Atmospheric aerosol composition is often analyzed using thermal desorptiontechniques to evaporate samples and deliver organic or inorganic moleculesto various designs of detectors for identification and quantification. Theorganic aerosol (OA) fraction is composed of thousands of individualcompounds, some with nitrogen- and sulfur-containing functionality and,often contains oligomeric material, much of which may be susceptible todecomposition upon heating. Here we analyze thermal decomposition productsas measured by a thermal desorption aerosol gas chromatograph (TAG) capableof separating thermal decomposition products from thermally stablemolecules. The TAG impacts particles onto a collection and thermaldesorption (CTD) cell, and upon completion of sample collection, heats andtransfers the sample in a helium flow up to 310 °C. Desorbedmolecules are refocused at the head of a gas chromatography column that is held at45 °C and any volatile decomposition products pass directlythrough the column and into an electron impact quadrupole mass spectrometer.Analysis of the sample introduction (thermal decomposition) periodreveals contributions of NO ( 30), NO ( 46), SO( 48), and SO ( 64), derived from either inorganic ororganic particle-phase nitrate and sulfate. CO ( 44) makes up amajor component of the decomposition signal, along with smallercontributions from other organic components that vary with the type ofaerosol contributing to the signal (e.g., 53, 82 observed here forisoprene-derived secondary OA). All of these ions are important for ambientaerosol analyzed with the aerosol mass spectrometer (AMS), suggestingsimilarity of the thermal desorption processes in both instruments. Ambientobservations of these decomposition products compared to organic, nitrate,and sulfate mass concentrations measured by an AMS reveal good correlation,with improved correlations for OA when compared to the AMS oxygenated OA(OOA) component. TAG signal found in the traditional compound elution timeperiod reveals higher correlations with AMS hydrocarbon-like OA (HOA)combined with the fraction of OOA that is less oxygenated. Potential toquantify nitrate and sulfate aerosol mass concentrations using the TAGsystem is explored through analysis of ammonium sulfate and ammonium nitratestandards. While chemical standards display a linear response in the TAGsystem, redesorptions of the CTD cell following ambient sample analysisshow some signal carryover on sulfate and organics, and new desorptionmethods should be developed to improve throughput. Future standards shouldbe composed of complex organic/inorganic mixtures, similar to what is foundin the atmosphere, and perhaps will more accurately account for any aerosolmixture effects on compositional quantification.
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