IPPC reports the aerosol radiative forcing per major aerosol category, like sulphate and fossil fuel derived carbon. Part of this carbon is reflective and part of the material (black carbon "soot") absorbs radiation.
We find that in the Netherlands sulphate contributes some 30% to the reflection. Nitrate contributes even more; an estimated 35%. The local importance of nitrate is acknowledged in the new IPCC-TAR, but it is stated that insufficient data exist to assess its importance outside of the Netherlands. The amount of "fossil fuel" carbon could not be directly quantified. The reason is that it consists of thousands of different chemical compounds that all have different physicochemical properties. However, by deduction we found that its concentration is substantial. The mentioned three components, nitrate, sulphate and carbon, are thus the dominant aerosol components in the regional aerosol radiative forcing.
As can be seen in the results, the forcing on partly cloudy days seems less because of a shorter sunshine duration. It should then be considered that on cloudy days the reflective power of the aerosol is higher due to the higher relative humidity and the associated uptake of water by the aerosol. This compensates for the shorter sunshine duration. Reflection of solar radiation caused by the aerosol is exerted by aerosol components that can be of a natural origin or produced by man. In our report we show, on the basis of the aerosol composition, that at least 85% of the aerosol is of a manmade origin and the aerosol reflection is therefore a forcing. The forcing is defined as the amount of solar radiation reflected back into space, and not available for heating of the earth due to the presence of manmade aerosol.