Impact of forest fires, biogenic emissions and high temperatures on the elevated Eastern Mediterranean ozone levels during the hot summer of 2007

International audienceThe hot summer of 2007 in southeast Europe has been studied using two regional atmospheric chemistry models; WRF-Chem and EMEP MSC-W. The region was struck by three heat waves and a number of forest fire episodes, greatly affecting air pollution levels. We have focused on ozone and its precursors using state-of-the-art inventories for anthropogenic, biogenic and forest fire emissions. The models have been evaluated against measurement data, and processes leading to ozone formation have been quantified. Heat wave episodes are projected to occur more frequently in a future climate, and therefore this study also makes a contribution to climate change impact research. The plume from the Greek forest fires in August 2007 is clearly seen in satellite observations of CO and NO2 columns, showing extreme levels of CO in and downwindof the fires. Model simulations reflect the location and influence of the fires relatively well, but the modelled magnitude of CO in the plume core is too low. Most likely, this is caused by underestimation of CO in the emission inventories, suggesting that the CO/NOx ratios of fire emissions should be re-assessed. Moreover, higher maximum values are seen in WRF-Chem than in EMEP MSC-W, presumably due to differences in plume rise altitudes as the first model emits a larger fraction of the fire emissions in the lowermost model layer. The model results are also in fairly good agreement with surface ozone measurements. Biogenic VOC emissions reacting with anthropogenic NOx emissions are calculated to contribute significantly to the levels of ozone in the region, but the magnitude and geographical distribution depend strongly on the model and biogenic emission module used. During the July and August heat waves, ozone levels increased substantially due to a combination of forest fire emissions and the effect of high temperatures. We found that the largest temperature impact on ozone was through the temperature dependence of the biogenic emissions, closely followed by the effect of reduced dry deposiion caused by closing of the plants' stomata at very high temperatures. The impact of high temperatures on the ozone chemistry was much lower. The results suggest that forest fire emissions, and the temperature effect on biogenic emissions and dry deposition, will potentially lead to substantial ozone increases in a warmer climate

Measures to reduce dynamic plunge pool pressures generated by a free jet

Spillways often include a flip bucket as terminal energy dissipator, combined with a plunge pool. To prevent scour at the river bed for large jet fall heights additional measures are required, such as terminal chute widening or increase of the plunge pool depth. The effect of these measures was investigated in hydraulic modeling. The dynamic plunge pool bottom pressures in the jet footprint area were systematically recorded. Both, the time-averaged and the fluctuating dynamic pressure heads are considered as references for the jet scour poten-tial, beside the related pressure coefficients. The investigated measures were proven to be effec-tive in terms of reduced pressures, especially in combination. The relevant parameters of the herein presented measures were systematically varied. This research relates to the Kárahnjúkar spillway model investigation, in which the principal working conditions as canyon topography, jet fall head and discharge spectrum were determined

Characterizing summertime chemical boundary conditions for airmasses entering the US West Coast

International audienceThe objective of this study is to analyze the pollution inflow into California during summertime and how it impacts surface air quality through combined analysis of a suite of observations and global and regional models. The focus is on the transpacific pollution transport investigated by the NASA Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission in June 2008. Additional observations include satellite retrievals of carbon monoxide and ozone by the EOS Aura Tropospheric Emissions Spectrometer (TES), aircraft measurements from the MOZAIC program and ozonesondes. We compare chemical boundary conditions (BC) from the MOZART-4 global model, which are commonly used in regional simulations, with measured concentrations to quantify both the accuracy of the model results and the variability in pollution inflow. Both observations and model reflect a large variability in pollution inflow on temporal and spatial scales, but the global model captures only about half of the observed free tropospheric variability. Model tracer contributions show a large contribution from Asian emissions in the inflow. Recirculation of local US pollution can impact chemical BC, emphasizing the importance of consistency between the global model simulations used for BC and the regional model in terms of emissions, chemistry and transport. Aircraft measurements in the free troposphere over California show similar concentration ranges, variability and source contributions as free tropospheric air masses over ocean, but caution has to be taken that local pollution aloft is not misinterpreted as inflow. A flight route specifically designed to sample boundary conditions during ARCTAS-CARB showed a prevalence of plumes transported from Asia and thus may not be fully representative for average inflow conditions. Sensitivity simulations with a regional model with altered BCs show that the temporal variability in the pollution inflow does impact modeled surface concentrations in California. We suggest that time and space varying chemical boundary conditions from global models provide useful input to regional models, but likely still lead to an underestimate of peak surface concentrations and the variability associated with long-range pollution transport

A search for doubly charged higgs production in z0 decays

Contains fulltext : 124394.pdf (preprint version ) (Open Access

Search for a scalar top quark using the OPAL detector

Contains fulltext : 124482.pdf (preprint version ) (Open Access

A Measurement of the electroweak couplings of up and down type quarks using final state photons in hadronic z0 decays

The production rate of final state photons in hadronic Z0 decays is measured as a function of ycut = Mij2/Ecm2 the jet resolution parameter and minimum mass of the photon-jet system. Good agreement with the theoretical expectation from an O(ααs) matrix element calculation is observed. Comparing the measurement and the prediction for ycut = 0.06, where the experimental systematic and statistical errors and the theoretical uncertainties are small, and combining this measurement with our result for the hadronic width of the Z0, we derived partial widths of up and down type quarks to be Γu = 333 ± 55 ± 72 MeV and Γd = 358 ± 37 ± 48 MeV in agreement with the standard model expectations. We compare our yield with the QCD shower models including photon radiation. At low γcut JETSET underestimates the photon yield, and ARIADNE describes the production rate well

A Search for scalar leptoquarks in Z0 decays

Contains fulltext : 125110.pdf (preprint version ) (Open Access