Comparison of advanced offline and in situ techniques of organic aerosol composition measurement during the CalNex campaign

[摘要] Our understanding of formation processes, physical properties, andclimate/health effects of organic aerosols is still limited in part due tolimited knowledge of organic aerosol composition. We present speciatedmeasurements of organic aerosol composition by two methods: in situthermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) andoffline two-dimensional gas chromatography with a time-of-flight massspectrometer (GC × GC/TOF-MS). Usingthe GC × GC/TOF-MS 153 compounds were identified, 123 of which were matched with 64 ions observedby the TD-PTR-MS. A reasonable overall correlation of 0.67 (r²) wasfound between the total matched TD-PTR-MS signal (sum of 64 ions) and thetotal matched GC × GC/TOF-MS signal (sum of 123 compounds) for theLos Angeles area. A reasonable quantitative agreement between the two methodswas observed for most individual compounds with concentrations which weredetected at levels above 2 ng m⁻³ using the GC × GC/TOF-MS.The analysis of monocarboxylic acids standards with TD-PTR-MS showed thatalkanoic acids with molecular masses below 290 amu are detected well(recovery fractions above 60 %). However, the concentrations of theseacids were consistently higher on quartz filters (quantified offline byGC × GC/TOF-MS) than those suggested by in situ TD-PTR-MSmeasurements, which is consistent with the semivolatile nature of the acidsand corresponding positive filter sampling artifacts.

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