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2005
2019
2015
We investigate the concentration fluctuations of passive scalar plumes emitted from small, localised (point-like) steady sources in a neutrally stratified turbulent boundary layer over a rough wall. The study utilises high-resolution large-eddy simulations for sources of varying sizes and heights. The numerical results, which show good agreement with wind-tunnel studies, are used to estimate statistical indicators of the concentration field, including spectra and moments up to the fourth order. These allow us to elucidate the mechanisms responsible for the production, transport and dissipation of concentration fluctuations, with a focus on the very near field, where the skewness is found to have negative values – an aspect not previously highlighted. The gamma probability density function is confirmed to be a robust model for the one-point concentration at sufficiently large distances from the source. However, for ground-level releases in a well-defined area around the plume centreline, the Gaussian distribution is found to be a better statistical model. As recently demonstrated by laboratory results, for elevated releases, the peak and shape of the pre-multiplied scalar spectra are confirmed to be independent of the crosswind location for a given downwind distance. Using a stochastic model and theoretical arguments, we demonstrate that this is due to the concentration spectra being directly shaped by the transverse and vertical velocity components governing the meandering of the plume. Finally, we investigate the intermittency factor, i.e. the probability of non-zero concentration, and analyse its variability depending on the thresholds adopted for its definition.
Cambridge University Press
2024
2012
2016
2013
2005
The deposition and fate of perfluorinated alkyl substances (PFAS) in the Norwegian Arctic snowpack. NILU F
2012
2012
2008
The Covid-19 pandemic and environmental stressors in Europe: synergies and interplays
This report provides an overview of the potential impacts of Covid-19 restrictions, in particular, focusing on review and assessment of Covid-19 impacts on air quality, for the year 2020. Complementary analyses address compliance with the National Emission reductions Commitments (NEC) Directive and noise. This expands the initial analysis of impacts of the pandemic-related restrictions on air quality based on data for the first months of 2020, presented in the EEA Air quality report for 2020. The results show a clear decline in NO2 short-term levels and annual average throughout Europe. Results for other pollutants are less uniform, and mostly do not show significant changes in annual average or other relevant metrics . The results regarding air quality are robust, obtained by a wealth of methods and consistent also with literature findings. The noise analysis shows a general decline in noise levels related to road traffic, though some areas show an increase. An analysis of policies and measures reported by Member States in 2021 for base year 2019 shows that additional measures related to emissions of NH3 are expected to be negatively impacted to the greatest extent by the Covid-19 related restrictions.
ETC/ATNI
2022
2003
2023
2021
Knowledge of the spatial distribution of the fluxes of greenhouse gases (GHGs) and their temporal variability as well as flux attribution to natural and anthropogenic processes is essential to monitoring the progress in mitigating anthropogenic emissions under the Paris Agreement and to inform its global stocktake. This study provides a consolidated synthesis of CH4 and N2O emissions using bottom-up (BU) and top-down (TD) approaches for the European Union and UK (EU27 + UK) and updates earlier syntheses (Petrescu et al., 2020, 2021). The work integrates updated emission inventory data, process-based model results, data-driven sector model results and inverse modeling estimates, and it extends the previous period of 1990–2017 to 2019. BU and TD products are compared with European national greenhouse gas inventories (NGHGIs) reported by parties under the United Nations Framework Convention on Climate Change (UNFCCC) in 2021. Uncertainties in NGHGIs, as reported to the UNFCCC by the EU and its member states, are also included in the synthesis. Variations in estimates produced with other methods, such as atmospheric inversion models (TD) or spatially disaggregated inventory datasets (BU), arise from diverse sources including within-model uncertainty related to parameterization as well as structural differences between models. By comparing NGHGIs with other approaches, the activities included are a key source of bias between estimates, e.g., anthropogenic and natural fluxes, which in atmospheric inversions are sensitive to the prior geospatial distribution of emissions. ...
2023
2021
The concept of essential use for determining when uses of PFASs can be phased out
Royal Society of Chemistry (RSC)
2019
2017