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

TLDR

The study employs a coupled regional‑to‑local model that combines the 5‑km EMEP4UK chemistry‑climate system with the ADMS‑Urban dispersion model, using adjusted NOx, NO2, PM10, and PM2.5 emission factors and evaluating performance against background and near‑road measurements across annual.

Abstract

Abstract. A coupled regional-to-local modelling system comprising a regional chemistry–climate model with 5 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 NOx and NO2 and non-exhaust emission rates of PM10 and PM2.5 which have been adjusted compared to standard factors to reflect real-world emissions, with increases in total emissions of around 30 % 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 PM2.5 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 % of the area of London exceeded the EU limit value of 40 µg m−3 for annual average NO2 in 2012, whilst areas of exceedances of the annual average limit values of 40 and 25 µg m−3 for PM10 and PM2.5 respectively were negligible.