VERTICAL PROFILING AND DETERMINATION OF LANDSCAPE FLUXES OF BIOGENIC NONMETHANE HYDROCARBONS WITHIN THE PLANETARY BOUNDARY-LAYER IN THE PERUVIAN AMAZON

Vertical profiles of volatile organic compounds (VOCs) within the conv ective boundary layer (CBL) were measured at a tropical forest site in the Peruvian Amazon during July 1996 from a tethered balloon sampling platform. A profiling technique based on the collection of VOCs onto solid adsorbent cartridges was used to take samples at altitudes up to 1600 m above ground. VOC analysis was performed by thermal desorption with gas chromatographic separation and mass spectrometric and flame ionization detection. A total of 26 VOCs were structurally identified. VOCs were dominated by biogenic compounds. Highest concentrations wer e observed for isoprene, followed by alpha-pinene, p-cymene, and beta- pinene. Combined, all monoterpenes accounted for approximately 15-20% of the total carbon from biogenic VOCs (BVOCs). The isoprene oxidation products methacrolein (MAC), methylvinylketone (MVK), and 3-methylfur an were observed throughout the CBL. Besides the ubiquitous chlorofluo rocarbons, anthropogenic VOC concentrations were at the lower end of c oncentration ranges observed in rural air. From the vertical profiles, BVOC surface flux estimates were derived. Emission rates were estimat ed from five vertical profiles using the mixed-layer gradient and CBL budget methods. Emission estimates varied depending on method and choi ce of statistics, but were within 3000-8200 mu g compound m(-2) h(-1) for isoprene, 120-370 mu g m(-2) h(-1) for alpha-pinene, 40-75 mu g m( -2) h(-1) for beta-pinene, about 16 mu g m(-2) h(-1) for p-cymene, and 40-50 mu g m(-2) h(-1) for camphene. The changes in the ratios of MAC and MVK to isoprene with altitude were utilized to estimate the mixin g times between the surface layer, mixed layer and lower troposphere.