Atmospheric photodegradation

Atmospheric photodegradation of DEHP and DBP has been shown to be rapid (51,53) with half-life times of less than 2 days, hence a large proportion of phthalate emissions to the air are broken down by photodegradation. 

Air atmospheric photodegradation, 0.62-1.4 d (Dilling et al. 1983) calculated tropospheric lifetime of 5-11 d due to calculated rate constant of gas-phase reaction with OH radicals for mono-chlorobiphenyls (Atkinson 1987) the tropospheric lifetime of 2.7-5.1 d based on the experimentally determined rate constant for gas-phase reaction with OH radicals for monochlorobiphenyls (Kwok et al. 1995). 

In neutral and acidic methanol solutions, BPA exhibits a slight absorption of UV light wavelengths exceeding 290 nm, while in basic methanol solution BPA exhibits significant absorption of UV exceeding 290 nm (Howard, 1989). These results indicate that BPA may well be photolyzed in the environment. In the atmosphere, photodegradation of a small amount of vapor-phase BPA occurs due to direct photolysis or the interaction with OH (Staples et al, 1998). In addition to direct photolysis, the photo-oxidation of BPA in surface water may also occur due to the interaction with OH. However, the rate constant for the reaction of OH with BPA is not known. 

The a- and [3-isomers of endosulfan undergo photolysis in laboratory tests after irradiation in polar solvents and upon exposure to sunlight on plant leaves. The a-isomer also undergoes isomerization to the P-isomer, which is relatively more stable (Dureja and Mukerjee 1982). A photolytic half-life of about 7 days was reported for endosulfan by EPA (1982c). The primary photolysis product is endosulfan diol, which is subsequently photodegraded to endosulfan a-hydroxyether. Endosulfan sulfate is stable to direct photolysis at light wavelengths of >300 nm however, the compound reacts with hydroxy radicals, with an estimated atmospheric half-life of 1.23 hours (HSDB 1999). 

Jang M, SR McDow (1997) Products of benz/a/anthracene photodegradation in the presence of known organic constituents of atmospheric aerosols. Environ Sci Technol 31 1046-1053. 

No information was found on the transformation of diisopropyl methylphosphonate in the atmosphere. Based on the results of environmental fate studies of diisopropyl methylphosphonate in distilled water and natural water, photolysis (either direct or indirect) is not important in the transformation of diisopropyl methylphosphonate in aquatic systems (Spanggord et al. 1979). The ultraviolet and infrared laser-induced photodegradation of diisopropyl methylphosphonate in both the vapor or liquid phase has been demonstrated (Radziemski 1981). Light hydrocarbon gases were the principal decomposition products. Hydrogen, carbon monoxide (CO), carbon dioxide (C02), and water were also detected. 

The photodegradation of para-aramid in an 0 atmosphere allows the differentiation between the accelerated experimental photooxidative conditions from its usual daylight exposure effects. This study illustrated an estimation of the rates of photooxidation of a commercial para-aramid product (i.e., DuPont s Kevlar-29 woven fabric) based on the oxygen-18-labelled carbon dioxide ( CC and CC ) decarboxylated from the sample. The oxygen-18-labelled atoms, which are inserted in the macromolecules, were analyzed for the photodegradation processes. This technique also allows the radial l O-distribution measurement from the fiber surface toward the fiber center. 

I,, = 0.7 h on silica gel, tA = 2.2 h on alumina and tA = 44 h on fly ash for different atmospheric particulate substrates determined in the rotary photoreactor (appr. 25 pg/g on substrate) (Behymer Hites 1985) direct photolysis tA = 9.08 h (predicted-QSPR) in atmospheric aerosol (Chen et al. 2001). Photodegradation k = 3 x 10-5 s in surface water during the summertime at mid-latitude (Fasnacht Blough 2002)... 

Photolysis half-lives on different atmospheric particulate substrates (approx. 25 (xg/g on substrate) t,2 = 7.0 h on silica gel, t,/2 = 22 h on alumina and t,/2 = 29 h on fly ash (Behymer Hites 1985) first order daytime photodegradation rate constants for adsorption on wood soot particles in an outdoor Teflon chamber k = 0.0077 min-1 with 1000-2000 ng/mg loading and k = 0.0116 min-1 with 30-350 ng/mg loading (Kamens et al. 1988) ... 

Hexachloroethane is quite stable in air. It is not expected to react with hydroxyl radicals or ozone in the atmosphere or to photodegrade in the troposphere (Callahan et al. 1979 Howard 1989). Degradation by photolysis may occur in the stratosphere. 

Field studies on the transformation of endrin in the atmosphere were not located in the available literature. Photochemical isomerization of endrin, primarily to the pentacyclic ketone commonly called delta ketoendrin or endrin ketone, was observed after exposure of thin layers of solid endrin on glass to sunlight (Burton and Pollard 1974). Minor amounts of endrin aldehyde were also formed in this reaction. Results of seasonal studies indicated that this isomerization would proceed with a half-life (first-order kinetics) of 5-9 days in intense summer sunlight, with complete conversion to the pentacyclic ketone in 15-19 days. Knoevenagel and Himmelreich (1976) reported that photodegradation of solid endrin in the laboratory... 

As in aquatic applications, weathering and hydrolysis are the dominant degradation mechanisms for terrestrial applications. Polymer articles covered with dirt can be problematic since photodegradation is not available however, the higher humidity levels and microbial activity in the soil when compared to the atmosphere are advantageous for degradation. 

Photolytic. Fukuda et al. (1988) studied the photodegradation of acenaphthene and alkylated naphthalenes in distilled water and artificial seawater using a high-pressure mercury lamp. Based upon a rate constant of 0.23/h, the photolytic half-life of acenaphthene in water is 3 h. Behymer and Hites (1985) determined the effect of different substrates on the rate of photooxidation of acenaphthene using a rotary photoreactor equipped with a 450-W medium pressure mercury lamp (X = 300-410 nm). The photolytic half-lives of acenaphthene absorbed onto silica gel, alumina, and fly ash were 2.0, 2.2, and 44 h, respectively. The estimated photooxidation half-life of acenaphthene in the atmosphere via OH radicals is 0.879 to 8.79 h (Atkinson, 1987). 

Jang and McDow (1997) studied the photodegradation of benzo[a]anthracene in the presence of three common constituents of atmospheric aerosols reported to accelerate benzo [a] anthracene, namely 9,10-anthroquinone, 9-xanthone, and vanillin. The photo-degradation experiments were conducted using a photochemical reactor equipped with a 450-W medium pressure mercury arc lamp and a water bath to maintain the solution temperature at 16 °C. The concentration of benzo [a] anthracene and co-solutes was 10" M. Irradiation experiments were conducted in toluene, benzene, and benzene-c/e- Products identified by GC/MS, FTIR, and NMR included benzo[a]an-thracene-7,12-dione, phthalic acid, phthalic anhydride, 1,2-benzenedicarboxaldehyde, naphtha-lene-2,3-dicarboxylic acid/anhydride, 7,12-dihydrobenzo[a]anthracene, 10-benzyl-10-hydroan-thracen-9-one, benzyl alcohol, and 1,2-diphenylethanol. 

Photolytic. Photodegrades under simulated atmospheric conditions to phosgene and nitrosyl chloride. Photolysis of nitrosyl chloride yields chlorine and nitrous oxide (Moilanen et al., 1978 Woodrow et ah, 1983). When aqueous solution of chloropicrin (10 M) is exposed to artificial UV light (X <300 nm), protons, carbon dioxide, hydrochloric and nitric acids are formed (Castro and Belser, 1981). 

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