URBAN ATMOSPHERIC CHEMISTRY MODELLING AT THE METEOROLOGICAL OFFICE Dick Derwent Climate Research

1. URBAN ATMOSPHERIC CHEMISTRY MODELLING AT THE METEOROLOGICAL OFFICEDick DerwentClimate Research Urban Air Quality Modelling APRIL Imperial College London Tuesday March 4th 2003

2. ACKNOWLEDGEMENTS This work has been sponsored by the Air and Environmental Quality Division DEFRA and by the Government Meteorological Research Programme of the Met Office. Thanks are to Derrick Ryall, Alison Redington and Alistair Manning.

3. LONG TERM STRATEGY FOR URBAN ATMSOPHERIC CHEMISTRY MODELLING To develop improved tools for predicting ozone and particles on all time and spatial scales from global to urban spatial scales from episodic to climate timescales for forecasting and research purposes Using as building blocks Master Chemical Mechanism Met Office Lagrangian Dispersion NAME model

4. ATMOSPHERIC CHEMISTRY MODELLING APPROACHES Tropospheric chemistry models have generally either been EULERIAN or LAGRANGIAN Eulerian models use a fixed co-ordinate framework through which the atmospheric flow moves. Lagrangian models describe the flow as a stream of air parcels which move in three-dimensions.

5. ON-LINE OR OFF-LINE Another important aspect of model formulation is whether the atmospheric chemistry is handled off-line or on-line. In an off-line model, the meteorology is calculated separately from the chemistry and there is no feedback between the chemistry and the meteorology. In an on-line or coupled model, the chemistry and meteorology are solved simultaneously allowing the possibility of chemical data assimilation.

6. EULERIAN VS LAGRANGIAN APPROACHES Met Office global 3-D chemistry transport model STOCHEM and regional scale UK PTM photochemical trajectory model have adopted a Lagrangian approach and so have more chemistry than most Eulerian models. Met Office NAME dispersion model has adopted a Lagrangian approach to atmospheric dispersion and chemistry. The new Unified Model is semi-Lagrangian and this will provide a very challenging framework for atmospheric chemistry modelling.

7. URBAN ATMOSPHERIC CHEMISTRY MODELLING Almost entirely Eulerian approaches have been adopted historically. The main approach in the USA is the Models-3 Eulerian modelling system which runs at 36 km, 12 km and 4 km and implements the Carbon Bond Mechanism version 4.0. A special version has been operated at sub 1-km to study air quality within the urban canopy. The main difficulties lie in the meteorological and emissions drivers and the limited nature of the chemical mechanisms employed.

8. COMPARISON OF MCMv3.0 AND CBMv4.0 CBMv4.0 is based on outdoor smog chamber studies which focus largely on ozone formation rather than free radical budgets CBMv4.0 is a compact mechanism involving up to 10 VOCs and 25 species latest version is CBM Morpho 2002 MCMv3.0 involves 123 VOCs, over 4300 species and 12000 reactions

9. Met Office NAME model • Atmospheric Dispersion model • predicts the transport of a wide range of airborne pollutants • 1-1000’s km, hours - days • driven by 3-D meteorology from Unified Model • Emergency response • national & international operational responsibilities • nuclear, volcanoes, fires • Air pollution • episode studies , air quality forecasts, policy support • Source attribution • where, when, how much ?

10. THE MET OFFICE NAME MODELNext generation acid deposition model 15-minute and 15 km resolution treatment of particulates and acid deposition from SO2, NOx and NH3 developed through funding from Environment Agency and DEFRA AEQ Division 3-hourly back attribution atlas developed through funding from Met Office GMR programme

11. PROGRESS REPORT COUPLING NAME AND THE MCM secondaryparticle sulphate and nitrate chemistry running in NAME secondary organic aerosol chemistry working but not yet in NAME urban ozone formation running in NAME for NERC URGENT/PUMA next step with NAME is to describe regional and global baseline fields for O3, NOy, CO, VOCs and particles

12. EPISODE STUDIESEast Midlands - High SO2

13. IMPACT OF SO2 EMISSIONSNottingham episode - 1998 Annual emissions Hourly emissions

15. BACK ATTRIBUTION - NAME • Identify possible source regions • Run NAME ‘backwards’ from receptor • Example - PM10>100mgm-3 on 12/09/2002 • Forecasts or episode analyses

16. LONDON ROUTINE COLUMN TRAJECTORY MODEL vertical column of air parcels from surface to 1300 metres vertical exchange using eddy diffusion coefficient, wind speed profile and dry deposition to surface hourly meteorological data taken from Heathrow Airport for 1995 NO - NO2 - O3 photochemistry LAEI NOx inventory for 1999, 2005 and 2010 with direct emissions of NO2 together with NAEI inventory for south-east region hourly ozone data from Harwell, Sibton and Lullington Heath

17. LRCTM MODEL The LRCTM model identifies and describes in some detail the following major sources of NO2 in London: direct emission of NO2 from NOx sources, assumed to be 5% by volume in the base case model oxidation of NO by ozone advected into the model from the global baseline or from regional-scale photochemical pollution events oxidation of NO in the NO + NO + O2 reaction in local-scale wintertime stagnation events

20. LRCTM MODEL RESULTS FOR 1999

21. LRCTM MODEL RESULTS FOR 2005

22. LRCTM MODEL RESULTS FOR 2010