Modern polymeric materials possess an ever increasing potential in a large variety of outdoor objects and structures
offering an alternative for many traditional materials. In outdoor applications, however, polymers are subject to a
phenomenon called weathering. This is primarily observed as unwanted property changes: yellowing or fading, chalking,
blistering, and even severe erosion of the material surface. One of the major weathering factors is UV radiation.
In spring 2005, the Finnish Meteorological Institute with its research and industrial partners launched a five-year
material research project named UVEMA (UV radiation Effects on MAterials). Within the framework of the project, a
weathering network of seven European sites was established. The network extends from the Canary Islands of Spain
(latitude 28.5°N) to the Lapland of Finland (latitude 67.4°N), covering a wide range of UV radiation conditions. Since
autumn 2005, the sites of the network have been maintaining weathering platforms of specimens of different kinds of
polymeric materials. At the same time, the sites have been maintaining their long-term monitoring programmes for
spectrally resolved UV radiation. Within UVEMA, these data are used for explaining the differences between the
degradation rates of the materials at each site and for correlating the UV conditions in accelerated ageing tests to those
under the Sun.
We will present the objectives of the UVEMA project aiming at deeper understanding of the ageing of polymers and
more reliable assessments for their service life time. Methodologies adopted within the project and the first results of the
project will be summarized.
Monitoring of the terrestrial solar ultraviolet irradiance by using a radiometer is often considered as expensive
and laborious or the data collected as insufficient in spatial coverage and in some cases in its temporal
resolution, too. Therefore, alternative methods, all relying on modelling in one way or the other, have been
developed. They differ in which input they receive, either standard meteorological information, space-based
radiance measurements or ground-based irradiances from broadband or multiband UV radiometer or from
pyranometer. A comparison of performance is presented between three methods during a 15-month period.
The ground reference instrument is the Brewer Mk-III #107 spectroradiometer of the Observatory of
Jokioinen, Finland. Compared to the reference, the space-based method overestimates the UV irradiance at
noon by 14.6% and the pyranometer-based by 0.9% with root-mean-square differences of 35.5% and 10.4%,
respectively. Daily erythemal doses agree by 3.8% for the space-based and 0.4% for the pyranometer-based
method with a scatter of 16.5% and 4.6%, respectively. Spectral irradiances generated by the pyranometerbased
model agree within 0.4% on average with a standard deviation of 17%. A rough estimate on the cost of
each approach suggests that none of them is clearly superior to the others and the actual nature of the data
needed may be used in decision making concerning monitoring strategies.