Hydroxyl radical reaction rate atmosphere

Gusten, H., Filby, W.G. and Schoaf, S., Prediction of Hydroxyl Radical Reaction Rates with Organic Compounds in the Gas Phase, Atmospheric Environ., 15 1763-1765 (1981). 

Atkinson R, Carter WPL, Aschmann SM, et al. 1985. Atmospheric fates of organic chemicals Prediction of ozone and hydroxyl radical reaction rates and mechanisms. Research Triangle Park, NC U.S. Environmental Protection Agency, Office of Research and Development. 

Baxley, J. S., and J. R. Wells, The Hydroxyl Radical Reaction Rate Constant and Atmospheric Transformation Products of 2-Butanol and 2-Pentanol, hit. J. Chem. Kinet., 30, 745-752 (1998). 

PCBTF received an exemption from VOC regulations based on the fact that its atmospheric hydroxyl radical reaction rate is slower than that of ethane [25]. A VOC is defined as any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic add, metallic carbides or carbonates, and ammoniiun carbonate, which partidpates in atmospheric photochemical reactions [26]. A VOC exemption petition for BTF was filed with the EPA on March 11,1997. Volatile organic compounds (VOCs) emission is controlled by regulation in efforts to reduce the tropospheric air concentrations of ozone. 

Markgraf, S.J., J. Semples, and J.R. Wells (1999), The hydroxyl radical reaction rate constant and atmospheric transformation products of 2-propoxyethanol, Int. J. Chem. Kinet, 31, 315-322. 

In the interest of conserving space in this handbook, a compact tabular presentation format has been adopted. Table 5.1.5.1 lists the chemical name, and its freon number (if applicable), molecular formula, molar weight and melting and boiling points. These data are available for virtually all substances in this group. Also shown in this table is the availability, expressed as a tick mark, of data on vapor pressure, solubility in water, octanol-water partition coefficient (Kqw) and the second order reaction rate constant with hydroxyl radicals. This rate constant is the critical determinant of persistence in the atmosphere. Tables 5.1.5.2 to Table 5.1.5.5 list the compounds and give the available property data with citations. 

Oxidation photooxidation t,/2 = 2.4-6.0 d, based on estimated rate constant for the vapor-phase reaction with hydroxyl radicals in the atmosphere (Atkinson 1985 quoted, Howard 1991) measured hydroxy radical reaction rate constant for dicamba 4.8 x 1012 M 1 /h (Armbrust 2000). Hydrolysis t,/2 > 133 d for 2 pg mL 1 to hydrolyze in dark sterile pond water at 37-39°C (Scifres et al. 1973 quoted, Muir 1991) ... 

Air t,/2 = 12.21 d, based on estimated rate constant for the vapor-phase reaction with photochemically produced hydroxyl radicals in the atmosphere (GEMS 1986 quoted, Howard 1991). 

Hydroxyl radical, OH, is the principal atmospheric oxidant for a vast array of organic and inorganic compounds in the atmosphere. In addition to being the primary oxidant of non-methane hydrocarbons (representative examples of these secondary reactions are given in Table 6), OH radical controls the rate of CO and CH4 oxidation. Furthermore, the OH reaction with ozone also limits the destruction of O3 in the troposphere, it also determines the lifetime of CH3CI, CHsBr, and a wide range of HCFC s, and it controls the rate of NO to HNO3 conversion. Concentration profiles for hydroxyl radical in the atmosphere are shown in Fig. 2. 

Benzene in the atmosphere exists predominantly in the vapor phase (Eisenreich et al. 1981). The most significant degradation process for benzene is its reaction with atmospheric hydroxyl radicals. The rate constant for the vapor phase reaction of benzene with photochemically produced hydroxyl radicals has been determined to be 1.3 10"12 cm3/molecule-second, which corresponds to a residence time of 8 days at an atmospheric hydroxyl radical concentration of 1.1 x 106 molecules/cm3 (Gaffney and Levine 1979 Lyman 1982). With a hydroxyl radical concentration of 1 x 108 molecules/cm3, corresponding to a polluted atmosphere, the estimated residence time is shortened to 2.1 hours (Lyman 1982). Residence times of 472 years for rural atmospheres and 152 years for urban atmospheres were calculated for the reaction of benzene with ozone (03) using a rate constant for 03 of 7 /1 O 23 cm3/molecule-second (Pate et al. 1976) and atmospheric concentrations for 03 of 9.6/1011 molecules/cm3 (rural) and 3/ 1012 molecules/cm3 (urban) (Lyman 1982). 

Oxidation rate constant k, for gas-phase second order rate constants, kojj for reaction with OH radical, k os with NO3 radical and ko3 with O3 or as indicated, data at other temperatures see reference exptl. photooxidation rate constant of 2.4 to 4.1 x 10 cm molecule s for the vapor-phase reaction with the photochemically produced hydroxyl radicals in the atmosphere (Conkle et al. 1975 Atkinson et al. 1979 Ambrose et al. 1981 Atkinson 1985, 1987 Drossman et al. 1988 quoted, Howard 1993) photooxidation half-life of 2.4-24 h for the gas-phase reaction with OH radical in air, based on the rate of disappearance of hydrocarbon due to reaction with OH radical (Darnall et al. 1976)... 

Howard et al. 1991 Lyman 1990 SRC 1995). Therefore, 2-butoxyethanol does not persist in the atmosphere. Based on a structure-reactivity relationship method (Atkinson 1987), the rate constant for the reaction of 2-butoxyethanol acetate with hydroxyl radicals in the atmosphere was estimated to be 2.1 10 cm /molecule-sec (Howard 1993 SRC 1995). Assuming an average (24-hour) day hydroxyl radical... 

In the atmosphere, the vapor-phase reaction of PCBs with hydroxyl radicals (photochemicaUy formed by sunlight) is the dominant transformation process (Brubaker and Hites 1998). The calculated tropospheric lifetime values for this reaction increases as the number of chlorine substitutions increases. The tropospheric lifetime values (determined using the calculated OH radical reaction rate constant and assuming an annual diurnally averaged OH radical concentration of 5x10 molecule/cm ) are 5-11 days for monochlorobiphenyls, 8-17 days for dichlorobiphenyls, 14—30 days for trichlorobiphenyls,... 

Aromatic compounds are of great interest in the chemistry of the urban atmosphere because of their abundance in motor vehicle emissions and because of their reactivity with respect to ozone and organic aerosol formation. The major atmospheric sink for aromatics is reaction with the hydroxyl radical. Whereas rate constants for the OH reaction with aromatics have been well characterized (Calvert et al. 2002), mechanisms of aromatic oxidation following the initial OH attack have been highly uncertain. Aromatic compounds of concern in urban atmospheric chemistry are given in Figure 6.16. 

Hydroxyl rate constant is the reaction rate constant of the solvent wifli hydroxyl radicals in the atmosphere. 

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