High-resolution chemical ionization mass spectrometry (ToF-CIMS): application to study SOA composition and processing
Open Access
- 26 November 2013
- journal article
- Published by Copernicus GmbH in Atmospheric Chemistry and Physics
- Vol. 6 (11), 3211-3224
- https://doi.org/10.5194/amt-6-3211-2013
Abstract
This paper demonstrates the capabilities of chemical ionization mass spectrometry (CIMS) to study secondary organic aerosol (SOA) composition with a high-resolution (HR) time-of-flight mass analyzer (aerosol-ToF-CIMS). In particular, by studying aqueous oxidation of water-soluble organic compounds (WSOC) extracted from α-pinene ozonolysis SOA, we assess the capabilities of three common CIMS reagent ions: (a) protonated water clusters (H2O)nH+, (b) acetate CH3C(O)O− and (c) iodide water clusters I(H2O)n− to monitor SOA composition. Furthermore, we report the relative sensitivity of these reagent ions to a wide range of common organic aerosol constituents. We find that (H2O)nH+ is more selective to the detection of less oxidized species, so that the range of O / C and OSC (carbon oxidation state) in the SOA spectra is considerably lower than those measured using CH3C(O)O− and I(H2O)n−. Specifically, (H2O)nH+ ionizes organic compounds with OSC ≤ 1.3, whereas CH3C(O)O− and I(H2O)n− both ionize highly oxygenated organics with OSC up to 4 with I(H2O)n− being more selective towards multi-functional organic compounds. In the bulk O / C and H / C space (in a Van Krevelen plot), there is a remarkable agreement in both absolute magnitude and oxidation trajectory between ToF-CIMS data and those from a high-resolution aerosol mass spectrometer (HR-AMS). Despite not using a sensitivity-weighted response for the ToF-CIMS data, the CIMS approach appears to capture much of the chemical change occurring. As demonstrated by the calibration experiments with standards, this is likely because there is not a large variability in sensitivities from one highly oxygenated species to another, particularly for the CH3C(O)O− and I(H2O)n− reagent ions. Finally, the data illustrate the capability of aerosol-ToF-CIMS to monitor specific chemical change, including the fragmentation and functionalization reactions that occur during organic oxidation, and the oxidative conversion of dimeric SOA species into monomers. Overall, aerosol-ToF-CIMS is a valuable, selective complement to some common SOA characterization methods, such as AMS and spectroscopic techniques. Both laboratory and ambient SOA samples can be analyzed using the techniques illustrated in the paper.Keywords
This publication has 52 references indexed in Scilit:
- High molecular weight SOA formation during limonene ozonolysis: insights from ultrahigh-resolution FT-ICR mass spectrometry characterizationAtmospheric Chemistry and Physics, 2012
- Atmospheric sulphuric acid and neutral cluster measurements using CI-APi-TOFAtmospheric Chemistry and Physics, 2012
- Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studiesAtmospheric Chemistry and Physics, 2011
- A field-deployable, chemical ionization time-of-flight mass spectrometerAtmospheric Chemistry and Physics, 2011
- A simplified description of the evolution of organic aerosol composition in the atmosphereGeophysical Research Letters, 2010
- The formation, properties and impact of secondary organic aerosol: current and emerging issuesAtmospheric Chemistry and Physics, 2009
- An experimental technique for the direct measurement of N2O5 reactivity on ambient particlesAtmospheric Chemistry and Physics, 2009
- Chlorine activation by N2O5: simultaneous, in situ detection of ClNO2 and N2O5 by chemical ionization mass spectrometryAtmospheric Chemistry and Physics, 2009
- Organic aerosol and global climate modelling: a reviewAtmospheric Chemistry and Physics, 2005
- Partially oxidised organic components in urban aerosol using GCXGC-TOF/MSAtmospheric Chemistry and Physics, 2004