Abstract

Large offshore wind farms are usually clustered around transmission grids to minimize the expense of transmission and due to space military zones, pipelines and constrains due to other uses such as nature preserves. However, this close proximity can undermine power production in downwind wind farms due to wakes from upwind wind farms. Therefore, the wind energy industry has great interest in determining the spatial dimensions of offshore wind farm wakes to assess the economical potential of planned wind farms. In this work we use wake measurements conducted by a research aircraft to evaluate the performance of a wind farm parameterization (WFP) in a mesoscale model during stably-stratified atmospheric conditions, in which the wake is expected to be the strongest. The observations were conducted on the 10 September 2016 within the project WIPAFF (Wind PArk Far Field) at the North Sea. The observations allow evaluation of both the horizontal and the vertical dimensions of the wake. The model simulates the length and most of the time the spatial dimensions of the wake. Further, we show that the largest potential for improving the performance of theWFP is rooted in an improvement of the background flow. This is due to the fact that the mesoscale model has problems representing the atmospheric boundary layer in the transition between land to open sea.

Abstract

The lockdown measures implemented worldwide to slow the spread of the COVID–19 pandemic have allowed for a unique real–world experiment, regarding the impacts of drastic emission cutbacks on urban air quality. In this study we assess the effects of a 7–week (23 March–10 May, 2020) lockdown in the Greater Area of Athens, coupling in situ observations with estimations from a meteorology–atmospheric chemistry model. Measurements in central Athens during the lockdown were compared with levels during the pre– and post–lockdown 3–week periods and with respective levels in the four previous years. We examined regulatory pollutants as well as CO"sub"2"/sub", black carbon (BC) and source–specific BC components. Models were run for pre–lockdown and lockdown periods, under baseline and reduced–emissions scenarios. The in–situ results indicate mean concentration reductions of 30–35% for traffic–related pollutants in Athens (NO"sub"2"/sub", CO, BC from fossil fuel combustion), compared to the pre–lockdown period. A large reduction (53%) was observed also for the urban CO"sub"2"/sub" enhancement while the reduction for PM"sub"2.5"/sub" was subtler (18%). Significant reductions were also observed when comparing the 2020 lockdown period with past years. However, levels rebounded immediately following the lift of the general lockdown. The decrease in measured NO"sub"2"/sub" concentrations was reproduced by the implementation of the city scale model, under a realistic reduced–emissions scenario for the lockdown period, anchored at a 46% decline of road transport activity. The model permitted the assessment of air quality improvements on a spatial scale, indicating that NO"sub"2"/sub" mean concentration reductions in areas of the Athens basin reached up to 50%. The findings suggest a potential for local traffic management strategies to reduce ambient exposure and to minimize exceedances of air quality standards for primary pollutants. Document type: Article

Abstract

Epidemiological studies suggest that the main part of chronic effects from air pollution is likely to be linked with particulate matter (PM). Oxidative potential (OP) of PM is gaining strong interest as a promising health exposure metric. This study combined atmospheric detailed composition results obtained for seven different urban background environments over France to examine any possible common feature in OP seasonal variations obtained using two assays (acid ascorbic (AA) and dithiothreitol (DTT)) along a large set of samples ( N > 700 ). A remarkable homogeneity in annual cycles was observed with a higher OP activity in wintertime at all investigated sites. Univariate correlations were used to link the concentrations of some major chemical components of PM and their OP. Four PM components were identified as OP predictors: OC, EC, monosaccharides and Cu. These species are notably emitted by road transport and biomass burning, targeting main sources probably responsible for the measured OP activity. The results obtained confirm that the relationship between OP and atmospheric pollutants is assay- and location-dependent and, thus, the strong need for a standardized test, or set of tests, for further regulation purposes. Document type: Article