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30 Jan 2024Exploring air quality model evaluation techniques

Comparisons of modelled and measured data are a key part of evaluating model performance. CERC's latest project for the Atmospheric Dispersion Modelling Liaison Committee (ADMLC) is investigating approaches to air quality model evaluation. A literature review is identifying established and emerging model evaluation techniques and performance metrics for a variety of model types and applications. Case studies will then be used to test the different performance metrics individually and in combination. The project aims to develop best practice recommendations for evaluating a broad range of model applications, reporting late in 2024.

CERC have extensive experience of model evaluation through assessments of the ADMS family of models and inter-comparisons with other models. Jenny Stocker, CERC's Associate Director (Research) has been a long-standing participant in the Forum for Air Quality Modelling (FAIRMODE) initiative which has developed model quality and model performance indicators. CERC have developed and made public the 'Model Evaluation Toolkit' which allows user-friendly access to a broad selection of graphical and statistical model evaluation analyses. The Model Evaluation Toolkit was originally developed under the FP7 PASODOBLE project and recently extended under the SPF Clean Air Programme MAQS-Health project. It makes use of Openair functions and can additionally generate the statistics and graphics recommended by FAIRMODE. The image shows polar plots of the measured and modelled variation of hourly average NOx concentrations (units ppb) with wind speed and direction at the Schildhornstrasse site in Berlin produced using the Model Evaluation Toolkit, as published in Seaton et al. (2022).


24 Jan 2024Published recommendations for use of NWP meteorological data in dispersion modelling

CERC's investigation of the impacts of using modelled (NWP) meteorological data on dispersion modelling outcomes has now been published by the Atmospheric Dispersion Modelling Liaison Committee (ADMLC). The project was commissioned to examine the effects of NWP model grid resolution on dispersion modelling, in both regulatory and emergency planning contexts, and to make recommendations for the use of NWP data in dispersion modelling.

The report begins with an evaluation of NWP outputs in comparison with meteorological observations at eight UK sites (shown on the map). This is followed by a comparison of ADMS and AERMOD dispersion outcomes for idealised sources at four locations with observed and modelled meteorological data. The report also includes an investigation of the interaction between fine-scale NWP data and local flowfield modelling using the FLOWSTAR model for flow over complex terrain in ADMS. Finally, there are results from the UK Health Security Agency (UKHSA) investigation of the effects of NWP grid resolution on the outcomes of probabilistic accident consequence modelling with the PACE model.

Interim results from the project were presented at CERC's ADMS User Group Meetings in 2022 and 2023; the presentations are available from the User Area. Christina Hood from CERC will also present the sensitivity of ADMS and AERMOD dispersion outputs to varying input meteorological data at the international conference on Harmonisation within Atmospheric Dispersion Modelling for Regulatory Purposes (Harmo) in June 2024.


19 Dec 2023Street-scale pollution maps for Ireland now available

Results from CERC's modelling of street-scale air pollution in Ireland have been published as part of the Irish Environmental Protection Agency (EPA) report 'Air quality in Ireland 2022'. The full CERC report with high-resolution maps for a wider range of regulated air pollutants is also available. The predicted concentrations were evaluated with measured concentrations with generally good performance for both years at all site types, meeting the FAIRMODE model quality objectives. Modelled concentrations were compared to current Irish air quality standards air quality standards, with exceedances generally associated with the major road network. Most of Ireland meets the World Health Organisation (WHO) guideline for annual average NO2 concentrations, with exceedences in urban areas, while a substantial proportion of Ireland does not meet the lowest guideline for annual average PM2.5 concentrations.

CERC were commissioned by the Irish EPA to provide street-scale modelling of Ireland for 2018 and 2019. This used the Multi-model Air Quality System (MAQS) coupled system (developed by CERC) to link regional scale hourly pollution predictions from the EMEP model with local ADMS-Urban modelling. The UK Centre for Ecology & Hydrology (UK CEH) ran the WRF mesoscale meteorological model and EMEP chemical transport model with 1 km horizontal grid resolution over Ireland. CERC carried out detailed road traffic emissions calculations in EMIT based on traffic flow data supplied by the National Transport Authority (NTA) and Transport Infrastructure Ireland (TII). Gridded emissions from non-traffic sources were obtained from the MapEire inventory.

Street canyon effects on dispersion were included in major urban areas. Three major road tunnels were also included in the modelling using the ADMS-Urban tunnels module, with high concentrations noticeable around the portals of the Dublin Port tunnel. The model output is at hourly temporal resolution and irregular spatial resolution. The MAQS PostProcessor utility was used to calculate annual average and high percentile hourly concentrations on regular grids for plotting, at 20 m resolution for whole country maps and 5 m resolution for individual cities.

The 2019 mapped concentrations were uploaded to the recent FAIRMODE composite mapping exercise, which combines and assesses modelling results for different parts of Europe. Preliminary results from this exercise were presented in October 2023, with CERC's modelling results showing good performance in the 'high resolution, unassimilated' category. Presentations describing the Irish emissions inventory development and coupled system modelling were given by CERC at the 2023 ADMS-Urban and ADMS-Roads User Group Meeting.


18 Dec 2023Review of methods for monitoring and modelling air quality

CERC recently contributed modelling expertise to a comprehensive Environment Agency (EA) report that reviewed methods for air quality monitoring and modelling, and their integration. The report examines both well-established techniques already employed by the EA, such as Gaussian plume dispersion for air quality modelling, and emerging technologies, such as data assimilation and machine learning for integration. Factors such as spatial-temporal resolution, cost considerations, the maturity of the technique, and requisite user expertise are evaluated. The report provides practical recommendations on the suitability of different air quality assessment techniques for EA requirements, including their regulatory responsibilities.

The report is a significant collaborative effort engaging experts across governmental, industrial and academic sectors, with specialist knowledge in emission measurements, air quality measurements, and modelling – many thanks to AQC, Aether and all involved! It offers valuable insight for those interested in the rapidly evolving landscape of air quality techniques.


12 Dec 20232023 ADMS User Group Meetings – presentations are available to download

Following this year’s ADMS User Group Meetings, which took place in York on 29-30 November, electronic copies of the presentations are now available to download from the CERC website User Area. Model users with a valid support contract, including all annual licence holders, are entitled to register for password-protected access to the User Area. To register, or to be reminded of your password, click here.

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