Inorganic salt interference on CO2+ in aerodyne AMS and ACSM organic aerosol composition studies

Pieber, Simone M., El Haddad, Imad, Slowik, Jay G., Canagaratna, Manjula R., Jayne, John T., Platt, Stephen M., Bozetti, Carlo, Daellenbach, Kaspar R., Fröhlich, Roman, Vlachou, Athanasia, Klein, Felix, Dommen, Jozef, Miljevic, Branka, Jiménez, José L., Worsnop, Douglas R., Baltensperger, Urs, & Prévôt, André S.H. (2016) Inorganic salt interference on CO2+ in aerodyne AMS and ACSM organic aerosol composition studies. Environmental Science and Technology, 50(19), pp. 10494-10503.

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Abstract

Aerodyne aerosol mass spectrometer (AMS) and Aerodyne aerosol chemical speciation monitor (ACSM) mass spectra are widely used to quantify organic aerosol (OA) elemental composition, oxidation state, and major environmental sources. The OA CO2+ fragment is among the most important measurements for such analyses. Here, we show that a non-OA CO2+ signal can arise from reactions on the particle vaporizer, ion chamber, or both, induced by thermal decomposition products of inorganic salts. In our tests (eight instruments, n = 29), ammonium nitrate (NH4NO3) causes a median CO2+ interference signal of +3.4% relative to nitrate. This interference is highly variable between instruments and with measurement history (percentiles P10–90 = +0.4 to +10.2%). Other semi-refractory nitrate salts showed 2–10 times enhanced interference compared to that of NH4NO3, while the ammonium sulfate ((NH4)2SO4) induced interference was 3–10 times lower. Propagation of the CO2+ interference to other ions during standard AMS and ACSM data analysis affects the calculated OA mass, mass spectra, molecular oxygen-to-carbon ratio (O/C), and f44. The resulting bias may be trivial for most ambient data sets but can be significant for aerosol with higher inorganic fractions (>50%), e.g., for low ambient temperatures, or laboratory experiments. The large variation between instruments makes it imperative to regularly quantify this effect on individual AMS and ACSM systems.

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ID Code: 99793
Item Type: Journal Article
Refereed: Yes
DOI: 10.1021/acs.est.6b01035
ISSN: 1520-5851
Subjects: Australian and New Zealand Standard Research Classification > CHEMICAL SCIENCE (030000) > ANALYTICAL CHEMISTRY (030100) > Analytical Spectrometry (030101)
Australian and New Zealand Standard Research Classification > EARTH SCIENCES (040000) > ATMOSPHERIC SCIENCES (040100) > Atmospheric Aerosols (040101)
Divisions: ?? acc-aqsm ??
Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > Institutes > Institute of Health and Biomedical Innovation
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2016 American Chemical Society
Deposited On: 11 Oct 2016 01:23
Last Modified: 25 Oct 2016 04:58

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