Air quality simulations for London using a coupled regional-to-local modelling system

• Main Authors: C. Hood, I. MacKenzie, J. Stocker, K. Johnson, D. Carruthers, M. Vieno, R. Doherty
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-08-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/18/11221/2018/acp-18-11221-2018.pdf

<p>A coupled regional-to-local modelling system comprising a regional chemistry–climate model with 5&thinsp;km horizontal resolution (EMEP4UK) and an urban dispersion and chemistry model with explicit road source emissions (ADMS-Urban) has been used to simulate air quality in 2012 across London. The study makes use of emission factors for NO_<i>x</i> and NO₂ and non-exhaust emission rates of PM₁₀ and PM_2.5 which have been adjusted compared to standard factors to reflect real-world emissions, with increases in total emissions of around 30&thinsp;% for these species. The performance of the coupled model and each of the two component models is assessed against measurements from background and near-road sites in London using a range of metrics concerning annual averages, high hourly average concentrations and diurnal cycles. The regional model shows good performance compared to measurements for background sites for these metrics, but under-predicts concentrations of all pollutants except O₃ at near-road sites due to the low resolution of input emissions and calculations. The coupled model shows good performance at both background and near-road sites, which is broadly comparable with that of the urban model that uses measured concentrations as regional background, except for PM_2.5 where the under-prediction of the regional model causes the coupled model to also under-predict concentrations. Using the coupled model, it is estimated that 13&thinsp;% of the area of London exceeded the EU limit value of 40&thinsp;µg&thinsp;m⁻³ for annual average NO₂ in 2012, whilst areas of exceedances of the annual average limit values of 40 and 25&thinsp;µg&thinsp;m⁻³ for PM₁₀ and PM_2.5 respectively were negligible.</p>