Mechanistic aspects of carbonaceous aerosol toxicity were examined with respect to the ability of particles to catalyse reactive oxygen species-generating redox cycling reactions.
To investigate the role of secondary organic material, we examined two systems. In the first, two-stroke engine exhaust particles were found to increase their ability to catalyse redox cycling in the presence of a reducing agent, dithiothreitol (DTT), when the exhaust was exposed to ozone. This occurred through deposition of redox-active secondary organic aerosol (SOA) onto the particle that was ten times more redox active per microgram than the primary engine particle.
In the second system, naphthalene SOA formed highly redox active particles. Activity was strongly correlated to the amount of the 1,4- and 1,2-naphthoquinone measured in the particle phase. However, these species and the newly quantified naphthalene oxidation product 5-hydroxy-1,4-naphthoquinone accounted for only 30% of the observed DTT decay from the particles. Gas-particle partitioning coefficients suggest 1,4- and 1,2-naphthoquinone are not strong contributors to ambient particle redox activity at 25°C. However, a large number of redox active species are unidentified. Some of these may be highly oxidised products of sufficiently low vapour pressure to be atmospherically relevant.
DTT activity of diesel particles was found to be high per unit mass. The activity was found to be associated with the insoluble fraction as filtration of the particles nearly eliminated DTT decay. Neither methanol nor dichloromethane extracts of diesel particles exhibited redox activity, indicating that the redox active species are associated with the black carbon portion of the particles.
Examination of particle concentration techniques found that use of water condensation to grow and concentrate particles introduced a large organic artefact to the particles. Experiments with concentrated inorganic particles suggest that the source of this artefact is from irreversible uptake of water-soluble volatile organic compounds.
Overall, carbonaceous redox active species can be thought of as a continuum from small, water-soluble species to redox active functionalities on elemental carbon backbones. In addition to clearly defined, quantifiable species, future research may need to consider examining broader chemical classes or redox-active chemical functionalities to overcome the inherent complexity of these constituents.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/35905 |
| Date | 09 August 2013 |
| Creators | McWhinney, Robert |
| Contributors | Abbatt, Jonathan P. D. |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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