Fine and Ultrafine Particles from Combustion Sources - Investigations with In-situ Techniques

Summary, in English

Fine airborne particles are associated with adverse health effects in the human population. The aim of this research was to develop and evaluate methods for in-situ characterisation of fine and ultrafine particles and to determine their deposition in the human airways. The aim was also to increase knowledge about health and environmentally relevant properties of aerosols from biomass combustion and selected indoor sources.



The methods include instrumental techniques such as Scanning Mobility Particle Sizer (SMPS), Electrical Low-Pressure Impactor (ELPI), Aerodynamic Particle Sizer (APS) and Tandem Differential Mobility Analysers (TDMA) based on volatility and hygroscopic growth. Filter samplers and impactors were used for collecting particles on substrates for subsequent chemical analysis. Emissions from local district heating plants (0.5-12 MW), based on moving grate combustion of woody fuels, were sampled with a dilution system and characterised. Particles from the indoor sources of cigarettes, incense and candles were examined in the laboratory by using an airtight 22 m3 stainless steel chamber. A set-up to determine respiratory deposition in humans was constructed. It was automatised and uses an electrical mobility spectrometer with an improved inversion algorithm to perform fast measurements of particles of different sizes in the inhaled and exhaled air. It was evaluated on human test-persons.



The investigated biomass combustion sources emit high concentrations of fine and ultrafine particles. The chemical composition is dominated by KCl and K2SO4; Zn, Cd and Pb were also quantified. Elemental carbon was identified in particles larger than 150 nm during periods of incomplete combustion. The particle concentration depends on the fuel ash content and the combustion efficiency. The aerosol is essentially internally mixed with hygroscopic growth factors significantly higher than reported for diesel exhaust and environmental tobacco smoke. The particles restructure from agglomerates to a more compact shape upon first exposure to moderately high relative humidity. This results in an increase in effective density and fractal dimension. Hygroscopic growth of these particles reduces the respiratory dose by a factor of 3-4 compared to hydrophobic particles of the same size. The biomass combustion particles mainly consist of soluble ash components and need to be treated differently in future health effect assessments compared to particles from incomplete combustion, e.g. from diesel engines, wood stoves and cigarette smoke.



Sidestream cigarette and incense smoke are well internally mixed aerosols dominated by organic compounds. Each particle consists of components with a relatively wide range in vapour pressure. The volatile fraction decreases at lower particle concentrations in the chamber and upon ageing, which is attributed to different degrees of evaporation from the particle to the gas phase. Four different particle types were identified in emissions from candles.



The feasibility of the ELPI and the APS to assess mass size distributions was investigated. It was found that the measurement quality is dependent on the size distribution of the aerosol.



The set-up for respiratory deposition has low inherent particle losses. Determinations of precision, accuracy and sensitivity show that it can be used for field measurements in typical urban and indoor environments.



Methods for characterisation of aerosols containing fine and ultrafine particles have been developed, evaluated and applied. The results can be used to improve exposure assessments in toxicological and epidemiological studies and for risk assessments.



Papers included in the thesis



I. Pagels J., Strand M., Rissler J., Szpila A., Gudmundsson A., Bohgard M., Lillieblad L., Sanati M. and Swietlicki E. (2003) Characteristics of Aerosol Particles Formed During Grate Combustion of Moist Forest Residue, Journal of Aerosol Science 34, 1043-1059



II. Wierzbicka A., Lillieblad L., Pagels J., Strand M., Gudmundsson A., Gharibi A., Swietlicki E., Sanati M. and Bohgard M. (2005) Particle Emissions from District Heating Units Operating on Three Commonly Used Biofuels, Atmospheric Environment 39, 139-150



III. Rissler J., Pagels J., Swietlicki E., Wierzbicka A., Strand M., Lillieblad L., Sanati M. and Bohgard M. (2005) Hygroscopic Behaviour of Aerosol Particles Emitted from Biomass Fired Grate Boilers, Submitted



IV. Pagels J., Gudmundsson A., Gustavsson E., Asking L. and Bohgard M. (2005) Evaluation of Aerodynamic Particle Sizer and Electrical Low-Pressure Impactor for Unimodal and Bimodal Mass-Weighted Size Distributions, Submitted



V. Pagels J., Löndahl J., Zhou J., Bohgard M. and Swietlicki E. (2005) A set-up for Field Studies of Respiratory Deposition in Humans, Manuscript