Grantee Research Project Results
Final Report: Development, Evaluation, and Application of a Fast Time Response Mass Spectrometric Method for Quantitative Monitoring of Oxidant Precursors
EPA Grant Number: R825256Title: Development, Evaluation, and Application of a Fast Time Response Mass Spectrometric Method for Quantitative Monitoring of Oxidant Precursors
Investigators: Shepson, Paul
Institution: Purdue University
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999 (Extended to October 30, 2000)
Project Amount: $440,262
RFA: Air Quality (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
The principal objective of this effort was to develop and evaluate an ion trap MS/MS (i.e., tandem mass spectrometry) method for fast determination of tropospheric ozone precursors. The focus of this effort has been on quantitative determinations of biogenic volatile organic compounds (VOCs) and their oxidation products, e.g., isoprene, methyl vinyl ketone (MVK), methacrolein (MACR), aldehydes, and terpenes. The project focused on development of methods based on chemical ionization (CI) coupled with ion trap mass spectrometry, to enable rapid, selective and sensitive determination of a variety of VOCs in a complex mixture, i.e., ambient air. An associated objective was to demonstrate the utility of the method in enabling unique data interpretation based on relatively high frequency measurement.
Summary/Accomplishments (Outputs/Outcomes):
The first objective to pursue in this study was to identify and evaluate a chemical ionization reagent that would enable sensitive and selective determination of atmospheric alkenes. This was achieved, using vinyl methyl ether (VME), which ionizes and then reacts with the biogenic VOC isoprene (derived largely from deciduous trees) to make a stable adduct. This adduct is then trapped in the ion trap, and made to decompose through a process known a collisionally induced decomposition (CID). This process produces a smaller fragment of the adduct, which is then detected with the ion trap mass spectrometer. The combination of selective ionization and CID-MS detection makes this a very selective as well as sensitive procedure for quantitative determination of the atmospheric concentration of this important ozone precursor.
A problem that was encountered involved sampling air containing large amounts of humidity, which confounds the mass spectrometry. This problem was solved using membrane separation of the organic analytes from the water. Air was sampled over a silicone membrane tube through which helium was allowed to flow. Isoprene and other organic analytes transferred through the membrane, while air and water pass through more slowly. The analytes were cryo-trapped in a small sample loop, then ballistically heated and injected directly into the mass spectrometer. This configuration allowed us to conduct measurements on a 5 minute time scale.
This effort had a substantial and important Quality Assurance component. As development of a verified new method for quantitative determinations of VOCs was the objective, utilization of proper reference standards was important. To enable calibration in the field, we designed and constructed a method for making compressed gas standards for various analytes. Comparison with NIST standards from the National Center for Atmospheric Research (NCAR) indicated the uncertainty of these standards was within ?1 percent, while our calculated uncertainty is ?0.5 percent. Using these standards, we showed that our method produced a linear response between 0.1 and 10 ppb (mole/mole), with a 0.1 ppb detection limit.
The principal field test of our method was conducted as part of the Program
for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET)
program, conducted at the University of Michigan Biological Station in the summer
of 1998. During that study we organized and conducted an intercomparison of
five different methods for quantitative determination of atmospheric isoprene
concentrations. All five of the methods involved automated "on-line"
instruments. A sample of some of the results from this study is shown in Figure
1 below. These data showed that our instrument enabled rapid and accurate
determinations of isoprene in ambient air.
Figure 1. Isoprene Intercomparison Data from the PROPHET98 Study
During the PROPHET98 study we used our method as part of an effort aimed at improving our understanding of the previously puzzling phenomenon of rapid decay of surface isoprene concentrations at night. During this study, we were part of a team that discovered that a significant part of the isoprene decay at the PROPHET site is caused by reaction with the hydroxyl radical (OH). It remains an open question as to why there are high concentrations of OH at night at this site.
In the summer of 1999, we participated in the Southern Oxidants Study in the
Nashville Tennessee area. We conducted measurements of isoprene and its oxidation
products, methyl vinyl ketone (MVK) and methacrolein (MACR). We used our data
and available measurements of nitrogen oxides (NOx) to test a model that we
developed which shows that isoprene chemistry is very sensitive to the concentrations
of nitrogen oxides, and that there is an optimum concentration of NOx in Eastern
North America for production of MVK and MACR, and, by inference, ozone. Our
work, funded through this STAR grant, will aid in assessment of the contribution
of isoprene to ozone production in various forested environments.
Journal Articles on this Report : 6 Displayed | Download in RIS Format
| Other project views: | All 20 publications | 6 publications in selected types | All 6 journal articles |
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Barket Jr. DJ, Hurst JM, Couch TL, Colorado A, Shepson PB, Riemer DD, Hills AJ, Apel EC, Hafer R, Lamb BK, Westberg HH, Farmer CT, Stabenau ER, Zika RG. Intercomparison of automated methodologies for determination of ambient isoprene during the PROPHET 1998 summer campaign. Journal of Geophysical Research–Atmospheres 2001;106(D20):24301-24313. |
R825256 (1999) R825256 (Final) R825257 (Final) R825419 (Final) |
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Barket Jr. DJ, Grossenbacher JW, Hurst JM, Shepson PB, Olszyna K, Thornberry T, Carroll MA, Roberts J, Stroud C, Bottenheim J, Biesenthal T. A study of the NOx dependence of isoprene oxidation. Journal of Geophysical Research-Atmospheres 2004;109(D11):D11310 (12 pp.). |
R825256 (Final) |
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Colorado A, Barket Jr. DJ, Hurst JM, Shepson PB. A fast-response method for determination of atmospheric isoprene using quadrupole ion trap mass spectrometry. Analytical Chemistry 1998;70(24):5129-5135. |
R825256 (1999) R825256 (Final) |
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Faloona I, Tan D, Brune W, Hurst J, Barket Jr. D, Couch TL, Shepson P, Apel E, Riemer D, Thornberry T, Carroll MA, Sillman S, Keeler GJ, Sagady J, Hooper D, Paterson K. Nighttime observations of anomalously high levels of hydroxyl radicals above a deciduous forest canopy. Journal of Geophysical Research–Atmospheres 2001;106(D20):24315-24333. |
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Hurst JM, Barket Jr. DJ, Herrera-Gomez O, Couch TL, Shepson PB, Faloona I, Tan D, Brune W, Westberg H, Lamb B, Biesenthal T, Young V, Goldstein A, Munger JW, Thornberry T, Carroll MA. Investigation of the nighttime decay of isoprene. Journal of Geophysical Research–Atmospheres 2001;106(D20):24335-24346. |
R825256 (1999) R825256 (Final) R825419 (Final) |
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Tan D, Faloona I, Simpas JB, Brune W, Shepson PB, Couch TL, Sumner AL, Carroll MA, Thornberry T, Apel E, Riemer D, Stockwell W. HOx budgets in a deciduous forest:results from the PROPHET summer 1998 campaign. Journal of Geophysical Research–Atmospheres 2001;106(D20):24407-24427. |
R825256 (Final) |
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Supplemental Keywords:
ion trap, mass spectrometry, membrane inlet, isoprene, ozone., RFA, Air, Scientific Discipline, Geographic Area, Toxics, EPA Region, State, tropospheric ozone, VOCs, Atmospheric Sciences, air toxics, air quality data, air sampling, mass spectrometry, environmental monitoring, measurement of oxygenated compounds, rapid sampling and analysis, Indiana, atmospheric monitoring, monitoring, Region 5, ambient air, ambient ozone data, field measurements, ozone, quantitative monitoring of oxidant precursors, IN, Michigan (MI)Relevant Websites:
http://www.eaps.purdue.edu/people/faculty-pages/shepson.html Exit
Program for Research on Oxidants: PHotochemistry, Emissions and Transport Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.