Abstract
Abstract. Biogenic volatile organic compounds (BVOC) produced by plants are known to have an important role in atmospheric chemistry. However, our knowledge of the range of BVOCs produced by different plant processes is still expanding, and there remain poorly understood categories of BVOCs. In this study, emissions of a novel class of BVOC emissions were investigated in a desert region. Our study considered 8 species of common desert plants: blackbrush (Coleogyne ramosissima), desert willow (Chilopsis linearis), mesquite (Prosopis glandulosa), mondel pine (Pinus eldarica), pinyon pine (Pinus monophylla), cottonwood (Populus deltoides), saguaro cactus (Carnegiea gigantea) and yucca (Yucca baccata). The measurements focused on BVOCs with relatively high molecular weight (>C15) and/or an oxygenated functional group. Significantly high emission rates of two salicylic esters were found for blackbrush, desert willow and mesquite with emission rates of 3.1, 1.0 and 4.8μgC dwg−1 h−1, respectively (dwg; dry weight of the leaves in gram). The salicylic esters were identified as 2-ethylhexenyl salicylate (2-EHS) and 3,3,5-trimethylcyclohexenyl salicylate (homosalate) and are known as effective ultraviolet (UV) absorbers. We propose that the plants derive a protective benefit against UV radiation from the salicylic esters and that the emission process is driven by the physical evaporation of the salicylic esters due to the high ambient temperatures. In addition, the salicylic esters are predicted to be an effective precursor of secondary organic aerosol (SOA) because they probably produce oxidation products that can condense onto the aerosol phase. We estimated the contribution of the sunscreen esters themselves and their oxidation products on the SOA formation for the Las Vegas area using a BVOC emission model. The contribution was estimated to reach 50% of the biogenic terpenoid emission in the landscapes dominated by desert willow and mesquite and 13% in the Las Vegas area. The contributions to biogenic SOA are likely to be higher due to the potentially high SOA yields of these compounds.
Highlights
IntroductionAerosol particles have a significant role for regional air quality and global climate change
Aerosol particles have a significant role for regional air quality and global climate change. In addition to their direct release into the atmosphere, aerosol can be formed by condensation of oxidation products of the atmospheric volatile organic compounds (VOCs) and is classified as secondary organic aerosol (SOA)
Two salicylic esters, which have the capacity to absorb UV radiation, have been identified as being significant emissions from plants living in a desert environment
Summary
Aerosol particles have a significant role for regional air quality and global climate change. Oxidation of monoterpenes led to SOA formation in a forest (Kavouras et al, 1999), and the oxidation products of isoprene contribute to the aerosol fraction (Matsunaga et al, 2003; Claeys et al, 2004; Matsunaga et al, 2005; van Donkelaar et al, 2007) Because of both SOA formation and gas phase photochemistry, BVOC emissions impact both regional air quality and the global climate. There are potentially many other BVOCs with high molecular weights that could be involved in SOA production; the esters 2-ethylhexenyl salicylate (2-EHS) and 3,3,5trimethylcyclohexenyl salicylate (homosalate) are two candidates These compounds are used as an active ingredient in commercial sunscreen products due to their UV absorption. These sunscreen esters represent a previously unknown source of SOA, and here we report for the first time the emission rates of the sunscreen esters from desert plants and a model estimate of the potential contribution of these esters to SOA production
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