Changes to the EPA

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Changes to the EPAs Air Quality Index (AQI) A
New Challenge in Forecasting and Communicating
Air Quality Information
Prepared by Dianne S. Miller Neal D.
Conatser Juli I. Rubin Sonoma Technology,
Inc. Petaluma, CA Scott Jackson U.S.
Environmental Protection Agency Research Triangle
Park, NC Presented to 2007 National Air Quality
Conferences Orlando, FL February 13, 2007
3078
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Background

• EPA lowered the PM2.5 24-hr standard from 65
  µg/m3 to 35 µg/m3 to protect public health.
• EPA is assessing whether to lower the thresholds
  for the following PM2.5 AQI categories
• Unhealthy for Sensitive Groups (USG)
• Unhealthy
• Very Unhealthy
• Hazardous
• Affects
• Local agencies (forecasting, outreach)
• Existing agencies and new agencies
• AIRNow program

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Potential New AQI Thresholds
Category AQI Value Current PM2.5 Concentrations (mg/m3) Potential New PM2.5 Concentrations (mg/m3)
Good 0-50 0.0-15.4 0.0-15.4
Moderate 51-100 15.5-40.4 15.5-35.4
Unhealthy for Sensitive Groups 101-150 40.5-65.4 35.5-55.4
Unhealthy 151-200 65.5-150.4 55.5-130.4
Very Unhealthy 201-300 150.5-250.4 130.5-215.4
Hazardous 301-400 250.5-350.4 215.5-305.4
Hazardous 401-500 350.5-500.4 305.5-435.4
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How Does It Affect Us?

• Additional days considered unhealthy
• More effort needed (outreach, forecasting)
• More close-call days
• Questions from public/media
• For example, July 2006 in Detroit

Potential New AQI
Current AQI
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Questions Addressed

• How many more USG days should we expect each year
  and each season?
• Will USG episodes be longer?
• During summer, are more USG days dominated by
  ozone or PM2.5?

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Data Used (1 of 2)

• Period 2003-2005 data
• Source AQS
• Data types Continuous and FRM
• Locations Forecast cities in AIRNow (AQS
  continuous data)
• Other cities (AQS FRM data)
• Metric 24-hr averaged values
• Some considerations
• 75 data completeness
• Continuous data useful because they are available
  in real time for forecasting and outreach
• Continuous data in AQS may not match the FRM-like
  data submitted to AIRNow
• Examined forecast cities in AIRNow and core-based
  statistical areas (CBSA)
• Frequency of collection of FRM data varied from
  daily to every sixth day

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Data Used (2 of 2)
AQS PM2.5 data completeness for forecast cities
in AIRNow
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How Many More USG Days Should We Expect Each Year
and Each Season? (1 of 2)
Average increase in USG days per year

• Many (70) cities will have at least twice as many
  USG days per year under the potential new AQI
  thresholds.
• Nearly all cities (141) will have at least a 50
  increase in the number of USG days per year.
• Examples
• Boston 5 to 9 days Atlanta 9 to 16 days
• Detroit 34 to 54 days Denver 2 to 3 days
• Tacoma 3 to 9 days

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How Many More USG Days Should We Expect Each Year
and Each Season? (2 of 2)
Peak PM2.5 season may change for many cities
Chicago winter to summer Terre Haute
summer to fall
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Will USG Episodes Be Longer?
Average number of episodes lasting three days or
more per year
Detroit
Annual Episodes

• Multi-day high PM2.5 events will become more
  frequent.

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During Summer, Will More USG Days Be Dominated by
Ozone or PM2.5?
Dominant pollutant at current and potential USG
threshold, May-September
Chicago, IL Chicago, IL Chicago, IL
Current Potential
USG days 11 15
O3 55 30
PM 45 70
Greenville-Spartanburg, SC Greenville-Spartanburg, SC Greenville-Spartanburg, SC
Current Potential
USG days 5 10
O3 60 20
PM 40 80
Memphis, TN Memphis, TN Memphis, TN
Current Potential
USG days 12 16
O3 50 30
PM 50 70
Many cities that previously had the majority of
their USG days dominated by ozone will now have
the majority of their USG days dominated by PM2.5
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Summary

• Changes to the AQI thresholds will likely cause
• Most cities to have at least a 50 increase in
  USG days observed per year due to PM2.5
• A shift from an ozone-dominated summer season to
  a PM2.5-dominated summer season for about 20 of
  the cities
• PM2.5 USG days in cities that have not had any in
  the past
• PM2.5 USG days in additional seasons in many
  cities
• A different peak PM2.5 season in some cities
• Want to know the details about your city?
• Handouts are available with city-specific
  statistics.