Transcript Modeling Guidance and Examples for Commonly Asked

Reece Parker and Justin Cherry, P.E.
Air Permits Division
Texas Commission on Environmental Quality
Advanced Air Permitting Seminar 2014
What Is PM2.5?
Direct
Chemical Formation
Stationary Sources
NOx and SO2
PM2.5
The chemical composition of PM2.5 can vary with the local
topography, source emissions, time of year, and weather.
PM2.5 Standards
 NAAQS:
 24-hr: 35 µg/m3
 Primary Annual: 12 µg/m3
 Secondary Annual: 15 µg/m3
 Increments:
 24-hr: 9 µg/m3
 Annual: 4 µg/m3
 SIL*:
 24-hr: 1.2 µg/m3
 Annual: 0.3 µg/m3
*with sufficient justification
Using the SIL
 PM2.5 SIL justification for NAAQS:
 Determine a representative background value
 Subtract the background from the NAAQS
 Compare the difference to the SIL
NAAQS
Background
Value
SIL
4 Assessment Cases
Case 1: Direct PM2.5 < 10 tpy SER; NOx and/or SO2 < 40 tpy SER

Primary impacts only
Case 2: Direct PM2.5 ≥ 10 tpy SER; NOx and/or SO2 < 40 tpy SER

Primary impacts, still must address secondary formation
Case 3: Direct PM2.5 ≥ 10 tpy SER; NOx and/or SO2 ≥ 40 tpy SER

Primary impacts AND secondary impacts
Case 4: Direct PM2.5 < 10 tpy SER; NOx and/or SO2 ≥ 40 tpy SER

Primary impacts AND secondary impacts
Case 1
Direct PM2.5 emissions < 10 tpy and SO2 and/or NOx
emissions < 40 tpy:
 Model direct PM2.5 emissions following guidance for a
NAAQS analysis
Case 2
Direct PM2.5 emissions ≥ 10 tpy:
 Model direct PM2.5 emissions following guidance for a
NAAQS analysis
SO2 and/or NOx emissions < 40 tpy:
 Discuss in AQA why proposed SO2 and NOx emissions are
not significant to the secondary formation of PM2.5
Case 3
Direct PM2.5 emissions ≥ 10 tpy:
 Model direct PM2.5 emissions following guidance for a
NAAQS analysis
SO2 and/or NOx emissions > 40 tpy:
 Provide a qualitative, hybrid qualitative/quantitative, or
quantitative assessment of the secondary formation of PM2.5
Case 3 Qualitative Approach
Ideas to consider:
 Peak impacts from direct
emissions and secondarily
formed PM2.5 likely do not
overlap
 Assessment of background
data and condition with the
NAAQS
Case 3 Qualitative Approach
(Continued)
Ideas to consider:
 Evaluation of speciated PM2.5 data:
 Magnitude of secondary PM2.5 precursor emissions from
existing sources
 Comparing project precursor emissions to those of existing
sources
 Limitations of chemical species necessary for
photochemical reactions to form secondary PM2.5
Case 3 Hybrid Approach
 Qualitative: Follow the Case 3 qualitative assessments
 General conclusions from existing photochemical
modeling
Case 3 Quantitative Approach
 Quantitative #1:

Assume 100% conversion from SO2 and NOx to PM2.5

Assess combined impacts of direct and equivalent direct PM2.5
emissions
 Quantitative #2:

Full quantitative photochemical grid modeling exercise*
*No requirement for photochemical modeling - this will be discussed
further
Case 4
Direct PM2.5 emissions < 10 tpy:
 Model direct PM2.5 emissions following guidance for a
NAAQS analysis
SO2 and/or NOx emissions ≥ 40 tpy:
 Provide a qualitative, hybrid qualitative/quantitative, or
quantitative assessment of the secondary formation of PM2.5
Case 3 Example
Direct PM2.5 emissions: 62 tpy
NOx emissions:
96 tpy
SO2 emissions:
10 tpy
Need to address secondary formation of PM2.5.
Case 3 Qualitative Example
 Slow transformation and small portions of NOx emissions
can convert to PM2.5
 Maximum concentration areas for secondary impacts of
NOx are not likely to overlap with direct impacts of PM2.5
Case 3 Example (Cont.)
Qualitative (Cont.):
 Speciated PM2.5 data shows nitrates make up 2% of total
PM2.5 concentration
 Regional NOx emissions have a magnitude of 25,000 tons
 Project emissions of NOx (96 tpy) are small and not likely to
contribute to secondary formation of PM2.5
Case 3 Example (Cont.)
Quantitative:
 Assume 100% conversion of NOx to (NH4)NO3
 Using NACAA formula: 1 µg/m3 of NOx could form
1.7391 µg/m3 of (NH4)NO3
 24-hr and annual NOx from the source predicted to be
2.9 µg/m3 and 0.3 µg/m3, respectively
 Using the formula, 24-hr and annual secondary formation
from the source would be 5 µg/m3 and 0.5 µg/m3,
respectively
Case 3 Example (Cont.)
Quantitative (Cont.):
 24-hr and annual predicted concentrations from the direct
emissions of PM2.5 were 2 µg/m3 and 1 µg/m3, respectively
 Add all components together for a total value
Secondary
Formation
from
Project
(µg/m3)
Background
(µg/m3)
Total
Predicted
Concentration
(µg/m3)
NAAQS
Pollutant
Averaging
Time
Project
GLCmax
(µg/m3)
PM2.5
24-hr
2
5
26
33
35
PM2.5
Annual
1
0.5
9.6
11.1
12
PM2.5 Increment
What to consider:
 Major source baseline date - October 20, 2010
 Trigger date - October 20, 2011
 Minor source baseline date - county specific
 SIL:
 Additional justification
 Output metric:
 Yearly H1H vs. 5-year average
PM2.5 SIL Justification for Increment
 Evaluate proposed direct PM2.5 emissions increases:
 Report the maximum predictions and not a 5-year average
 Provide justification for using the SILs to compare with
the model predictions
PM2.5 SIL Justification for Increment
PM2.5 Monitoring for Increment
5 years of monitoring data (µg/m3):
24-hr
Concentrations
2009
2010
2011
2012
2013
H1H
23.4
23.2
22.9
23.5
23.3
H2H
21.9
22.1
21.4
22.3
22.9
Increment
Standard
Increment
Consumed
2013-2010
SIL
PM2.5 Increment
When predictions are greater than the SIL or if the
SIL cannot be justified:
 Evaluate increment affecting sources together with the
project sources
 Document approach to identify increment affecting
sources
 Receptors - the extent of the receptor grid needs to
capture maximum concentrations from the project and
show that concentrations are decreasing
PM2.5 Increment (continued)
Further detail:
 PSD major sources were further evaluated:
 Projects with completion dates 18 months prior to the major
source baseline date up to the minor source baseline date
were identified
 Projects were reviewed to determine if PM2.5 was associated
with project
 The extent of the modeling domain used to limit search
for PSD major sources:
 24-hr and annual GLCmax locations, distance from property
line, etc.
PM2.5 Increment (continued)

Reece Parker


(512) 239-1348
[email protected]
Air Permits Division





Justin Cherry
(512) 239-0955
[email protected]
Air Permits Division