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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
19 May 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
An Evaluation of three methods for measuring black carbon at Alert, Canada
Sangeeta Sharma1, W. Richard Leaitch1, Lin Huang1, Dan Veber1, Felicia Kolonjari1, Wendy Zhang1, Sarah J. Hanna2, Allan K. Bertram2, and John A. Ogren3 1Climate Chemistry Measurements and Research, Climate Research Division, Atmospheric Science and Technology Directorate, Environment and Climate Change Canada, 4905 Dufferin Street, Toronto, ON M3H 5T4, Canada
2Department of Chemistry, University of British Columbia, Vancouver BC, Canada
3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309 USA and 4NOAA/ESRL Global Monitoring Division, 325 Broadway R/GMD, Boulder, CO 80305 USA
Abstract. Absorption of sunlight by black carbon (BC) warms the atmosphere, which may be important for Arctic climate. The measurement of BC is complicated by the lack of a simple definition of BC and the absence of techniques that are uniquely sensitive to BC (e.g. Petzold et al., 2013). At the Global Atmosphere Watch baseline observatory at Alert, Nunavut (82.5 °N), BC mass is estimated in three ways, none of which fully represent BC: conversion of light absorption measured with an Aethalometer to give equivalent black carbon (EBC), thermal desorption of elemental carbon from weekly-integrated filter samples to give elemental carbon (EC), and measurement of incandescence from the refractory black carbon (rBC) component of individual particles using a Single Particle Soot Photometer (SP2). Based on measurements between March 2011 and December 2013, EBC and EC are 2.7 and 3.1 times higher than rBC respectively. The EBC and EC measurements are influenced by factors other than just BC, and higher estimates of BC are expected from these techniques. Some bias in the rBC measurement may result from calibration uncertainties that is difficult to estimate here. Considering a number of factors, our best estimate of BC mass at Alert, which may be useful for evaluation of chemical transport models, is an average of the rBC and EC measurements with a range bounded by the rBC and EC combined with the respective measurement uncertainties. Winter, spring, summer, and fall averaged (± atmospheric variability) estimates of BC mass at Alert for this study period are 49 ± 28 ng m−3, 30 ± 26 ng m−3, 22 ± 13 ng m−3, and 29 ± 9 ng m−3, respectively. Average coating thicknesses estimated from the SP2 are 25 % to 40 % of the 160–180 nm diameter rBC core sizes. For particles of approximately 200–400 nm optical diameter, the fraction containing rBC cores is estimated to be between 10 % and 16 %, but the possibility of smaller undetectable rBC cores in some of the particles cannot be excluded. Mass absorption coefficients (MAC) ± uncertainty at 550 nm wavelength, calculated from light absorption measurements divided by the best estimates of BC mass concentrations, are 8 ± 4, 8 ± 4, 5 ± 2.5 and 9 ± 4.5 m2 g−1, for winter, spring, summer and fall respectively. Adjusted to better estimate absorption by BC only, the winter and spring values of MAC are 7.6 ± 3.8 and 7.7 ± 3.8 m2 g−1. There is evidence that the MAC values increase with coating thickness.

Citation: Sharma, S., Leaitch, W. R., Huang, L., Veber, D., Kolonjari, F., Zhang, W., Hanna, S. J., Bertram, A. K., and Ogren, J. A.: An Evaluation of three methods for measuring black carbon at Alert, Canada, Atmos. Chem. Phys. Discuss.,, in review, 2017.
Sangeeta Sharma et al.
Sangeeta Sharma et al.
Sangeeta Sharma et al.


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Short summary
A new and unique data set on BC properties at the highest latitude observatory in the world, at Alert, Canada evaluates three techniques for estimating black carbon (BC) and gives seasonal best estimates of the BC mass concentrations and BC Mass absorption Coefficients (MAC) for 2.5 yrs of data. As a short-lived climate forcer, better estimates of the properties of BC are necessary to ensure accurate modelling of aerosol climate forcing of the Arctic atmosphere for mitigation purposes.
A new and unique data set on BC properties at the highest latitude observatory in the world, at...