Biogenic volatile organic compounds in the ambient air and plant emissions of a Tasmanian native forest, and the relationship between emission rates and essential oil content

Abstract

The biogenic volatile organic compounds (VOCs) in the ambient air of the Hobart Air Shed and in the emissions from selected Tasmanian native trees and understorey shrubs were measured. The emission rates were then related to the plants' essential oils content, which had been extracted by hydro-distillation. The VOCs in the ambient air of native forests have not previously been studied in Australia. This study used multi-adsorbent cartridge adsorption/thermal desorption and Gas Chromatography-Mass Spectrometry. The type, quantity, source and variation of the VOCs were investigated. The concentration of VOCs in the atmosphere surrounding vegetation in the Hobart Air Shed was determined. In all, 129 compounds of eight classes were detected. Ofthese, 11 compounds were National Pollutant Inventory substances and 32 were considered biogenic; however, this estimate is conservative. The concentration of total VOCs in these ambient air measurements varied between 4.43 x 10- 10 g L- 1 and 3.04 x 10-9 g L-1 depending on the site sampled and meteorological conditions. The relative standard deviation ranged between 3.50/0 and 51.8% in the dual air samples. The emission rates of VOCs were determined for 14 plant species within the Hobart Air Shed, using an enclosure bottle technique. In all, 284 compounds of 10 classes were detected. Emission rates varied between 1.98 x 10-8 and 5.43 x 10-6 g g-l (wet weight) h-1 depending on the species sampled and prevailing conditions. The relative standard deviation was estimated to be 31.1 %. The VOC emission rate for the entire eucalypt forest in Tasmania was estimated as 8200 kg h-1 and for the Hobart Air Shed 59 kg h-1. The error could be as large as a factor of three. The essential oil compositions of the species examined were identified. Linear relationships between VOC oil concentration and emission rates were found in 10 of the 13 analyses.