A national inventory of biogenic hydrocarbon emissions

Abstract

Emission rate vs temperature algorithms for different vegetation types, ind more than half of these emissions occur in the summer, and approximately halfarise in the SE and SW U.S. Total emission rates ofisoprene from deciduous forest and a-pincne from deciduous and coniferous forests are 4.9 and 6.6 Mt annually. Emissions from agricultural cropscontribute less than 3 % of'the annual total. The average flux of biogcnic NMHC in the U.S. is estimated to be 450 pg mm2 h- ' which is 20 times less than reported emissions of anthropogenic NMHC averaged over urban land areas in the US. Geochemical NMHCemissions from hydrocarbon rich soils in the U.S. are estimated to be negligible compared to vegetative sources. The uncertainty in the inventory is estimated IO be on the order of a factor of three. Key word index: Biogenic, hydrocarbons. isoprene, a-pinene, emission inventory, natural sources, vegetation. Estimates of natural hydrocarbon (HC) emissions from vegetation have been of interest for more than a decade. The reasons for this interest include concern for the role of natural HCs in photochemical oxidant formation, uncertainty in the global carbon cycle, and recent r~ognition of significant contributions of or- ganic acids to acidic deposition in rural and urban areas, In response to these questions about the emis- sions of natural HCs, a number of extensive, but localized studies of biogenic NC emissions rates have been conducted, Zimmerman (1979a, b) developed a vegetation enclosure procedure and made more than 600 measurements of biogenic HC emissions in Tampa Bay, FL and Houston, TX. Tkis data base covers 69 specific types of vegetation in 10 broad categories. Winer et ol. (1983) reported a similar detailed investi- gation of natural emissions in the Los Angeles basin. Vegetative enclosure samples were collected from 60 species in 5 categories. Other HC emissions data have been described by Lamb et ai. (198s) for trees and crops in Pennsylvania and Georgia and for Pse~d~zs~gff d~~glasii (Rouglas fir) in Washington state. Emission rates from Quercuf garryunu (Oregon white oak) have also been recently reported (Lamb er al., 1986). In these latter studies, emission measure- ments obtained with an enclosure technique were in reasonable agreement with results from a micro- meteorological method and with an atmospheric tracer approach. Additional estimates of HC emissions from trees have been reported by Knoerr and Mowry