A presentation at the 2015 Midwest Environmental Compliance Conference, May 13-14, 2015, Overland Park, KS

1. 11
PM2.5 “Regulatory” Guidance Overview
and Case Studies for Secondary Formation
of PM2.5 from Precursors
Kasi Dubbs, P.E., C.M.
Midwest Environmental Compliance Conference
May 13, 2015

2. 2
“Regulatory” History on PM2.5
and NSR/PSD (1/4)
˃ July 18, 1997 – First PM2.5 NAAQS established (annual
= 15 µg/m3, 24 hr = 65 µg/m3)
˃ October 23, 1997 – PM10 surrogate policy memo (Use
PM10 as a surrogate for PM2.5)
˃ October 17, 2006 – PM2.5 24 hr NAAQS revised from
65 µg/m3 to 35 µg/m3
˃ May 16, 2008 – EPA finalizes partial PM2.5 NSR and
PSD Implementation Rule
 PSD and NSR Major Source Thresholds (MSTs)
 Significant Emission Rates (SERS) for direct PM2.5 as well
as secondary PM2.5 precursors (NOx and SO2)
 Offset ratios for PM2.5 as well as interpollutant trading
ratios

3. 3
“Regulatory” History on PM2.5
and NSR/PSD (2/4)
˃ February 11, 2010 – EPA announces PM10 Surrogate Policy
coming to an end (Can no longer use PM10 as a surrogate
for PM2.5 in modeling and BACT analyses)
˃ March 23, 2010 – Memo on Modeling Procedures for
PM2.5 NAAQS (“Page Memo”)
 Addresses form of the standard for modeling vs. form
of NAAQS monitoring design value
 Special attention to background concentrations
 Speaks to technical complications with secondary
formed PM2.5, but refers to future guidance

4. 4
“Regulatory” History on PM2.5
and NSR/PSD (3/4)
˃ October 20, 2010 – EPA finalizes Final PM2.5 PSD
Implementation Rule
 PM2.5 Significant Impact Levels (SILs)
 PM2.5 Increments
 PM2.5 Significant Monitoring Concentration (SMC)
˃ January 7, 2011 – National Association of Clear Air
Agencies (NACAA) issues PM2.5 Modeling
Implementation Document
 PM2.5 Emission Inventories
 Secondary Formation of PM2.5
 Background Concentrations for PM2.5

5. 5
“Regulatory” History on PM2.5
and NSR/PSD (3/4)
˃ May 16, 2011 - Surrogate policy ended July 21,
2011 – EPA revokes interpollutant trading ratios
from May 2008 PM2.5 NSR/PSD Implementation
Rule
˃ December 14, 2012 – PM2.5 Annual NAAQS
revised from 15 µg/m3 to 12 µg/m3
˃ January 22, 2013 – Court decision: PM2.5 SMC
vacated, PM2.5 SILs vacated and remanded
˃ May 20, 2014 – Final EPA guidance for PM2.5
permit modeling
 Emphasizes qualitative vs. quantitative approaches
for evaluating secondary PM2.5

6. 6
Interpollutant Trading Ratios
˃ Sources applying for permits in PM2.5 nonattainment
areas can offset emissions increases of direct PM2.5
emissions with reductions of PM2.5 precursors using
interpollutant trading ratios (also called “PM2.5
offset ratios”).
 For example, an existing source can increase PM2.5
emissions by X tons in exchange for reducing SO2
emissions by Y tons.
 EPA 2008 (but later rescinded)
♦ NOx:PM2.5 = 200:1 (Eastern US)
♦ NOx:PM2.5 = 100:1 (Western US)
♦ SO2:PM2.5 = 40:1 (Nation-wide)

7. 7
Equivalent Primary PM2.5
Emissions
˃ PM2.5 offset trading ratios can be used to account for
secondary formation of PM2.5.
˃ NACCA introduced an approach in their 2011 report
˃ Convert SO2 and NOx emissions into “equivalent” direct
PM2.5 emissions.
 100:1 100 TPY SO2 = 1 TPY direct PM2.5
 10:1 100 TPY SO2 = 10 TPY direct PM2.5
 1:1* 100 TPY SO2 = 100 TPY direct PM2.5
 0.5:1 100 TPY SO2 = 200 TPY direct PM2.5
*This is ~100% conversion of SO2 to (NH4)2SO4
˃ Model the total primary PM2.5 including the actual primary
PM2.5 plus the total equivalent primary PM2.5 determined
from the precursor emissions and offset ratio
˃ Lower PM2.5 offset ratios will produce more secondary
PM2.5.

8. 8
PM2.5 Offset Ratios and PSD (1/2)
˃ The approach for developing PM2.5 offset
ratios involves the following steps:
 Define the geographic area
 Conduct a series of sensitivity runs with
appropriate air quality models to develop
data that correlates modeled PM2.5
concentration changes associated with
reductions of direct PM2.5 emissions and
PM2.5 precursor emissions

9. 9
PM2.5 Offset Ratios and PSD (2/2)
˃ July 2014 Minnesota Modeling Guidance (based on
limited analysis)
 NOx:PM2.5 = 100:1
 SO2:PM2.5 = 10:1
˃ Georgia Work in Progress
 Sensitivity runs to evaluate how PM2.5 offset ratios
varied by:
♦ Distance from the source
♦ Season of the year
♦ Stack height
♦ Grid resolution
♦ Location in the state
 Goal to provide county-specific offset ratios in modeling
guidance

10. 10
EPA May 2014 PM2.5 Guidance (1/2)
Compliance with PM2.5 NAAQS for PSD:
Modeled impact of primary PM2.5 emitted
from industrial sources in an area
+
Impact of NOx and SO2 as Secondary PM2.5
+
Background Concentration

11. 11
EPA May 2014 PM2.5 Guidance (2/2)
EPA Recommended Approaches for Assessing Primary and Secondary
PM2.5 Impacts
Source: Page 21 of EPA’s Draft Guidance for
PM2.5 Permit Modeling, March 2013
AERMOD
Model

12. 12
Secondary PM2.5 Assessment
Methods
˃ Qualitative - Develop “appropriate conceptual
description of PM2.5”
˃ Hybrid Qualitative/Quantitative
 Use of local/region specific “offset ratios” for
precursor emissions
 Analysis of “offset ratios” for precursor emissions
specific to region (i.e., how readily nitrates and
sulfates form in the modeled domain due to
environmental influences such as NH3 concentrations)
˃ Quantitative - Photochemical models or other
models, as applicable, i.e., CAMx or CMAQ

13. 13
Since May 2014 Guidance,
What are States Doing?
˃ Some States have already been requiring, and
will continue to require, hybrid approach type
assessments for secondary PM2.5.
˃ Some States looking for guidance on what can
justify qualitative versus hybrid versus
quantitative.
˃ A common theme: case by case assessment.
 State requirements regarding secondary PM2.5 will be a
constantly changing and evolving theme over the coming
years.
 The analysis your facility may have been allowed to do
in one State, may not be acceptable (or desired) in
another State.

14. 14
Summary of Secondary PM2.5 Assessments
Project
Description
Case Approach Status
Virginia 1 Case 3 Hybrid Qualitative/Quantitative – Georgia EPD Offset
Ratios
Permit Issued, No EPA comment
North Carolina 1 Case 3 Qualitative Application Under Review
North Carolina 2 Case 3 Qualitative Application Under Review
Michigan Generating
Station
Case 3 Hybrid Qualitative/Quantitative – CSAPR Modeling Ratios Permit Issued, No EPA Comment
Texas Generating
Station
Case 3 Hybrid Qualitative/Quantitative – CSAPR Modeling Ratios Application Under Review, Method
approved by TCEQ
Texas LNG Plant Case 3 Qualitative Undergoing TX Contested Case Process
Louisiana 1 Case 3 Qualitative Permit Issued, No EPA comment
Alaska Oil/Gas Case 3 NA – relied on March 2010 Page memo using H1H model
result
Permit Issued, No EPA comment
Idaho Fertilizer Plant Case 3 Hybrid Qualitative/Quantitative – Applied monitoring-based
ratios
Draft Permit Issued, No EPA comment to-
date
Oregon 1 Case 3 Simplified Hybrid Qualitative/Quantitative – Used codified
offset ratios
Permit Issued, No EPA comment
Washington 1 Case 3 Hybrid Qualitative/Quantitative – Applied monitoring-based
ratios
Permit Issued
Georgia 1 Case 3 NA – relied on March 2010 Page memo using H1H model
result
Permit Issued, No EPA comment
South Carolina 1 Case 3 Qualitative Permit Issued, No EPA Comment
Georgia 2 Case 3 NA – relied on March 2010 Page memo using H1H model
result
Modeling Protocol Reviewed, Application
in Progress
Alabama 1 Case 3 NA – relied on March 2010 Page memo using H1H model
result
Modeling Protocol Reviewed, Application
in Progress

15. 15Missouri Case Study: CSAPR
Response Factors vs Offset Ratios
to Quantify Secondary PM2.5
˃ CSAPR utilizes CAMx, a photochemical
model, to quantify impacts of SO2 and
NOX emissions on PM2.5 concentrations at
ambient monitoring locations around
U.S.
˃ Can use data for monitors addressed in
CSAPR to develop response factors
(ratios of expected reduction in PM2.5
concentrations per ton of reduction in
precursor emissions)

16. 16
Case Study: Monitor Selection (1/3)
˃ Guidance allows use
of existing monitor if
representative.
˃ Proposed using PM2.5
data collected at an
existing PM2.5
ambient air monitor
in El Dorado Springs,
Missouri.

17. 17
Case Study: Monitor Options (2/3)
˃ Located all PM2.5
monitors near
facility.
˃ Narrowed options
based on:
 Data currentness
 Data quality
 Speciation of PM2.5
 Meteorological
conditions in region

18. 18
Case Study: Monitor Selection (3/3)
˃ Which monitor is representative of the
concentration in area of proposed
facility?
 Things to Consider:
♦ Wind direction & air parcel trajectories
♦ Climatology
♦ Demographics of region
♦ Surrounding sources of precursor
pollutants

19. 19
Case Study: Wind Analysis (1/3)
˃ Determine average wind speed and
direction near proposed facility location
 5 year analysis for 3 nearby airports

20. 20
Case Study: Wind Analysis (2/3)
˃ Narrowed data by putting emphasis on
winter season months
 Cooler temperatures are more ideal for nitrate
formation and thus, secondary PM2.5
formation.
 Wind roses using data from October – March for
5 years.

21. 21
Case Study: Wind Analysis (3/3)
˃ Joplin Airport closest
weather station to
facility
˃ 20% of time analyzed
had wind direction
between 170º (S) and
200º (SSW)
˃ Grove & Monett -
more variation
 Stronger SSE and NW
components

22. 22
Case Study: Forward Trajectories
(1/2)
˃ Demonstrates path
air parcel took from
a point of origin.
˃ Used NOAA’s
HYSPLIT Model.
˃ Image of December
2013 trajectories.
˃ 13% (4 days) air
advected within 17º
sector of El Dorado
Springs monitor.

23. 23
Case Study: Forward Trajectories
(2/2)
˃ Findings:
 Top 3 monitors with most trajectory hits from
October 2013 – March 2014:
♦ Liberty, MO = 20 (11%)
♦ El Dorado Springs, MO = 17 (9.3%)
♦ Stilwell, OK = 13 (7.1%)
˃ Determined Liberty, MO monitor not
representative of concentrations near
proposed plant due to close proximity to
densely populated Kansas City.

24. 24
Case Study: Back Trajectories
˃ Demonstrates path air parcels have taken prior
to arriving at monitor site.
˃ Again used NOAA’s HYSPLIT (Hybrid Single
Particle Lagrangian Integrated Trajectory
Model).
˃ Only used cold season days when the monitor
showed exceedance of 12 µg/m3 (annual
NAAQS primary PM2.5 standard)
 Information from EPA Air Quality website
 El Dorado Springs = 8 exceedances, 0 hits within 10 km
 Liberty = 17 exceedances, 1 hit
 Stilwell = 10 exceedances, 0 hits

25. 25
Case Study: Final Justification for
Monitor of Choice
˃ Location
 84 km northeast of facility
♦ Far enough distance to allow secondary PM2.5 formation
♦ Close enough to experience similar weather conditions
˃ Wind & Trajectory Analysis
 South and southwest winds common near Joplin
 Advect air toward monitor
˃ Data Quality
 Deployed by the state/local air monitoring stations
(SLAMS), reports to Missouri Laboratory Services
Program

26. 26
Case Study: Cross-State Air
Pollution Rule (CSAPR)
˃ Use CSAPR data to find 2014 base and control case
data in MO for annual and 24-hr PM2.5 design values.
˃ Calculate response factors to estimate the
concentration of secondary PM2.5 per ton of NOx and
SO2 per year.

27. 27
Case Study: Cross-State Air
Pollution Rule (CSAPR)
˃ The response factor was multiplied by the
proposed project’s total SO2 and NOx PTE values to
find estimated impact on secondary formation of
PM2.5 at monitor.

28. 28
Case Study: Cross-State Air
Pollution Rule (CSAPR)
˃ Impacts of combined primary and secondary PM2.5
on NAAQS analysis.

29. 29
Case Study: Pollutant Offset Ratio
˃ Using EPA Offset Ratios to Estimate Secondary PM2.5
and treat the same as primary PM2.5: Model using
AERMOD or screening model
 Pollutant offset ratios of 40:1 for SO2 and 200:1 for NOx
Secondary PM2.5 Emissions =
𝑁𝑂𝑥 𝑡𝑝𝑦
200
+
𝑆𝑂2 𝑡𝑝𝑦
40
 Result = 1.49 lb/hr of secondary PM2.5
 Use screening model (SCREEN3) to assess downwind
impact of emission rate
♦ Enter stack information, meteorology and terrain options
♦ Does not account for chemical reactions in formation of PM2.5
just gives estimate of downwind concentration.
♦ PM2.5 concentration = 2.93 µg/m3 approximately 2,506 m from
source.

30. 30
Case Study: Pollutant Offset Ratio
˃ Regional emissions of NOx and SO2 are
known so used offset ratios to also find
secondary PM2.5 emissions from region.
Secondary PM2.5 Emissions =
𝑁𝑂𝑥 𝑡𝑝𝑦
200
+
𝑆𝑂2 𝑡𝑝𝑦
40
˃ Compared the regional PM2.5 emissions to
proposed project’s expected emissions.
˃ Findings: Proposed project would
contribute ~2.8% of total regional
secondary PM2.5 emissions.

31. 31
Case Study: Secondary PM2.5 Analysis
for PSD Permit Conclusions
˃ Using both CSAPR Response Factors and
Pollutant Offset Ratios showed low amounts of
secondary PM2.5 formed from NOx and SO2
˃ Maximum impacts from primary and secondary
PM2.5 would not occur at same time & location,
unlikely secondary PM2.5 would result in
violation of NAAQS
˃ Compared secondary PM2.5 value found from
pollutant offset ratios to regional values
obtained from MDNR
 Plant contributes about 3% to the total regional
value

32. 32
Questions?
Anna Henolson
ahenolson@trinityconsultants.com
Phone: 253-867-5600