Hydroxyl radical chemical measurement

Hard et al (reference 110, 125, and submitted to/. Geophys, Res. 1991) have developed a system for the chemical conversion of HO2 to HO via the reaction HO2 + NO —> HO -I- N02. The hydroxyl radical is then measured by their low-pressure laser-induced-fluorescence instrument. Their multi-sample-channel LIF PAGE system is thus capable of simultaneous measurements of [HO ] (directly) and [H02 ] (by conversion to HO ). 

Many deleterious effects have been associated with photochemically polluted air ozone is deflnitely associated with respiratory problems, plant damage, and material damage PAN has deflnitely been associated with plant damage, and some other members of this class of chemical compounds have been associated with eye irritation the hydroxyl radical is considered to be an important factor in the conversion of gas-phase intermediates to end products, such as sulfur dioxide to particulate sulfate the particulate complex is responsible for haze formation and has also been associated with eye irritation and respiratory effects. The aldehydes have been associated with eye irritation. Ozone and PAN themselves do not cause eye irritation. For purposes of control, much more research is needed, in order to relate the laboratory data about the concentrations of these various materials that have significant effects to their formation in the atmosphere from emission and their atmospheric distribution. The lack of convenient measurement methods has hindered progress in gaining this understanding. 

The result of QSAR models can be rationalized in terms of oxidation necessary for the activation energy of these chemicals, because HOMO is a measure of the ability of a molecule to release electrons, and hydroxyl radicals serve as oxidants that accept electrons. As the energy of the HOMO increases, the ability of organic compounds to behave as nucleophiles increases therefore, the increased oxidation activity of compounds with hydroxyl radicals increases and leads to higher kinetic rate constants. 

The atmospheric chemical kinetics of linear perfluorinated aldehyde hydrates, Cx-F2x+iCH(OH)2, have been measured for x = 1,3, and 4, focusing on formation (from aldehyde, by hydration), dehydration, and chlorine atom- and hydroxyl radical-initiated oxidation.211 The latter reaction is implicated as a significant source of perfluorinated carboxylic acids in the environment. 

The mechanism of the hydroxyl radical-initiated oxidation of /i-pincnc in the presence of NO has been investigated using a discharge-flow system. Propagation of hydroxyl radicals was observed after the addition of O2 and NO, and the measured concentration profiles were compared with simulations based on both the master chemical mechanism and the regional atmospheric chemistry mechanism for /i-pinene oxidation.228... 

As we noted in Section 4.01.1, the ability of the troposphere to chemically transform and remove trace gases depends on complex chemistry driven by the relatively small flux of energetic solar UV radiation that penetrates through the stratospheric O3 layer (Levy, 1971 Chameides and Walker, 1973 Crutzen, 1979 Ehhalt et al., 1991 Logan et al, 1981 Ehhalt, 1999 Crutzen and Zimmerman, 1991). This chemistry is also driven by emissions of NO, CO, and hydrocarbons and leads to the production of O3, which is one of the important indicators of the oxidizing power of the atmosphere. But the most important oxidizer is the hydroxyl free radical (OH), and a key measure of the capacity of the atmosphere to oxidize trace gases injected into it is the local concentration of hydroxyl radicals. 

MIC may be released to the environment as a result of its manufacture and use as a chemical intermediate. If MIC is released to soil, it will be expected to rapidly hydrolyze if the soil is moist, based upon the rapid hydrolysis observed in aqueous solution. If released to water, it will be expected to rapidly hydrolyze with half-lives of 20 and 9 min at 15°C and 25°C, respectively, calculated from measured overall hydrolysis rate constants. The products of hydrolysis may include N-carboxymethylamine, methylamine, carbon dioxide, and N,N -dimethylurea. Since it rapidly hydrolyzes, bioconcentration, volatilization, and adsorption to sediment and suspended solids are not expected to be significant processes. No data were located concerning biodegradation, but MIC will probably abiotically hydrolyze significantly faster than it will biodegrade. If released to the atmosphere, it will be expected to exist almost entirely in the vapor phase based upon its vapor pressure. It will be susceptible to photooxidation via vapor phase reaction with photochemically produced hydroxyl radicals. Hydrolysis of MIC in moist air may be significant based upon its rapid hydrolysis in aqueous solution. 

Alkanes. In most of the chemical reactions observed in irradiation chambers, saturated hydrocarbons—even highly-branched ones such as p-menthane (l-isopropyl-4-methylcyclohexane)—have been quite unreac-tive. Since attack of alkanes by hydroxyl radical (26), atomic oxygen (27, 28), or ozone (29) follows the C-H reactivity order, tertiary > secondary > primary, the chemical measurements with alkanes would be expected to follow a clear pattern. However some alkanes (e.g., p-menthane) with tertiary hydrogens do not react more rapidly than those (e.g., n-octane) with only secondary and primary hydrogens, and hydrogen abstraction reactions often do not appear to be rate-determining steps. 

Oxidation, Hydrolysis and Reduction. 2,3,7,8-TCDD is not susceptible to hydrolysis at environmental temperatures ( ) and is highly stable to chemical oxidation. TCDD exhibits thermal stability at environmental temperatures. Indeed, the thermal stability of TCDD is such that temperatures of 1400 F to 2400 F are used for efficient (>99.9999%) degradation of 2,3,7,8-TCDD from contaminated soils (30). Reaction rates with hydroxyl radicals have not been measured, although Podoll and co-workers (3 ) esgimaJed the vapor phase rate constant to be on the order of 3 x M s. Using average OH... 

---