Atmospheric Aerosol and Ultraviolet Radiation

Ultraviolet (UV) radiation plays very important role in bio-geo-chemical cycle. Their harmful effects include skin cancer, cataract, immune suppression, reduction in crop yield, etc. Beneficial effects are synthesis of vitamin D in human body, treatment of psoriasis, etc (Lucas et al., 2006). My interest in UV radiation is how it interacts with atmospheric aerosols.

Aerosols are one of the many factors which determines amount of surface reaching UV radiation. While scattering type of aerosols may reduce surface reaching UV radiation, they increase the actinic flux which in turn increases the photolysis rate for smog formation (Dickerson et al., 1997). Relation of aerosol and UV radiation is not one-way; while aerosols affect surface reaching UV radiation, they are affected by surface reaching UV radiation. This is particularly true for naturally produced sulfate aerosol. Recently scientific community has shown a lot of interest to study UV induced sulfate aerosol production to better understand effect solar variability on climate change. Joyce Penner presented a talk on connection between Solar variability, Dimethyl sulfide (DMS) production, and climate change in Yoram Kaufman Symposium on Aerosols, Clouds and Climate (30-31 May 2007). The symposium was organized in honor of Yoram Kaufman at Goddard Space Flight Center, NASA, Maryland, USA. Presentations are available for download at this link.

Penner presented the details on solar variability and DMS production and showed how the matter is complicated due to cloud feedback. The connection works as following; increase in ultraviolet radiation decreases the marine biota, which in turn reduces production of DMS . Reduction in DMS reduces aerosol amount, which ultimately leads to cloud modification. The poorly understood connections between aerosol and cloud as well as cloud and marine biota makes it difficult to interpret solar variability connection of climate change. Two references cited repeatedly in her talk were Larsen (2005) and Vallina and Simo (2007).

References:-

Lucas, R., T. McMichael, W. Smith. and B. Armstrong (2006), Global burden of disease from solar ultraviolet radiation, Environmental burden of diseases series no. 13, ed. A. Pruss-Ustun, H. Zeeb, C. Mathers and M. Repacholi, World Health Organization Public Health and the Environment, Geneva, 2006.

R. R. Dickerson, S. Kondragunta, G. Stenchikov, K. L. Civerolo, B. G. Doddridge, and B. N. Holben, The Impact of Aerosols on Solar Ultraviolet Radiation and Photochemical Smog , Science 31 October 1997 278: 827-830 [DOI: 10.1126/science.278.5339.827]

Larsen, S. H. (2005), Solar variability, dimethyl sulphide, clouds, and climate, Global Biogeochem. Cycles, 19, GB1014, doi:10.1029/2004GB002333.

Vallina, S. M. and R. Simo (2007), Strong Relationship Between DMS and the Solar Radiation Dose over the Global Surface Ocean, Science, Vol. 315, No. 5811. pp. 506-508