Measurement of tropospheric OH concentrations by laser long-path absorption spectroscopy

Abstract

Tropospheric hydroxyl (OH) radical concentrations were measured in summer 1987 in Jiilich by broadband laser long-path absorption (laser-LPA) spectroscopy observing the Q₁(2), Q₂₁ (2).Q₁(3).Q₂₁(3). and P₁ (1) rotational absorption lines around 308 nm. The measurement technique was improved using a multichannel spectrometric detector to record the OH absorption spectra. Now a much wider spectral interval can be observed at high resolution; thus, registration and correction of overlapping absorption features of interfering trace gases is improved. Simultaneous to the OH measurements, the concentrations of nitrogen dioxide (NO₂), formaldehyde (HCHO), and sulfur dioxide (SO₂) were monitored by a second LPA spectrometer. Ozone (O₃ aerosol concentrations, meteorological parameters, and absolutely calibrated photolysis frequencies of O₃ and NO₂ were also recorded. Carbon monoxide (CO), methane (CH₄), and light hydrocarbons were determined by gas chromatographic analysis. OH concentrations ranged up to 6.8.10⁶ molecules/cm³. At one day in July, an 'asymmetric' diurnal profile of the OH concentration was observed, which could be qualitatively explained by a strong decrease in the NO₂ concentration during the morning hours. DOI: 10.1111/j.1600-0889.1988.tb00115.x