Atmospheric black carbon concentrations in North America from 1850 to 2014

Elemental or black carbon (BC) produced during incomplete combustion, strongly absorbs solar radiation and contributes to global warming. Long-term atmospheric BC concentration, [BC]atm, data are needed to evaluate models used for predicting global climate change. However, little long-term [BC]atm data are available. Earlier Husain et al. (2008) reported [BC]atm from 1850 to 2005 by calibrating 30 years of BC aerosol filter measurements against BC sediment measurements thru [EC]sed = K[EC]atm, where K is a deposition rate. In this work, we have investigated the possibility of determining K in regions that lack long-term [BC]atm through development of a mathematical model for K based on lake and meteorological parameters. BC was determined in sediment cores collected recently using freeze coring techniques, and in cores collected previously using gravity coring technique. Results show identical BC sediment deposition profiles in all the lakes with peak levels occurring 1920-1950, and peak levels was 10 times higher than background levels of pre-1850. Recent BC levels are 20 ng m-3 higher than those of pre-1850 levels. Comparison of observed measurements with the US BC emission estimates by Bond et al. [2007] suggested that the historic BC emission inventory for the US during the 20th century are seriously underestimated. The mathematical model estimated K values was found to agree with the observed values when the catchment contribution of BC is close to the ratio of surface area to the catchment area of that particular lake. However, additional data from more lakes are required for applicability of this model.