Transcript Dispersion Modeling Challenges for Air Permitting Presentation

Dispersion Modeling Challenges for
Air Permitting
Justin Fickas
Christine Haman
Jake Stewart
Overview
Many new challenges hindering our ability
to find modeling solutions for PSD
projects
1. Recently Revised
NAAQS
2. Building
Downwash Issues
3. PM2.5 Proposed
Annual NAAQS
National Ambient Air Quality Standards (NAAQS)
Pollutant
PM10
PM2.5
Averaging
Period
Primary
3
(µg/m )
(ppm)
Secondary
3
(µg/m )
(ppm)
Annual
50
--
50
--
24-hour
150
--
150
--
Form (i.e., How Standard is Applied)
Annual arithmetic mean, averaged over 3 years
REVOKED
Not to be exceeded more than 3 times in 3
consecutive years
Annual arithmetic mean from single or multiple
monitors, averaged over 3 years
98th percentile of concentrations in a given year,
averaged over 3 years
Annual
15.0
--
15.0
--
24-hour
35
--
--
--
Annual
24-hour
(80)
(365)
0.03
0.14
---
---
3-hour
--
--
(1,300)
0.5
1-hour
(196)
0.075
NO2
Annual
1-hour
(100)
0.053
0.100
(100)
--
0.053
--
Annual arithmetic mean
Ozone
8-hour
(147)
0.075
(147)
0.075
1-hour
(235)
0.12
(235)
0.12
3-year average of annual 4th highest daily
maximum 8-hour concentrations
Not to be exceeded more than 3 times in 3
consecutive years REVOKED
8-hour
(10,000)
9
--
--
1-hour
(40,000)
35
--
--
0.15
--
0.15
--
SO2
CO
Lead
Rolling 3month average
Annual arithmetic mean REVOKED
Not to be exceeded more than once per calendar
year REVOKED
Not to be exceeded more than once per calendar
year
3-year average of the 99th percentile of the annual
distribution of daily maximum 1-hour concentrations
3-year average of the 98th percentile of the annual
distribution of daily maximum 1-hour concentrations
Not to be exceeded more than once per calendar
year
Not to be exceeded more than once per calendar
year
Maximum (not-to-be-exceeded) rolling 3-month
average evaluated over a 3-year period
Building Downwash Issues
Changes to the way AERMOD handles
building downwash have altered model
results from the 09292 version to now
Building Downwash Issues
˃ Downwash calculated based on the “EPA
Formula Height”
HGEP = Hb + 1.5L
Hb = building height above stack base
L = lesser of building height and projected
building width
˃ Good Engineering Practice (GEP) Height
 Equal to the greater of the following two values:
EPA Formula Height or 65 meters
Building Downwash Issues
Version 09292
Building downwash
effects were turned off
if stack height was
greater than or equal
to EPA formula height
Even though
downwash was off
modelers were still
allowed to take credit
for the “true” height
Building Downwash Issues
Versions 11059 and Later
Subroutine WAKFLG was
modified:
No longer ignore potential
downwash effects for stack
heights that equal or
exceed the EPA formula
height (Not the same as
GEP Height!)
PRIME downwash
algorithm:
Determines when and
how to apply downwash
Building Downwash Issues
1. Intent is to remove discontinuity in
AERMOD building downwash treatment
2. Discontinuity did not exist prior to use of
PRIME
3. Brings downwash back in play for
sources that otherwise would have been
“exempt”
Downwash Example One
Setup:
24.38 m
104 m
HGEP = Hb + 1.5L
HGEP = 24.38 m + 1.5(24.38 m) = 61 m
Downwash Example One
˃ Experiment varying stack height slightly below
and above HGEP (HGEP = 61 m)
˃ Modeled identical emission rate
Modeled
Stack Height
(m)
Version 09292
1-hour Result
(µg/m3)
Version 12060
1-hour Result
(µg/m3)
60
178
178
62
88
160
˃ Stack height above EPA equation is now
subject to downwash and results are not as
favorable
Downwash Example Two
Setup:
Variable Heights
HGEP = Hb + 1.5L
Stack HGEP = 19.05 m
GEP Height = 65 m
Downwash Example Two
Concentration (µg/m3)
70
V09292
V12060
HGEP
60
50
40
30
20
10
0
15
20
25
30
35
Stack Height (m)
40
45
50
Building Downwash Issues
Conclusions:


Complexity of the downwash algorithms and the
direction-dependent nature of downwash effects
are such that the magnitude of the differences
between different versions of AERMOD vary by
scenario
Change to the treatment of downwash with respect
to stack heights in the currently approved version
of AERMOD has the potential to cause large
increases in model-predicted concentrations
PM2.5 Proposed NAAQS Revision
Published in the Federal Register on 29
June 2012
1.
2.
Reduce the current annual standard from 15
µg/m3 to a value between 12 and 13 µg/m3
Aims to “provide increased protection
against health effects associated with longand short-term exposures”
PM2.5 Proposed NAAQS Revision
Challenges:



PM2.5 standards already some of the most difficult
standards to comply with
AERMINUTE data has increased difficultly in
modeling compliance for low dispersion PM sources
Background concentrations typically leave little to
no room for companies to implement projects for
PM2.5
PM2.5 Proposed NAAQS Revision
Conclusions:



Facilities in many cases will have to reduce fugitive
impacts in order to demonstrate modeled
compliance with the new standard
Compliance “gap” between background monitor
values and the standard will shrink in some areas,
and altogether disappear in others
Projects that have previously passed the NAAQS
may no longer be able to expand (and trigger PSD
for PM2.5) without taking restrictions
Questions?
Justin Fickas
53 Perimeter Center East
Suite 230
Atlanta, GA 30346
Office: (678) 441-9977
Cell: (678) 549-9755
Fax: (678) 441-9978
http://www.trinityconsultants.com/atlanta/
[email protected]
Annual Concentrations
5
4.5
4
3.5
3
Series1
2.5
Series2
2
1.5
1
0.5
0
45
65
85
105
125
145