Inorganic Salt Interference on CO2+in Aerodyne AMS and ACSM Organic Aerosol Composition Studies.
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.
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Simone M
SM
Pieber
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Imad
I
El Haddad
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Jay G
JG
Slowik
Aerodyne Research, Inc. , Billerica, Massachusetts 01821, United States.
Manjula R
MR
Canagaratna
Aerodyne Research, Inc. , Billerica, Massachusetts 01821, United States.
John T
JT
Jayne
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.|Norwegian Institute for Air Research , P.O. Box 100, NO-2027 Kjeller, Norway.
Stephen M
SM
Platt
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Carlo
C
Bozzetti
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Kaspar R
KR
Daellenbach
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Roman
R
Fröhlich
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Athanasia
A
Vlachou
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Felix
F
Klein
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Josef
J
Dommen
Queensland University of Technology, International Laboratory for Air Quality and Health, Institute of Health and Biomedical Innovation , Brisbane, Queensland 4001, Australia.
Branka
B
Miljevic
Department of Chemistry & Biochemistry and CIRES, University of Colorado , Boulder, Colorado 80309, United States.
José L
JL
Jiménez
Aerodyne Research, Inc. , Billerica, Massachusetts 01821, United States.
Douglas R
DR
Worsnop
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
Urs
U
Baltensperger
Paul Scherrer Institute, Laboratory of Atmospheric Chemistry , CH-5232 Villigen, Switzerland.
André S H
AS
Prévôt
D000336:Aerosols; D002244:Carbon; D013058:Mass Spectrometry; D012965:Sodium Chloride; D017673:Sodium Chloride, Dietary
D000336:Aerosols; D017673:Sodium Chloride, Dietary; D012965:Sodium Chloride; D002244:Carbon