Novel optical absorption approach for black carbon (BC) measurement in snow


Snow is potentially an excellent archive of aerosol deposition history to the polar regions of the world. Black carbon (BC) is an useful tracer of combustion processes and is likely to be relatively stable in snow for periods of time relevant for the reconstruction of climate and atmospheric aerosol histories. The BC content of snow may also influence albedo. However, levels of BC (0.1-4 micrograms per kilogram) in pristine snow are very low and measurements quite challenging. Artifacts (e.g., filter sorption and colloid passage) in methods that are currently being applied may result in significant biases. To overcome these limitations we have developed a direct optical method for BC measurement in melted snow. We're applying long-path (1 meter) optical cells and low-noise spectrophotometry to capture the absorption spectrum of suspended BC. After correction for absorption by non-BC components and dissolved species, one can isolate the BC signal. Calibrations with a variety of BC-containing standards are linear and reproducible and detection limits are adequate for quantifying trace levels of BC in snow.