Abstract
A three-part study was conducted to quantify the impact of landscaped vegetation on air quality in a rapidly expanding urban area in the arid southeastern United States. The study combines in situ, plant-level measurements, a spatial emissions inventory, and a photochemical box model. Maximum plant-level basal emission rates were moderate: 18.1 μgC gdw −1 h −1 ( Washingtonia spp., palms) for isoprene and 9.56 μgC gdw −1 h −1 ( Fraxinus velutina, Arizona ash) for monoterpenes. Sesquiterpene emission rates were low for plant species selected in this study, with no measurement exceeding 0.1 μgC gdw −1 h −1. The high ambient temperatures combined with moderate plant-level emission factors resulted in landscape emission factors that were low (250–640 μgC m −2 h −1) compared to more mesic environments (e.g., the southeastern United States). The Regional Atmospheric Chemistry Mechanism (RACM) was modified to include a new reaction pathway for ocimene. Using measured concentrations of anthropogenic hydrocarbons and other reactive air pollutants (NO x , ozone), the box model employing the RACM mechanism revealed that these modest emissions could have a significant impact on air quality. For a suburban location that was downwind of the urban core (high NO x ; low anthropogenic hydrocarbons), biogenic terpenes increased time-dependent ozone production rates by a factor of 50. Our study demonstrates that low-biomass density landscapes emit sufficient biogenic terpenes to have a significant impact on regional air quality.
Highlights
As the population of southern Nevada has grown, the increase in vehicle use has caused exceedances of US federal government air quality standards
Very little is currently known about biogenic volatile organic compounds (BVOCs) emissions from native desert and forest plants and non-native plants used in landscaping and the concomitant effects on air quality
Our leaf-level dataset is beneficial in that novel isoprene and MT emission factors have been obtained that are specific to the climate of Las Vegas, and SQT emissions have been measured from these plants for the first time
Summary
As the population of southern Nevada has grown, the increase in vehicle use has caused exceedances of US federal government air quality standards. Efforts to control air pollution sources require modeling both anthropogenic and biogenic sources of chemical species involved in ozone formation. Very little is currently known about biogenic volatile organic compounds (BVOCs) emissions from native desert and forest plants and non-native plants used in landscaping and the concomitant effects on air quality. The majority of BVOCs emitted by vegetation make up the volatile component of a larger group of plant-produced chemicals known as terpenoids. These BVOC terpenoids can be classified into four categories: isoprene, monoterpenes (MTs), sesquiterpenes (SQTs), and oxygenated hydrocarbons (Guenther et al, 1995; Helmig et al, 1999; Fall, 2003). Recent, indirect evidence suggests that reactive terpenoids are emitted in much higher amounts than MTs (see further discussion below)
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