Several recent studies have found a disagreement between modelled and measured clear-sky surface irradiances and have suggested an anomalous atmospheric absorber. This motivated us to study the role of aerosols in the shortwave (solar) radiation balance in The Netherlands. A detailed comparison between measurements and model calculations of direct and diffuse irradiances at ground level on cloud-free days is made. The model, MODTRAN 4.1, is fed with a large number of atmospheric measurements including measurements of aerosol properties.

For the case considered here, the modelled and measured irradiances agree within the total uncertainty. The largest model uncertainties in the global irradiance are due to uncertainties in the measured aerosol absorption and size distribution. The use of standard rural and urban aerosol models for radiative transfer calculations can lead to serious errors in the irradiances. It is recommended to increase the accuracy of the irradiance measurements.