Source apportionment of carbonaceous aerosol - Measurement and model evaluation

Sammanfattning: Aerosol particles are found in the whole troposphere. Research regarding these particles has gained increased attention because of the effect the particles have on both health and climate. In the atmosphere, aerosol particles scatter incoming solar radiation and this has a cooling effect on the Earth’s climate. But there are particles, especially those containing soot, which can absorb sun light and therefore having a heating effect on the Earth’s climate. Soot and other carbonaceous particles are problematic in atmospheric models. They originate from several sources and their emission factors are uncertain. Model parameterisations and emission inventories for carbonaceous aerosol have recently been improved in the EMEP model. To evaluate the changes to the atmospheric model and its input, the model results must be compared with measurements. Measurements of carbonaceous aerosol and their sources are therefore important to improve the models and to be able to accurately determine how atmospheric aerosol concentrations would be influenced by future changes of the emissions. In this thesis, radiocarbon, OC/EC and organic tracers was used as input in to a receptor model to determine the sources to carbonaceous aerosols. The result was subsequently used to evaluate simulations from the EMEP model. Radiocarbon is, as a radioactive carbon isotope, depleted in fossil fuels and therefore a good tracer for modern sources of carbonaceous particles such as biomass burning and the biota. The carbon mass required for radiocarbon analysis has within the frame of this work been lowered to 11 µg. This is an important step to be able to measure radiocarbon in aerosol samples that contain low amounts of carbon. Using tracers and OC/EC, I have found that carbonaceous particles in Southern Sweden originate from mainly biogenic sources in the summer and mainly combustion of fossil fuels and biomass burning in the winter. Model comparison showed that the model could reproduce carbonaceous aerosol concentrations fairly well although not reproduce the sources’ individual contributions. However, a newly developed emission inventory for residential wood combustion improved the model’s results compared to the measurements. A similar method that was used to determine the sources of atmospheric particles was used to determine to what extent diesel particles originated from the fuel and the lubrication oil. The soot (EC) was mainly formed from the fuel whereas the oil contributed to hydrocarbons in the exhaust. A method comparison showed that the method usually used by the engine manufactures will underestimate the influence of the lubrication oil.