Estimates of mass absorption cross sections of black carbon for filter-based absorption photometers in the Arctic

• Published in: Atmospheric Measurement Techniques
• Main Authors: Ohata, Sho, Mori, Tatsuhiro, Kondo, Yutaka, Sharma, Sangeeta, Hyvärinen, Antti, Andrews, Elisabeth, Tunved, Peter, Asmi, Eija, Backman, John, Servomaa, Henri, Veber, Daniel, Eleftheriadis, Konstantinos, Vratolis, Stergios, Krejci, Radovan, Zieger, Paul, Koike, Makoto, Kanaya, Yugo, Yoshida, Atsushi, Moteki, Nobuhiro, Zhao, Yongjing, Tobo, Yutaka, Matsushita, Junji, Oshima, Naga
• Format: Text
• Language: English
• Published: 2021
• Subjects: Arctic; Canada; Ny-Ålesund; Pallastunturi; Svalbard; Barrow; black carbon; Ny Ålesund; Alaska
• Online Access: https://doi.org/10.5194/amt-14-6723-2021; https://amt.copernicus.org/articles/14/6723/2021/

Long-term measurements of atmospheric mass concentrations of black carbon (BC) are needed to investigate changes in its emission, transport, and deposition. However, depending on instrumentation, parameters related to BC such as aerosol absorption coefficient ( b abs ) have been measured instead. Most ground-based measurements of b abs in the Arctic have been made by filter-based absorption photometers, including particle soot absorption photometers (PSAPs), continuous light absorption photometers (CLAPs), Aethalometers, and multi-angle absorption photometers (MAAPs). The measured b abs can be converted to mass concentrations of BC ( M BC ) by assuming the value of the mass absorption cross section (MAC; M BC = <math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>b</mi><mi mathvariant="normal">abs</mi></msub><mo>/</mo></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="93c2a2385251a0658a2cfb15159de417"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6723-2021-ie00001.svg" width="29pt" height="14pt" src="amt-14-6723-2021-ie00001.png"/></svg:svg> MAC). However, the accuracy of conversion of b abs to M BC has not been adequately assessed. Here, we introduce a systematic method for deriving MAC values from b abs measured by these instruments and independently measured M BC . In this method, M BC was measured with a filter-based absorption photometer with a heated inlet (COSMOS). COSMOS-derived M BC ( M BC (COSMOS)) is traceable to a rigorously calibrated single particle soot photometer (SP2), and the absolute accuracy of M BC (COSMOS) has been demonstrated previously to be about 15 % in Asia and the Arctic. The necessary conditions for application of this method are a high correlation of the measured b abs with independently measured M BC and long-term stability of the regression slope, which is denoted as MAC cor (MAC derived from the correlation). In general, b abs – M BC (COSMOS) correlations were high ( r 2 = 0.76–0.95 for hourly data) at Alert in Canada, Ny-Ålesund in Svalbard, Barrow (NOAA Barrow Observatory) in Alaska, Pallastunturi in Finland, and Fukue in Japan and stable for up to 10 years. We successfully estimated MAC cor values (10.8–15.1 m 2 g −1 at a wavelength of 550 nm for hourly data) for these instruments, and these MAC cor values can be used to obtain error-constrained estimates of M BC from b abs measured at these sites even in the past, when COSMOS measurements were not made. Because the absolute values of M BC at these Arctic sites estimated by this method are consistent with each other, they are applicable to the study of spatial and temporal variation in M BC in the Arctic and to evaluation of the performance of numerical model calculations.