Questions about SO2 Forecasting and Messaging,

a New Hampshire Case Study.

Anne McWilliamsEPA Region 1

U.S. EPA’s 2011 National Air Quality ConferenceMarch 9, 2011

Revised SO2 Standard• On June 2, EPA strengthened the SO2 standard from 140 ppb evaluated

over 24-hours, and 30 ppb evaluated over an entire year to a 1-hour standard of 75 ppb.

• In the same ruling, EPA revised the Air Quality Index (AQI)

Category AQI 1-Hour SO2 Concentration

Good 0 - 50 0 – 35 ppb

Moderate 51 - 100 36 – 75 ppb

Unhealthy for Sensitive Groups

101 - 150 76 – 185 ppb

Unhealthy 151 - 200 186 – 304 ppb

Very Unhealthy 201 - 300 305 – 604 ppb

Forecasting the AQI for SO2

“EPA recommends and encourages air quality forecasting but it is not required (64 FR 42548; August 4, 1999). We agree that there will be new challenges associated with creating and communicating an SO2 forecast, and will work with State and local agencies that want to develop an SO2 forecasting program on issues including, but not limited to, forecasting air quality for short time periods. We plan to work with State and local air agencies to figure out the best way to present this information to the public using the AQI.” (75 FR 35587; June 22, 2010)

New Hampshire SO2 Monitoring

Locations

Suncook to Manchester – ~10 miles

Suncook to Portsmouth –~40 miles

Number of SO2 Exceedance Days based on the 1-Hour Standard of 75 ppb

2007 2008 2009 2010

Manchester, NH 1 1 1 1

Suncook, NH 54 35 80 95

Portsmouth, NH 0 1 0 0

Suncook, NH Air Monitor

PSNH Merrimack StationA 433-megawatt coal-fired power plant.

Factors contributing to SO2 concentrations at Suncook Village, NH

• Wind Direction• Wind Speed• Power Plant Emissions

SO2 concentrations are higher with Northwest flow.

Figure 5-6. Average hourly SO2 Levels by Wind Direction: Exchange Street, Mar 2004-Feb 2006

7.1

2.7 2.53.7

2 2.6 3.2 2.7

22.6

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Wind Direction

Ave

rage

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rly S

O2 L

evel

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ts p

er b

illio

n)

Figure Courtesy of New Hampshire Department of Environmental Services

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Monitored SO2 at Suncook, NH vs monitored wind direction by decending SO2 concentration

January 2009Monitored SO2 (ppb) Wind Dir (Degrees)

Sunc

ook

Mon

itore

d 1

Hour

SO

2 (p

pb)

Win

d Di

recti

on (D

egre

es)

Highest Concentrations during with NW flow.

For northwest winds, SO2 concentrations are higher at wind speeds above 15 mph

Figure 5-7. Average hourly SO2 levels by wind speed: Northwest winds only, Exchange Street, Mar 2004-Feb 2006

22.6

13.1

22.9

37.8

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All NW Winds <10 mph 10-14 mph 15-19 mph 20+ mphWind Speed

Ave

rage

Hou

rly S

O2 L

evel

(par

ts p

er b

illio

n)

Figure Courtesy of New Hampshire Department of Environmental Services

SO2 concentrations are dependant upon power plant operations

1/1/

2010

1/8/

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1/15

/201

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Daily Measured 1-Hour Maximum SO2 Concentration at Suncook, NH and Daily SO2 Emissions from Merrimack Station

2010

2010 SO2 (tons) 1 Hr Max SO2

Daily

SO

2 Em

issio

ns (t

ons)

Mea

sure

d Da

ily M

axim

um 1

-Hou

r SO

2 Co

ncen

trati

on (p

pb)

What happens to ambient concentrations in other directions and distances from the source?

What is the spatial extent of the unhealthy air quality?

What should we be forecasting?

• For the 1-hour ozone standard, an entire day was considered “unhealthy” if any hour was expected to “exceed” the standard.

• Ozone is well behaved in that, in absence of cloud cover , concentrations increase to a peak value, usually in the late afternoon.

• Will we use the same approach for SO2 forecasting?

• High SO2 concentrations can happen any time of the day for a variable length of time.

Suncook, NH Monitor Data January 9, 2009 and April 12, 2009

Date and TimeMeasured SO2 (ppb)

Wind Direction (Degrees)

Wind Speed (mph)

1/9/2009 0:00 279 1.61/9/2009 1:00 297 11/9/2009 2:00 6.1 301 1.61/9/2009 3:00 6.7 303 2.21/9/2009 4:00 5.9 297 1.61/9/2009 5:00 0.7 299 1.11/9/2009 6:00 1.1 307 11/9/2009 7:00 5.7 294 1.71/9/2009 8:00 1.3 301 3.51/9/2009 9:00 2.6 303 3.61/9/2009 10:00 1.4 293 31/9/2009 11:00 2.4 299 3.91/9/2009 12:00 101 313 4.31/9/2009 13:00 66.4 316 4.61/9/2009 14:00 84.4 321 4.51/9/2009 15:00 41.6 316 4.91/9/2009 16:00 97.2 321 4.31/9/2009 17:00 46.4 319 2.81/9/2009 18:00 21.6 316 2.31/9/2009 19:00 9.2 320 2.71/9/2009 20:00 27.5 313 4.31/9/2009 21:00 26.5 317 3.71/9/2009 22:00 5.3 319 3.21/9/2009 23:00 23.7 315 1.8

Date and TimeMeasured SO2

(ppb)Wind Direction

(Degrees)Wind Speed

(mph)4/12/2009 0:00 146 322 4.24/12/2009 1:00 132 331 4.94/12/2009 2:00 139 326 5.24/12/2009 3:00 16.6 327 4.94/12/2009 4:00 107 329 3.44/12/2009 5:00 57.4 328 4.94/12/2009 6:00 60.1 328 5.44/12/2009 7:00 72.3 326 6.24/12/2009 8:00 61.9 331 6.94/12/2009 9:00 33.4 326 6.14/12/2009 10:00 17.3 331 5.74/12/2009 11:00 56.3 326 5.84/12/2009 12:00 81 323 5.64/12/2009 13:00 125 315 5.84/12/2009 14:00 74.3 316 5.64/12/2009 15:00 94.2 318 5.74/12/2009 16:00 71.3 316 4.94/12/2009 17:00 24.4 308 44/12/2009 18:00 88.6 313 4.34/12/2009 19:00 58.7 314 4.24/12/2009 20:00 25.7 310 3.64/12/2009 21:00 12.3 306 3.34/12/2009 22:00 16.7 306 2.84/12/2009 23:00 2.7 302 2.9

What is the message?

• Do we specify the source of the SO2?– The source is slated for control in 2012, but an advocacy

group is calling for the complete shut-down of the source.

• What is the health messaging?– Do people just avoid strenuous outdoor activities?

• What actions can people take?– Do we advocate energy conservation?