Characteristics of fresh and aged carbonaceous aerosol from anthropogenic combustion sources

Abstract: Emissions from anthropogenic combustion sources, such as light duty vehicles and small scale biomass combustion, contribute significantly to ambient aerosol particle concentrations both on local and global scales. These emissions have controlling impacts on public health and global climate. The overall aim of this thesis was to investigate how atmospheric transformation and combustion conditions affect the health and climate relevant characteristics of anthropogenic combustion aerosol. The formation of secondary organic aerosol (SOA) from photo-oxidized gasoline vehicle exhaust was studied in a smog chamber. The physical and chemical properties of particulate emissions from small scale biomass combustion were investigated as a function of burn rate with on-line instrumentation including differential mobility analyzer-aerosol particle mass analysis (DMA-APM) and aerosol mass spectrometry (AMS). Samples of fresh and aged biomass combustion aerosol were collected to investigate the toxicological properties. Finally, the mass-mobility relationship and mixing state of urban aerosol were investigated with the DMA-APM technique. SOA production clearly dominated over primary organic emissions for gasoline vehicle exhaust, opposite to diesel exhaust. Up to 60% of the SOA formed from gasoline vehicle exhaust originated from traditional light aromatic SOA precursors, significantly higher than previous data for diesel exhaust. Particulate phase polycyclic aromatic hydrocarbons (PAHs) were quantified with high time resolution during different phases of the combustion cycle. PAH emissions were a factor seven higher for high burn rate compared to nominal operation of the wood stove. The majority of PAHs was emitted during the intermediate (flaming) phase of the combustion. Three main types of biomass combustion particles were found: spherical organic aerosol, soot agglomerates and compact inorganic ash particles. The combustion conditions affected the mass mobility relationship of the aerosol from full combustion cycles. Effects on cell viability were strongest for less efficient combustion (high PAHs and OA fraction). The genotoxic response increased upon dark aging with ozone, possibly due to PAH degradation products. The particles observed during the urban campaign could be divided into two groups according to their mass-mobility relationship, soot (less compact) and long-range transport particles (more compact). The long-range transport particles were to a higher extent present during days of polluted easterly winds. The soot particles in urban air had similar properties as soot particles emitted from diesel engines in laboratory studies. The results presented in this thesis show that the physical, chemical and toxicological properties of carbonaceous aerosol from combustion are affected by source, combustion conditions and atmospheric aging. This needs to be taken into account when assessing health and climate effects of aerosol particles.