Estimation of uncertainty of direct radiative forcing of the aerosol for a rural site in central Europe

Direct climate forcing due to scattering and absorption of the main aerosol components (ammonium sulfate and total carbon) was estimated seasonally in Hungary by a box model. Ammonium sulfate played an important role in the direct forcing while the carbonaceous aerosol contributed significantly to the development of extinction. In summer, the scattering effect of both species showed a maximum (ammonium sulfate: −2.21±1.73 W m−2, total carbon: −0.88±0.73 W m−2), while the absorption of carbon was the most significant in autumn (+0.40±0.41 W m−2). Uncertainty of these data was obtained by using the theory of error propagation and by taking into consideration the standard deviation of the experimental parameters. The relatively high values of the calculated relative standard deviations of the climate forcing data were attributed partly to the large number of the model parameters (9 and 11) and partly to their large uncertainty. The calculated uncertainties of various forcings were found to be in between the factors of 1.7 and 2.1 which were lower than those generally applied in forcing calculations. Parameter sensitivity analysis of the model equation proved that the reliability of the calculated data could be improved if attention is paid to the measurement of certain parameters such as: mass concentration, cloud coverage, surface albedo, upscattered fraction, single-scattering albedo and the fractional transmittance of the atmosphere.