AQUM

Short model description

AQUM is a limited area configuration of the Met Office Unified Model (MetUM), which uses the UKCA chemistry scheme (Savage et al., 2013). AQUM uses the RAQ (Regional Air Quality) chemistry scheme, which has 40 transported species (16 emitted) plus 18 non-advected species, and has 116 gas-phase reactions and 23 photolysis reactions. For aerosols, AQUM uses the CLASSIC scheme.

Operationally, AQUM runs at 12km resolution over a domain covering the UK and western Europe, producing a five day air quality forecast.

Model setup

AQUM version 8.3 was used, with the addition of new emissions branch to allow split between fire and anthropogenic emissions and the output of emission totals.

Model grid

The domain corresponds to the CORDEX-EU-44 domain with additional grid cells at the borders

• Rotated pole: lon = 198.0 , lat = 39.25
• startlon = 328.27
• startlat = -26.73
• dlon = 0.22
• dlat = 0.22
• nx = 238
• ny = 244

Emissions for 2010 simulation

Anthropogenic emissions

• From TNO/MACC for 2009
• Time variation:
  • Day-of-week and monthly-variation taken into account when producing daily gridded emissions data.
  • Hourly variation taken into account within model for gas-phase species to allow for longitudinal-based local time variations.
• NMVOC speciation (based on UK NAEI emissions speciation):

Species	HCHO	C2H4	C3H6	OXYL	TOLUEN	CH3CHO	C2H6	C3H8	C4H10	ME2CO	CH3OH
Fraction	0.0550	0.0784	0.0342	0.0241	0.0952	0.0153	0.1563	0.1090	0.2382	0.0784	0.1158

• Vertical profile:
  • Aerosols:
    • Area sources are emitted at the surface (20m)
    • Point sources are emitted in level 6 (320m)
  • Gas phase:

Height(m)	0-34.8	34.8-72.8	72.8-123.6	123.6-186.9	186.9-263.0
Fraction	0.5	0.3	0.1	0.05	0.05

Biogenic emissions

• Hourly varying emissions from TNO, averaged to give daily gridded emissions. The model then applies diurnal cycle within its code.

Biomass burning emissions

• From FMI at 0.1$^\circ$ resolution
• Gas emission scaling (CO, NOx, NH3, SO2, NMVOC) and TPM set to PM following recommendations on wiki
• NMVOC mass emissions are 32% of total PM emissions and mapped onto the RAQ species with the following fractions (kg species / kg NMVOC):

Species	HCHO	C3H6	CH3CHO	C2H6	C3H8	C4H10	ME2CO	C5H8	NO2
Fraction	0.031323	0.79029	0.041314	0.021633	0.003801	0.115453	0.008713	0.007917	0.016586

• Vertical distribution of gas-phase emissions as follows (approximates recommendation of emitting 50% in lowest 200 m and 50% between 200 and 1000 m):

Height(m)	0-34.8	34.8-72.8	72.8-123.6	123.6-186.9	186.9-263.0
Fraction	0.0714133	0.1071470	0.1428800	0.1785600	0.0476190

Height(m)	263.0-351.8	351.8-453.3	453.3-567.5	567.5-694.5	694.5-834.2	834.2-968.7
Fraction	0.0555595	0.0634881	0.0714286	0.0793690	0.0872976	0.0952381

• SO2 and NH3 emissions are inserted at level 6 (320m).
• PM emissions are spread 9.1625% into level 1 (20m), with the remainder spread equally into levels 2-11 (53.3-953m).

Boundary and initial conditions

Meteorological IC/BC

• Meteorological initial and boundary conditions are provided by running a Global, meteorology-only version of the MetUM at ~60km resolution, 70 vertical levels to 80km. Boundary conditions for the regional domain are output every 6 hours.

Chemical IC/BC

• Chemical/Aerosol LBCs are from the MACC reanalysis every 6 hours. The speciation into AQUM species are as follows:

MACC	MetUM
10% SO4	Aitken mode SO4
90% SO4	Accumulation mode SO4
SO2	SO2
Dust Bin 1	Split equally between Bins 1-3
Dust Bin 2	Bin 3
60% Dust Bin 3	Bin 4
30% Dust Bin 3	Bin 5
10% Dust Bin 3	Bin 6
BIGALK (=zero)	C3H8
CH2O	HCHO
GO3	O3
NO, NO2, C2H6, PAN, HNO3, CH4, CO	NO, NO2, C2H6, PAN, HNO3, CH4, CO
Fresh OC, Aged OC	Fresh OC, Aged OC
Fresh BC, Aged BC	Fresh BC, Aged BC

References

• Savage N. H., Agnew P., Davis L. S., Ordóñez C., Thorpe R., Johnson C. E., O’Connor F. M. and Dalvi M. (2013), “Air quality modelling using the Met Office Unified Model (AQUM OS24-26): model description and initial evaluation”. Geosci. Model Dev.,Vol. 6, pp. 353-372, doi:10.5194/gmd-6-353-2013.