University of Cambridge > Talks.cam > Centre for Atmospheric Science seminars, Chemistry Dept. > Urban street canyons: Coupling dynamics, chemistry and within-canyon chemical processing of emissions/Low-cost Sensors for Air Quality Monitoring: Personal Exposure Studies and High Density Network for Air Quality Assessment

Urban street canyons: Coupling dynamics, chemistry and within-canyon chemical processing of emissions/Low-cost Sensors for Air Quality Monitoring: Personal Exposure Studies and High Density Network for Air Quality Assessment

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Dr Vivien Bright Urban street canyons: Coupling dynamics, chemistry and within-canyon chemical processing of emissions.

Atmospheric composition within the urban environment, particularly within street canyons (formed by a road running between two rows of buildings), has a direct effect on the air quality of an environment in which a large majority of people live and work. The composition of air within a street canyon is determined by the composition of background air mixed in from above, advection of air into and out of the canyon, vehicle exhaust and other emissions from within the street, together with the mixing and chemical processing of pollutants within the canyon. This occurs on a timescale of a few seconds to minutes and as a result, within-canyon atmospheric processes can have a significant effect on atmospheric composition on such timescales.

This paper outlines the results of a modelling study of composition on the street canyon scale, integrating the combined effects of emissions, dynamics and chemistry. The work builds upon an existing dynamical model of canyon atmospheric motion (Large Eddy Simulation (LES) model) by adding a detailed chemical reaction scheme. Previous studies have considered basic NOX -O3 cycles with only a small number of chemical reactions included.

Initially, a zero-dimensional box model was used to develop and assess the accuracy of a suitable reduced chemical scheme to be included within the LES . The reduced chemical scheme, based upon a subset of the Master Chemical Mechanism (MCM), includes 51 chemical species and 136 reactions. Vehicle emissions taken from the UK National Atmospheric Emissions Inventory (NAEI) were subsequently added to the box model. These elements were then combined with the canyon dynamics simulated by the Large Eddy Simulation (LES) model. Previous work demonstrates that the enhanced model is a suitable tool to be used to further investigate the combined effects of mixing and chemical processing upon air quality within the street canyon.

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Dr Olalekan Popoola

Low-cost Sensors for Air Quality Monitoring: Personal Exposure Studies and High Density Network for Air Quality Assessment

Outdoor air quality and its impact on human health and the environment have been well studied and it has been projected that poor air quality will surpass poor sanitation as the major course of environmental premature mortality by 2050 (IGAC / IGBP , release statement, 2012). Transport-related pollution has been regulated at various levels by enactment of legislations at local, national, regional and global stages. As part of the mitigation measures, routine measurements of atmospheric pollutants such as carbon monoxide (CO), nitric oxide (NO) and nitrogen dioxide (NO2) have to be established in areas where air quality problems are identified. In addition, emission inventories are also generated for different atmospheric environments including urban areas and airport required for air quality models.

Whilst recognising that most of the existing monitoring networks provide high temporal measurements, spatial distribution of these often variable pollutants are not captured, making it difficult to adequately characterise the highly heterogeneous air quality. Spatial information is often obtained from model data which can only be constrained using measurements from the sparse monitoring networks.

The work presented here shows the application of low-cost electrochemical sensor networks in monitoring road transport pollutants including CO, NO and NO2 in an urban environment. Results from personal exposure studies involving short-term (few hours) field deployments in four different cities including Cambridge (UK), London (UK), Valencia (Spain) and Lagos (Nigeria) are presented. In addition, long-term studies (2.5 months) involving a network of 46 static sensor nodes of in Cambridge will also be presented.

Current work involves a new generation of these instruments which include additional species such as O3, SO2 , VOCs and CO2 as well as size-speciated particulates (0.38 to 17.4 ┬Ám). These are currently deployed at London Heathrow Airport (LHR) as part of the Sensor Networks for Air Quality at London Heathrow (SNAQ-Heathrow) project. Meteorological data such as temperature, relative humidity, wind speed and direction are also measured. The network will consist of 50 sensor nodes, deployed in and around the airport perimeter. Early results from the SNAQ -Heathrow are presented. These include: examples of regional pollution events influenced by meteorology, as well as localised pollution effects related to aircraft taxiing, take-off and landing at the airport, in addition to other sources e.g. roads in close proximity to the airport.

This talk is part of the Centre for Atmospheric Science seminars, Chemistry Dept. series.

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