CERC — Environmental Software and Services

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MAQS (formerly ADMS-Urban RML)

Multi-Model Air Quality System

What is MAQS?

The Multi-Model Air Quality System (MAQS) is an automated system for coupling the high-resolution ADMS-Urban air dispersion model to a regional air quality model with hourly concentration output such as CMAQ, CAMx, EMEP, CHIMERE or WRF-Chem. Other regional models are supported via generic model file formats. Gridded annual average background concentration data (for instance, as generated by PCM in the UK) can be used in lieu of hourly regional model data. Coupled system output comprises predictions of pollutant concentrations for a specified domain, which takes into account both regional and local pollutant transport and chemistry effects.

The aim of the MAQS coupled system is to combine the complementary 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 act over long spatial and temporal scales, and can model the accumulation of concentrations in very low wind speed conditions. These grid-based chemical transport models (CTMs) do not resolve the high gradients of concentration close to individual sources such as roads.
  • Local (usually Gaussian-type plume) models can represent the fine-scale concentration gradients from explicitly defined sources in detail, but generally only account for simplified chemical mechanisms and spatially homogeneous meteorological data, limiting their applicability for receptors far from the source (e.g. more than 50 km).

Coupling local and regional models allows both the resolution of high concentration gradients close to a source, and the accurate representation of transport and chemistry over large spatial and temporal scales. MAQS combines regional and local concentrations in such a way as to minimise double-counting of emissions, while remaining computationally efficient and user-friendly. Meteorological data from the WRF meso-scale model (or another model with output converted to 'generic' input file format) is used for both the regional modelling and the local modelling.

MAQS runs on Linux and comprises:

  • The ADMS-Urban dispersion model (Linux executable and Windows interface)
  • Tools to process the regional model data
  • Software to automate running these components, including parallelisation
  • A post-processing suite for generating spatial and temporal subsets

MAQS is supplied with an ADMS-Urban Windows interface for generating input files containing local emissions and specifying output point locations. Under the MAQS-Health project, CERC developed MAQS to support a 'generic' input format for meteorological and concentration data, allowing data from other regional models to be converted for use in the system.

Typical applications of MAQS include:

  • Developing and testing the impact of regional and local air quality management policies on pollutant concentrations throughout complex urban areas
  • Exposure assessments
  • Provision of detailed street-scale air quality forecasts for an urban area in combination with a regional scale forecast for surrounding rural area

Who uses MAQS?

PRAISE-HK Air Quality and Exposure Health Risk information app
HKUST logo

PRAISE-HK Air Quality and Exposure Health Risk information app.

MAQS is for current users of regional air dispersion models who wish to increase the resolution of their modelling over urban areas to take account of street-scale concentration gradients in a computationally efficient way, and for users of ADMS-Urban who wish to account for regional variations in meteorology and background pollutant concentrations. The MAQS design allows regional and local modelling to be performed separately, facilitating collaborations between regional and local modelling specialists and allowing a single set of regional modelling data to be used to test many local modelling scenarios.

Image of West Midlands NO2 and PM2.5 concentration contours

Annual average NO2 and PM2.5 concentrations for the West Midlands (UK), modelled at street scale resolution using MAQS as part of the WM-Air project. From Zhong et al. (2022).

Pioneering uses of MAQS include:

Why use MAQS?

Image of Scotload NOx concentration contours for 2018

Annual average NOx concentrations for Scotland in 2018, modelling with the MAQS-Health coupled system led by the University of Edinburgh.


Coupled system annual average NO2 pollution maps

Coupled system annual average NO2 pollution maps for 2019 with high resolution insets of Dublin, Galway, Limerick, Cork and Waterford.

Coupling the local model ADMS-Urban within a regional model using MAQS allows both the resolution of high concentration gradients close to a source, and the accurate representation of transport and chemistry over larger spatial and temporal scales. MAQS combines the regional and local concentrations in such a way as to minimise double-counting of emissions, while remaining computationally efficient and user-friendly.

The principal features of MAQS are:

  • An automated control system with logging of progress to file and screen
  • Option for use of the GNU Parallel approach for distributing runs across multiple machines
  • Compatibility with CMAQ, CAMx, CHIMERE, EMEP and WRF-Chem regional air pollution models, with options to link to other regional models via generic input file formats
  • Automatic division of a large coupled model domain into separate runs for each regional model grid cell, with appropriate local meteorology from the meso-scale meteorological model and regional background concentrations
  • Flexibility regarding the size and shape of the nesting domain
  • No requirement to re-run the regional air quality or meteorological models
  • Inclusion of advanced modelling techniques for urban areas through the use of ADMS-Urban: street canyons, tunnels, elevated roads, noise barriers and urban canopy flow field calculations

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