# Presentation: 691092

## Changes to the EPA’s Air Quality Index (AQI): A New Challenge in Forecasting and Communicating Air Quality Information

**Scott Jackson****1**** ,Dianne S. Miller****2****, Neal D. Conatser****2****, Juli I. Rubin****2**
**2007 National Air Quality Conference**
**Orlando, FL**
**February 13, 2007**
**1****U.S. Environmental Protection Agency, Research Triangle Park, NC**
**2****Sonoma Technology, Inc. Petaluma, CA**

## Acknowledgements

- Analysis performed by Sonoma Technology Incorporated under EPA Work Assignment 3-13
- Findings are preliminary.
- Final report due due in mid-March 2007.

## 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
(g/m3) | Potential New PM2.5 Concentrations
(g/m3) |
| --- | --- | --- | --- |
| Good | 0-50 | 0.0-15.4 | 0.0-15.4 |
| Moderate | 51-100 | 15.5-40.4 | 15.5-35.4 |
| Unhealthy of 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
- 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 episodes (USG+) be longer?
- During summer, are more USG days dominated by ozone or PM2.5?
- Can USG occur with different meteorology conditions?
- What cities might need to begin forecasting due to the potential AQI thresholds?

## 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-hour averaged values
- Some considerations:
- 75% data completeness
- Continuous data useful because 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
- 		– Detroit: 34 to 54 days	 – Denver: 2 to 3
- 		– 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 episodes (USG+) be longer?

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

- Detroit

- Annual Episodes

- Average number of three or more day episodes 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 new USG threshold, May-September

## Can USG Levels Occur With Different Meteorology?

- Lower criteria for USG may result in different meteorological conditions conducive for USG levels
- This could impact existing forecast tools
- Conceptual models for USG levels
- Synoptic and local weather
- Transport
- Classification and Regression Trees
- Conducted limited case study and statistical analyses

## Conceptual Findings - Example (1 of 2)

- Richmond, Virginia, for 2004 and 2005
- 8 USG days under current USG threshold
- 16 USG days under potential new USG threshold
- Occurred in summer only
- Limited analysis showed that the additional USG days can occur under a transient short-wave ridge
- These transient meteorological events were not common on days in which PM2.5 levels were greater than 40.5 ug/m3

## Conceptual Findings - Example (2 of 2)

- 500 mb height contours at 7:00 a.m. EST, July 21, 2005.
- Richmond’s PM2.5 concentration was 36 μg/m3.

## Statistical Findings - Example

- Louisville, Kentucky, for 2003 through 2005
- 12 USG days under current USG threshold with meteorological data
- 22 USG days under potential new USG threshold with meteorological data
- Higher daily average wind speed on additional 10 days
- 2.6 knots for current USG days
- 3.0 knots for additional USG days
- Similar temperature and relative humidity between current and additional USG days

## What cities might want to consider forecasting due to the potential AQI thresholds?

## Summary

- Change in AQI threshold 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 for additional seasons in many cities
- A different peak PM2.5 season in some cities
- PM2.5 USG days to occur under new meteorological conditions
-      Want to know the details about your city?
- Handouts are available with city-specific statistics