ABSOLUTE OH QUANTUM YIELDS IN THE LASER PHOTOLYSIS OF NITRATE, NITRITE AND DISSOLVED H2O2 AT 308 AND 351 NM IN THE TEMPERATURE-RANGE 278-353 K

Absolute quantum yields for the formation of OH radicals in the laser photolysis of aqueous solutions of NO3-, NO2- and H2O2 at 308 and 351 nm and as a function of pH and temperature have been measured. A scavenging technique involving the reaction between OH and SCN- ions and the time resolved detection by visible absorption of the (SCN)2- radical ion was used to determine the absolute OH yields. The following results were obtained: (1) NO3--photolysis:{Mathematical expression} Selected experiments at 351 nm indicate that these results are essentially unchanged. (2) NO2--photolysis:{Mathematical expression} (3) H2O2-photolysis:{Mathematical expression} Together with the absorption coefficients and an assumed actinic flux within atmospheric droplets of twice the clear air value, the partial photolytic lifetimes (τOH) of these molecules at 298 K are estimated as 10.5 d, 5.4 h and 30.3 h for NO3-, NO2- and H2O2, respectively. These lifetimes will increase by a factor of two (NO3-, NO2-) and by 15% (H2O2) at T=278 K. Using average ambient concentrations in tropospheric aqueous droplets, the photolytic OH source strengths from these species are calculated to be 2.8×10-11, 1.3×10-11 and 1.4×10-11 mol 1-1 s-1 for NO3-, NO2- and H2O2 respectively. © 1990 Kluwer Academic Publishers.