A SPATIALLY AND TEMPORALLY RESOLVED BIOGENIC HYDROCARBON EMISSIONS INVENTORY FOR THE CALIFORNIA SOUTH COAST AIR BASIN

Spatially and temporally resolved inventories for green leaf biomass a nd biogenic hydrocarbon emissions were developed for the California So uth Coast Air Basin (SoCAB) using a geographic information system (GIS ) and digitized land-use data based on low altitude aerial imagery. Ur ban, agricultural, and natural land-use distributions in the SoCAB wer e combined with biomass factors for each land-use category to produce a spatially resolved biomass inventory. As of 1990, about 80% of the a pproximately 6 x 10(6) metric tons of green leaf biomass was concentra ted primarily in the forested mountains on the northern and eastern bo undaries of the SoCAB. A biogenic hydrocarbon emissions inventory was developed by combining the biomass inventory with hourly emission rate s for 278 tree, shrub, and ground cover species identified in the stud y area. Correcting for environmental factors, including light intensit y, canopy shading, and temperature (from data for the period 9/87-6/92 ), combined isoprene and monoterpene emissions were estimated to be ap proximately 125-140 tons d(-1) (td(-1)) for an average summer day, 180 -200 td(-1) for an average high ozone-episode day, and approximately 4 0 td(-1) for an average winter day. The ratio of monoterpene to isopre ne emission inventories ranged between approximately 1 and 2 for the s ummer and winter, respectively. Isoprene emissions were highest in the mountains and certain urbanized portions of the SoCAB whereas monoter pene emissions were highest in the mountains and the sagebrush/chaparr al-dominated portions of the study area. On a mass basis, the biogenic hydrocarbon emissions inventory for the SoCAB obtained in this study represents approximately 10% of the anthropogenic VOC emissions in the Basin on a summer day. (C) 1997. Published by Elsevier Science Ltd.