The aerosol forcing efficiency in the UV region and the estimation of single scattering albedo at a typical West European site

The measurements of aerosol optical depth, total ozone and UV irradiance from a Brewer spectrophotometer located at Uccle, Belgium, were used to estimate, for the first time at a typical site in Western Europe, the aerosol radiative forcing efficiency (the forcing performed per unit of aerosol optical depth). The study was performed at selected solar zenith angles during the period July 2006–May 2010. In the 300–360 nm spectral region, the highest values were revealed at 30° (−6.9 ± 0.9 W m−2), while at 60° the RFE was almost 2.5 times lower (−2.7 ± 0.1 W m−2). In the UV-B region (300–315 nm), the RFE value at 60° (−0.069 ± 0.005 W m−2) was 5 times lower than the corresponding value at 30° (−0.35 ± 0.04 W m−2). Extending previous studies for the estimation of aerosol single scattering albedo in UV-A wavelengths down to 340 nm, an attempt was made, taking advantage of the Brewer measurements, to provide estimates at low UV-A wavelengths and in the UV-B region. The estimated monthly averages of the Brewer single scattering albedo at 320 nm are in very close agreement (within ±0.01) with measurements at 440 nm from a collocated CIMEL sunphotometer. Due to increased measurement uncertainties and the effect of ozone absorption, large differences between the two instruments were found at 306.5 nm. For the rest of wavelengths, average differences up to 0.03 were revealed.