Aerosol particles are ubiquitous in the atmosphere and their properties impact on the atmospheric energy balance. They scatter and absorb incoming sunlight and can perturb cloud microphysical properties, which affects cloud lifetimes and albedo. Africa is one of the worldâs largest sources of aerosol due to both its large deserts and prolific biomass burning during the dry seasons. Nevertheless, the continent's atmosphere has, to date, been among the least studied in the world. The southern coast of West Africa is developing rapidly, with both population and anthropogenic emissions being predicted to increase substantially in coming years. It is therefore becoming ever more important to understand the characteristics of aerosols in this region, which will have consequences for issues as diverse as local health and global climate change. This project addresses this problem in two ways: first, laboratory experiments were carried out to characterise biomass burning aerosol at source. Biomass burning is one of the most poorly understood aerosol sources, but one of the most prevalent in tropical regions. Second, aircraft observations were made in southern West Africa during the Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) field campaign in summer 2016, to observe the broad-scale distribution of chemical and physical aerosol properties. Results were collected in-situ with Aerodyne Aerosol Mass Spectrometers (AMS) and other online aerosol instrumentation; they were considered alongside observations from DACCIWA ground sites and model results. Distinguishable chemical signatures were reliably observed during three phases of combustion events in the laboratory study. This gave insight into the mechanisms linking combustion phases and emissions. Airborne observations in southern West Africa revealed a remarkably consistent background of aged, accumulation mode aerosol present across the region in the boundary layer, including in the region upwind of the cities on the south coast. It was demonstrated that this likely originated from large-scale biomass burning in central and southern Africa, which had become entrained into the boundary layer above the Atlantic and transported north. A second result from the DACCIWA campaign showed that the hygroscopic growth of these particles, due to the high humidity in the region during June and July, more than doubled the mean dry aerosol optical depth. Taken together, these findings shed light on the substantial impacts that biomass burning aerosol, in particular, has on the atmosphere above southern West Africa.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:756850 |
| Date | January 2018 |
| Creators | Haslett, Sophie |
| Contributors | Allan, James ; Coe, Hugh |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/physical-and-chemical-properties-and-sources-of-aerosol-across-southern-west-africa-during-the-monsoon(fcfa2fe3-5e83-4d06-b2ce-0eb431369018).html |
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