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 and biogenic hydrocarbon emissions were developed for the California South Coast Air Basin (SoCAB) using a geographic information system (GIS) and digitized land-use data based on low altitude aerial imagery. Urban, agricultural, and natural land-use distributions in the SoCAB were combined with biomass factors for each land-use category to produce a spatially resolved biomass inventory. As of 1990, about 80% of the approximately 6 × 106 metric tons of green leaf biomass was concentrated primarily in the forested mountains on the northern and eastern boundaries of the SoCAB. A biogenic hydrocarbon emissions inventory was developed by combining the biomass inventory with hourly emission rates for 278 tree, shrub, and ground cover species identified in the study area. Correcting for environmental factors, including light intensity, canopy shading, and temperature (from data for the period 9/87-6/92), combined isoprene and monoterpene emissions were estimated to be approximately 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 40 td−1 for an average winter day. The ratio of monoterpene to isoprene emission inventories ranged between approximately 1 and 2 for the summer and winter, respectively. Isoprene emissions were highest in the mountains and certain urbanized portions of the SoCAB whereas monoterpene emissions were highest in the mountains and the sagebrush/chaparral-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.