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AirWareAirWare: : RRelease R5.3 betaelease R5.3 beta

AERMOD/AERMETAERMOD/AERMET

DDr. Kurt FedraDDr. Kurt FedraEnvironmental Software & Services GmbH Environmental Software & Services GmbH A-2352 GumpoldskirchenA-2352 Gumpoldskirchen AUSTRIA AUSTRIAinfo@ess.co.at http://www.ess.co.at/AIRWAREinfo@ess.co.at http://www.ess.co.at/AIRWARE

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AERMODAERMODEPA REGULATORY MODEL, developed from

ISC-ST2/ISC3AERMOD is a

steady-state Gaussian plume modelBasic assumptions:• Homogeneous meteorological conditions in

time and space over the aggregation period;• Constant emissions• Aggregation period: minimally the time

needed to reach steady state (function of domain size and wind speed)

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AERMODAERMODModel provide an analytical solution to the

dispersion equations in 3D;Horizontal and vertical concentration

distributions are assumed to follow Gaussian (bell shaped) distribution.

Vertical “complications”: – Terrain following or impacting;– Partial reflection at mixing height.

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AERMODAERMODBasic principle: conservation laws

heightstack effective g/semission

y andin x ion concentrat ..m/s) (downwind, windspeed

zy,at x,ion concentrat ,,:

2exp

2exp

.2

exp(.2

),,(

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2

eff

z

eff

z

eff

y

HQ

ofDSuzyxC

where

HzHz

yuQzyxC

zy

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turbulenceturbulenceISC used tabulated stability classes (Pasquill)

defined by wind speed, cloud cover, day/night (heat flux)

AERMOD uses boundary layer physics,• Roughness length (Monin-Obukhov Length, L)

• surface roughness length, z0

• surface friction velocity, u• surface heat flux, H• convective scaling velocity, w .

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turbulenceturbulenceRoughness length (Monin-Obukhov Length, L)Measure of “surface roughness”, approximately 1/10 of

obstacle physical vertical dimensions, varies, also seasonally (vegetation), from

• 0.0001 m (water surfaces) to • 1 m (cities)• 1.3 m (forests)

Roughness sub-layer: wind speeds deviates from a vertical logarithmic profile.

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turbulenceturbulenceSurface friction velocity, u

Wind speed at reference height corrected by a vertical logarithmic profile to the roughness sub-layer and Monin-Obukhov length.

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turbulenceturbulence

Monin-Obukhov length, L,

• A function of temperature,

• wind speed • and heat flux.

constant sKarman' von ,4.0air ofdensity

air ofheat specific constantgravity

where

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k

cg

kgHuTc

L

p

refp

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turbulenceturbulence

Surface (sensible) heat flux, H

Bowen ratio:Related to soil

moisture:0.1: wet10: very dry

RadiationNet Rfluxheat Sensible

RatioBowen :

/119.0

n

0

0

HB

where

BRH n

BQQQEF

QQ

QQB

he

e

e

h

e

h

11

on)(evaporati heatinglatent T)(air heating sensible where

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turbulenceturbulence

Convective scaling velocity, w .

Now: Deardorff velocity, scale of wind speed

In the convective mixed layer:

typically 1 m s-1 …..

flux re temperatupotential

depthlayer mixing average re temperatuabsolute

onaccelerati nalgravitatio where

''

3/1'''*

i

v

iv

zTg

zTgw

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Performance:Performance:Needs to be solved for each source (but

offers the possibility for source apportioning)

Needs to be solved for each receptor point (grid cell, but can be solved for any arbitrary location)

Steady state solution: provides an upper estimate of concentration

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Data requirements:Data requirements:• Emission data (stack properties)• Meteorology:

– Single station data (episode, or 24 hours, one year (hourly)): wind speed/direction, air temperature (plume rise)

– Vertical profile (mixing layer) one morning sounding (value)

– Solar radiation, cloud cover (heat budget)

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AERMET pre-processor:AERMET pre-processor:AERMET operates on data from:• National Weather Service (NWS)

hourly surface observations, • NWS twice-daily upper air soundings, • data collected from an on-site

measurement program such as from an instrumented tower.

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AERMET data requirements:AERMET data requirements:Hourly Surface Observations:• wind speed and direction;• ambient temperature;• opaque sky cover; in the absence of opaque sky

cover, total sky cover;• station pressure is recommended, but not

required, Upper Air Soundings:• morning sounding (the 1200 GMT sounding for

applications in the United States).

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AERMOD implementation:AERMOD implementation:For City/local domains (< 30 km), • Hourly now-cast runs;• Daily 24 hour forecast runs;• Interactive scenario analysis:

– 24 hours daily runs (domains)– Annual runs (domains);– EIA for domains (24 hours)– EIA for single sources (annual, hourly)– Monitoring station location (annual, hourly)

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AERMOD implementation:AERMOD implementation:High-resolution (10 m) convolution model

(kernel), for all models that include traffic emissions (large number of segments).

Includes a mixing-zone approach over the street surface.

Unit emission kernel scaled for each road segment (10 m elements).

Transparently integrated with all AERMOD runs.

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AERMOD configuration:AERMOD configuration:For each mode of operation (nowcast,

forecast, interactive scenarios, single source EIA, MS location, traffic)

the model needs:

•A model scenario•A meteorological scenario•An emission scenario

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AERMOD scenarios:AERMOD scenarios:Nowcast scenarios are organised by

domain, and shown for the current (latest) run;

Configuration of a nowcast scenarios:• Select NEW from the scenario list;• Edit the scenario (domain,

meteorlogy, emissions)• Edit the shell script entry (ADMIN only)

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AERMOD implementationAERMOD implementationInteractive scenarios:• 24 hour runs including comparison of

scenarios (domain level impact assessment);

• High-resolution 1 hour runs for individual street segments

• Annual runs for monitoring station location (single source)

• Annual runs for single source impact assessment.

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AERMOD interactive:AERMOD interactive:

24 hour runs including comparison of scenarios (domain level impact assessment);

• Listing of scenarios with name, simulation date, pollutant simulated, run status (results, ready to runready to run, running).

• NEW button for creating a new scenario

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AERMOD implementationAERMOD implementationInteractive scenarios:• High-resolution 1 hour runs for

individual street segments• High resolution kernel/convolutions for

24 hourly runs, transparently combined with AERMOD for point and area sources.

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AERMOD implementationAERMOD implementationInteractive scenarios:Annual runs for monitoring station location

(single source):• Finds the N locations (for possible

monitoring stations) with a user defined minimum distance AROUND an emission source with the highest annual average concentration over populated areas.

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AERMOD implementationAERMOD implementationInteractive scenarios:Annual runs for single source impact

assessment:• Computes annual average

concentration on an hourly basis around a single source, at user defined or automatically located simulated monitoring stations.

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