Evaluation of ground‐based black carbon measurements by filter‐based photometers at two Arctic sites

Long‐term measurements of the light absorption coefficient (babs) obtained with a particle soot absorption photometer (PSAP), babs(PSAP), have been previously reported for Barrow, Alaska, and Ny‐Ålesund, Spitsbergen, in the Arctic. However, the effects on babsof other aerosol chemical species coexisting with black carbon (BC) have not been critically evaluated. Furthermore, different mass absorption cross section (MAC) values have been used to convert babsto BC mass concentration (MBC= babs/MAC). We used a continuous soot monitoring system (COSMOS), which uses a heated inlet to remove volatile aerosol compounds, to measure babs(babs(COSMOS)) at these sites during 2012–2015. Field measurements and laboratory experiments have suggested that babs(COSMOS) is affected by about 9% on average by sea‐salt aerosols. MBCvalues derived by COSMOS (MBC(COSMOS)) using a MAC value obtained by our previous studies agreed to within 9% with elemental carbon concentrations at Barrow measured over 11 months. babs(PSAP) was higher than babs(COSMOS), by 22% at Barrow (PM1) and by 43% at Ny‐Ålesund (PM10), presumably due to the contribution of volatile aerosol species to babs(PSAP). Using babs(COSMOS) as a reference, we derived MBC(PSAP) from babs(PSAP) measured since 1998. We also established the seasonal variations of MBCat these sites. Seasonally averaged MBC(PSAP) decreased at a rate of about 0.55 ± 0.30 ng m−3yr−1. We also compared MBC(COSMOS) and scaled MBC(PSAP) values with previously reported data and evaluated the degree of inconsistency in the previous data. We evaluated the accuracy of black carbon (BC) measurements at Barrow, Alaska, and Ny‐Ålesund, Spitsbergen, in the ArcticAt Barrow, seasonally averaged BC mass concentrations decreased in winter and summer at a rate of 0.55 ± 0.30 ng m−3yr−1during 1998–2015We established seasonal variations of BC at the two sites and evaluated the causes of the inconsistency of the previously reported data