Total ozone column, water vapour and aerosol effects on erythemal and global solar irradiance in Marsaxlokk, Malta

Observations of erythemal (LIVER; 280-400 nm) and total solar shortwave irradiance (SW; 305-2800 nm), total ozone column (TOC), water vapour column (w), aerosol optical depth (AOD) and Angstrom exponent (alpha) were carried out at Marsaxlokk, in south-east Malta. These measurements were recorded during a measurement campaign between May and October 2012, aimed at studying the influence of atmospheric compounds on solar radiation transfer through the atmosphere. The effects of TOC, AOD and w on LIVER and SW (global, diffuse and direct) irradiance were quantified using irradiance values under cloud-free conditions at different fixed solar zenith angles (SZA). Results show that LIVER (but not SW) irradiance correlates well with TOC. LIVER variations ranged between -0.24% DU-1 and -0.32% DU-1 with all changes being statistically significant. Global SW irradiance varies with water vapour column between -2.44% cm(-1) and -4.53% cm(-1), these results proving statistically significant and diminishing when SZA increases. The irradiance variations range between 42.15% cm(-1) and 20.30% cm(-1) for diffuse SW when SZA varies between 200 and 700. The effect of aerosols on global LIVER is stronger than on global SW. Aerosols cause a LIVER reduction of between 28.12% and 52.41% and a global SW reduction between 13.46% and 41.41% per A0D550 unit. Empirical results show that solar position plays a determinant role, that there is a negligible effect of ozone on SW radiation, and stronger attenuation by aerosol particles in LIVER radiation. (C) 2014 Elsevier Ltd. All rights reserved.