Grantee Research Project Results
Final Report: RO2 and HOx Radicals in Urban and Rural Air: Measurements of OH and RO2 Formation From Ozone-Alkene Reactions, and the Rate Coefficients of the Reactions of High Molecular Weight RO2 Radicals with HO2
EPA Grant Number: R826236Title: RO2 and HOx Radicals in Urban and Rural Air: Measurements of OH and RO2 Formation From Ozone-Alkene Reactions, and the Rate Coefficients of the Reactions of High Molecular Weight RO2 Radicals with HO2
Investigators: Paulson, Suzanne , Sander, Stanley
Institution: University of California - Los Angeles
EPA Project Officer: Hahn, Intaek
Project Period: January 15, 1998 through January 14, 2001
Project Amount: $440,323
RFA: Ambient Air Quality (1997) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air
Objective:
UCLA Component. Recent results indicate that the OH, RO2, and HO2 (=HOx, because these radicals rapidly cycle between one another in the presence of NO) radical yields from O3-alkene reactions can be the dominant source of new HOx radicals in urban air, producing more HOx at noon than O3 photolysis. O3-alkene reactions also are a significant source of HOx in rural air. Several OH radical yields have been measured, and range from 0.1 to 1 per O3-alkene reaction, with an uncertainty of a factor of ±1.5 or more. The most plausible mechanism for OH formation predicts an equal amount of RO2 concomitant with OH formation. This mechanism doubles the radical yields from O3-alkene reactions, but has yet to be experimentally proven. A high performance liquid chromatography (HPLC)-fluorescence system will be built to quantify peroxides that result from this reaction. The main objectives of this research project were to: (1) quantify OH radical yields with high precision (±15 percent); and (2) probe RO2 and hydroperoxide formation from O3-alkene reactions.
Jet Propulsion Laboratory (JPL) Component. The oxidizing capacity of the troposphere under low-NOx conditions is influenced strongly by reactions of HO2 with RO2 radicals produced from the OH and O3-initiated oxidation of biogenic alkenes. Reaction of these RO2 radicals with HO2 rather than NO produces higher molecular weight products that may contribute to particulate formation. The existing database of rate constants for reactions of larger RO2 radicals with HO2 is highly inadequate for the purposes of atmospheric modeling in both the accuracy and the number of reactions studied. The main objective of this research project was to accurately measure the rate coefficients for HO2 reactions with representative large RO2 radicals derived from OH and O3-initiated oxidation of hydrocarbons.
Summary/Accomplishments (Outputs/Outcomes):
UCLA Component
Goal 1: Quantification of OH Formation. Photochemical smog forms in rural and urban air when hydrocarbons and oxides of nitrogen react in the presence of sunlight. Free radicals, particularly the OH radical, are the currency of smog formation; OH initiates most reactions that lead to smog formation. Higher levels of radicals translate into more smog, and some reactions result in net production of copious radicals while others result in net consumption. Until recently, O3 reactions with alkenes were considered to produce fewer radicals than they consumed. Prior to the initiation of this study, a series of experiments carried out primarily by groups at the University of California at Riverside (UCR) and UCLA indicated that radical yields from these reactions are quite high and, in most cases, lead to the direct production of OH with concomitant production of RO2 radicals. OH formation yields vary widely, between about 0.1 and 1.0, depending on the structure of the alkene. In urban air during daytime, OH cycles rapidly with HO2 and RO2 radicals, allowing three radicals to be grouped together as HOx (= OH + HO2 + RO2).
In an earlier project, Paulson and Orlando estimated, based on early studies, that O3-alkene reactions can be the dominant source of OH radicals in urban air, and a significant source in rural air (see Figure 1). This has a very pronounced effect on the reactivity; hence, smog formation is predicted by models. Paulson and Orlando's estimates were based on existing OH formation yield data, which carried significant uncertainty. One of the primary objectives of this proposal was to expand the suite of alkenes for which OH formation yields are known, and improve the accuracy of OH yields for the most important alkenes.
Figure 1 shows the diurnal variation of the sources of radicals for representative Los Angeles data. In the early morning, before O3 builds up (or is transported down from aloft), photolysis of carbonyls and HONO dominate radical production. After 8:00 a.m., the reaction of O3 with alkenes is the largest single HOx source, and it is especially significant after 4:00 p.m. when the O3 levels are still high and photolysis has decreased. During the night, these calculations indicate that NO3 reactions with alkenes are the dominant HOx source. However, the importance of this source may have been significantly overestimated, because the products of the NO3 reaction are HO2 and RO2 radicals, and rapid interconversion between RO2, HO2, and OH does not take place without NO, and very low levels of NO are often observed to accompany higher values of NO3.
Figure 1. Diurnal Variation of the Sources of Radicals for Representative Los Angeles Data.
Figure 1 shows HOx formation rates for an average of two moderately polluted Los Angeles stations, using an average speciated mix for VOCs. Hourly NMHC, O3, and NOx measurements for central Los Angeles and Reseda during August 26-29, 1987, were averaged. The maximum NMHC and O3 values for this dataset were: 1 ppm C at 6:00 a.m. and 112 ppb at 2:00 p.m., respectively. Estimates of NO3 and HONO were made by averaging time resolved NO3 and HONO measurements collected at Claremont (also in the Los Angeles Air Basin) for the summers of 1987 and 1993. It should be noted that while HONO is frequently undetectable, it is sometimes observed at 40 times the peak concentrations used here.
Figure 2 shows a detailed breakdown of the contributions to HOx production from the alkene mix assumed for Figure 1. The most active alkenes include several species that are observed only at low concentrations, particularly the internal alkenes. For example, the top four contributors are trans-2-butene, 2-methyl-2-pentene, and cis- and trans-2-pentene. These account for 77 percent of the HOx from alkenes, yet are only 5 percent of the total alkenes, and less than 2 percent of the total VOCs (on a carbon basis). Calculations of HOx production for other cities show that internal alkenes are again the dominant contributors. Our analysis suggests that for both the U.S. Environmental Protection Agency (EPA) 29 city average speciated hydrocarbon mix and the mix observed in London, internal alkenes account for 80 percent or more of the HOx production from O3 reactions with alkenes. The U.S. EPA dataset is unique in that it includes alkenes with 6-8 carbons, and these alone contribute 25 percent of the source, indicating that trace species that are not routinely measured can be significant contributors. By contrast, ethene and propene, which are commonly included in the chemistry module of airshed models, account for less than 10 percent of the new HOx arising from O3-alkene reactions. Radical formation from internal alkenes is high (see Table 1), but more importantly, internal alkenes react more rapidly (by a factor of 10 or more) with O3 than do terminal alkenes.
Figure 2. HOx Formation Rates for the Reactions of O3 with Alkenes by Type for the Hydrocarbon Mix Assumed in Figure 1.
Experimental evidence prior to this proposal (1996 and earlier) indicates direct formation of OH from O3-alkene reactions; yields are from 8 to 115 percent. The existing dataset carries uncertainty factors of 1.5 (e.g., +50 percent, -33 percent). We propose to enlarge the OH yield dataset and improve its precision to ±15-25 percent for several alkenes that are critical in urban and regional oxidant formation. The larger internal alkenes are the primary targets, which are expected to have a large impact in urban air, due to their high O3-alkene reaction rate constants, reasonable concentrations, and high OH yields.
The OH formation yield work resulted in six publications: Paulson, Fenske, et al., 1999; Paulson Chung, Hasson, 1999; Fenske, Kuwata, et al., 2000; Kramp and Paulson, 2000; Fenske, Hasson, et al., 2000; and Orzechowska and Paulson, 2002. Results from these papers are summarized in Table 1. The literature values in italics in Table 1 indicate work that was published before beginning this project. Paulson, Fenske, et al. (1999) outline the small-ratio-relative-rate method we used to derive OH formation data from straightforward experiments, and provides results for the simplest anthropogenic alkenes. The later papers present results for some 21 additional alkenes, together with additional material that expands upon the initial goals outlined in the proposal for this project. Kramp and Paulson (2000) consider production of toxic epoxides from butadiene, together with OH formation and other aspects of the butadiene oxidation mechanism. Paulson, Chung, Hasson (1999); Fenske, Kuwate, et al. (2000); and Fenske, Hasson, et al., (2000) investigate the mechanism of OH formation by studying model alkenes, measuring the pressure dependence of OH formation, and through quantum chemical calculations. The quantum chemistry was developed through a collaboration with UCLA's Professor K.N. Houk, and K.T. Kuwata, who is now a professor at McAlester College. We performed ab initio calculations, which have led to the first results to provide insight into the bottleneck in ozone-alkene reactions that control OH production, and why OH formation is sensitive to the structure of the alkene.
The results of this work are being incorporated into air quality models, and the impact on predicted levels of OH radicals and organic peroxide formation is large. For example, Ariya, Sander, and Crutzen used a box model for suburban conditions and observed ROOH and OH concentrations that were approximately double those as predicted by the model without these key aspects of ozone-alkene reactions. In the last year or so, the production of OH from O3 reactions with alkenes has gained wide acceptance in the modeling community, and has been or is being added to most air quality models.
Table 1. OH Yields (values in italics are results prior to the initiation of this project)
Alkene | OH Yield | |
This Work | Literature | |
Ethene | 0.18 ± 0.06 | 0.12 +0.06, -0.04 0.14 ± 0.06 0.39 0.08 |
Propene | 0.36 ± 0.08 | 0.33 +0.32, -0.21 |
1-butene | 0.29 ± 0.06 | 0.41 +20, -13 |
1-pentene | 0.24 ± 0.04 | 0.37 +19, -11 |
1-hexene | 0.18 ± 0.04 | 0.32 +17, -11 |
1-octene | 0.10 ± 0.03 | 0.18 +9, -6 |
trans-2-butene | 0.64 ± 0.12 | 0.64 +0.32, -0.21 0.24 ± 0.02 0.54 ± 0.11 |
cis-2-butene | 0.33 ± 0.05 | 0.41 +0.21, - 0.14 0.17 ± 0.02 0.33 ± 0.07 |
trans-2-pentene | 0.46 ± 0.08 | - |
cis-2-pentene | 0.29 ± 0.06 0.27 ± 0.07 | - |
trans-3-hexene | 0.53 ± 0.08 | - |
cis-3-hexene | 0.36 ± 0.07 | - |
2-methyl-2-butene | 0.98 ± 0.24 0.80 ± 0.12 | 0.89 +0.44, -0.30 0.93 ± 0.14 0.81 ± 0.16 |
2,3-dimethyl-2-butene | 0.91 ± 0.14 | 0.80 ± 0.12 1.0 +0.5, -0.33 0.7 ± 0.1 0.36 ± 0.04 0.89 ± 0.24 |
Styrene | 0.07 ± 0.04 | - |
trans-β-methyl styrene | 0.22 ± 0.09 | - |
α-methyl styrene | 0.23 ± 0.12 | - |
cyclopentene | 0.62 ± 0.12 | 0.61 +0.3, -0.2 |
cyclohexene | 0.54± 0.13 | 0.68 +0.34, -0.22 |
cycloheptene | 0.36± 0.08 | - |
1-methylcyclohexene | 0.91 ± 0.2 | 0.90 +0.45, -0.3 |
1,3-butadiene | 0.13 | - |
Goal 2: OH and RO2 Formation. The proposed mechanism for direct OH formation from O3-alkene reactions predicts the formation of equal amounts of RO2, essentially doubling the radical yield. In addition, some HO2 may be formed directly. For example, for Trans-2-butene, the ozonolysis sequence proceeds as follows:
(R1)
(R2)
The resulting carbonyl oxides can have either a syn or anti configuration. There is a relatively high barrier to interconversion between syn and anti carbonyl oxides (ΔH0 ~ 30 kcal/mol; (Fenske, Kuwate, et al., 2000). The syn isomers can undergo a rapid 1,4-hydrogen shift (ΔH0 ~ 15 kcal/mol) (R3), and the resulting vinyl hydroperoxide can easily cleave to produce OH plus alkoxy radicals (ΔH0 = 10-15 kcal/mol). Because of the low barrier, it is likely that most syn carbonyl oxides formed from gas phase reactions will produce OH.
(R3)
We proposed to measure the RO2 formation from O3 reacting with a small number of alkenes. These experiments used a fast-turbulent flow reactor coupled to a long-path gas cell/FTIR, with a reaction zone and a zone where radicals are trapped with HO2 generated in a Beenaker cavity. The resulting H2O2 and ROOH is scrubbed into the aqueous phase and analyzed with an HPLC/fluorescence system built for this purpose. A number of experiments were performed, which showed that acetonylhydroperoxide, the hydroperoxide expected to be co-produced when OH radicals are eliminated from the carbonyl oxide formed in ozonolysis of 2,3-dimehtyl-2-butene, is formed in increasing quantities as more HO2 is added. This result is consistent with co-production of RO2 radicals with OH during alkene ozonolysis. The quantity of acetonylhydroperoxide and other peroxides generated in the experiments was not consistent with that predicted by theory. Because several RO2-HO2 reactions are involved, and these reaction rate constants are so uncertain (this is the subject of the JPL component) that we decided it would not be possible at this time for us to achieve quantitative results, and thus decided to take the research in a different direction. We have investigated hydroperoxide formation from the stabilized carbonyl oxides generated from O3-alkene reactions. This work was initiated under this grant and completed under a grant from the National Science Foundation.
Part of the motivation for the peroxide work is to investigate the source of secondary organic aerosol. During recent years, research into aerosols has escalated, due to recognition of the role of aerosols, particularly those smaller than 2.5 microns (PM2.5), in delivering potentially toxic compounds deep into the lungs. Recent epidemiological studies indicate that increases in human mortality are associated with significantly lower concentrations of sulfates and fine particles (PM2.5) than those previously thought. Furthermore, aerosols are a key part of the climate change puzzle. Aerosols generated by gas-phase reactions of biogenic alkenes (terpenes and terpenoids) have been estimated at 19 Tg/year globally, resulting in an atmospheric loading similar to that of black carbon, nitrates, and ammonium aerosols. Alkenes, particularly those with cycles of seven or more carbon atoms, are known to produce significant quantities of aerosol, competing with aromatics as the largest source of secondary organic aerosol in urban air. For many years, it had been assumed that organic acids form a substantial part of the rather uncertain link between gas-phase chemistry and secondary organic particle formation. Numerous organic acids have been measured in particles, in ambient samples from rural and urban air, and in chamber studies, particularly from ozone reactions with alkenes. Known pathways for acid formation in the gas-phase remain very uncertain.
Ozone reactions with alkenes, together with HO2 reactions with acylperoxy radicals, are generally assigned as the dominant photochemical acid production pathways. However, recent studies of the gas-phase chemistry of β-pinene suggest that acid formation from ozone-alkene reactions may be quite limited, with dominant products identified as hydroperoxides. Furthermore, recent direct measurements of the chemical composition of aerosols from ozone-alkene reactions indicate a strong contribution from organic peroxides, dominating the acid contribution.
Ozone-alkene reactions generate stabilized Criegee intermediates (of the form R1R2COO), which are believed to react with water molecules to form organic hydroperoxides, hydrogen peroxide, and carboxylic acids. These reactions are thought to be significant sources of these environmentally important compounds, yet both the yields of stabilized Criegee Intermediates and the branching ratios from their reaction with water are not well known. The formation of hydrogen peroxide and organic hydroperoxides was investigated in the gas-phase ozonolysis of anthropogenic alkenes, for humidities from 0 and 80 percent by gas chromatography with flame ionization detection (GC-FID) and HPLC with fluorescence detection. The reactions of stabilized Criegee intermediates with water were found to proceed almost entirely via organic hydroperoxide or hydrogen peroxide formation with little acid formation. This implies that production of organic acids observed in particles do not arise in large quantity from production in the gas phase from O3-alkene reactions, followed by partitioning into the particle phase. This work is presented in Hasson, Orzechowska, Paulson, 2001; and Hasson, Ho, et al., 2001.
JPL Component
Goal 3: Accurate measurements of the rate coefficients for HO2 reactions with representative large RO2 radicals derived from OH and O3-initiated oxidation of hydrocarbons. The component of the research undertaken at JPL involves the measurement of rate constants for reactions of the HO2 radicals with several organic peroxy radicals of atmospheric interest, including: CH3O2, C2H5O2, CH3C(O)CH2O2, HOCH2CH2O2, and (CH3)2C(OH)C(O2)(CH3)2. Measurements were conducted using an Infrared Kinetic Spectroscopy (IRKS) apparatus. The essential components of the IRKS apparatus consist of a temperature-controlled reaction cell, a photolysis laser, a UV light source, and an infrared (IR) light source. The reaction cell permits kinetic measurements to be made over the temperature range 220-373 K. To achieve uniform temperature control, component gases are pre-cooled in a sidearm. Temperature uniformity is maintained to within 1°C. A purge gas system is used in the mirror mounting blocks to minimize contamination of the Herriott mirrors and constrain the temperature-controlled region in the cell. The photolysis source is an Xe-Cl excimer laser that emits 150 mJ pulses at 308 nm. The sources of the UV light are a D2 lamp or a Xe-arc lamp. The UV source probes HO2, RO2, and NO2 using the strong UV absorbances associated with these species. The UV beam completes one traversal through the reaction cell. The IR source is generated by a distributed-feedback (DFB) laser that was manufactured at JPL and emits light at a wavelength of 1.51 µm. The IR source probes [HO2] via a ro-vibrational transition of the O-H stretch of HO2. Merriott mirrors in the reaction cell fold the IR beam in such a manner that it makes 30 passes back and forth through the reaction cell. To enhance detection sensitivity, a heterodyne detection scheme is employed in which the wavelength of the emitted light is modulated at 6.8 MHz and, after probing [HO2] in the reaction cell, demodulated at the detector at 13.6 MHz (2f-heterodyne detection). This detection scheme permits the detection of absorbances on the order of 10-4 with a 10 kHz bandwidth, which is comparable to that achieved by Cavity-Ringdown techniques.
HO2 + NO2. We conducted a comprehensive kinetics study of the HO2 + NO2 + M reaction, to ascertain the effectiveness of the IRKS apparatus towards measuring the kinetics of reactions involving HO2. The temperature and pressure dependences of the reaction rate coefficient were measured over the range 219-298 K and 20-150 Torr of N2. The results generated by the IRKS apparatus were more precise and accurate than prior measurements. We attained higher precision by employing FM spectroscopy on HO2, which improved the signal-to-noise by over a factor of 10 in comparison with prior, direct absorption measurements. Furthermore, we monitored, using NO2 UV spectroscopy, a significant improvement over prior studies that used calibrated flowmeters. We attained greater accuracy because of two reasons. First, the rate enhancement effect of CH3OH, a precursor used in prior studies, was examined and the true rate of HO2 + NO2, in the absence of CH3OH, was measured. Second, because measurements were conducted in the IR, spectral interference from species that could render rate measurements inaccurate was negligible. We observed that kinetic processes such as NO2 + NO2 <–> N2O4 significantly influenced UV measurements of HO2 + NO2 at temperatures below 250 K.
HO2 + HO2. A detailed understanding of the reaction mechanism for HO2 + HO2 –> H2O2 + O2 is required to understand and interpret the more complex studies of HO2 + RO2 reactions. Although the HO2 + HO2 reaction was studied, certain key features remain uncertain. We focused on the temperature dependence of the reaction between 220-298 K and the effect of added CH3OH on the reaction rate and mechanism. CH3OH, a precursor for HO2 for many kinetics studies, forms a strongly-bound complex with HO2, which is more reactive toward HO2 than uncomplexed HO2. We studied the temperature dependence of the CH3OH enhancement on the HO2 self-reaction and obtained rate constants for the CH3OH "enhancement factor" in the range at 220-298 K. At 231 K, the measured rate constant for HO2 + HO2, in the absence of CH3OH, was nearly a factor of 2 less than that recommended by the National Aeronautics and Space Administration data evaluation panel, which has important implications for stratospheric chemistry. These studies suggest that pre-cursor gases can significantly affect the measured reaction rate. Because many prior studies of reactions that involve HO2, including many HO2 + RO2 reactions, used precursor gases that may have influenced observed results, a re-examination of the rates of these reactions is warranted.
To more fully examine the atmospheric implications of these results, the expression for k([M],T) obtained in this work was incorporated into a one-dimensional atmospheric model. The vertical profile of the H2O2 mixing ratio calculated by the model was compared with measurements from two balloon-borne FTIR spectrometers: the JPL Mark IV solar occultation instrument, and the SAO FIRS-2 instrument. Use of the new rate constant expression resulted in much better agreement between models and measurements (see Figure 3).
CH3O2 + CH3O2. As with the HO2 + HO2 reaction, this reaction must be understood in order to interpret the HO2 + RO2 studies. The pathway forming methoxy (CH3O) radicals is particularly important because the HO2 radicals formed from the CH3O reaction must be accounted for in the kinetic analysis. In this work, we used the IRKS apparatus to measure the branching ratio for CH3O formation by monitoring the yield of HO2. Use of the IRKS apparatus was a significant improvement in the study of CH3O2 + CH3O2, because HO2 had not been directly monitored in prior studies. The measured branching ratio at 298 K was found to be significantly smaller than the value inferred from previous studies that used FTIR end-product analysis. At 231 K, the CH3O branching ratio was much higher than what was observed in prior experiments.
Figure 3. Measured and Modeled Profiles of Hydrogen Peroxide for Two Seasons Near Fort Sumner. NM as indicated at the top of each panel. The solid lines show calculated H2O2 profiles using standard (JPL 00-3) kinetics. The dashed lines show profiles using slightly different assumptions concerning the rates of the OH + O3 and HO2 + O3 reactions.
HO2 + CH3O2. We conducted preliminary studies of the HO2 + CH3O2 reaction. In conjunction with the results of our study of CH3O2 + CH3O2, the rate coefficient measured at 298 K was about 50 percent smaller than the average of the values reported by previous groups. Studies at low temperature are currently underway.
Journal Articles on this Report : 10 Displayed | Download in RIS Format
Other project views: | All 30 publications | 10 publications in selected types | All 10 journal articles |
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Christensen LE, Okumura M, Sander SP, Salawitch RJ, Toon GC, Sen B, Blavier J-F, Jucks KW. Kinetics of HO2 + HO2--> H2O2 + O2:implications for stratospheric H2O2. Geophysical Research Letters 2002;29(9):1299 (4 pp.). |
R826236 (Final) |
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Christensen LE, Okumura M, Sander SP, Friedl RR, Miller CE, Sloan JJ. Measurements of the rate constant of HO2 + NO2 + N2--> HO2NO2 + N2 using near-infrared wavelength-modulation spectroscopy and UV-visible absorption spectroscopy. The Journal of Physical Chemistry A 2003;108(1):80-91. |
R826236 (Final) |
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Christensen LE, Okumura M, Hansen JC, Sander SP, Francisco JS. Experimental and ab initio study of the HO2•CH3OH complex: thermodynamics and kinetics of formation. The Journal of Physical Chemistry A 2006;110(21):6948-6959. |
R826236 (Final) |
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Fenske JD, Kuwata KT, Houk KN, Paulson SE. OH radical yields from the ozone reaction with cycloalkenes. Journal of Physical Chemistry A 2000;104(31):7246-7254. |
R826236 (1999) R826236 (Final) |
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Hasson AS, Orzechowska G, Paulson SE. Production of stabilized Criegee intermediates and peroxides in the gas phase ozonolysis of alkenes:1. Ethene, trans-2-butene, and 2,3-dimethyl-2-butene. Journal of Geophysical Research-Atmospheres 2001;106(D24):34131-34142. |
R826236 (Final) |
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Hasson AS, Ho AW, Kuwata KT, Paulson SE. Production of stabilized Criegee intermediates and peroxides in the gas phase ozonolysis of alkenes:2. Asymmetric and biogenic alkenes. Journal of Geophysical Research-Atmospheres 2001;106(D24):34143-34153. |
R826236 (Final) |
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Kramp F, Paulson SE. The gas phase reaction of ozone with 1,3-butadiene:formation yields of some toxic products. Atmospheric Environment 2000;34(1):35-43. |
R826236 (Final) |
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Orzechowska GE, Paulson SE. Production of OH radicals from the reactions of C4-C6 internal alkenes and styrenes with ozone in the gas phase. Atmospheric Environment 2002;36(3):571-581. |
R826236 (Final) |
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Paulson SE, Fenske JD, Sen AD, Callahan TW. A novel small-ratio relative-rate technique for measuring OH formation yields from the reactions of O3 with alkenes in the gas phase, and its application to the reactions of ethene and propene. Journal of Physical Chemistry A 1999;103(13):2050-2059. |
R826236 (1998) R826236 (Final) |
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Paulson SE, Chung MY, Hasson AS. OH radical formation from the gas-phase reaction of ozone with terminal alkenes and the relationship between structure and mechanism. Journal of Physical Chemistry A 1999;103(41):8125-8138. |
R826236 (1998) R826236 (Final) |
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Supplemental Keywords:
atmospheric chemistry, organic radicals, hydroxyl radical, air, ambient air, atmosphere, ozone, acid deposition, indoor air, stratospheric ozone, tropospheric, health effects, chemicals, toxics, particulates, volatile organic compound, VOC., RFA, Scientific Discipline, Air, particulate matter, air toxics, Environmental Chemistry, tropospheric ozone, Atmospheric Sciences, Environmental Engineering, ambient air quality, urban air toxics, particle size, particulates, ozone-alkene reactions, air pollutants, chemical characteristics, ozone occurrence, photochemical radical, ambient air, ozone, ambient measurement methods, ambient monitoring, chemical composition, smog, urban air pollutants, photochemical smog, atmosphere, infrared spectroscopy, chain reactions, Volatile Organic Compounds (VOCs), Alkene reactions, photochemical assessmentProgress 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.