Grantee Research Project Results
2009 Progress Report: Production of Secondary Organic Aerosol from Multiphase Terpene Photooxidation
EPA Grant Number: R833750Title: Production of Secondary Organic Aerosol from Multiphase Terpene Photooxidation
Investigators: Shepson, Paul
Institution: Purdue University
EPA Project Officer: Chung, Serena
Project Period: November 1, 2007 through October 31, 2010 (Extended to October 31, 2011)
Project Period Covered by this Report: November 1, 2008 through October 31,2009
Project Amount: $333,397
RFA: Sources and Atmospheric Formation of Organic Particulate Matter (2007) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air
Objective:
The objective of this research is to improve our quantitative and mechanistic understanding of the production of secondary organic aerosol, an important type of air pollutant, from the atmospheric oxidation of α- and β-pinene. We aim to determine product yields for major gas phase OH- and O3-induced oxidation products with much smaller uncertainty bounds than have previously been reported, thereby improving the capability of air quality models that simulate aerosol production from BVOCs. We will study the oligomerization of aerosol phase species, and study the extent to which photochemistry in aerosols and in cloud water contributes to secondary organic aerosol production. The information produced from the linked laboratory and field studies will be used to develop improved computer model modules that describesecondary organic aerosol from these important terpenes.
Progress Summary:
1. Development and Testing of the Proton Transfer Reaction Linear Ion Trap (PTRLIT). An objective of this work is to apply a newly developed technology, the PTRLIT, to studies of terpene oxidation and the nature of oxidation products that may undergo gas-to-particle conversion. While the PTRLIT was developed with methyl vinyl ketone (MVK) and methacrolein (MACR) as test cases, it had not been previously evaluated for terpenes and their oxidation products. We have completed a series of experiments in which we evaluated the ability to trap and selectively detect terpene isomers through collision-induced-dissociation (CID) experiments. The PTRLIT was intercompared with a conventional triple quadrupole mass spectrometer. We find that the CID spectra are very similar in the two cases. However, the PTRLIT enables ion chemistry in the trap for pursuit of improved selectivity. These results are described in our manuscript, Müller, et al., 2009, published in December of 2009 in the journal Atmospheric Measurement Techniques. While we have found that the PTRLIT can conduct measurements of terpenes and their oxidation products, this is a great challenge for atmospheric measurements because the CID spectra are often very similar for isomeric VOCs and their isomeric oxidation products. It will be necessary to utilize selective ion chemistry to pursue direct MS-based measurements, and we are currently studying the prospects for doing this.
During the summer of 2008, we conducted measurements of a variety of VOCs in the atmosphere above the mixed deciduous/coniferous forest at the University of Michigan Biological Station (UMBS), using the PTRLIT. The PTRLIT was very successfully deployed, and we made quantitative measurements of isoprene, the isomeric products MVK and MACR, acetone, and total terpenes. The ability to conduct isoprene measurements via MS/MS with the PTRLIT showed that under specific conditions (e.g. nighttime) there are significant interferences in the "straight" PTRMS measurement. We utilized the PTRMS data along with previous flux measurements from the UMBS canopy, and literature values for the yield measurements to calculate (and rank order) the "aerosol reactivity" of all the BVOCs, i.e. isoprene, the terpenes, and the sesquiterpenes at this site. This analysis showed that in terms of aerosol production in the local environment, it should be dominated by ozonolysis of α-terpinene and β-caryophyllene. Given the recent information that indicates the potential importance of organic nitrates as aerosol precursors, we calculated the "organic nitrate reactivity", i.e., the relative rate of production of organic nitrates, both from OH chemistry and NO3 chemistry, for all the BVOCs at this site. While isoprene dominates organic nitrate production during the day, total production or organic nitrates via NO3 chemistry is comparable at night, and the largest production rates are from α-terpinene, γ-terpinene, α-phellandrene, and β- myrcene. These observations and calculations will help direct us to future measurements of the specific oxidation products from these BVOC precursors. Graduate student Levi Mielke completed his Ph.D. in December 2009, and went on to a postdoc with Hans Osthoff. We are in the process of writing a manuscript describing this work.
2. Photochemical reaction chamber studies of α-pinene oxidation. We have been conducting a series of experiments in which α-pinene oxidation is studied in our 5500 liter all-PFA photochemical reaction chamber. Thus far, these have involved traditional VOC/NOx irradiations, during which NO, NO2, NOy, total PANs, and total organic nitrates have been measured using our newly developed chemiluminescence-based NOx instrument, that enables measurement of total PANs and total organic nitrates using a thermal decomposition (TD) inlet that converts the nitrate species to NO2, followed by photolysis to produce NO, which is then detected. O3 is measured with traditional UV absorption instruments, and particle size distributions and number are determined using our Scanning Mobility Particle Spectrometer (SMPS), purchased through this grant. Thus far, we have been focused on determination of the terpene nitrate yields (RONO2), as many recent publications have reported evidence of nitrate functionalities in ambient aerosol from forest-impacted air masses. We have synthesized the “terpene nitrates” (TNs) that originate from OH radical addition across the double bond, so that these (two) specific isomers can be quantitatively determined, using GC/ECD methods. However, a significant fraction of OH reaction with α-pinene occurs via H-atom abstraction from saturated carbon atoms; we are in the process of synthesis of some of the organic nitrates that are produced from H-atom abstraction, plus one nitrate that is produced from a rearrangement of the initially formed C-centered radical. 3 different organic nitrate yields have been quantified, with a total yield of 16%. This is consistent with the previous measurement from Noziere et al., and resolves a conflict in the literature. That work was done by graduate student Judy Yu, who obtained her Ph.D. in December of 2009, from University of Michigan. Shepson was the co-advisor with Profs. Carroll and Barker at University of Michigan, and the work was done at Purdue University.
We are in the process of measuring aerosol yields as a function of the extent of photochemical reaction, specific to OH(only)-, O3, and NO3 oxidation of α-pinene. During the experiments, we are collecting filter samples for species-specific chemical analysis, and study of condensed phase photochemistry, via MS analysis.
3. Analysis of the mechanisms for methacrolein oligomerization in the presence of H2SO4. We have been studying the nature of the oligomer produced in the condensed phase reaction of methacrolein with itself, in the presence of H2SO4, as a simple model system involving a multifunctional atmospheric OVOC. DESI-MS analysis of the oligomeric material was conducted; while the initial indications pointed to a Diels-Alder cyclization mechanism, we synthesized the Diels-Alder product, and found that the CID spectrum was different from that found in the oligomer. We are thus now investigating alternative reaction mechanisms that can explain the rich oligomeric spectra. In addition, H2SO4 acts to initiate oxidation and hydrolysis reactions that influence the composition of the aerosol. Interestingly, there are also H2 addition reactions (i.e. reduction) simultaneously occurring in the oligomeric mixture., under these acidic conditions. This work was done mostly by graduate student Marc Fiddler, who completed his Ph.D. in September of 2009. At the same time, we used DESI-MS and electrospray-MS to analyze cloud water samples acquired from our ALAR aircraft and cloud water collector. We found evidence for oligomeric material in the cloud water samples, and evidence for organo-sulfates in the oligomers. A manuscript is currently being revised by Dr. Fiddler.
4. Studies of aerosol production at the UMBS. During the summer of 2008, graduate student Nate Slade conducted aerosol measurements at UMBS, using the SMPS instrument. During that effort, several instances of particle nucleation were observed at this site, in the near-canopy environment. These measurements were conducted simultaneously with other VOC and OVOC measurements, e.g., for terpenes, MVK and MACR, HCHO, and glyoxal (in collaboration with the Keutsch group at U. Wisc.), as well as OH, HO2, NOy species, and meteorological variables (and CO2 fluxes). We are in the process of investigating the data, in pursuit of the hypothesis that terpene oxidation can contribute to nucleation events, in clean air conditions. In order to pursue this hypothesis, we installed the SMPS instrument in the ALAR (http://www.chem.purdue.edu/shepson/alar.html) aircraft, a light twin engine aircraft. In the summer of 2009, we conducted aerosol vertical profile measurements above the UMBS forest, with the expectation that terpene-based nucleation of new particles would manifest itself in a steep gradient of Aitken particles above the canopy. What we observed was a peak in the distribution of total particle number in the mid-boundary layer, consistent with depositional losses to the canopy. However, in flying control profiles upwind over Lake Michigan, we made a remarkable discovery, that there is a very steep gradient of small particles over the lake (i.e. large concentrations near the water surface), with an exponential dependence on wind speed, in other words, on wave height. The size distribution of these particles is consistent with what one would expect from the evaporation of water from film droplets, leaving the non-volatile solutes behind as the observed particles. It is possible that such particle ejection into the atmosphere above the Great Lakes may be a significant mechanism for water-atmosphere flux of persistent organic pollutants. A manuscript is in preparation in a collaboration between Purdue and Washington State U. on this subject. This work was presented by graduate student Jonathan Slade at the Fall 2009 AGU meeting. We note that the process of instrumenting the aircraft for this study enabled a set of experiments in which we developed a mass balance approach for measurement of area-wide pollutant fluxes using ALAR. While this development was conducted for CO2 and CH4 (in part for ease of analysis, and using independent funding), the intent is to apply this to area-wide effective aerosol fluxes. Because some of the aircraft development was enabled by this grant, we credit this grant in that publication, Mays, et al., 2009.
Future Activities:
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A workshop for the CABINEX project will be held in April at U. Mich., where the collaborators will develop plans for publications, including a number of collaborative publications about aerosol production and loss in the UMBS forest environment.
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We will be conducting further vertical profiles over Lake Michigan in the winter of 2010, to test the hypothesis that some of the new particles could be biogenically produced.
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Smog chamber experiments. We will be conducting a series of experiments in which OH-only, O3-only, and NO3-only chemistry will be involved in the oxidation of α-pinene, and α-terpinene, conducting aerosol yield measurements, and studying the composition and photochemical changes of the aerosol phase constituents.
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Chemical mechanism formulation. We are in the process of formulation of an explicit and detailed mechanism for gas phase chemistry, and gas to particle conversion in the α-pinene system.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 14 publications | 7 publications in selected types | All 7 journal articles |
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Type | Citation | ||
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Mays KL, Shepson PB, Stirm BH, Karion A, Sweeney C, Gurney KR. Aircraft-based measurements of the carbon footprint of Indianapolis. Environmental Science & Technology 2009;43(20):7816-7823. |
R833750 (2009) R833750 (2010) R833750 (Final) |
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Mielke LH, Pratt KA, Shepson PB, McLuckey SA, Wisthaler A, Hansel A. Quantitative determination of biogenic volatile organic compounds in the atmosphere using proton-transfer reaction linear ion trap mass spectrometry. Analytical Chemistry 2010;82(19):7952-7957. |
R833750 (2009) R833750 (2010) R833750 (Final) |
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Muller M, Mielke LH, Breitenlechner M, McLuckey SA, Shepson PB, Wisthaler A, Hansel A. MS/MS studies for the selective detection of isomeric biogenic VOCs using a Townsend Discharge Triple Quadrupole Tandem MS and a PTR-Linear Ion Trap MS. Atmospheric Measurement Techniques 2009;2(2):703-712. |
R833750 (2009) R833750 (2010) R833750 (Final) |
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Relevant Websites:
http://www.chem.purdue.edu/shepson/new-soa.htmlhttp://aoss-research.engin.umich.edu/prophet/CABINEX.html
http://www.chem.purdue.edu/shepson/ptrlit.html
http://www.chem.purdue.edu/shepson/alar.html
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.