Quantification Of Cooking Organic Aerosol In The Indoor Environment Using Aerodyne Aerosol Mass Spectrometers

The Aerodyne aerosol mass spectrometer (AMS) is used extensively to study the composition of non-refractory submicron aerosol composition during atmospheric field studies. During two recent studies of indoor environments, HOMEChem and ATHLETIC, the default ambient organic aerosol AMS quantification parameters resulted in a large discrepancy with co-located instruments while sampling cooking organic aerosol (COA). Instruments agreed within uncertainty estimates during all other sampling periods. Assuming a collection efficiency (CE) of unity, adjustments to the AMS relative ionization efficiency (RIE) were required to reach agreement with co-located instruments. The range of RIECOA observed (ATHLETIC: RIECOA = 4.26-4.96, HOMEChem: RIECOA = 4.70-6.50) was consistent with RIE measured in the laboratory for cooking-specific molecules. These results agree with prior AMS studies which have indicated that more oxidized outdoor ambient organic aerosol has a relatively constant RIE of 1.4 +/- 0.3 while more reduced organics have higher RIE. The applicability of a higher RIE was considered for two ambient datasets, and agreement between the AMS and co-located instruments improved when an increased response factor (RIE x CE) was applied to positive matrix factorization-derived primary organic aerosol (POA). Based on the observations presented here and the literature, we recommend AMS users consider applying RIECOA=4.2 to source and indoor studies of COA and evaluate a higher POA response factor of the order of similar to 1.5 in outdoor studies at urban background sites, and similar to 2 at sites impacted by fresh sources. This study aims to improve AMS quantification methodology for reduced POA and highlights the importance of careful intercomparisons in field studies.