NP to wood burning
brown carbon UV light absorption. We show that these five NPs are
potentially important contributors to absorption at 370 nm measured
by an aethalometer and account for 4 ± 2% of UV light absorption
by brown carbon. They can thus affect atmospheric radiative transfer
and photochemistry and with that climate and air quality