The ACRG uses a suite of global and regional chemical transport models to simulate the emissions and transportation of species linked to air quality. 

Global modelling – STOCHEM-CRI

STOCHEM-CRI is a global 3-dimensional chemistry transport model in which the troposphere is split into 50,000 constant mass air parcels. The air parcels are advected every three hours using a 4th order Runge-Kutta scheme via a Lagrangian approach. It is an offline model with the transport and radiation driven by archived meteorological data from the UK Meteorological Office Unified Model which operates at a grid resolution of 1.25° longitudes by 0.83° latitude and twelve unevenly spaced vertical levels, with an upper boundary up to 100 hPa. The chemical processes that occur within the parcel, together with emission, deposition (both dry and wet) and removal processes are generally uncoupled from transport processes to enable local determination of the chemistry timestep The chemical mechanism in this model is the common representative intermediates mechanism version 2, reduction 5 (CRI v2-R5), which consists of 229 chemical species competing in 627 reactions. STOCHEM-CRI outputs onto grid cells with a resolution of 5° longitude by 5° latitude and has 9 vertical levels, which span from the surface up to an altitude of 16km.  It has been used extensively to simulate a range of tropospheric gases and aerosols & evaluated in model inter-comparison studies.

Regional modelling – WRF-Chem

WRF-Chem is a regional 3-dimensional meteorological model with online chemistry. It has a 15km horizontal resolution and 41 vertical levels, with enhanced resolution within the boundary layer.  Meteorology is driven using ECMWF ERA-Interim reanalysis data with a 6 hourly time resolution, and surface data extracted on a N256 gaussian grid, while volume data was extracted at a lower resolution on a N128 gaussian grid. WRF-Chem simulates the emission, transport, mixing and chemical processing of trace gases on the same time step as the meteorology. This makes the model ideal for investigating the impacts of weather on atmospheric composition (and vice versa) on a regional scale. The gas phase chemistry in the model is treated using the CRI-v2R5 mechanism and the aerosol scheme used is MOSAIC with 8 size bins (from 0.03-10 μm).