M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / Biogenic volatile organic compounds (BVOCs), in the presence of nitrogen oxide gases
(NOx), play a role in the production of tropospheric ozone (O3) which is an effective
greenhouse gas and is hazardous to human health (Haagen-Smit, 1952, Chameides et al,
1988, Atkinson, 2000, Kanakidou et al, 2004). Isoprene is a single BVOC that accounts
for over 50% of all emitted BVOCs. Isoprene emissions are species specific and vary
according to temperature, light and leaf area index. Climate change studies predict that
the geographic distribution of species, temperature ranges, light intensity and leaf area
index will shift, thus altering future isoprene emissions.
Several attempts to model BVOC emissions have been undertaken in an effort to quantify
BVOC emission rates and the impact on ozone formation. The most widely used and
empirically tested emission algorithms to date were developed by Guenther et al (1993)
and are incorporated into the emission model Model of Emissions of Gases and Aerosols
from Nature (MEGAN). MEGAN is used in this study to model isoprene emission rates
over southern Africa under current and future climate conditions. Current and future
climate conditions are taken from the regional climate model, Conformal-Cubic
Atmospheric Model (C-CAM), which has been shown to simulate current climate well
for the region. Emissions were modelled for January and July only, to represent summer
and winter conditions.
January isoprene emission rates for the current climate range from 0 to 1.41 gm-2month-1
and total 0.938 Tg of isoprene for the study domain. The highest emission rates are
caused by combinations of driving variables which are: high temperature only; high
temperature and high leaf area index; high emission factor and high leaf area index.
Emission rates effectively shut down in July due to low temperatures and low leaf area
index. July emission rates range from 0 to 0.61 gm-2month-1 and total 0.208 Tg of
isoprene. Temperature is shown to cause the greatest variation in isoprene emission rates,
and thus future scenarios represent an increase in temperature only. The spatial
distribution of future emission rates does not shift when compared to current emission
rates, but does show an increase in magnitude. Future emission totals for January increase
iv
by 34% to 1.259 Tg of isoprene and the July emission total increases by 38% to 0.289 Tg
of isoprene.
Future emission rates responded to temperature as expected, increasing in magnitude, rate
of change and range of temperature over which the greatest rate of change occurs. Three
areas demonstrating the highest increase in emission rates and highest future emission
rates were identified. As temperature was the only variable altered in future scenarios,
these areas can be deemed as areas most sensitive to changes in temperature. These areas
are situated near the Angola-Namibia border, the Northern Interior of South Africa and
the low-lying areas of Mozambique.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/11356 |
| Date | 27 February 2012 |
| Creators | Weston, Michael John |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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