Urban air quality

Quick links: MAQS-Health Coupling ADMS-Urban Optimising using sensors CAMS Defra model evaluation CureAir AIRPRO PROMOTE ADMLC reviews

The air quality in urban areas is currently a subject of acute public interest, as many cities worldwide exceed targets for pollutants such as NO₂ and PM_2.5. CERC’s model ADMS-Urban can be used to investigate urban air quality at street-scale resolution throughout an urban area, allowing for the dispersion of all types of pollutant emissions including those from road vehicles, domestic and industrial combustion and other forms of transport such as non-electrified railways.

The ADMS-Urban RML modelling system combines the ADMS-Urban model with outputs from mesoscale meteorological modelling and regional air quality modelling to allow consideration of the effects on an urban area of emissions over a wider region.

Accurate estimates of pollutant emission rates are key to successful modelling of urban air quality. CERC’s EMIT tool can be used to combine activity data, such as traffic counts, with emission factors and vehicle fleets which can be adjusted to reflect local conditions or specific interventions such as low-emission zones.

ADMS-Urban has been developed to include detailed representations of local dispersion effects relating to road sources, such as street canyons and road tunnels.

MAQS-Health – A Multi-Model Air Quality System for Health Research

This ambitious SPF Clean Air project, led by CERC, has developed a world-leading coupled air quality modelling system spanning national to urban street scales and accounting for physical and chemical processes at all relevant temporal and spatial scales: from thousands of kilometres to metres; and from seconds to days or weeks. The interactive map shows example output from the system, creating using data sources including Defra background mapped air pollutant concentration data, DUKEMS major road emissions data, and UKCEH WRF meteorological data.

The system is flexible, linking the most advanced regional chemical transport models available, including CMAQ, CAMx, EMEP, AQUM/UKCA and WRF-CHEM, to a new street-scale dispersion model, ADMS-Local, and to CERC’s widely used ADMS-Urban model. ADMS-Local is computationally efficient, calculates gradients in pollutant concentrations at street-scale resolution including allowance for chemical reactions relevant at local scales, and accounts for the impacts of complex urban morphology, including street canyons, on flow and dispersion. The system’s verification module enables validation of predictions against measurements even where there are large gradients in concentration (as often found in urban environments), which is not possible with grid based regional models. The system predictions are available at a wide range of spatial and temporal resolution enabling personal exposure and health impact modelling using a range of metrics at national, city, neighbourhood and local scales. Researchers using the system are able to assess a wide range of national and local policy measures, such as Clean Air Zones and reduced ammonia emissions from farming, and also investigate health inequalities.

The project team was led by CERC, and brought together our experts in software development and application of local dispersion models (ADMS), and regional modelling experts from the universities of Birmingham, Edinburgh, Hertfordshire and Lancaster who trialled the system across different regions of the UK. The project team worked closely with the Met Office, and liaised with government, academic and commercial stakeholders throughout the project. The coupled system and ADMS-Local are available for research projects. Please do contact us to discuss your use of the system.

Coupling of ADMS-Urban with regional models

A system to couple the ADMS family of local air dispersion models with regional models has been developed by CERC. The coupled system has been used to model London, with ADMS-Urban as the local model and either CMAQ (Stocker et al.,2012) or EMEP4UK as the regional model. In collaboration with the Hong Kong University of Science and Technology, the system is currently being extended for use within the PRAISE-HK air qality forecasting system for Hong Kong; it is also being used within research projects for China, Malaysia and India.

The ADMS-Urban Regional Model Link, which is the automated system for coupling ADMS-Urban with the regional air quality models CAMx, CMAQ, WRF-CHEM, CHIMERE and EMEP4UK, is now available for use by other organisations. The system is designed so that it can be developed to be compatible with additional regional models, please contact CERC if you would like to use the ADMS-Urban RML with output from a different regional model.

The aim of a coupled system is to combine the advantages of regional and local models to improve the prediction of concentration values for all types of receptors. Regional (usually Eulerian) models contain complex chemistry mechanisms, which can operate over long spatial and temporal scales, and can model the accumulation of concentrations in very low wind speed conditions. The gridded nature of their emissions data and dispersion calculations, however, does not allow them to match the high gradients of concentration found in the immediate vicinity of an individual source such as a road. Local (usually Gaussian-type plume) models can represent the fine-scale concentration gradients from explicitly defined sources in detail, but generally only include simplified chemical mechanisms and spatially homogeneous meteorological data, limiting their applicability for receptors far from the source (typically defined as > 50 km). They are also of limited applicability in very low wind speed conditions. Coupling a local model within a regional model allows both high resolution of concentration gradients close to a source, and accurate representation of transport and chemistry over larger spatial and temporal scales. It is important, however, to design the system to minimise the double-counting of emissions modelled in both the regional and local models.

Optimising ADMS-Urban modelling using low cost pollution sensor data

CERC are taking part in an ongoing project to optimise ADMS-Urban modelling using data from a network of low cost pollution sensors. This work forms part of a wider collaboration between CERC, Cambridge University, Cambridge City Council, Cambridgeshire County Council and AQMesh to investigate how modelled and monitored data can be used together to improve urban air quality assessment.

The optimisation scheme, developed at CERC, minimises the part of dispersion model error which is due to emissions data error by adjusting emission rates on an hourly basis to optimise model performance in comparison with sensor data; the scheme accounts for estimated uncertainty in the sensor and emissions data and complex co-variance between individual source emissions error and individual sensor error. The initial scheme design and results were presented at the IAQM conference for dispersion modellers, DMUG 2017, with the presentation available online.

CAMS: Copernicus Atmosphere Monitoring Service

The EU’s Copernicus Atmosphere Monitoring Service (CAMS) combines state-of-the-art atmospheric modelling with Earth observation data to provide operational services such as:

• Daily near-real-time European air quality forecasts – there is a map on the CERC homepage which shows the latest CAMS forecast for the UK;
• Daily near-real-time forecasts of global atmospheric composition;
• Reanalyses providing consistent multi-annual global datasets of atmospheric composition;
• Reanalyses providing consistent annual datasets of European air quality;
• Products to support policy users, adding value to “raw” data products;
• Solar and UV radiation products;
• Greenhouse gas surface flux inversions for CO₂, CH₄ and N₂O;
• Climate forcings from aerosols and long-lived (CO₂, CH₄) and shorter-lived (stratospheric and tropospheric ozone) agents; and
• Anthropogenic emissions for the global and European domains and global emissions from wildfires and biomass burning.

CAMS is led by the European Centre for Medium-range Weather Forecasting (ECMWF), which is based in Reading in the UK. CERC’s role in CAMS is as part of the ‘User Interaction’ team, working in partnership with the German Aerospace Agency DLR, the Norwegian Air Research Institute NILU and the French company Transvalor. CERC took a similar role in the predecessor MACC projects. The overall goal of the ‘User Interaction’ team is to ensure the best possible use of the CAMS products by its users, through:

• Understanding and documenting user requirements;
• Organizing user workshops and additional user feedback mechanisms; and
• Monitoring the service product portfolio against the user requirements.

Defra Urban Model Evaluation

Defra carried out an urban modelling intercomparison study based on validation against London monitoring data with the final report published in 2013. CERC ran ADMS-Urban using LAEI emissions to calculate concentrations at monitoring sites, source apportionment and areas where air quality objectives were exceeded. In general ADMS-Urban was found to perform well against the measurements compared to the other models and modelling systems considered, some of which also included components from the ADMS family of models.

Coupling Urban and Regional processes: Effects on Air Quality (CureAir)

CERC are collaborating with the Universities of Edinburgh and Leeds and the Centre for Ecology and Hydrology on the NERC-funded CureAir project which is investigating regional and local effects on urban air quality. CERC are contributing to a coupled EMEP4UK and ADMS-Urban model for London, with the ADMS-Urban RML developed to send ADMS-Urban runs to the ARCHER high-performance computing system.

Working in collaboration with the University of Leeds, the ADMS-Urban GRS chemistry scheme has been evaluated in comparison with the Master Chemical Mechanism. CERC have also extended the ADMS-Urban chemistry scheme to include some effects of HONO and Isoprene. Continuing work involves further evaluation of the coupled model results and investigation of the effects on air quality of the urban heat island temperature predicted by the ADMS-Urban Temperature and Humidity model under current and future climate scenarios.

An Integrated Study of Air Pollution Processes in Beijing (AIRPRO)

CERC are a partner in the NERC-funded AIRPRO project along with ten UK universities, two other research organisations, three Chinese research institutes and one Chinese university. The project aims to improve the understanding of Beijing’s air quality by conducting two intensive measurement campaigns and using the data to inform model developments. A linked PhD studentship aims to develop ADMS-Urban to predict interactions between haze and air quality by allowing particulate concentrations and humidity to affect the meteorological conditions and the solar radiation available for local photochemistry.

Process analysis, observations and modelling – Integrated solutions for cleaner air for Delhi (PROMOTE)

CERC are collaborating in the NERC-funded PROMOTE project with five UK universities and Indian research institutes. This project will investigate the interactions between meteorological processes such as winter fog events and poor air quality, as well as the relative importance of local and regional pollutant emissions and possible mitigation approaches. ADMS-Urban will be used to model street-scale air quality in Delhi.

Reviews on Urban Dispersion for ADMLC

CERC conducted a review of ‘Dispersion from Accidental Releases in Urban Areas’ in 2003 and also subsequently contributed to ‘A review of urban dispersion modelling’ in 2013. Both reviews were conducted for ADMLC (Atmospheric Dispersion Modelling Liaison Committee).

The 2003 report considers dispersion from localised sources released suddenly, or over longer periods, in urban areas, together with the related air flow and meteorology. It considers these phenomena and their modelling over the three spatial ranges relevant to urban areas, namely mesoscale, neighbourhood and building/street scales. The report reviews current understanding, experimental and numerical simulation data and the relative merits of different modelling approaches.

The 2013 report focuses on advances in the understanding of urban meteorology and dispersion from localised sources in urban areas, with special emphasis on recent developments since the 2003 review.

Learn more

• ADMLC website