An investigation of the rate of biogenic volatile organic carbon emissions from commercial crop and plantation species in the Mpumalanga Province

Abstract

Volatile Organic Carbons (VOCs) are extremely reactive compounds and play an important role in the ozone chemistry of the atmosphere. Biogenic Volatile Organic Compounds (BVOCs) are estimated to contribute ~1015 g C y-1 per year to the atmosphere which constitutes ~80 % of the chemically reactive VOCs added to the atmosphere each year. In the last decade considerable scientific effort has focused on quantifying biogenic emission rates in South Africa, mainly from indigenous savanna species. The Mpumalanga province occupies 6.7 % of the land area of South Africa. There is a high species diversity and variable land use which includes forestry, cropping agriculture, grazing and nature conservation. The aim of this study was to measure the emission rates of isoprene, β-pinene, α-pinene, limonene and linalool from five selected plant species. These plant species were Mangoes, Avocados and Bananas (subtropical crops) and Pines and Eucalyptus (exotic forestry species). The experimental work, which was all conducted in the field, was designed to demonstrate the effect of environmental conditions on emission rates, especially temperature and water availability. A rapid screening technique was carried out in the initial phase of the study and a more detailed leaf level study was carried out over the 2007-2008 growing season. Plantation species, emitted higher levels of BVOCs than crop species. Isoprene emission rates were similar for two functional groups of plants, however, selected monoterpene (β-pinene, α-pinene, limonene and linalool) emission rates were higher in the plantation. Isoprene emissions represented 41.6 % of the total emissions measured followed by monoterpenes: β-pinene 31.5 % and limonene, α-pinene and linalool the remaining 26.8 % of total emissions. Emissions increased immediately after the onset of the spring rains and responded to the annual cycle with increasing values in the summer months and rapid decreases in winter. The measured emission rates were higher from the selected species than those published from temperate regions of the world. The data from this study can be used in the future to develop a regional emission budget.