Outi Meinander

Scots pines after exposure to elevated ozone and carbon dioxide probed by reflectance spectra and chlorophyll a fluorescence transients

Summary Natural Scots pines have been exposed to filtered air, ambient air and air with elevated O3 or/and CO2 in open top chambers. The trees showed no differences in their optical responses prior to the fumigations. After the fumigation period of three months the plants were in good health. The position of the maximum derivative of the green light reflectance in carbon dioxide fumigated pines was shifted from the control pines inflection point, by approximately 4 nm towards shorter wavelengths. The position of the red edge derivative maximum showed no significant changes. By fluorescence techniques (as OJIP-fast fluorescence transients) nearly no change was found in the quantum yield for electron transport (Ωo or excitation energy trapping ϕpo. However, the estimated activities as absorption, trapping or electron transport per cross-section increased considerably for all samples with elevated O3 or CO2. This increased activity seems to be due to an increased antenna size in O3 treated samples. At elevated CO2 the antenna size is decreased whereas the density of reaction centers per cross-section increased. This means that two different stress-adaptation mechanisms can lead to a similar macroscopic phenomenon like e.g. an increased metabolic activity.

Spike detection and correction in Brewer spectroradiometer ultraviolet spectra

The occurrence of spikes in Brewer UV spectra is studied. Use is made of continuous measurement data over several years, com- prising more than 90,000 spectra, from one single-monochromator and two double-monochromator Brewers. It is shown that the double mono- chromators, especially, may suffer from more than 200 spikes per ;5000 annual spectra. The spikes are not always randomly distributed over the wavelength range. The single monochromator is found to have an an- nual average of only 36 spikes above 300 nm, but it is noted that there were a significant number of spikes at shorter wavelengths, indicating possible bias in the stray light correction unless taken into consideration. The error caused by noncorrected spikes varies greatly from case to case. In an intensive study of 150 spectra measured during one summer week, the effect of one moderate-size spike was found to be more than 5% on a DNA action dose rate and close to 1% on a DNA action daily dose. When high accuracy of in situ UV measurements is required, our results suggest a need to remove spikes from the spectra. A simple statistical approach is employed. The method is applicable to any single- or double-monochromator Brewer spectroradiometer. However, under rapidly changing cloudiness it can be difficult to distinguish between noise spikes and the variation in irradiance due to changes in the state of the sky. Our data show that ancillary radiation measurements may be

Spectral scattering properties of Scots pine shoots

Studies the relationship between optical and geometrical properties of Scots pine (Pinus sylvestris) shoots. For the purpose, measurements of shoot bidirectional reflectance (BDR), bidirectional reflectance distribution function (BRDF) as well as shoot spectral reflectance at different incident and view angles were carried out under laboratory conditions. In addition, different geometrical parameters of needles and shoots were measured. The results indicated that scattering from the Pinus sylvestris shoots, modeled as a cylinder, drastically differs from Lambertian surface: the essential part of the incident light beam is transferred forward due to transparency, but the scattered radiation is usually concentrated around the backscattering direction. In directions perpendicular to incident beam direction (scattering angles 90/spl deg/ and 270/spl deg/) scattering is small, especially in the blue and red spectral regions. The shape of the BRDF as function of scattering angle is maximally smooted in the near infrared (NIR) spectral region and most variable in the blue region. One of the important factors that determines the shape of the BRDF seems to be the specular reflection, intensity of which is determined by Fresnels law.<<ETX>>

UV exposure in artificial and natural weathering: A comparative study

We report on a study focusing on UV exposure conditions in three different types of chambers used for accelerated ageing of materials. The first chamber is equipped with four 300-W UVA/UVB mercury vapour lamps (Ultra-Vitalux/Osram). The second chamber uses four 40-W UVA fluorescent lamps (QUV-340/Q-Lab). The third chamber is Weather-Ometer Ci3000+ from Atlas with a 4500-W xenon arc lamp. UV irradiance prevailing in each chamber was measured using Bentham DM150 double monochromator spectroradiometer. The results were compared to measurements of solar spectral UV irradiance at Jokioinen, Finland, with a Brewer MkIII double monochromator spectrophotometer. The spectral shapes of the exposing UV radiation in the different chambers were found to notably differ from each other and from the solar UV spectrum. Both spatial inhomogeneities and temporal variability caused by various factors, like the ageing of the lamps, were detected. The effects were found to strongly depend on wavelength of the exposing UV radia...

25 years of spectral UV measurements at Sodankylä

At Sodankyla (67°N), spectra of solar ultraviolet radiation (UVR) have been measured with a Brewer spectroradiometer since 1990. The time series is one of the longest in the European Arctic region. In this work, the time series 1990-2014 was homogenized, and the data were corrected with respect to known error sources using laboratory characterizations and theoretical approaches. Methods for cosine correction, temperature correction and determination of long-term changes in spectral responsivity were applied. Bad measurements were identified by using various quality assurance tools including comparisons with reconstructed UV dose rates, synchronous broadband UV dose rates, global radiation and clear sky model calculations. We calculated daily maximum UV indices from the spectral time series. The daily maxima reached on average a value of 5 in midsummer, whereas the maximum UV index value of 6 was measured only twice: in 2011 and in 2013. We calculated the relative spectral changes in measured UV irradiance...

Effects of terrestrial UV radiation on selected outdoor materials: an interdisciplinary approach

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.

Calibrating six years of multiband UV measurements at Ushuaia and Marambio for model and satellite comparisons

An Antarctic UV-monitoring network established in 1999 as a Spanish-Finnish-Argentinian co-operation consists of multiband filter radiometers located at Belgrano, Marambio, and Ushuaia. To provide with quality controlled and assured calibrated groundbased Antarctic UV data, bi-weekly lamp tests were used on every site and visits of travelling reference instruments on two of the sites. Along the six years of operation, the sensitivity in some of the instrument channels was found to drift up to 61%. In both stations, always the same channels showed the best stability or worst instability. The rigorous quality assurance programme ensured that reliable time series of solar data could be produced, however. The most recent Antarctic ozone depletion period of 2005/2006 was studied by comparing OMI satellite-based erythemally weighted daily doses with the measured polynomial corrected data for August 2005-March 2006 for Ushuaia and Marambio. The root mean square (RMS) of difference between the groundbased and satellite-retrieved daily doses was on monthly basis smaller for Ushuaia (19 - 28 %) than for Marambio (17-58 %), possibly due to e.g. bigger heterogeneity of the ground albedo, and variability of the cloudiness. Our final task of combining the polynomial corrected lamp calibration factors and the traveling reference calibration factors, to produce the final calibrated Antartic UV data, is discussed, too.

UV measurements at Marambio and Ushuaia during 2000–2010

Kaisa Lakkala1,2, Alberto Redondas3, Outi Meinander1, Laura Thölix1, Britta Hamari1, Antonio Fernando Almansa3, Virgilio Carreno3, Guillermo Deferrari4,5, Hector Ochoa6, Germar Bernhard7, Ricardo Sanchez8, and Gerardus de Leeuw1 1Finnish Meteorological Institute, Climate Research, Helsinki, Finland 2Finnish Meteorological Institute, Arctic Research, Sodankylä, Finland 3Izaña Atmospheric Research Center, Agencia Estatal de Meteorología, Tenerife, Spain 4Centro Austral de Investigaciones Cientificas (CADIC/CONICET), Ushuaia, Argentina 5Universidad Nacional de Tierra del Fuefo, Ushuaia, Argentina 6Dirección Nacional del Antártico-Instituto Antártico Argentino, Buenos Aires, Argentina 7Biospherical Instruments, Inc., San Diego, U.S.A 8Servicio Meteorológico Nacional, Argentina Correspondence to: Kaisa Lakkala (kaisa.lakkala@fmi.fi)

Two decades of spectral UV measurements at Sodankylä

A Brewer spectrophotometer MK II measures UV irradiances since 1990 at Sodankyla (67.4°N, 26.6°E), Finland. In this work, the observed spectral features of the time series 1990-2011 are studied. The data have been corrected for temperature, cosine, noise spike and the wavelength-shift. The long-term spectral responsivity is scaled to the irradiance scale of the Aalto University, and the quality of the measurements has been assessed during intercomparison campaigns. In order to study long-term changes in the spectral UV irradiance, a linear regression line is fitted to the monthly mean irradiances from April to August. No statistically significant changes are observed for any months for the 22-year period. However, one single year can have special features. In 2011, UV index 6 was measured for the first time, and the ratio of UV-B irradiance at 305 nm to UV-A irradiance at 324 nm exceeded the 1990-2010 average by 16%.