# Presentation: 691091

## Changes to the EPA’s 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

## 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

## 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 |
|  | 401-500 | 350.5-500.4 | 305.5-435.4 |

## 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

- Current AQI

- Potential New AQI

## 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?

## 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

## Data Used (2 of 2)

- AQS PM2.5 data completeness for forecast cities in AIRNow

## How Many More USG Days Should We Expect Each Year and Each Season? (1 of 2)

- 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

- Average increase in USG days per year

## 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

## Will USG+ Episodes Be Longer?

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

- Detroit

- Annual Episodes

- Average number of episodes lasting three days or more per year

## During Summer, Will More USG Days Be Dominated by Ozone or PM2.5?

- 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

| Chicago, IL |  |  |
| --- | --- | --- |
|  | Current | Potential |
| USG days | 11 | 15 |
| O3 | 55% | 30% |
| PM | 45% | 70% |

| Greenville-Spartanburg, SC |  |  |
| --- | --- | --- |
|  | Current | Potential |
| USG days | 5 | 10 |
| O3 | 60% | 20% |
| PM | 40% | 80% |

| Memphis, TN |  |  |
| --- | --- | --- |
|  | Current | Potential |
| USG days | 12 | 16 |
| O3 | 50% | 30% |
| PM | 50% | 70% |

- Dominant pollutant at current and potential USG threshold, May-September

## 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.