An In-Situ Instrument for Speciated Organic Composition of Atmospheric Aerosols:<u>T</u>hermal Desorption<u>A</u>erosol<u>G</u>C/MS-FID (TAG)

Abstract

We introduce a new in-situ instrument, Thermal desorption Aerosol GC/MS-FID (TAG), capable of hourly measurements of speciated organic compounds in atmospheric aerosols. Aerosol samples are collected into a thermal desorption cell by means of humidification and inertial impaction. The sample is thermally desorbed and transferred with helium carrier gas into a gas chromatography (GC) column, with subsequent detection by both quadrupole mass spectrometer (MS) and a flame ionization detector (FID). The collection and analysis steps are automated, yielding around the clock speciation. This approach builds on the extensive body of knowledge available for quantification and source apportionment of organic aerosols from past research using filter-based GC/MS analyses, but it is the first instrument to achieve in-situ time resolved measurements for an essentially unlimited number of samples, making it possible to analyze changes in organic aerosol speciation over timescales ranging from hours to seasons.