Variability-lifetime relationship for organic trace gases: A novel aid to compound identification and estimation of HO concentrations

In this study we report aircraft-borne measurements of organic species made during March 1998 in Surinam, an unpolluted region on the northeast coast of South America Measurements included the following: CO by tunable diode l aser; a wide variety of organics including acetone, acetonitrile, and isopr ene by proton transfer mass spectrometry (PTR-MS); and nonmethane hydrocarb on measurements by gas chromatography-flame ionization detection. Here we c ompare the standard deviation of the natural logarithm of the mixing ratio (Sigma_1nX) to the estimated lifetime of these species. This relationship h as been used to support identification of masses measured by the PTR-MS; as certain the consistency and quality of hydrocarbon measurement data; and to provide information concerning sinks of important trace species. A selecti on of the data is used to indirectly determine an average HO concentration of 2.0 X 10(5) molecules cm(-3) along the back trajectory for air encounter ed during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia-Coope rative LBA Airborne Regional Experiment (LBA-CLAIRE) measurement campaign b etween 0-1 km over the tropical rain forest. The lower than expected HO con centration derived could have been caused by significant atmospheric or oce anic photochemical production of acetone and MEK along the back trajectory.