ADMS ADMS 3.3 Modelling Summary of Model Features

ADMS ADMS 3.3 CERC –“New Generation” Model –Detailed description of atmosphere based on boundary layer properties Features –Point, area, line, volume and jet sources –Multiple sources and pollutants –Buildings and Topography –Plume rise –Single condition or statistical meteorology –Odours, radioactivity, plume visibility –Deposition (Wet and Dry) –Statistics, long and short term, percentiles

ADMS Factors Influencing Dispersion –Meteorology Wind Speed and direction Atmospheric stability (Monin–Obukhov Length and Boundary Layer Height) –Release point and conditions Elevation Velocity Temperature Ground roughness –Buildings If > 1/3 stack height –Topography If steeper than 1:10 slope

ADMS Meteorology Older Models –Passive dispersion model Pasquill-Gifford Stability Classes (A – G) Wind speed, direction ADMS –Boundary Layer Model Boundary layer height Monin – Obukhov length Wind speed, direction

ADMS Meteorological Parameters Boundary Layer Height –Height at which surface effects influence dispersion –ADMS calculates boundary layer properties for different heights based on meteorology Monin-Obukhov Length –Measure of height at which mechanical turbulence is more significant than convection or stratification –ADMS calculates M-O length based on meteorology and ground roughness

ADMS Meteorology Options Specific Data Wind speed, wind direction, date, time, latitude, boundary layer height, cloud cover Met Office Data Statistical data (10 years) –2200 lines of data (medium run times) Hourly sequential data (1 – 5 years) –Can be used to identify specific conditions for known dates and times –8760 lines of data per year (long run times) –Use to compare releases against environmental standards (preferred option by EA)

ADMS Meteorology Effects Typical atmospheric conditions within the UK. Pasquill - Gifford Stability Classes as modelled in ADMS No exact correlation between boundary layer parameters Stability Class Wind Speed (m/s) Boundary Layer Height (m) Monin – Obukhov Length (m) Conditions A Convective - Hot Still Day B Convective C Convective D5800∞Neutral - Normal UK Day E Stable F210020Stable - Still Night G11005Stable

ADMS Example of A – G Conditions Stack Release –SO 2,150 g/s –50 m stack –5 m diameter, –20 m/s velocity –15°C

ADMS A – G conditions Centre Line Ground Level Concentrations

ADMS A1 Conditions Contour Plot Convective - Hot Still Day

ADMS D5 Conditions Contour Plot Neutral - Normal UK Day

ADMS F2 Conditions Contour Plot Stable - Still Night

ADMS Buildings Can have significant effects –Entrain pollutants into leeward cavity of building –Increased concentrations close to building –Decreased concentrations further away –Only relevant if >1/3 stack height –ADMS allows 10 buildings

ADMS Building Effects – Tall Stack Tall Stack –Release of NOx from a 50 m stack (3 m diameter, 5 m/s velocity, 30°C, 1 g/s NOx) –Unstable weather conditions –Stack is at the centre point of the building –Building is 30 m high, 30 m wide, 67 m long

ADMS Tall Stack – No Building

ADMS Tall Stack – With Building

ADMS Building Effects – Short Stack Short Stack –Release of NOx from a 35 m stack (3 m diameter, 5 m/s velocity, 30°C, 1 g/s NOx) –Unstable weather conditions –Stack is at the centre point of the building –Building is 30 m high, 30 m wide, 67 m long

ADMS Short Stack - Without Building

ADMS Short Stack - With Building

ADMS Topography Can effect dispersion –Changes plume trajectory –May increase or decrease concentrations –Include if terrain exceeds 1:10 (maximum 1:3) –Terrain data available from Ordnance Survey

ADMS Topography Example –Release of NOx from a 65 m stack –5 m diameter –5.25 m3/s flowrate –69°C, –1 kg/s NOx –Neutral weather conditions 10 m/s wind Boundary layer 1000 m –Simple hill 2.6 km to the East and 1 km South of the release

ADMS Without Hill

ADMS With Hill

ADMS 3D Hill

ADMS Statistical Meteorology 10 years statistical data 1 – 5 years hourly sequential data Can calculate –Annual averages –Percentiles (worst case conditions) –No of exceedences/year –Areas affected Direct comparison with UK Legislation (NAQS, PPC)

ADMS Statistical Results

ADMS Statistical + Topography Reproduced from Ordnance Survey® Panorama Digital Data, by permission of Ordnance Survey® on behalf of the Controller of Her Majesty’s Stationary Office. © Copyright All rights reserved. Licence No

ADMS Digital Maps Available from Ordnance Survey 1:50000 or 1:10000 Can overlay release contours onto maps

ADMS Digital Map Example Reproduced from Ordnance Survey® 1:10K Raster Data, by permission of Ordnance Survey® on behalf of the Controller of Her Majesty’s Stationary Office. © Copyright All rights reserved. Licence No

ADMS Digital Map + Topography + Concentrations Reproduced from Ordnance Survey® Panorama Digital Data and1:10K Raster Data, by permission of Ordnance Survey® on behalf of the Controller of Her Majesty’s Stationary Office. © Copyright All rights reserved. Licence No

ADMS Odours Model as Odour Units –ou: Number of times the mixture must be diluted at STP to reach detection limit of 1 ou. –ou E : The mass of pollutant that when evaporated into 1m 3 of gas at STP is 1 ou. –Information on detection limit is required. ADMS –Input and output in terms of ou or ou E.

ADMS Odour Example Release from landfill site –Odours in ou E –Two area sources, one line source Landfill 1: 100 m x 100 m, 10 ou E /m 2 /s Landfill 2: 100 m x 100 m, 5 ou E /m 2 /s Line 1: 200 m, 2 ou E /m/s –Flat terrain, no buildings –Neutral conditions 10 m/s wind Boundary layer 1000 m –Short term hourly average concentration

ADMS Odour Example - Sources

ADMS Odour Example - Results

ADMS Time Varying Releases Release rates often vary with production Time varying releases –Hourly sequential meteorological data –Details of release for each hour of met data flow, temperature, concentration, velocity Results can differ considerably when compared to average releases

ADMS Fluctuations Meteorology usually stable over 1 hour Turbulence causes short duration fluctuations Interest in lower times for exposure –Odours –NAQS (SO 2, 15 minute mean) ADMS turbulence calculations –Percentiles –Probability distribution function –Toxic response

ADMS Other Features Variable surface roughness Treatment of land sea internal boundary layer Puffs NOx Chemistry Radioactive decay Plume visibility (condensed plume)