The distribution of aerosol and trace gases in the lower troposphere over South Africa
Date
2016
Authors
Burger, Roelof Petrus
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Abstract
Numerous studies on the sources, transport and fates of criteria air pollutants and greenhouse
gases have been done in southern Africa. However, debate on the priority pollutants and areas
of concern continue despite a growing national air quality monitoring network. This study
attempts a novel approach to characterise sources and ambient air quality over major industrial
and urban areas using a single suite of instrumentation to provide information to improve
management of air quality. Over 200 hours of data were collected from an airborne platform.
Another 5 ground-based campaigns characterised sources and areas out of reach of the aircraft.
The central aim of this study is to prioritise sources and areas of concern with regards to air
quality management, using a mobile platform. This complements other modelling and spatial
assessments and provides in situ validation for many contemporary debates. The specific aims
were to characterise major anthropogenic sources; estimate the state of air quality; investigate
the vertical distribution of pollutants; and prioritise sources and areas of concern for effective
air quality management in South Africa.
The research has delivered many original contributions to the body of knowledge of air quality
over South Africa. These findings can be divided into spatial and temporal relationships
between sources and receptors, characterising source contributions and understanding the contribution
of atmospheric emissions. High resolution measurements show that spatial scales of
prominent atmospheric plumes are much smaller than current remote sensing estimates.This
underscores the difficulty of accurately assessing environments with diverse, clustered sources
and complex meteorology through modelling studies and satellite based remote sensing.
The current conceptual model of absolute stable layers is biased because of limited data availability
where a limited number of levels are reported. At least 60 levels should be reported
in soundings to study absolutely stable layers. The inclusion of the standard reporting levels,
(850 hPa, 700 hPa, 500 hPa and 300 hPa), further biases the detection of atmospheric stable
layers. The number of observed persistent levels change in number and character when these
are omitted from the analysis. Numerous vertical profiles further show that the thermodynamic
model of stability as the main driver of stratification is oversimplified, especially close
to source regions where different pollutants are observed to peak at different levels unrelated
to absolutely stable layers. This suggests that the original buoyancy which is governed by
the release temperature, exit velocity and height are important drivers for the stratification of
pollutants.
The overall conclusion is made that a small team with a set of regular instrumentation can
prioritise pollutants and areas of concern on a national scale. This method could be valuable
for countries with limited resources and infrastructures and could be used in combination with
modelling and satellite based remote sensing to assess priorities. The ability to obtain in situ
data of a large number of variables over vast areas in a short time may offsets the caveats
associated with mobile measurements and a limited sample volume.
Description
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy.
September 2016.
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Citation
Burger, Roelof Petrus (2016) The distribution of aerosol and trace gases in the lower troposphere over South Africa, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21740>