No abstract

As part of the Large Scale Biosphere-Atmosphere Experiment in Amazô nia (LBA), we have developed a bottom-up approach for estimating canopy-scale fluxes of isoprene. Estimating isoprene fluxes for a given forest ecosystem requires knowledge of foliar biomass, segregated by species, and the isoprene emission characteristics of the individual tree species comprising the forest. In this study, approximately 38% of 125 tree species examined at six sites in the Brazilian Amazon emitted isoprene. Given logistical difficulties and extremely high species diversity, it was possible to screen only a small percentage of tree species, and we propose a protocol for estimating the emission capacity of unmeasured taxa using a taxonomic approach, in which we assign to an unmeasured genus a value based on the percentage of genera within its plant family which have been shown to emit isoprene.Combining this information with data obtained from 14 tree censuses at four Neotropical forest sites, we have estimated the percentage of isoprene-emitting biomass at each site. The relative contribution of each genus of tree is estimated as the basal area of all trees of that genus divided by the total basal area of the plot. Using this technique, the percentage of isoprene-emitting biomass varied from 20% to 42% (mean 5 31%; SD 5 8%).Responses of isoprene emission to varying light and temperature, measured on a sunadapted leaf of mango (Mangifera indica L.), suggest that existing algorithms developed for temperate species are adequate for tropical species as well. Incorporating these algorithms, estimates of isoprene-emitting biomass, isoprene emission capacity, and site foliar biomass into a canopy flux model, canopy-scale fluxes of isoprene were predicted and compared with the above-canopy fluxes measured at two sites. Our bottom-up approach overestimates fluxes by about 50%, but variations in measured fluxes between the two sites are largely explained by observed variation in the amount of isopreneemitting biomass.

The occurrence of 2‐nitrofluoranthene and 2‐nitropyrene in particulate matter collected in urban, suburban, forest, and remote areas located in Europe, America, Asia, and Antarctica was investigated. The results obtained confirm the photochemical origin of these components by gas phase reactions with OH radicals and their ubiquitous occurrence in the troposphere. An important role in their formation and dispersion seems to be played by carbon particles.

According to recent assessments, tropical woodlands contribute about half of all global natural non-methane volatile organic compound (VOC) emissions. Large uncertainties exist especially about #uxes of compounds other than isoprene and monoterpenes. During the Large-Scale Biosphere/Atmosphere Experiment in Amazonia } Cooperative LBA Airborne Regional Experiment 1998 (LBA-CLAIRE-98) campaign, we measured the atmospheric mixing ratios of di!erent species of VOC at a ground station at Balbina, Amazonia. The station was located 100 km north of Manaus, SE of the Balbina reservoir, with 200}1000 km of pristine forest in the prevailing wind directions. Sampling methods included DNPH-coated cartridges for carbonyls and cartridges "lled with graphitic carbons of di!erent surface characteristics for other VOCs. The most prominent VOC species present in air were formaldehyde and isoprene, each up to several ppb. Concentrations of methylvinyl ketone as well as methacroleine, both oxidation products of isoprene, were relatively low, indicating a very low oxidation capacity in the lower atmospheric boundary layer, which is in agreement with a daily ozone maximum of (20 ppb. Total monoterpene concentration was below 1 ppb. We detected only very low amounts of VOC species, such as benzene, deriving exclusively from anthropogenic sources.

No abstract