Indirect photolysis with hydroxyl radical

Indirect Photolysis in the Atmosphere (Troposphere)—Reactions with Hydroxyl Radical (HO )... 

Indirect photolysis rate constant, usually with oxidant specified e.g., kHO for oxidation by hydroxyl radical... 

Air t,/2 = 8 h, based on a rate constant k = 3.0 x 10-11 cm3 molecules-1 s-1 for the reaction with 8 x 10-5 molecules/cm3 photochemically produced hydroxyl radical in air (GEMS 1986 quoted, Howard 1989). Surface water estimated t,/2 = 3.2 d in Rhine River in case of a first order reduction process (Zoeteman et al. 1980) midday t,/2(calc) = 45 min in Aucilla River water due to indirect photolysis using an experimentally determined reaction rate constant k = 0.92 h-1 (Zepp et al. 1984 quoted, Howard 1989) estimated t,/2 = 3.2 d for a river 4 to 5 m deep, based on monitoring data (Zoeteman et al. 1980 quoted, Howard 1989). 

PROBABLE FATE photolysis direct photolysis is slow, indirect photolysis may be important, vapor phase aldrin residues expected to react with photochemically produced hydroxyl radicals with a half-life of 35.46 min oxidation reacts to form dieldrin, photooxidation by ultraviolet light in aqueous medium 90-95°C forms 25% CO2 in 14.1 hr, 50% CO2 in 28.2 hr, 75% CO2 in 109.7 hr, photooxidation half-life in air 0.9-9.1 hrs hydrolysis too slow to be an important process volatilization an important process, evaporation rate from water 3.72x10 m4ir, will volatilize from soil surfaces sorption an important process, adsorption to sediment is... 

PROBABLE FATE photolysis, photooxidation to chlorinated biphenyls and benzophe-nones probable, indirect photolysis may be significant based on the behavior of the related compound DDT, direct photolysis half-life in water >150 yrs, photooxidation half-life in air 13.3-133 hrs oxidation, not an important process, vapor phase half-life in the atmosphere 1.71 days from reaction with photochemically produced hydroxyl radicals hydrolysis, not an important process, will not hydrolyze in soil volatilization expected to be an important process, evaporation half-life 1.82 days from a river 1 m deep, flowing at Im/sec with a wind velocity of 3 m/sec sorption is an important process, expected to adsorb to sediment if released to water biological processes biotransformation and bioaccumulation are important processes biodegradation expected to be slow... 

PROBABLE FATE photolysis no direct photolysis, indirect photolysis too slow to be environmentally important, photooxidation half-life in water 2.4-12.2 yrs, photooxidation half-life in air 7.4 hrs-2.5 days oxidation not important, reaction with photochemically produced hydroxyl radicals gives a half-life of 18 hrs hydrolysis hydrolysis (only in surface waters) believed to be too slow to be important, first-order hydrolytic half-life 10 yrs volatilization not expected to be an important transport process sorption sorption onto particulates and com-plexation with organics are dominant transport processes biological processes bioaccumulated in many organisms, biodegraded rapidly in natural soil, some biotransformation, all biological processes are important fates... 

PROBABLE FATE photolysis no direct photolysis, half-life from surface waters 3500 hr, indirect photolysis is too slow to be important, photodegradation by hydroxyl radicals will occur with a half-life of 23.8 hrs oxidation not an important process, photooxidation half-life in air 4.7 days-46.6 days hydrolysis too slow to be important under natural conditions, first-order hydrolytic half-life 1163 days volatilization possible, but not important sorption sorption onto particles and biota and complexation with humic substances principal transport mechanism, little adsorption to soil or sediment is expected to occur biological processes bioaccumulation, biodegradation, and biotransformation by many organisms (including humans) are very significant fates... 

The (indirect) photodegradation - reaction with reactive species formed by photochemical processes - has been recognized as the major transformation pathway for chemicals in the troposphere. The electrophilic addition of tropospheric radicals constitutes the principal degradation pathway. The relevant reactive species are hydroxyl radicals (OH ) and ozone (O3) during day time and N03 radicals at night. The hydroxyl radicals result from reactions of oxygen atoms with water vapour, photolysis of HNO2 and reactions of HO2 (a... 

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