Multi AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) instruments, as solar straylight satellites, require an accurate characterization and elimination of Fraunhofer lines from solar straylight spectra to measure the atmospheric column abundance of reactive gases that destroy toxic and heat trapping ozone and form climate cooling aerosols, like glyoxal (CHOCHO), iodine oxide (IO), or bromine oxide (BrO). The currently achievable noise levels with state-of-the-art DOAS instruments are limited to δ'_DL ≈ 10^-4 (noise equivalent differential optical density, δ'); further noise reductions are typically not straightforward, and the reason for this barrier is not well understood. Here we demonstrate that the nonlinearity of state-of-the-art CCD detectors poses a limitation to accurately characterize Fraunhofer lines; the incomplete elimination of Fraunhofer lines is found to cause residual structures of δ' ≈ 10^-4, and only partially accounted by fitting of an "offset" spectrum. We have developed a novel software tool, the CU Data Acquisition Code that overcomes this barrier by actively controlling the CCD saturation level, and demonstrates that δ'_DL on the order of 10^-5 are possible without apparent limitations from the presence of Fraunhofer lines. The software also implements active control of the elevation angle (angle with respect to the horizon) by means of a Motion Compensation System for use with mobile MAX-DOAS deployments from ships and aircraft. Finally, a novel approach to convert slant column densities into line-of-sight averaged concentrations is discussed.

Column aerosol absorption properties in the visible wavelengths are measured routinely in worldwide locations by NASA AERONET network (http://aeronet.gsfc.nasa.gov), while similar optical properties in UV can be derived from diffuse and global irradiance measurements measured with Multifilter Rotating Shadowband Radiometer (MFRSR) instruments of the USDA UV-MFRSR network (http://uvb.nrel.colostate.edu). To enable direct comparisons between the two techniques, we have modified our UV-MFRSR by replacing standard 300nm filter with 440nm filter used in AERONET network. The modified UV/VIS-MFRSR has been mostly deployed at AERONET calibration site at NASA GSFC in Greenbelt, MD, but also at number of field campaigns. While the UV-MSFRSR instrument is highly susceptible to calibration drifts, these drifts can be accurately assessed using co-located AERONET direct-sun AOT data. In 2006 quartz dome has been installed atop the MFRSR diffuser, which stabilized calibration drifts in 2007-2009. After correcting for remaining calibration changes, the AOT and single scattering albedo (SSA) at the UV wavelengths can be accurately inferred by fitting the measurements of global and diffuse atmospheric transmittances with the forward RT model at each UV-MFRSR spectral channel. Derived AOT and SSA at common wavelength 440nm by two different techniques are generally in good agreement. We also found that SSA becomes smaller in the UV wavelengths and has strong wavelength dependence across blue and near-UV spectral range. The measured enhanced UV absorption might suggest the presence of selectively UV absorbing aerosols. High spectral resolution SSA measurements in UV-VIS wavelengths are called for.

Ultraviolet irradiance (UV from 290 nm to 325 nm) reaching the earth's surface has significantly increased at all latitudes except the equatorial zone since 1979. The annual average increase was caused by a corresponding decrease in ozone amount from1979 to 1998. After 1998, mid-latitude annual average ozone amounts and UV irradiance levels have been approximately constant. Cloud plus aerosol changes over the period from 1979 to 2008 have caused significant moderation of the clear-sky UVB trends based on a preliminary analysis of UV (340 nm) scene reflectivity data from multiple satellites.

Constructed wetlands are a very efficient, clean and economical way to remove organic contaminants from waste water. In the whole water cleaning process, some other complex processes, such as physical sedimentation, filtration, chemical precipitation, and material absorption by vegetation, are involved. The Nitrogen absorption efficiency by heliconnia psitacorumm, was studied at laboratory scale in a small reactor simulating a subsurface flow constructed wetland. Chlorophyll increasing was measured by fluorescence, using blue LED, 460 [nm] as excitation light source. Besides, spectral differences were observed in the spectral signal and in its derivative, indicating changes in the plant physiological response.

The most important aerosol properties for determining aerosol effect in the solar radiation reaching the earth's surface are the aerosol extinction optical depth and the single scattering albedo (SSA). Most of the latest studies, dealing with aerosol direct or indirect effects, are based on the analysis of aerosol optical depth in a regional or global scale, while SSA is typically assumed based on theoretical assumptions and not direct measurements. Especially for the retrieval of SSA in the UV wavelengths only limited work has been available in the literature. In the frame of SCOUT-O3 project, the variability of the aerosol SSA in the UV and visible range was investigated during an experimental campaign. The campaign took place in July 2006 at Thessaloniki, Greece, an urban environment with high temporal aerosol variability. SSA values were calculated using measured aerosol optical depth, direct and diffuse irradiance as input to radiative transfer models. The measurements were performed by co-located UV-MFRSR and AERONET CIMEL filter radiometers, as well as by two spectroradiometers. In addition, vertical aerosol profile measurements with LIDAR and in-situ information about the aerosol optical properties at ground level with a nephelometer and an aethalometer were available. The ground-based measurements revealed a strong diurnal cycle in the SSA measured in-situ at ground level (from 0.75 to 0.87 at 450nm), which could be related to the variability of the wind speed, the boundary layer height and the local aerosol emissions. The reasons for SSA differences obtained by different techniques are analyzed for the first time to provide recommendations for more accurate column SSA measurements.

Lately a number of studies related with UV irradiance estimates from satellite data based on the Ozone Monitoring Instrument (OMI) have shown a high correlation with ground-based measurements but a positive bias in many locations, the satellite derived UV being higher. One of the key factors that this bias has been attributed to is the boundary layer aerosol absorption not taken into account in the current OMI UV algorithm. In this work we have used a correction procedure based on climatological global aerosol absorption data taken from AeroComm aerosol initiative. This dataset includes aerosol optical depth and aerosol single scattering albedo assembled by combining, ground-based aerosol measurements from AERONET and information from several global aerosol models. The results of this correction were compared with synchronous ground-based measurements from 9 UV monitoring stations. The results generally showed a significantly reduced bias of 7-20%, a lower variability, and an unchanged, high correlation coefficient.

The U.S. National Science Foundation's (NSF's) Ultraviolet Spectral Irradiance Monitoring Network (UVSIMN) has been measuring global UV irradiance at seven locations in Antarctica, South America, Southern California, and the Arctic, starting in 1988. Data products include spectra of global (sun and sky) irradiance, sampled quarter-hourly between 280 and 600 nm; integrated irradiance (e.g., UV-B, UV-A); biologically effective dose-rates (e.g., the UV Index); total ozone; effective albedo; cloud optical depth; actinic flux; photoloysis rates; and complementing spectra calculated with a radiative transfer model. Data are disseminated via the project's website www.biospherical.com/NSF. During the last year, data have also been submitted to international data repositories, including (1) the World Ozone and UV Data Center (WOUDC), which is part of the World Meteorological Organization's Global Atmosphere Watch (GAW) program; (2) the Cooperative Arctic Data and Information Service (CADIS), which supports the Arctic Observing Network (AON), an NSF initiative for the International Polar Year (IPY); and (3) the SeaWiFS Bio-optical Archive and Storage System (SeaBASS), which serves NASA's calibration and validation activities for ocean-viewing satellites. We also plan to submit a subset of the dataset to (4) the Network for the Detection of Atmospheric Composition Change (NDACC). The main objective of NDACC is to further understanding of stratospheric changes to the troposphere. UVSIMN data have been adjusted to better serve the needs of these diverse research communities. This paper details the background, format, and volume of these new datasets.

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.

The combination of Cavity Enhanced Absorption Spectroscopy (CEAS) with broad-band light sources (e.g. Light- Emitting Diodes, LEDs) lends itself to the application of cavity enhanced DOAS (CE-DOAS) to perform sensitive and selective point measurements of multiple trace gases with a single instrument. In contrast to other broad-band CEAS techniques, CE-DOAS relies only on the measurement of relative intensity changes, i.e., does not require knowledge of the light intensity in the absence of trace gases and aerosols (I₀). We have built a prototype LED-CE-DOAS instrument in the blue spectral range (420-490nm) to measure nitrogen dioxide (NO₂), glyoxal (CHOCHO), iodine monoxide (I_O), water (H₂O) and oxygen dimers (O₄). Aerosol extinction is retrieved at two wavelengths by means of observing water and O₄ and measuring pressure, temperature and relative humidity independently. The instrument components are presented, and the approach to measure aerosol extinction is demonstrated by means of a set of experiments where laboratory generated monodisperse aerosols are added to the cavity. The aerosol extinction cross section agrees well with Mie calculations, demonstrating that our setup enables measurements of the above gases in open cavity mode.

We present first results from the newly developed remote sensing instrument CLEO (CLear Sky Observatory). CLEO consists of a commercially available CCD miniature spectrometer (Hamamatsu C10082CAH) and foreoptics to measure the global and diffuse solar irradiance. The irradiance is measured through a teflon diffuser. The diffuse irradiance is obtained moving a 180° metal band in the optical path to block the solar direct beam. CLEO measures simultaneously UV and Visible radiation from 163nm to 845nm, in steps of 0.3nm with a resolution of 1nm. The spectrometer is temperature controlled to 10°C to stabilize its optical properties. The dark count is frequently measured using a motorized four positions filterwheel with an opaque disc at one position that acts as a shutter used to block the light input. The system automatically adjusts the integration time to optimize the signal-to-noise. Another difference to previous shadowband instruments is that CLEO moves the shadowband over the whole hemisphere instead of just a few positions in and around the sun's direction. This has the advantage of simplifying the installation procedure and solves the problem with the shadow only partially covering the diffuser due to instrument misalignment.

To evaluate the stratospheric process in the response to the increased surface CFCs emissions, some simulations were carried out by the NCAR interactive chemical, dynamical and radioactive two-dimensional (SOCRATES) model. The investigation showed that when the surface CFCs emissions increased by 30%, these chemical components would be transported into the stratosphere and would play an important roles in stratospheric chemistry and radiation. In the layers from 40km to 48km, the relative variety of active component was ClOx by 20%, HOx by -2%, NOx by -2% and O3 by -5%, respectively. At the same time, temperature reduced by 0.6K.

Fluorescent tracer trials are performed to obtain useful information for hydrodynamic modeling. Particularly they have been used in constructed wetlands, aimed for residual water treatment, in order to find residence time distribution for particles entering the system and, in general, to know the flux pattern. Nevertheless, it has been reported that some tracers, as Rhodamine WT, exhibit adsorption phenomena over the substrate. This situation has to be considered in the analysis of residence time distribution curves, taking into account advection-dispersion processes which are given by the diffusion modified equation. Laser Induced Fluorescence (LIF) with a Nd:YAG laser (532 nm; 35mW), was used to determine Rhodamine WT accumulated concentration. Through adsorption coefficients obtained experimentally, an advection - dispersion model for solute transport in a subsurface flow constructed wetland was evaluated. Including this phenomenon allows to optimize the model, and another important condition is added in the behavior prediction of these complex ecosystems.