Monitoring potential photochemical interference in laser-induced fluorescence measurements of atmospheric OH

In situ laser-induced fluorescence measurements of atmospheric OH are susceptible to interference from laser generated OH, particularly in the troposphere. To quantify this interference we implement the addition of perfluoropropene, C3F6, for the chemical removal of OH from the ambient air. The removal rate of OH by C3F6 is determined in the laboratory using the discharge flow technique. Over the temperature range 249 to 296 K the rate constant is (6.0 +/- 0.8) x 10(-13) exp[(370 +/- 40)/T] cm(3) molecule(-1) s(-1), independent of pressure. In situ measurements using C3F6 addition are performed in both aircraft-borne and ground-based experiments. These studies show that laser excitation bf the (2) Sigma(+)(v=1)<--2 Pi(v=0) transition (282 nm) at high pulse repetition rates and low peak power can provide reliable and sensitive measurements of tropospheric OH.