Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

PM2.5 in the UK
166
PM2.5 Emission sensitivity coefficient
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
SOx NOx VOC NH3 CO EC OC
Emitted species
Figure A2.6.2: Fractional reduction in annual mean PM2.5 at Harwell,
Oxfordshire, for a given reduction in the emissions of each precursor species.
A2.7: FRAME
51. FRAME is a Lagrangian model using straight line trajectories with a 1 o angular
resolution which runs at either a 1 km or a 5 km resolution over the British Isles
and 50 km resolution over Europe. The model includes 33 layers with a fine
vertical grid spacing (1 m at the surface layer). Area emissions are injected into
sector-dependent levels and point source emissions are treated with a plume
rise routine. Vertical diffusion in the air column is calculated using K-theory eddy
diffusivity. Wet deposition is calculated using a “constant drizzle” approximation
driven by an annual rainfall map. Five land classes are considered and a
vegetation-specific canopy resistance parameterisation is employed to calculate
dry deposition. The model chemistry includes gas phase and aqueous phase
reactions of oxidised sulphur and oxidised nitrogen leading to the formation
of fine ammonium sulphate and ammonium nitrate aerosol as well as a large
nitrate aerosol category. The modelled concentrations of secondary inorganic
aerosol have been validated by comparison with measurements from the UK
Acid Gases and Aerosols Monitoring Network (AGANet). Modelled nitrate
aerosol across the UK and validation against measurements for the year 2008
is illustrated in Figure A2.7.1. A comprehensive validation of the modelled
aerosol concentrations is given in Dore et al. (2007) and, for the year 2003, in
the report of the Defra model inter-comparison (Carslaw et al., 2011). Both
the measurements and the model show a strong decreasing gradient in nitrate
aerosol concentrations from the south-east to the north-west of the UK.
52. Source–receptor matrices of particulate concentrations have been generated
for use in the UK Integrated Assessment Model (UKIAM) (Oxley et al., 2003).
This involves calculating the contribution to particulate matter from different
emissions sources (SO2, NOx, NH3, etc.) according to sub-SNAP sector and
region (England, Scotland, Wales, Northern Ireland and London), as well
as from European sources and international shipping. The UKIAM source–
receptor matrices are the basis for calculating future changes in particulate
concentrations driven by implementation of policies to abate targeted primary
emissions.