# Presentation: 021572

## PM2.5 – AirNow versus FRM

- David Mintz (for Mark Schmidt)
- Air Quality Assessment Division
- OAQPS / EPA

## PM2.5 – AirNow versus FRM

- Comparison of the PM2.5 continuous data in AirNow to the Federal Reference Method (FRM) data in the Air Quality System (AQS)

- 	[Continuous PM2.5 data in AirNow are presumed to be FRM-like.  FRM data in AQS are the regulatory gold standard (i.e., “truth”)]

_**Presentation Points**_

## PM2.5 – AirNow versus FRM

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS** **

- Highlight some of the benefits of AirNow PM2.5 data aside from real-time public reporting

_**Presentation Points**_

## Highlight some of the benefits of AirNow PM2.5 data beyond real-time public reporting

- The AirNow PM2.5 continuous data are extremely useful for ‘previewing’ U.S. concentration levels before FRM AQS data are available.
- FRM data for the last quarter of a calendar year are not overdue in AQS until April 1st of the following year.
- States have until July 1st to ‘certify’ their previous year of data.
- Based on past experience, there will still be some isolated data holes  beyond those dates.
- Missing data (e.g., last quarter) can be estimated but that is sometimes difficult to do with metrics such as 98th percentile
- AirNow PM2.5 continuous data are replete as of January 1st.
**Example on following 2 pages**:

## FRM 1999 -2005

- _FRM 1999 -2005_

- _AirNow 2005-2006_

- Benefits of AirNow PM2.5 data beyond real-time public reporting: They provide early preview of FRM levels

*PM**2.5** FRM national average concentrations were declining steadily until 2005 (which was a bad met year)*
*AirNow data provided an early picture of the 2006 results ... the levels declined significantly!*

**Note:  Trend lines do not line up in the two graphs because each utilize a different set of sites**

## Changes in 98th Percentiles – 2006 versus 2005

- Increase _>_ 20% (51 sites)
- Increase < 20% (78 sites)
- No change (+2% to -2%) (28 sites)
- Decrease < 20% (176 sites)
- Decrease _>_ 20% (125 sites)

- Changes in _98__th__ Percentiles_ – 2006 versus 2005
- Using AirNow Data

- Average site decline of 3%
- Median site decline of 10%

- Benefits of AirNow PM2.5 data beyond real-time public reporting: They provide early preview of FRM levels

## Highlight some of the benefits of AirNow PM2.5 data beyond real-time public reporting

- The PM2.5 AirNow data are useful for ascertaining what occurred on FRM non-sample days.
- FRM monitors typically sample on an ‘every third day’ schedule.  AirNow data can show what happened the other two days.
- The AirNow data provide estimates of PM2.5 concentration levels in areas without FRM monitors.
- There are hundreds of PM2.5 continuous monitoring locations (sites) that do not have collocated FRM instruments
- The AirNow PM2.5 data are utilized extensively in detailed time-resolved analysis ... such as ...diurnal analyses; evaluations of pollution transport (especially for areas with mixed wind signals like offshore/onshore breezes); meteorological adjustment analyses; etc.
- Health researchers are increasingly utilizing the PM2.5 continuous data in various capacities.

## Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS

- AirNow data queried from AirNow – Tech in January (2007)
-   Approximately 440K 24-hr observations
- FRM (/FEM) data extracted from AQS also in January (many sites still missing 4th quarter 2006)
-   Approximately 386K 24-hr observations
- About 112K matched pairs
-   Matched by site-day
- Analyses focused on three areas:
-   Estimates of bias
-   Calculation of correlations
-   AQI category (color) comparisons

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS

_**Analysis Details**_

## AirNow : FRM bias, 2004-2006

- _Overall bias_:
- 61,157 pairs
- 	 (where FRM _>_ 10 μg/m3)
- Average = +5.1%

- _By site __(w/ 30+ pairs where FRM > 10)__:_

- _AirNow : FRM bias, 2004-2006_
- (FRM concentrations _>_ 10 μg/m3)

- bias ...
- > +10% (69 sites)
- +/- 10% (175)
- < -10% (38)

*National overall average bias is +5%*
*Average site bias is +4%*
*62% of the mapped sites have an average bias of +/- 10% *

- Bias calculated as ...
**(AirNow - FRM) / FRM**
*Positive bias means AirNow is higher than FRM!*

**282 sites**

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS.

## AirNow : FRM bias by ‘cold’ / ‘warm’ season, 2004-2006

- (FRM concentrations _>_ 10 μg/m3)

- bias ...
- > +10% (36 sites)
- +/- 10% (117)
- < -10% (61)

- bias ...
- > +10% (67 sites)
- +/- 10% (132)
- < -10% (18)

***Sites w/ 30+ obs where FRM > 10 μg/m3***

**217 sites**

**214 sites**

_**Cold Season**_
- (Dec. – Mar.)

_**Warm Season**_
_**(Jun. – Sep.)**_

*More negative bias during winter (especially in East)*
*55% of the sites have a bias of +/- 10%*
*More positive bias during summer (especially in West)*
*61% of the sites have a bias of +/- 10%*

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS.

## AirNow : FRM correlations, 2004-2006

- _Overall_:
- 111,667 pairs
- R = 0.88
- r-square = 0.77

- _By site (w/ 30+ pairs):_

- _AirNow : FRM correlations, 2004-2006_
- All concentrations

- Correlation (r) ...
- _>_ 0.90 (198 sites)
- 0.7 - 0.9 (110)
- < 0.7 (11)

*National overall r is 0.88*
*Average site r is 0.90; median  is 0.92*
*62% of the sites have an r *_*>*_* 0.90*

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS.

**319 sites**

## AirNow:FRM AQI category (color) comparison, 2004-2006

- _Do AirNow and FRM 24-hour AQI categories match?_

- _AirNow vs. FRM_

- _FRM vs. AirNow_

- _Summary_

*AirNow and FRM match 88% of the time*
*But, AirNow was only correct 43% of the time when the displayed color was orange and above*

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS.

## AirNow:FRM AQI category (color) comparison, 2004-2006

- _>_ 90% of the time (189 sites)
- 80% – 90% of the time (92 sites)
- < 80% of the time (38 sites)

- _By site (w/ 30+ pairs):_

- _AirNow:FRM AQI category (color) comparison, 2004-2006_
- _Do AirNow and FRM 24-hour AQI categories match?_

- _All Concentrations_

- Comparison of the PM2.5 continuous data in AirNow to the FRM data in AQS.

**319 sites**

*59% of the sites have 90%+ agreement*
*88% of the sites have 80%+ agreement*

## PM2.5 – AirNow versus FRM

- The PM2.5 continuous data in AirNow provide hourly and daily estimates of AQI levels which help protect public health
- Plus, the PM2.5 continuous data in AirNow have significant utility beyond real-time public reporting.  They provide early, preliminary estimates of FRM levels; they help ‘fill in the blanks’ for days and areas without FRM data; they permit time resolved analyses not available with the current FRM measurements; and they are increasingly being utilized by health researchers.
- Overall, national estimates of bias and correlation (for AirNow vs. FRM) appear to be within targets.  Also, the AQI categories displayed in AirNow appear to be correct a majority of the time.
- However, there is ample room for improvement, especially in certain locations.
- States should periodically retrospectively ground-truth their submitted AirNow data with FRM data.  Tools are available to help make their continuous data more FRM-like.  Increased communication among the data submitters is also encouraged, especially those with similar environments and/or monitoring/adjustment methods

_**Summary**_