Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications
Elemental compositions of organic aerosol (OA) particles provide useful constraints on OA sources, chemical evolution, and effects. The Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is widely used to measure OA elemental composition. This study evaluates AMS measurem...
| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/15/253/2015/acp-15-253-2015.pdf |
| _version_ | 1811259329474461696 |
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| author | M. R. Canagaratna J. L. Jimenez J. H. Kroll Q. Chen S. H. Kessler P. Massoli L. Hildebrandt Ruiz E. Fortner L. R. Williams K. R. Wilson J. D. Surratt N. M. Donahue J. T. Jayne D. R. Worsnop |
| author_facet | M. R. Canagaratna J. L. Jimenez J. H. Kroll Q. Chen S. H. Kessler P. Massoli L. Hildebrandt Ruiz E. Fortner L. R. Williams K. R. Wilson J. D. Surratt N. M. Donahue J. T. Jayne D. R. Worsnop |
| author_sort | M. R. Canagaratna |
| collection | DOAJ |
| description | Elemental compositions of organic aerosol (OA) particles provide useful
constraints on OA sources, chemical evolution, and effects. The Aerodyne
high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is
widely used to measure OA elemental composition. This study evaluates AMS
measurements of atomic oxygen-to-carbon (O : C), hydrogen-to-carbon
(H : C), and organic mass-to-organic carbon (OM : OC) ratios, and of carbon oxidation state
(<span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub>) for a vastly expanded laboratory data set
of multifunctional oxidized OA standards. For the expanded standard data set,
the method introduced by Aiken et al. (2008), which uses experimentally
measured ion intensities at all ions to determine elemental ratios (referred
to here as "Aiken-Explicit"), reproduces known O : C and H : C ratio values
within 20% (average absolute value of relative errors) and 12%,
respectively. The more commonly used method, which uses empirically
estimated H<sub>2</sub>O<sup>+</sup> and CO<sup>+</sup> ion intensities to avoid gas phase air
interferences at these ions (referred to here as "Aiken-Ambient"),
reproduces O : C and H : C of multifunctional oxidized species within 28 and
14% of known values. The values from the latter method are systematically
biased low, however, with larger biases observed for alcohols and simple
diacids. A detailed examination of the H<sub>2</sub>O<sup>+</sup>, CO<sup>+</sup>, and
CO<sub>2</sub><sup>+</sup> fragments in the high-resolution mass spectra of the standard
compounds indicates that the Aiken-Ambient method underestimates the
CO<sup>+</sup> and especially H<sub>2</sub>O<sup>+</sup> produced from many oxidized
species. Combined AMS–vacuum ultraviolet (VUV) ionization measurements
indicate that these ions are produced by dehydration and decarboxylation on
the AMS vaporizer (usually operated at 600 °C). Thermal decomposition
is observed to be efficient at vaporizer temperatures down to 200 °C.
These results are used together to develop an "Improved-Ambient" elemental
analysis method for AMS spectra measured in air. The Improved-Ambient method
uses specific ion fragments as markers to correct for molecular
functionality-dependent systematic biases and reproduces known O : C (H : C)
ratios of individual oxidized standards within 28% (13%) of the known
molecular values. The error in Improved-Ambient O : C (H : C) values is smaller
for theoretical standard mixtures of the oxidized organic standards, which
are more representative of the complex mix of species present in ambient OA.
For ambient OA, the Improved-Ambient method produces O : C (H : C) values that
are 27% (11%) larger than previously published Aiken-Ambient values; a
corresponding increase of 9% is observed for OM : OC values. These results
imply that ambient OA has a higher relative oxygen content than previously
estimated. The <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> values calculated for
ambient OA by the two methods agree well, however (average relative
difference of 0.06 <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> units). This indicates
that <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> is a more robust metric of oxidation
than O : C, likely since <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> is not affected by
hydration or dehydration, either in the atmosphere or during analysis. |
| first_indexed | 2024-04-12T18:29:47Z |
| format | Article |
| id | doaj.art-03a6759c34a74e23a592012b9f381ab1 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-12T18:29:47Z |
| publishDate | 2015-01-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-03a6759c34a74e23a592012b9f381ab12022-12-22T03:21:07ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242015-01-0115125327210.5194/acp-15-253-2015Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implicationsM. R. Canagaratna0J. L. Jimenez1J. H. Kroll2Q. Chen3S. H. Kessler4P. Massoli5L. Hildebrandt Ruiz6E. Fortner7L. R. Williams8K. R. Wilson9J. D. Surratt10N. M. Donahue11J. T. Jayne12D. R. Worsnop13Aerodyne Research, Inc., Billerica, MA, USADepartment of Chemistry and Biochemistry, and Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USADepartment of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USADepartment of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USADepartment of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USAAerodyne Research, Inc., Billerica, MA, USAMcKetta Department of Chemical Engineering, and Center for Energy and Environmental Resources, The University of Texas at Austin, Austin, TX, USAAerodyne Research, Inc., Billerica, MA, USAAerodyne Research, Inc., Billerica, MA, USALawrence Berkeley National Lab, Berkeley, CA, USADepartment of Environmental Science and Engineering, University of North Carolina, Chapel Hill, NC, USACenter for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USAAerodyne Research, Inc., Billerica, MA, USAAerodyne Research, Inc., Billerica, MA, USAElemental compositions of organic aerosol (OA) particles provide useful constraints on OA sources, chemical evolution, and effects. The Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is widely used to measure OA elemental composition. This study evaluates AMS measurements of atomic oxygen-to-carbon (O : C), hydrogen-to-carbon (H : C), and organic mass-to-organic carbon (OM : OC) ratios, and of carbon oxidation state (<span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub>) for a vastly expanded laboratory data set of multifunctional oxidized OA standards. For the expanded standard data set, the method introduced by Aiken et al. (2008), which uses experimentally measured ion intensities at all ions to determine elemental ratios (referred to here as "Aiken-Explicit"), reproduces known O : C and H : C ratio values within 20% (average absolute value of relative errors) and 12%, respectively. The more commonly used method, which uses empirically estimated H<sub>2</sub>O<sup>+</sup> and CO<sup>+</sup> ion intensities to avoid gas phase air interferences at these ions (referred to here as "Aiken-Ambient"), reproduces O : C and H : C of multifunctional oxidized species within 28 and 14% of known values. The values from the latter method are systematically biased low, however, with larger biases observed for alcohols and simple diacids. A detailed examination of the H<sub>2</sub>O<sup>+</sup>, CO<sup>+</sup>, and CO<sub>2</sub><sup>+</sup> fragments in the high-resolution mass spectra of the standard compounds indicates that the Aiken-Ambient method underestimates the CO<sup>+</sup> and especially H<sub>2</sub>O<sup>+</sup> produced from many oxidized species. Combined AMS–vacuum ultraviolet (VUV) ionization measurements indicate that these ions are produced by dehydration and decarboxylation on the AMS vaporizer (usually operated at 600 °C). Thermal decomposition is observed to be efficient at vaporizer temperatures down to 200 °C. These results are used together to develop an "Improved-Ambient" elemental analysis method for AMS spectra measured in air. The Improved-Ambient method uses specific ion fragments as markers to correct for molecular functionality-dependent systematic biases and reproduces known O : C (H : C) ratios of individual oxidized standards within 28% (13%) of the known molecular values. The error in Improved-Ambient O : C (H : C) values is smaller for theoretical standard mixtures of the oxidized organic standards, which are more representative of the complex mix of species present in ambient OA. For ambient OA, the Improved-Ambient method produces O : C (H : C) values that are 27% (11%) larger than previously published Aiken-Ambient values; a corresponding increase of 9% is observed for OM : OC values. These results imply that ambient OA has a higher relative oxygen content than previously estimated. The <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> values calculated for ambient OA by the two methods agree well, however (average relative difference of 0.06 <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> units). This indicates that <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> is a more robust metric of oxidation than O : C, likely since <span style="border-top: 1px solid #000; color: #000;">OS</span> <sub>C</sub> is not affected by hydration or dehydration, either in the atmosphere or during analysis.http://www.atmos-chem-phys.net/15/253/2015/acp-15-253-2015.pdf |
| spellingShingle | M. R. Canagaratna J. L. Jimenez J. H. Kroll Q. Chen S. H. Kessler P. Massoli L. Hildebrandt Ruiz E. Fortner L. R. Williams K. R. Wilson J. D. Surratt N. M. Donahue J. T. Jayne D. R. Worsnop Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications Atmospheric Chemistry and Physics |
| title | Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications |
| title_full | Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications |
| title_fullStr | Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications |
| title_full_unstemmed | Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications |
| title_short | Elemental ratio measurements of organic compounds using aerosol mass spectrometry: characterization, improved calibration, and implications |
| title_sort | elemental ratio measurements of organic compounds using aerosol mass spectrometry characterization improved calibration and implications |
| url | http://www.atmos-chem-phys.net/15/253/2015/acp-15-253-2015.pdf |
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