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

Abstract

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, C_3F_6, for the chemical removal of OH from the ambient air. The removal rate of OH by C_3F_6 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) × 10^(−13) exp[(370±40)/T] cm^³ molecule^(−1) s^(−1), independent of pressure. In situ measurements using C_3F_6 addition are performed in both aircraft-borne and ground-based experiments. These studies show that laser excitation of the ^²Σ^+(v=1)← ^²Π(v=0) transition (282 nm) at high pulse repetition rates and low peak power can provide reliable and sensitive measurements of tropospheric OH.

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