Time-resolved measurements of black carbon light absorption enhancement in urban and near-urban locations of southern Ontario, Canada 1ASTB/STB Environment Canada, 335 River Road South, Ottawa, Ontario, K1V 0H3, Canada
20 Oct 2011
2ASTB/STB Environment Canada, 4905 Dufferin Street, Toronto, Ontario, M3H 5T4, Canada
3National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario, K1A 0R6, Canada
Received: 13 August 2010 – Published in Atmos. Chem. Phys. Discuss.: 24 August 2010 Abstract. In this study a photoacoustic spectrometer (PA), a laser-induced
incandescence instrument system (LII) and an Aerosol Mass Spectrometer were
operated in parallel for in-situ measurements of black carbon (BC) light absorption
enhancement. Results of a thermodenuder experiment using ambient particles
in Toronto are presented first to show that LII measurements of BC are not
influenced by the presence of non-refractory material thus providing true
atmospheric BC mass concentrations. In contrast, the PA response is enhanced
when the non-refractory material is internally mixed with the BC particles.
Through concurrent measurements using the LII and PA the specific absorption
cross-section (SAC) can be quantified with high time resolution (1 min).
Comparisons of ambient PA and LII measurements from four different locations
(suburban Toronto; a street canyon with diesel bus traffic in Ottawa;
adjacent to a commuter highway in Ottawa and; regional background air in and
around Windsor, Ontario), show that different impacts from emission sources
and/or atmospheric processes result in different particle light absorption
enhancements and hence variations in the SAC. The diversity of measurements
obtained, including those with the thermodenuder, demonstrated that it is
possible to identify measurements where the presence of externally-mixed
non-refractory particles obscures direct observation of the effect of
coating material on the SAC, thus allowing this effect to be measured with
more confidence. Depending upon the time and location of measurement (urban,
rural, close to and within a lake breeze frontal zone), 30 min average
SAC varies between 9 ± 2 and 43 ± 4 m2 g−1. Causes of this
variation, which were determined through the use of meteorological and
gaseous measurements (CO, SO2, O3), include the particle emission
source, airmass source region, the degree of atmospheric processing.
Observations from this study also show that the active surface area of the
BC aggregate, which is measured by the LII as the PPS, is an important
parameter for inferring the degree of particle collapse of a BC particle. In
addition, PPS could be a useful measurement for indicating the importance of
recently emitted BC (e.g. from gasoline or diesel engines) relative to the
total measured BC in the atmosphere.
Revised: 17 September 2011 – Accepted: 06 October 2011 – Published: 20 October 2011
Citation: Chan, T. W., Brook, J. R., Smallwood, G. J., and Lu, G.: Time-resolved measurements of black carbon light absorption enhancement in urban and near-urban locations of southern Ontario, Canada, Atmos. Chem. Phys., 11, 10407-10432, doi:10.5194/acp-11-10407-2011, 2011.