Abstract
Abstract. The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65° N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m−2 and for the snow-albedo effect 0.016 W m−2 in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26 % since 1950.
Highlights
Black carbon aerosols (BC) are emitted to the atmosphere from incomplete combustion of biomass and fossil fuel
In our study we focus on the direct aerosol effect and the BC-albedo effect and how the concentration and deposition of BC have changed from pre-industrial times until present
Oslo CTM2 is a large scale off-line chemical transport model driven by meteorological data generated by the Integrated Forecast System (IFS) model at the European Centre for Medium-Range Weather Forecasts (ECMWF)
Summary
Black carbon aerosols (BC) are emitted to the atmosphere from incomplete combustion of biomass and fossil fuel. Radiative forcing time series for the direct aerosol effect of BC from fossil fuel and biofuel sources and RF-time series for BC snow albedo effect from fossil fuel and biofuel combustion are presented This is important for knowing how much BC has contributed to global warming and for constraining the climate sensitivity The atmospheric chemistry transport model Oslo CTM2 (Berglen et al, 2004; Berntsen et al, 2006; Søvde et al, 2008; Myhre et al, 2009; Rypdal et al, 2009) is used to calculate BC concentration in the atmosphere and the deposition of BC on snow surfaces using emission inventories for fossil fuel, biofuel and open biomass burning. Simulations with regional emissions from the main emissions regions are done for the years 1930 and 2000
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