Global and direct UV irradiance variation in the Nahuel Huapi National Park (Patagonia, Argentina) after the eruption of Puyehue-Cordon Caulle (Chile)

• Global irradiance at 305 nm showed mean decrease near 20%, after the eruption.
• The reduction in global irradiance decreased with increasing wavelength.
• At 380 nm, no decrease was observed, except particular days with large aerosol load.
• The effect was larger at lower altitude and in the direct than the global irradiance.
• Large variability was observed in all the studied parameters, after the eruption.

On June 4th, 2011, the Puyehue-Cordon Caulle volcanic complex (40°35′25″S 72°07′02″W, Chile) started eruption, sending ash 45,000 feet into the atmosphere. After the initial period, the eruption continued for several months, with less intensity. Changes in global irradiance in the UV-B and UV-A, and direct irradiance and AOD in the UV-A, as consequence of the eruption, were studied. Global irradiance has been permanently measured at the Laboratory of Photobiology (LPh) (41.13S, 71.42W, 804 msl) since 1998. In addition, in the frame of a project to study altitude effect on direct and global irradiance, field campaigns were performed during September 17th to 23rd, 2010 and September 14th to 18th, 2011, in the region of the Nahuel Huapi National Park, near 100 km from the eruption. In those periods, simultaneous measurements of direct and global irradiance and aerosol optical depth (AOD) were carried out at three sites: Laboratory of Photobiology (LPh), Mt Otto (41.15S, 71.38W, 1386 msl) and Mt Catedral (41.17S, 71.48W, 1930 msl). The analysis of aerosols in 2011, three to four month after the eruption started, showed the presence of larger particles and more variability than in 2010, at all sites. Global irradiance, at LPh, also exhibited larger variability, compared to 1999, when no eruption or any other event that could have produced major changes in aerosols occurred. The mean decrease, as consequence of the volcano activity, at LPh, was around 20%, at 305 nm and closed to 10%, at 320 nm. At 380 nm, the decrease was very small and not statistically significant, although in particular days, with large aerosol load, a significant decrease was observed. Direct irradiance, in the UV-A, showed larger decrease than global irradiance. The effect of the eruption was more pronounced at the low altitude site.