Abstract
Atmospheric concentrations of ozone and other air pollutants, in some regions, are sensitive to surface fluxes of volatile organic compounds (VOCs). Plant foliage is the source of at least half of all VOC emissions in the United States and more than two-thirds of global VOC emissions. Observed spatial and seasonal variations in foliar VOC emissions range over several orders of magnitude. Land characteristics data are an important component of the modeling techniques used to estimate VOC emission rate variations due to seasonal and spatial changes in species composition, foliar density, and other factors. Model techniques and land characteristics databases are compared and evaluated in this paper. Significant differences in VOC fluxes are predicted depending on spatial resolution, procedures used to develop land characteristics databases, and foliar density models. Satellite and ground observations can be combined to generate the accurate estimates of the species composition and foliar density required for natural VOC emission models.
Highlights
The chemistry of the atmosphere is strongly influenced by ecological processes that control the emission of water and trace gases from plants. Went (1960) recognized that foliar emissions of volatile organic compounds (VOCs) could have a significant impact on tropospheric chemistry by influencing the processes that control the formation of atmospheric haze. Rasmussen (1972) made the first U.S estimate of isoprene and monoterpene emissions. lsoprene and monoterpenes are typically regarded as the predominant voes emitted by plants
The average moderate spatial resolution (MSR) estimate for the eight locations, is only 12% higher for isoprene and 5% lower for monoterpenes and the total range in estimates is similar. These results suggest that landscape heterogeneity can significantly influence predicted voe emissions at a particular location, but there is no apparent overall bias
The magnitude and distribution of natural VOC emission rate estimates are sensitive to land cover characteristics data
Summary
The chemistry of the atmosphere is strongly influenced by ecological processes that control the emission of water and trace gases from plants. Went (1960) recognized that foliar emissions of volatile organic compounds (VOCs) could have a significant impact on tropospheric chemistry by influencing the processes that control the formation of atmospheric haze. Rasmussen (1972) made the first U.S estimate of isoprene and monoterpene emissions. lsoprene and monoterpenes are typically regarded as the predominant voes emitted by plants. The Zimmerman database results in an average U.S monoterpene emission potential of 4.7 μg e.g-1·h-1 This is approximately a factor of 5 higher than the other estimates This is due to high estimates of monoterpene emission rates for individual plant species, as discussed by Guenther et al (1994), and due to the underestimation of total cropland area. Note: Isoprene and monoterpene emission potentials, e (mg C·m-2·h-1 at a temperature of 30°C and PAR of 1000 μmol photons·m-2·s- 1), are estimated as the mean of 400 individual l-km grids (high spatial resolution, HSR) or as the mean emission potential factor of the two most dominant landscapes in the 400 km region (moderate spatial resolution, MSR) using the LCC-AVHRR (Land Cover Characteristics-Advanced Very High Resqlution Radiometer) database. The Geoecology data underestimate the isoprene emission potential for one site by =50% by neglecting the presence of sweetgum trees
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