Air Pollution as a Climate Forcing: A Workshop
Day 1 Presentations
Historical (1875-1990) Aerosol Emissions and Simulations
Dorothy Koch*+, Tica Novakov°, Ina Tegen± and James Hansen*
* NASA Goddard Institute for Space Studies
+ Rutgers University
° Lawrence Berkeley Laboratory
± Max Planck Institute for Biogeochemistry — Jena, Germany
In order to simulate and study the climate change during the previous century, the anthropogenic influences on the aerosol distribution must be accurately depicted. We improve upon our historical anthropogenic sulfate and carbonaceous aerosol simulations by updating our emissions and extending our study back to 1875.
Industrial SO2 emissions came mostly from coal and mining in the early part of the century, with increasing amounts from oil. We derive our emissions from the Lefohn et al. (1999) inventory. The carbonaceous aerosol emissions came mostly from coal with increasing amounts from diesel fuel. Our emissions from 1950-1990 are from the United Nations energy statistics [Tegen et al., 2000], using the method of Cooke and Wilson . We modify these in some regions, based on a detailed BC emissions study of 6 countries (USA, UK, PRC, India, and Germany). BC emissions were calculated from data on coal consumed by domestic/commercial, industrial and electric utility (for PRC and India) consumption sectors. Diesel emission factors were assumed to decrease in industrialized countries. Fuel data by sectors for these countries were taken from International Energy Agency data base [Energy statistics and Balances, International Energy Agency, (diskette service), Paris, 2000]. For the years prior to 1950, the BC emissions are based on the coal component of the Lefohn et al. (1990) S emissions, using a conversion factor BC/S derived from the 1950-70 SO2 and BC emissions. Organic carbon emissions are based on the BC emissions. Biomass burning and natural emissions are assumed to remain constant. Aerosol simulations for the years 1875, 1900, 1925, 1950, 60, 70, 80 and 90 are performed in a 9-layer version of the GISS GCM, using the approaches of Koch et al., 1999 and Koch 2001.
Results show that the global sulfate burden doubles from 1875 to 1950, and again from 1950 to 1990. Black carbon, which has a substantial biomass burning fraction, increases by about 30% between 1875 and 1950, and by another 50% between 1950 and 1990. Since sulfate increases faster than the carbonaceous aerosols, the global fraction of the aerosol mass that is sulfate also increases (doubles) from 0.2 to 0.4 during the century.
We compare the model output with deposition observations in ice cores from Greenland (sulfate) and the Alps (sulfate and carbonaceous aerosols). The model follows the observed trends, although the sulfate does not peak as much as observed in the last quarter of the century and the carbonaceous aerosols are too low (although this is not unusual for the carbonaceous aerosol model [Koch, 2001]).
The global (industrial) aerosol radiative forcing is dominated by sulfate (since the black carbon and organic carbon approximately cancel one another); it descends approximately linearly to -0.2 W/m2 in 1950 and then more steeply to about -0.55 W/m2 in 1990. Black carbon has the greatest radiative impact at high latitudes.
The study has substantial uncertainties, including the lack of biofuel emissions, the assumption of constant biomass burning, uncertainty in treatment of carbonaceous aerosol precipitation scavenging, simplistic OC emissions and lack of global information on sulfur release factors.