Transcript Document

AERMET Training
Roger W. Brode
U.S. EPA/OAQPS/AQAD
Air Quality Modeling Group
NESCAUM Permit Modeling Committee
Annual Meeting
New London, Connecticut
May 31, 2007
Presentation Outline

Brief History of AERMOD

Basic Physics of Air Dispersion

AERMET Scaling Parameters

AERMOD Sensitivity Analysis with Example

Meteorological Data Sets

Meteorological Data Issues

Recent AERMET Updates
Brief History of AERMOD






Developed by AMS/EPA Regulatory Model
Improvement Committee (AERMIC)
Proposed as Replacement for ISCST3 April 2000
EPRI-sponsored PRIME Downwash Algorithms
Incorporated in AERMOD in 2001
Notice of Data Availability (NDA) for AERMOD with
PRIME Issued September 2003
Promulgated as EPA’s Preferred Model on December
9, 2005
One-year Grandfather Period Expired on
December 9, 2006
AERMOD Design Criteria

Up-to-date Science

Simple – Captures Essential Physical Processes

Robust – Applies Over Range of Meteorology

Easily Implemented – Simple I/O, User-friendly

Can Evolve – Easily Updated
Basic Physics of Dispersion

Air dispersion is driven by two main forces –
buoyancy effects and shear stress effects

Buoyancy controlled by solar heating (day)
and radiative cooling (night)

Shear stress (friction) controlled by surface
roughness elements and aerodynamic effects
Physics of Dispersion - Daytime

Buoyancy caused by daytime solar heating
generates large scale convective cells

Convection causes rapid vertical spread
of plumes and growth of the mixed layer

Strength of convection controlled by solar
angle (time-of-day and latitude), cloud
cover and surface characteristics (albedo
and Bowen ratio)
Physics of Dispersion - Daytime

Albedo
–
–

Measure of reflectivity of surface, from 0 to 1
Typical values ranges from about 0.1 for water to
0.6 or higher for full snow cover
Bowen Ratio
–
–
–
Ratio of sensible to latent heat flux
Determines how much solar heating goes to
evaporation of surface moisture
Ranges from about 0.1 (very wet) to 10 (very dry)
Physics of Dispersion - Nighttime

Radiative cooling at night causes stable
lapse rate to develop – suppresses
propagation of turbulence

Generation of turbulence dominated by
friction-induced shear stress

Shear stress or mechanical turbulence
controlled by wind speed and surface
roughness
Physics of Dispersion - Nighttime

Surface Roughness Length (zo)
–
Height at which wind speed goes to zero (0), based
on theoretical logarithmic profile
–
Related to the surface roughness elements, but is
not = height of elements
–
Ranges from about 0.001m (1mm) over water to
1.0m or higher for forests and urban areas
–
May vary by season and wind sector
AERMOD Similarity Theory
Concepts




Wind, temperature and turbulence are scaled with
height based on Similarity Theory
Mechanical (shear stress) turbulence scaled by friction
velocity (u*)
Convective turbulence scaled by convective velocity
scale (w*)
Monin-Obukhov length (L) stability parameter
–
–
Positive for stable conditions; negative for unstable
~ Height at which friction and buoyant forces balance
Sensible Heat Flux – H


If H > 0 PBL is convective; H < 0 stable
Daytime – Convective
0.9  Rn
H
1  1B
o
Bo = Bowen ratio
Rn = Net radiation

Nighttime – Stable
H     Cp  u*  *
θ* = Temperature scale
Friction Velocity – u*
u* 






k


u*  uref 

 zref 
 ln
  stability _ terms 
  z0 

Monin-Obukhov Length – L
Represents height at which mechanical (friction) and
buoyant “forces” balance:
3

c
 p   T   u* 
  
L  
 H   g  k 
Monin-Obukhov Length (L) vs.
PG Stability Class
Roughness
0.1 m
~L (m)
-12.5
-25
-65
-+65
+30
PG Stability Class
A
B
C
D
E
F
Roughness
0.5 m
~L (m)
-16
- 50
-100
-+100
+50
PG Stability Class
A
B
C
D
E
F
AERMOD CBL Treatment



Turbulence in the CBL is driven by convection
Convective cells grow during the day creating
areas of updrafts and downdrafts
AERMOD accounts for non-Gaussian vertical
structure of dispersion in the CBL
–
–
Portions of plume released into updrafts vs.
downdrafts are simulated separately
Full or partial penetration of plume through top of
mixed layer also simulated
CBL Dispersion Comparisons –
Crosswind Integration Concentrations

ISCST3

AERMOD

Tank Study
Convective Velocity Scale – w*
13
 g zic H 

w*  
 c  
 p

AERMOD Sensitivity Analysis

Varied Surface Characteristics:
–
–
–

Albedo Test: α=0.1-0.6 (Bo=1.0, zo=0.1)
Bowen Ratio Test: Bo=0.1-10 (α=0.2, zo=0.1)
Surface Roughness Test: zo=0.001-1.3m
(α=0.2, Bo=1.0)
Varied Stack Heights and Buoyancy
–
5,10,15,20,25,30,50,75,100,150,200m non-buoyant
–
100,150,200m very buoyant (VB)
AERMOD Sensitivity Analysis

Two meteorology sites:
–
–


Pittsburgh
Oklahoma City
Rural and Urban (population=2.4 million)
24-hr and Annual averages
AERMOD Sensitivity Analysis

Changes in albedo and Bowen ratio affect
convective turbulence
–
–

↓ Albedo
↑ Convective turbulence
↑ Bowen ratio
↑ Convective turbulence
Changes in surface roughness affect
mechanical turbulence
–
↑ Surface roughness
↑ Mechanical turbulence
Albedo – Normalized Percent Differences
Bowen Ratio – Normalized Percent
Differences
Surface Roughness – Normalized
Percent Differences
Sensitivity Analysis Conclusions

AERMOD is most sensitive to changes in zo for
low-level releases
–

This is due to the impact of changes in zo on mechanical
turbulence:
↑ Surface roughness will ↑ Mechanical turbulence
Some sensitivity to changes in albedo and Bowen
ratio, especially for taller, more buoyant stacks
–
Lower albedo or higher Bowen ratio will increase
convective turbulence and bring plume down quicker
AERMOD Sensitivity Example


Ground-level volume source based on “haul
road” example
Meteorological data based on two sets of
surface characteristics:
–
–

With snow cover:
zo=0.01m, α = 0.6, Bo= 1.5
Without snow cover: zo=0.1m, α =0.16, Bo= 0.8
Snow cover characteristics based on literal
interpretation of look-up tables for winter, which
assume continuous snow cover – sometimes
overlooked by users
Sensitivity Example Results – 1hr
AERMOD Comparisons - Ground-level Volume Source
1-hr Concentrations for "State Met" vs. "AQMG Met"
35,000
Concentration (ug/m^3)
30,000
25,000
20,000
State 1-hr
AQMG 1-hr
15,000
10,000
5,000
0
0
100
200
300
400
Downwind distance (m)
500
600
Sensitivity Example Results – 24hr
AERMOD Comparisons - Ground-level Volume Source
24-hr Concentrations for "State Met" vs. "AQMG Met"
8,000
Concentration (ug/m^3)
7,000
6,000
5,000
State 24-hr
AQMG 24-hr
4,000
3,000
2,000
1,000
0
0
100
200
300
400
Downwind distance (m)
500
600
Identification/Selection of Met Data

NWS surface data formats
–
–
–
–
–
–
CD144 (original data format – stands for “card deck” 144)
SCRAM (1984-1992)
SAMSON (through 1990)
HUSWO (1990-1995)
TD-3280 (24-hour records by element – NCDC may not support)
ISHD (TD-3505) – full archival format, not abbreviated format


Note that ISHD surface data is reported in GMT, not local time!
NWS upper air formats
–
–
TD-6201
FSL
AERMET On-site Met Data

Surface (single value) measurements
–
Functional:







–
sky cover
net radiation
Solar radiation (insolation)
temperature differences between levels
mixing height
surface roughness length
surface friction velocity and others.
Not yet functional: surface heat flux & others.
AERMET On-site Met Data

Tower (multi-level) measurements
–
Functional


–
Height, sa, sw, temp., wind speed and direction
Relative humidity
Not yet functional

Vertical wind component

su, s e, sv

Dew point
AERMET Meteorological Data Issues

Automated Surface Observing System (ASOS)
–
–
–
–
–
NWS began replacing observer-based system with
ASOS in 1992
Hourly ASOS data now available for over 900 stations
within U.S.
Ceilometer cloud cover limited to 12,000 feet
Cloud cover (total only – no opaque) reported by
category (CLR, SCT, BKN, OVC)
Increased incidence of calms
ASOS vs. Observer-based Calms
AERMET Meteorological Data Issues

Adoption of METAR standard for reporting
weather observations
–
–
–
–
Began on July 1, 1996
Introduced variable wind code (VRB) for wind speeds
up to 6 knots
Variable winds now coded as missing WD with nonmissing WS – previous versions of AERMET coded
variable winds as calms
Added new cloud cover code (CLR, FEW, SCT, BKN,
OVC)
AERMET Meteorological Data Issues

Surface NWS data format issues
–
ASOS cloud cover data reported as four categories:

–
METAR introduced fifth category:

–
–
–
–
CLR, SCT, BKN, OVC
CLR, FEW, SCT, BKN, OVC
Abbreviated ISHD data does not include “FEW” cloud cover
code – combined with “SCT” cloud code
TD-3280 cloud cover codes mapped to upper bound of category
in tenths
Numerous additional cloud cover codes available in TD-3280
format not supported by AERMET – no plans to include these
Full archival ISHD format appears to be the best resource
AERMET Meteorological Data Issues

ASOS station location uncertainties
–
–
–
–
Excel file with ASOS commission dates and station locations
available on NCDC website appears to be unreliable for location
information
Additional data available for about 200 ASOS stations as part of
tropical cyclone wind study appears to be reliable
Many station locations appear to be off by several hundred
meters (median value of about 500m)
Use of erroneous station locations in AERSURFACE could
invalidate results
ASOS Met Station Locations – Cyclone
Wind Study
ASOS Met Station Locations
Comparison of ASOS Station Locations from Two References
Call
KIJD
KAQW
KBED
KBOS
KBVY
KCQX
KEWB
KFIT
KHYA
KMVY
KORE
KOWD
KPYM
KTAN
KFWN
KSMQ
KVAY
KALB
KBGM
KELM
KGFL
KISP
KJFK
KPEO
KPOU
KPSF
KSYR
KUCA
KPVD
KUUU
KWST
KDDH
WBAN
54767
54768
14702
14739
54733
94624
94726
4780
94720
94724
54756
54704
54769
54777
54793
54785
93780
14735
4725
14748
14750
4781
94789
54778
14757
14763
14771
94794
14765
14787
14794
54781
NCDC ASOS List
Lat-ASOS Lon-ASOS
41.7419
72.1836
42.6958
73.1708
42.4700
71.2894
42.3606
71.0106
42.5842
70.9175
41.6875
69.9933
41.6764
70.9583
42.5519
71.7558
41.6686
70.2800
41.3931
70.6150
42.5700
72.2911
42.1908
71.1736
41.9097
70.7294
41.8756
71.0211
41.2003
74.6231
40.6239
74.6694
39.9406
74.8411
42.7481
73.8033
42.2078
75.9814
42.1594
76.8919
43.3411
73.6103
40.7939
73.1017
40.6553
73.7956
42.6425
77.0564
41.6267
73.8842
42.4272
73.2892
43.1092
76.1033
43.1450
72.3839
41.7219
71.4325
41.5300
71.2836
41.3497
71.7989
42.8914
73.2469
ASOS Cyclone Wind Study
Lat-PHOTO Lon-PHOTO
41.7420
72.1830
42.6970
73.1700
42.4680
71.2940
42.3590
71.0200
42.5840
70.9160
41.6880
69.9930
41.6750
70.9570
42.5520
71.7560
41.6690
70.2710
41.3920
70.6170
42.5720
72.2780
42.1910
71.1740
41.9070
70.7280
41.8760
71.0210
41.2000
74.6170
40.6170
74.6670
39.9500
74.8500
42.7470
73.7990
42.2070
75.9800
42.1570
76.9030
43.3380
73.6100
40.8000
73.1000
40.6330
73.7670
42.6440
77.0530
41.6260
73.8820
42.4170
73.2890
43.1110
76.1040
43.1440
75.3840
41.7230
71.4330
41.5300
71.2840
41.3500
71.7990
42.8940
73.2490
Delta-Lat
0.000
-0.001
0.002
0.002
0.000
-0.001
0.001
0.000
0.000
0.001
-0.002
0.000
0.003
0.000
0.000
0.007
-0.009
0.001
0.001
0.002
0.003
-0.006
0.022
-0.002
0.001
0.010
-0.002
0.001
-0.001
0.000
0.000
-0.003
Delta-Lon
0.001
0.001
-0.005
-0.009
0.002
0.000
0.001
0.000
0.009
-0.002
0.013
0.000
0.001
0.000
0.006
0.002
-0.009
0.004
0.001
-0.011
0.000
0.002
0.029
0.003
0.002
0.000
-0.001
-3.000
-0.001
0.000
0.000
-0.002
Dist (km)
0.061
0.143
0.498
0.956
0.151
0.060
0.193
0.017
0.900
0.226
1.327
0.042
0.308
0.046
0.606
0.731
1.297
0.446
0.159
1.132
0.312
0.634
3.622
0.370
0.226
1.022
0.195
300.011
0.117
0.039
0.030
0.332
ST
CT
MA
MA
MA
MA
MA
MA
MA
MA
MA
MA
MA
MA
MA
NJ
NJ
NJ
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
NY
RI
RI
RI
VT
Station Name
Willimantic Windham Airport
North Adams Harriman
Bedford Hanscom Field
Boston Logan Intl Airport
Beverly Municipal Airport
Chatham Municipal Airport
New Bedford Municipal Airport
Fitchburg Municipal Airport
Hyannis Barnstable Municipal Airpor
Martha's Vineyard Airport
Orange Municipal Airport
Norwood Memorial Airport
Plymouth Municipal Airport
Taunton Municipal Airport
Sussex Airport
Somerville Somerset Airport
Mount Holly South Jersey Regional
Albany County Airport
Binghamton Regional Airport
Elmira Corning Regional Airport
Glens Falls Airport
Islip Long Island Macarthur Airport
New York J F Kennedy Intl Airport
Penn Yan Airport
Poughkeepsie Dutchess Co Airport
Pittsfield Municipal Airport
Syracuse Hancock Intl Airport
Utica Oneida County Airport
Providence Green State Airport
Newport State Airport
Westerly State Airport
Bennington Morse State Airport
Recent AERMET Update: Bug Fixes

Significant changes to processing of NWS Integrated
Surface Hourly Data (ISHD) surface data (TD-3505)
–
–
–
–
–
Selection of which record to process for hours with multiple
records
Processing of cloud cover codes
Initialization of “additional” character variable – caused data from
previous hours to be used
Identify “variable” winds as missing WD and non-missing WS
rather than calm
Corrected problem that allowed observation hour to be
incremented prematurely
Recent AERMET Update: Bug Fixes




Corrected treatment of “variable” winds for TD-3280
format – coded as missing WD with non-missing WS
Corrected treatment of missing data codes for WS/WD
for HUSWO format
Modified upper and lower bounds for surface pressure
for FSL upper air data to avoid skipping valid soundings
at high or low elevations
Corrected bugs in calculation of critical solar angle –
affecting transition hours
Recent AERMET Update: Enhancements


Single AERMET executable – still needs to be
run in 3 stages
Optional station elevation for ISHD data to
substitute for missing elevation in estimating
surface pressure
Recent AERMET Update: Miscellaneous



Impose lower limit of 0.001 meters for userspecified surface roughness, for consistency
with AERMOD model
User-specified time window for ISHD data
removed – default window of 30 minutes
preceding the hour used
Given range of changes affecting results,
AERMOD modified to require reprocessing of
met data with 06341
Unresolved AERMET Issues/
Planned Updates

Format problem with some ISHD data may
cause AERMET to crash
–


FIXISHD utility program – interim fix released in April
Data (record-period) gap in ISHD data
Inconsistencies between NWS surface data
formats
–
–
TD-3280 sky cover codes
Abbreviated ISHD (TD-3505) sky cover
Questions