MEASURING OH AND HO2 IN THE TROPOSPHERE BY LASER-INDUCED FLUORESCENCEAT LOW-PRESSURE

The hydroxyl radical OH oxidizes many trace gases in the atmosphere. I t initiates and then participates in chemical reactions that lead to s uch phenomena as photochemical smog, acid rain, and stratospheric ozon e depletion. Because OH is so reactive, its volume mixing ratio is les s than 1 part per trillion volume (pptv) throughout the troposphere. I ts close chemical cousin, the hydroperoxyl radical HO2, participates i n many reactions as well. The authors have developed an instrument cap able of measuring OH and HO2 by laser-induced fluorescence in a detect ion chamber at low pressure. This prototype instrument is able to dete ct about 1.4 x 10(5) molecules cm(-3) (0.005 ppty) of OH at the ground in a signal integration time of 30 s with negligible interferences. T he absolute uncertainty is a factor of 1.5. This instrument is now bei ng adapted to aircraft use for measurements throughout the troposphere .