Modelling photochemistry in alpine valleys

Peer reviewe

Interactions between downslope flows and a developing cold-air pool

A numerical model has been used to characterize the development of a region of enhanced cooling in an alpine valley with a width of order (Formula presented.) km, under decoupled stable conditions. The region of enhanced cooling develops largely as a region of relatively dry air which partitions the valley atmosphere dynamics into two volumes, with airflow partially trapped within the valley by a developing elevated inversion. Complex interactions between the region of enhanced cooling and the downslope flows are quantified. The cooling within the region of enhanced cooling and the elevated inversion is almost equally partitioned between radiative and dynamic effects. By the end of the simulation, the different valley atmospheric regions approach a state of thermal equilibrium with one another, though this cannot be said of the valley atmosphere and its external environment.Peer reviewe

Pollutant dispersion in a developing valley cold-air pool

Pollutants are trapped and accumulate within cold-air pools, thereby affecting air quality. A numerical model is used to quantify the role of cold-air-pooling processes in the dispersion of air pollution in a developing cold-air pool within an alpine valley under decoupled stable conditions. Results indicate that the negatively buoyant downslope flows transport and mix pollutants into the valley to depths that depend on the temperature deficit of the flow and the ambient temperature structure inside the valley. Along the slopes, pollutants are generally entrained above the cold-air pool and detrained within the cold-air pool, largely above the ground-based inversion layer. The ability of the cold-air pool to dilute pollutants is quantified. The analysis shows that the downslope flows fill the valley with air from above, which is then largely trapped within the cold-air pool, and that dilution depends on where the pollutants are emitted with respect to the positions of the top of the ground-based inversion layer and cold-air pool, and on the slope wind speeds. Over the lower part of the slopes, the cold-air-pool-averaged concentrations are proportional to the slope wind speeds where the pollutants are emitted, and diminish as the cold-air pool deepens. Pollutants emitted within the ground-based inversion layer are largely trapped there. Pollutants emitted farther up the slopes detrain within the cold-air pool above the ground-based inversion layer, although some fraction, increasing with distance from the top of the slopes, penetrates into the ground-based inversion layer.Peer reviewe

Assessment of 2010 air quality in two Alpine valleys from modelling: Weather type and emission scenarios

Original article can be found at: http://www.sciencedirect.com/science/journal/13522310 Copyright Elsevier Ltd. DOI: 10.1016/j.atmosenv.2006.07.021Alpine valleys are sensitive to anthropogenic emissions. Local atmospheric dynamics are a key factor that may lead to an accumulation of pollutants in the bottom of the Chamonix and Maurienne valleys. Assessment of 2010 pollutant concentrations variability needs to take these specificities into account. A meteorological data classification is combined with different emission scenarios in order to run an air quality model. Using simulations of representative scenarios rather than complete years allows for a fine spatial and temporal representation of local atmospheric dynamics and gives access to detailed chemical breakdowns. Results demonstrate the variability of primary and secondary species due to emissions and the predominance of local effects on pollutant concentrations.Peer reviewe

Production of ozone in the Chamonix Valley (France)

Original article can be found at: https://www.inderscience.com/browse/index.php?journalID=9 Copyright Inderscience DOI: 10.1504/IJEP.2005.007394Peer reviewe

Evolution of cold-air-pooling processes in complex terrain

This document is the Accepted Manuscript version. The final publication is available at Springer via: https://doi.org/10.1007/s10546-013-9885-zElucidating cold-air-pooling processes forms part of the longstanding problem of parametrizing the effects of complex terrain in larger-scale numerical models. The Weather Research and Forecasting model has been set-up and run at high resolution over an idealized alpine-valley domain with a width of order 10 km, to investigate the four-dimensional variation of key cold-air-pooling forcing mechanisms, under decoupled stable conditions. Results of the simulation indicated that the total average valley-atmosphere cooling is driven by a complex balance/interplay between radiation and dynamical effects. Three fairly distinct regimes in the evolution of cold-air-pooling processes have been identified. Starting about 1 h before sunset, there is an initial 30-min period when the downslope flows are initiated and the total average valley-atmosphere instantaneous cooling is dominated by radiative heat loss. A period of instability follows, when there is a competition between radiation and dynamical effects, lasting some 90 min. Finally, there is a gradual reduction of the contribution of radiative cooling from 75 to 37 %. The maximum cold-air-pool intensity corresponds to the time of minimum radiative cooling, within the period of instability. Although, once the flow is established, the valley atmosphere cools at broadly similar rates by radiation and dynamical effects, overall, radiation effects dominate the total average valley-atmosphere cooling. Some of the intricacies of the valley mixing have been revealed. There are places where the dynamics dominate the cooling and radiation effects are minor. Characteristics of internal gravity waves propagating away from the slopes are discussedPeer reviewe

Odour-impact assessment around a landfill site from weather-type classification, complaint inventory and numerical simulation

'This is the author's version of a work that was accepted for publication in Journal of Environmental Management. Changes resulting from the publishing process, such as structural formatting and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Environmental Management, 93, 1, (2012) 10.1016/j.jenvman.2011.08.016'Gases released from landfill sites into the atmosphere have the potential to cause olfactory nuisances within the surrounding communities. Landfill sites are often located over complex topography for convenience mainly related to waste disposal and environmental masking. Dispersion of odours is strongly conditioned by local atmospheric dynamics. Assessment of odour impacts needs to take into account the variability of local atmospheric dynamics. In this study, we discuss a method to assess odour impacts around a landfill site located over complex terrain in order to provide information to be used subsequently to identify management strategies to reduce olfactory nuisances in the residential neighbourhoods. A weather-type classification is defined in order to identify meteorological conditions under which olfactory nuisances are to be expected. A non-steady state Gaussian model and a full-physics meteorological model are used to predict olfactory nuisances, for both the winter and summer scenarios that lead to the majority of complaints in neighbourhoods surrounding the landfill site. Simulating representative scenarios rather than full years make a high resolution simulation of local atmospheric dynamics in space and time possible. Results underline the key role of local atmospheric dynamics in driving the dispersion of odours. The odour concentration simulated by the full-physics meteorological model is combined with the density of the population in order to calculate an average population exposure for the two scenarios. Results of this study are expected to provide helpful information to develop technical solutions for an effective management of landfill operations, which would reduce odour impacts within the surrounding communities.Peer reviewedFinal Accepted Versio