|XU, WEN - Aerodyne Research|
|LAMBE, ANDREW - Aerodyne Research|
|Silva, Philip - Phil|
|HU, WEIWEI - University Of Colorado|
|ONASH, TIMOTHY - Aerodyne Research|
|WILLIAMS, LEAH - Aerodyne Research|
|CROTEAU, PHILIP - Aerodyne Research|
|ZHANG, XUAN - Aerodyne Research|
|RENBAUM-WOLFF, LINDSEY - Aerodyne Research|
|FORTNER, EDWARD - Aerodyne Research|
|JIMENEZ, JOSE - University Of Colorado|
|JAYNE, JOHN - Aerodyne Research|
|WORSNOP, DOUGLAS - Aerodyne Research|
|CANAGARATNA, MANJULA - Aerodyne Research|
Submitted to: Aerosol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2018
Publication Date: 2/27/2018
Citation: Xu, W., Lambe, A., Silva, P.J., Hu, W., Onash, T., Williams, L., Croteau, P., Zhang, X., Renbaum-Wolff, L., Fortner, E., Jimenez, J.L., Jayne, J.T., Worsnop, D., Canagaratna, M. 2018. Laboratory evaluation of species-dependent relative ionization efficiencies in the Aerodyne Aerosol Mass Spectrometer. Aerosol Science and Technology. 52(6):626-641. https://doi.org/10.1080/02786826.2018.1439570.
Interpretive Summary: This paper describes the characterization of the performance of an aerosol mass spectrometer for detecting and quantifying particulate matter. Aerosol mass spectrometry has become a common technique for identifying and quantifying chemical species within atmospheric particulate matter. The method has been used for research studies in numerous areas including studying dust particles from agriculture, urban particulate matter chemistry, and natural processes in remote locations. A recent controversy has arisen regarding the ability of the mass spectrometer to quantitate particulate matter accurately due to different efficiencies of detection that potentially affects studies published by USDA and academic collaborators but also EPA, NOAA, NASA, and others. This report introduces a new calibration protocol for the instrument as well as results for new laboratory characterization experiments. This study indicates that inorganic species and oxidized organic species have detection efficiencies that are consistent with values that have been used for previously published literature. However, detection of pure hydrocarbon species and reduced organic species may deviate from the typical detection efficiencies assumed, thus users of aerosol mass spectrometry should be careful in understanding the sample characteristics when publishing data.
Technical Abstract: Mass concentrations of chemical species calculated from the aerosol mass spectrometer (AMS) depend on two factors: particle collection efficiency (CE) and relative ionization efficiency (RIE, relative to the primary calibrant ammonium nitrate). While previous studies have characterized CE, RIE is relatively less well-characterized, especially for organic species. We present a new RIE calibration protocol with combined size and mass selection of calibrant particles and a light scattering probe to measure CE. A capture vaporizer with CE ~ 1 for ambient aerosols is also used to directly measure RIE. Pure inorganic and organic particles, including laboratory-generated secondary organic aerosol particles, and particles containing organic/NH4NO3 binary mixtures are examined. While the RIE of pure hydrocarbons and reduced species is high, RIE drops sharply for oxidized organics typical of most ambient primary and secondary organic aerosol (OA). RIE values overlap within uncertainties of the value of 1.4 ± 0.3 currently used by the AMS community for the analysis of ambient OA. Since laboratory particles do not perfectly mimic the complexity of ambient particles, we recommend further ambient and laboratory research to more precisely constrain the value(s) of RIE for ambient OA. Our laboratory results suggest that reduced ambient OA species could have larger errors. However, published field analyses do not support these, possibly due to differences between laboratory and field particles, or due to the presence of compensating errors.