Modeling the New 1-Hour Nitrogen Dioxide (NO2) and Sulfur Dioxide (SO2)

NAAQS

Alan DresserResearch Scientist I

October 14, 2011

Overview of New NO2 NAAQS

1-hr NO2 = 100 ppb (189 ug/m3)

Effective on April 12, 2010

Based on 98th percentile of annual distribution of daily max. 1-hour values

Current NJ 1-Hour Background Levels:

37% to 67% of NAAQS

NO2 1-Hour Modeling

EPA Guidance Memos of June 28, 2010 and March 1, 2011:

Interim SIL (7.5 ug/m3)

3-Tiered NO to NO2 conversion approach

Treatment of intermittent emissions (limits modeling of start-up/shutdown, emergency equipment)

NO2 1-Hour Modeling

NJDEP Guidance:

Interim SIL of 10 ug/m3 (NESCAUM)

July 29, 2011 memo – Emergency generator and fire pump exemptions from modeling 1-hour NO2/SO2 impacts

(specific to combined-cycle plants, case- by-case for others)

Example of 1-Hour NO2 Modeling

LS Power West Deptford Station

600 MW Combined-Cycle Plant

Natural gas with 0.05% sulfur oil backup

Modeled before EPA and NJDEP guidance memos (intermittent sources; emergency generator/fire pumps)

Scenarios of Interest

Normal Operations

(NOx natl. gas = 37 lb/hr, NOx oil = 70 lb/hr)

Startup Operations (NOx = 323 lb/hr)

Emergency Generator (NOx = 10 lb/hr)

Fire Pump (NOx = 1.3 lb/hr)

1-Hour NO2 Impacts(Highest 98th percentile / 8th high concentration)

Normal Operations (70 lbs/hr, oil) = 8.1 ug/m3

Startup Operations (323 lbs/hr) = 42 ug/m3

Emergency Equipment(11.3 lbs/hr) = 43 ug/m3

(no testing during turbine startup/shutdown)

(1-hour NO2 NAAQS = 189 ug/m3)

Lesson : Smaller sources with short stacks and transitional scenarios at large facilities can cause big 1-hr NO2 impacts!

Overview of New SO2 NAAQS

1-hr SO2 = 75 ppb (196 ug/m3)

Effective on August 23, 2010

Based on 99th percentile of annual distribution of daily max. 1-hour values

Current NJ 1-Hour Background Levels:

18% - 47% of NAAQS

SO2 1-Hour Modeling

August 23, 2010 EPA Guidance Memos:

Suggested interim SIL (7.8 ug/m3)

Methods of demonstrating NAAQS compliance, calculating background, etc.

24-hour and annual SO2 NAAQS revoked

Intermittent emissions not as important as with NO2

Example of 1-Hour SO2 Modeling

Portland Power Plant

Coal-fired Unit 1 – 160 MW / 1958 Unit 2 – 240 MW / 1962

No existing emission controls for SO2

Average 2007 – 2010 annual emissions of 29,067 tons

1-Hour SO2 Modeling Conducted with Two EPA Models

1. AERMOD (guideline model)

2. CALPUFF (complex terrain model)

Designed for locations with complex wind fields

Must conduct a model validation showing it performs better for the given application than EPA’s guideline model

(see June 2011 JAWM article)

CALPUFF – Allowable Emissions

Max. Impact 1.4 times over 3-hr NAAQS

Summary of CALPUFF Results 1-Hour SO2 NAAQS (196 ug/m3)

Meteorological Time Period

Emissions

Days Violating NAAQS

% Over NAAQS

2002 Allowable 39

1662 %

(~ 17 x NAAQS)

2002

Actual

(CEM data) 27

1019 %

(~ 10 x NAAQS)

(background not included)

M

m

Summary of AERMOD Results 1-Hour SO2 NAAQS (196 ug/m3)

Meteorological Time Period

Emissions

Days Violating NAAQS

% Over NAAQS

1993-94 Allowable 42

615 %

(~ 6 x NAAQS)

1993-94

Actual

(avg. monthly) 5

138 %

(~ 1.4 x NAAQS)

(No predicted violations of the 3-hour or 24-hour NAAQS,

background not included)

Columbia Lake SO2 Monitor

Data collected at Columbia Lake Monitor since Sept. 23, 2010

31 exceedances of the 1-hour SO2 NAAQS of 75 ppb (196 ug/m3) recorded since Sept. 23, 2010

Monitor located where both models predicted high impacts but not maximum

Columbia Lake - Sept. 23, 2010 to Sept. 15, 2011

1-Hour SO2 Modeling Conclusions

SO2 1-Hour NAAQS is much more easily violated than the 3 and 24-Hour NAAQS

Columbia Lake monitoring confirms both CALPUFF and AERMOD predictions of 1-hour NAAQS violation at that location

Principal sources of concern are older, large sources burning No. 6 oil or coal

(especially after Sub. 9 Sulfur in Fuel Rule)