modeling using the Pollution Climate Mapping (PCM) model UK NO X and NO 2

Transcription

1 UK NO X and NO 2 modeling using the Pollution Climate Mapping (PCM) model Susannah Grice, John Stedman, Sally Cooke, Andrew Kent, Daniel Brookes, Helen Walker and Keith Vincent 8th December 2010

2 Presentation overview

3 Presentation overview

4 Policy context: European directives EU directives are key drivers in shaping UK air quality policy priorities The Air Quality Directive (2008/50/EC) and 4 th Daughter Directive (2004/107/EC) Limit values, critical levels, target values, exposure reduction target and long term objectives NO X, NO 2, PM 10, PM 2.5, SO 2, CO, C 6 H 6, O 3, Pb, As, Cd, Ni and B[a]P Assessments carried annually 43 UK zones Assess compliance with the environmental objectives listed above Questionnaire reports base year measurements and modelling results to EU Model projections calculated for 2010, 2015 and 2020 Air quality plans generated for pollutants with exceedances Demonstrates how compliance will be achieved by the deadline specified in the directives

5 Policy context: NO X and NO 2 NO 2 and NO X limit values/critical levels Pollutant Averaging period Description Number of zones exceeding in 2009 NO 2 Calendar year 40 µgm Hourly NO 2 compliance challenges No more than 18 hourly exceedances of 200 µgm -3 in a calendar year NO X calendar year 30 µgm -3 (selected vegetation areas only) * assessment based on measurements only (no model data available) Direct NO 2 emissions from diesel vehicle exhausts often high Reflects UK fleet mix 2* 0 Projected downwards trends in NO X emissions from traffic over optimistic Even with optimistic downwards trends compliance by 2010 (or even 2015) is difficult

6 Presentation overview

7 Introduction to the PCM model: UK air quality management tool Pollution Climate Mapping (PCM) model Operated as part of the UKAAQA contract for defra (PM John Stedman) Brings together information from ambient concentration measurements, emissions inventories and air quality models Model results used for reporting under the directives Provides strategic policy analysis to defra Help understand and quantify the current AQ situation Source apportionment analysis Provide projections of future air quality What if scenario modelling Modelling potential AQ impacts of possible policy measures Model run time 2-3 hours (once input data are set up)

8 Introduction to the PCM model: Model overview GIS based model UK wide maps 1km x 1km grid resolutions for background concentrations Concentrations along urban major road links Maps built up from layers Regional background (interpolated from Rural measurements) Point sources modelled using dispersion model Area sources modelled using a dispersion kernel approach Roadside increment model Calibrated using automatic monitoring data from the AURN NO 2 calculated from NO X using oxidant partitioning model

9 Presentation overview

10 NO X model layers: Regional background Regional background NO X concentrations i.e. NO X from distant sources Input data NO X measurements at 11 remote/rural automatic sites (AURN) NO X estimated from 15 rural NO 2 diffusion tubes (acid deposition network) Correction applied to monitoring data to remove contributions from local sources Estimated contribution from area source components based on previous year Contributions from large point sources for current year Contributions from small point sources for current year Map of regional background NO X concentrations Grid (5km x 5km resolution) Calculated using a bi-linear interpolation of corrected measurements

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12 NO X model layers: Point sources Definition Emissions of a known amount from a known location (e.g. a power station) Input data: NAEI point sources emissions Point sources stack parameter information database Met data Large point sources Annual NO X emission > 500 tonnes and/or stack parameters already available in the database Emissions data and stack parameters processed in PCM point sources database Each point source modeled explicitly in ADMS For 2009 mapping >1000 individual point sources modeled

13 NO X model layers: Point sources Small points Annual NO X emission < 500 tonnes and stack parameters unavailable in the database Modelled using small points kernel method Based on pre-run model results from ADMS Assumes all point sources are IPPC compliant, so stack height varies with emission Calculations done in PCM point sources database and GIS Outputs: 1km x 1km grid of concentrations resulting from point source emissions

14 NO X model layers: Point sources Large points Small points Combined

15 NO X model layers: Area sources Definition Diffuse emissions from many unspecified locations. (e.g. emissions from domestic heating, or from shipping) Input data 1km x 1km NAEI area source emissions maps NAEI emissions projections Met data AURN monitoring data

16 NO X model layers: Area sources Method outline 1. Generate dispersion kernels These kernels calculate the concentration in each UK grid square based on the emissions in the surrounding grid squares Calculate the concentration resulting from unitary emission in centre 1km x 1km square for evenly spaced receptor grid (33km x 33km) using ADMS 4.2 Post processing of kernels so source becomes receptor 2. Calibrate kernels using monitoring data Apply to NAEI 1km x 1km emission maps to calculate an uncalibrated area source concentration grid for the UK Calibrate by comparing with measured concentrations at monitoring sites Measurements corrected for regional background and point source contributions 3. Apply the calibrated kernels to the area source emissions grids

17 NO X model layers: Area sources Outputs 1km x 1km grids of concentrations resulting from area source emissions for each pollutant Groups of kernels developed Road traffic Volume source of height 10m Applied to road transport emissions Non-road traffic sources Volume source of height 30m Applied to all other area source emissions Conurbations, other urban and rural dispersion site conditions Surface roughness Minimum Monin Obukhov length (LMO)

18 NO X model layers: Area sources

19 NO X model layers: Area sources

20 NO X model layers: Total background, 2009

21 NO X model layers: Roadside increment Definition The additional local concentration component from urban major UK roads Added to the background concentration to give a total NO X concentration for each road Input data Road link mapped emissions data from the NAEI Data on road type, vehicle flows for each individual road link AURN monitoring data Method Empirically based approach (similar to DMRB) For each road link, applies adjustment to emission depending on traffic flow to account for different factors that influence dispersion Calibrated using AURN monitoring data Outputs Corrected for total background i.e. measured roadside increment = total measured modeled background concentration Concentration estimates for each road link included in the model

22 NO X model layers: Total roadside, 2009

23 NO X model layers: Projections Maps calculated for future years 2010, 2015 and 2020 Background and roadside locations Regional background Base year regional background concentrations divided into UK, EU and shipping components based on EMEP model source apportionment Emissions projections for each source used to scale that component for future years Area sources and point sources Base year non-road transport NAEI emissions maps scaled forwards using NAEI emissions projections Road transport emissions re-mapped and concentrations re-modelled Assumes that base year calibration applies for future years Roadside increment model NAEI road link data calculated for future years Fleet weighted emission factors and projected traffic flows Roadside increment model re-run

24 Presentation overview

25 NO 2 model: Oxidant partitioning model The model Developed by Jenkins (2004), improved by Murrells et al (2008) Enables annual mean NO 2 concentrations to be calculated from annual mean NO X!"!## $ [OX] described on subsequent slides f-no X One equation for an idealised relationship Assumes annual average NO X applies for all hours of the year + other simplifying assumptions Analytical solution Four equations for realistic cases Takes into account hourly variations in NO X concentrations throughout the year

26 NO 2 model: Oxidant partitioning model Regional oxidant concentrations [OX] B Two components Hemispheric background [OX] H High in SW, lower in NE Regional modification [OX] R Summer: increase due to photochemical generation of oxidant Winter: decrease due to dry deposition

27 NO 2 model: Oxidant partitioning model Local oxidant %!###!# &"'(! Non-road traffic sources f-no 2 constant with time Road traffic sources f-no 2 generally increasing with time Road link specific f-no 2 calculated using Fleet weighted f-no 2 for each vehicle type from NAEI NO X road link emissions by vehicle type Local oxidant map calculated NO X concentration maps (split into road and non-road components) x relevant f-no 2

28 NO 2 model: Oxidant partitioning model Example of how fleet weighted f-no2 for specific vehicle types varies with time Reflects different Euro standards within the vehicle fleet mix

29 NO 2 model: Oxidant partitioning model Applying the oxidant partitioning model Model tested by calculating NO 2 from measured NO X concentrations Background and roadside considered separately Comparison of modeled NO 2 with measured Model calibrated as a function of NO X

30 Background NO 2, 2009 Roadside NO 2, 2009

31 Model results Background, 2009 Roadside, 2009

32 Presentation overview

33 Model results Used for reporting on under the air quality directives Base year modeling and projections to 2010, 2015 and 2020 Source apportionment analysis Identification of appropriate measures Development of air quality plans for reporting

34 Model results 2009 results not yet published, so 2008 results presented here Total number of zones with exceedances in 2008 >40 > Background Roadside Total Background Roadside Total Annual mean NO 2 > 40µm Background area exceeding 0.03% 0.01% 0.01% 0.00% 0.00% Population in exceeding area 0.85% 0.30% 0.10% 0.04% 0.00% Road length exceeging 26.56% 15.83% 7.80% 3.55% 0.18%

35 Model results

36 Model results

37 Model results

38 Summary PCM model is used for directive reporting and policy analysis/development NO X model is made up of a number of layers Each treated differently within the model Background layers: regional background, point sources, area sources Roadside increment NO 2 concentrations calculated from NO X concentrations Oxidant partitioning model Model results suggest that compliance with the limit values for NO 2 is going to be difficult to achieve Results can be processed to help understand the causes of exceedances e.g. source apportionment analysis More model information available from:

39 AEA Susannah Grice Specialist Consultant AEA, The Gemini Building Fermi Avenue Harwell Didcot OX11 0QR Tel: +44 (0) E: W: Copyright AEA Technology plc This presentation is submitted by AEA. It may not be used for any other purposes, reproduced in whole or in part, nor passed to any organisation or person without the specific permission in writing of the Commercial Manager, AEA Technology plc.