Emissions, Properties and Mixing State of Aerosols in a Range of Combustion Sources

Abstract

Atmospheric aerosols are ubiquitous in the atmosphere and have an impact on human health and atmospheric energy balance. Black carbon (BC) is the highly light-absorbing aerosol that affects climate warming by absorbing solar radiation, which is mainly produced by incomplete combustion of carbonaceous matter, including mobile sources, solid fuel burning and open biomass burning. The BC from solid fuel burning has been paid increased attention due to its strong emission at highly populated region, causing both climatic and health effect. Due to the changes in energy sources, biomass burning emissions have been globally identified to be a major source of the atmospheric aerosols. However, because of the complexity to characterise the emissions of biomass burning and the limitation of the previous instrumentation, the uncertainties of the BC properties and source apportionment for solid fuel burning still exist. This project provides the insights on investigating a variety of BC sources by three experiments. First, comparisons were made between source apportionment techniques to investigate the causes of the difference between different source apportionment techniques, using the data from a comprehensive suite of aerosol measurements and the outputs from various source apportionment studies obtained from the cooperated groups of the Clean Air for London (ClearfLo) project. Data from a single particle soot photometer (SP2), Aethalometer, the outputs of positive matrix factorisation (PMF) of organic aerosol mass spectra measured by a high-resolution aerosol mass spectrometer (HR-AMS) and chemical mass balance (CMB) were used in this study. The results presented here indicated that oxygenated organic aerosols (OOA) and the assumption of absorption Angstrom exponent (αwb) for wood burning have an effect on Aethalometer model, estimating the contribution of the biomass burning emissions to BC. In addition, it was found that the estimate of the carbonaceous matter contributed by wood burning derived by Aethalometer model in the previous studies were likely to be overestimated due to the attribution of the non-biomass burning organic matter to the biomass burning emissions. Second, a cruise campaign was carried out along the Yangtze River (YR), where one of the most polluted regions in China. The first time continuous measurements of BC and gaseous pollutants over YR on the regional scale indicated that the shipping emissions significantly contributed to air pollution during the highly polluted periods. BC with smaller mass median core diameter (MMD) of 120-180nm was found to be largely produced by the local sources, whereas a larger MMD of ~200nm was found for mixed sources from the regional transport. The consistency between the PM2.5 from the measurements on the river and the official monitoring sites in the coastal cities supported the inference that the YR basin was strongly affected by the regional pollution. Finally, laboratory experiments were conducted to characterise the solid fuel combustion emissions at source, using three commercial cookstoves with various solid fuels, which have been widely used in developing countries. The results provided a useful insight into interactions between BC and OM, which were parameterised according to modified combustion efficiency. In addition, the finding of the relationship between the OM fraction in PM1 and mixing state of BC can aid in assessment of the absorption enhancement of BC in models, where the BC source profile of solid fuel combustion emissions is not available. In summary, these findings provide an in-depth understanding of BC emissions from a variety of sources in real world, which can underpin either the future research or the mitigation strategies.

Date of Award	1 Aug 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	James Allan (Supervisor) & Hugh Coe (Supervisor)