The Measurement of Tropospheric Trace Gases at Fritz Peak Observatory, Colorado, by Long-Path Absorption: OH and Ancillary Gases

The determination of the concentration of the hydroxyl radical in the troposphere is of fundamental importance to an understanding of the chemistry of the lower atmosphere. Described here are experiments located at Fritz Peak Observatory, Colorado, that measure the OH concentration to a sensitivity limit of about 5×105 cm−3 (0.025 pptv) with absolute error approximately ±30% and, simultaneously, measure the concentrations of H20, SO2, CH2O, NO2, NO3, HONO, 03, and other trace gases in the troposphere that affect OH concentration to provide a test of photochemical theories of OH formation and destruction. An informal OH intercomparison campaign that occurred at Fritz Peak in 1991 and the 1993 Tropospheric OH Photochemistry Experiment are discussed.