Emission of sunscreen salicylic esters from desert vegetation and their contribution to aerosol formation

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 4.8?gC dwg?? h??, 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.