Measurement of Atmospheric Black Carbon Concentrations, [BC]atm, in the Arctic Region from ~1700 to 2013

Abstract:

Atmospheric black carbon (BC) aerosols play a key role in Earth’s climate through direct and indirect effects. Due to a lack of long-term BC data, climate models are used to estimate BC based on fuel inventories, which have large uncertainties. Hence, long term BC data is needed to verify global models. We report here the first measurements of atmospheric BC concentrations, [BC]_atm, from ~1700 to 2013 using sediments from Finnish lakes, Saanajarvi (SJ)(69⁰ 44^’ N, 20⁰ 52^’ E), and Vuoskojarvi (VJ)(69⁰44^’N, 26⁰57^’E). The cores were collected from the deepest parts of the lakes using a HTH gravity corer, sliced in 0.25 cm sections; freeze dried, and ages determined using ²¹⁰Pb dating method. The BC was chemically separated, and [BC] determined by the thermal optical method. The [BC] varied from 50 to 1140µg/g_{dry weight} in SJ; and 20 to 130µg/g_{dry weight} in VJ. Husain et al.,(JGR, vol 113, D13102,doi:10.1029/2007JD009398, 2008) showed that the atmospheric deposition of BC into lake sediments depends on the characteristic of individual lakes, BC washout ratios, precipitation intensity, and sedimentation rates. The deposition rate, K, for a lake is defined by, [BC]_sed = K[BC]_atm where [BC]_sed, is the concentration of BC in the sediment. We have measured [BC]_atm from 1970 to 2010 in Kevo, Finland, where VJ and SJ are located. The [BC]_atm from Kevo, and [BC]_sed from VJ, and SJ were used to determine K for each of the lake. Owing to the availability of the long term atmospheric BC data from 1970 to 2010 multiple measurements of K were made, and provided a high measure of precision. The mean values of K for VJ, and SJ were 226 ± 60, and 830 ± 290 (m³air/ g_{dry weight}). The K values were used to determine [BC]_atm for the years before 1970. The [BC]_atm from 2013 to 2006 was 82ng/m³. It increased slowly reaching a peak value of about 947 ± 322 ng/m³.The concentrations decreased subsequently to 244 ± 83ng/m³ in 1920, and changed little ~ 1774.The lowest concentration, 77 ± 26 ng/m³, was observed ~ 1700. The high atmospheric concentrations beyond 1850, perhaps, suggest a proportionally larger component from wood burning for heating. We plan to estimate [BC]_atm using OsloCTM3 model, and inventory of fossil fuel, and biomass burning, and compare it with our measurements.