Spatial and temporal variations in biogenic volatile organic compound emissions for Africa south of the equator

Abstract

Improved vegetation distribution and emission data for Africa south of the equator were developed for the Southern African Regional Science Initiative (SAFARI 2000) and were combined with biogenic volatile organic compound (BVOC) emission measurements to estimate BVOC emissions for the southern Africa region. The BVOCs are estimated to total 80 Tg C yr-1 for the region, with isoprene and monoterpenes contributing 56 and 7 Tg C yr-1, respectively. The large uncertainties, particularly in terms of basal emission capacity assignment, associated with these outputs are discussed. Woodlands are predicted to be the dominant vegetation type, covering 23% of southern Africa, and are the largest annual source of isoprene (20 Tg C), monoterpenes (3 Tg C), and other VOCs (4 Tg C). Mopane savannas and woodlands are predicted to contribute over 75% of all monoterpenes, primarily from light-dependent emission processes. Rain forests cover only 3.5% of the total area but have high annual emission rates (9.8 g C m-2 yr-1). In the tropical regions with high rainfall, warm temperatures, and high plant productivity throughout the year, the seasonal variation in VOC emissions was small. In subtropical regions, dominated by highly seasonal savannas and grasslands, large variations were predicted, with emissions declining by up to 85% during dry winter periods (June-August) due to low leaf area index after leaf drop.