Chemical and source characterisation of ambient fine particles with off-line and on-line methods

Atmospheric aerosols have a significant effect on people and the environment. They cause adverse health effects especially for cardiorespiratory patients. Atmospheric aerosols also affect the Earth’s climate directly by scattering and absorbing solar radiation and indirectly by modifying amounts and properties of clouds. Reliable characterisation and quantification of airborne particles and their sources are essential for developing control strategies for atmospheric pollution and decreasing the uncertainties of estimating particles effects on climate change. Aerosols can be divided into fine and coarse particles based on their size. This thesis concentrated on fine particles, which are either directly emitted into the atmosphere (primary particles) or formed in the atmosphere through gas-to-particle conversion (secondary particles). The main sources of atmospheric fine particles are natural and anthropogenic combustion, industry and secondary aerosol formation (biogenic and anthropogenic). The overall objective of this thesis was to investigate the chemical composition of fine particles with different temporal and seasonal time-scales. For this purpose, a variety of different sampling techniques, off-line analytical methods and on-line instruments were used to characterise the main chemical species of fine particles in simultaneous and independent campaigns at several sites mainly in southern Finland but also in South Africa. More specific objectives were to investigate the dominant sources of particulate organic matter in the Helsinki area and chemically characterise the fine particles originating from biomass burning. Determining the effect of air mass origin on the chemical composition and concentration of fine particles was also one of the specific aims. In this thesis, it was found that the chemical composition of fine particles had strong spatial and temporal variation, although on average the mass concentrations of fine particles were quite similar between different sites. The main components in fine particulate matter in southern Finland was particulate organic matter (POM), followed by sulphate, whereas sulphate had the highest contribution to particulate mass in South Africa. Source apportionment analysis of POM revealed clear primary sources from traffic and from biomass burning. However, the secondary organic aerosol had the largest contribution of POM, even though the campaigns were conducted in specific environments such as residential areas where biomass combustion is commonly used or traffic environments. Occasionally, the contribution of biomass burning organic aerosol increased substantially as ambient air temperature decreased. Additionally, simultaneous measurements pointed out a high contribution of common regional or longrange transported sources over large areas of southern Finland. Similarly, the air mass passing over either clean or polluted areas showed a significant effect on the mass concentrations in Finland and South Africa. Publishing unit Finnish Meteorological Institute, Atmospheric Composition Research Classification (UDC)