Changes to Air Quality and Ozone Forecasts This Season

This is a note from SEP meteorologist Sean Nolan:

 

 

First, let me thank you for being a subscriber to the Lehigh Valley / Berks AreaAir Quality Forecast.  As you are aware, we issue Air Quality Action Days when we foresee air quality conditions reaching the Code ORANGE status or higher on EPA’s Air Quality Index (AQI) scale (for more details, seehttp://www.airnow.gov/index.cfm?action=static.aqi).

 

That said, I wanted to make you aware of some changes that are forthcoming for the upcoming summer season. 

 

1.) We will begin forecasting for ozone starting today, Monday, April 28th.  Therefore, the forecast for the Lehigh Valley / Berks area will include a forecast for both ozone and PM 2.5 through the summer months.  In addition, the April 28th to May 2nd period marks Air Quality Awareness Week (for more details, see http://www.epa.gov/airnow/airaware/airaware.html).  The inclusion of ozone to our forecast leads us to item 2.).

 

2.) We will most likely be forecasting for more Air Quality Action Days for Ozone this summer.  The reason: We are adopting the new ozone Air Quality Index (AQI) scale that EPA has released.  The history: Back in March, 2008, EPA released a new ozone standard, changing the 8-hour ozone threshold from 85 ppb to 76 ppb.  For more information on this change, go tohttp://www.epa.gov/air/ozonepollution/actions.html.  In the past, the Code YELLOW to Code ORANGE cutpoint on the AQI was at 85 ppb.  When the new 8-hour ozone standard was lowered to 76 ppb, EPA adjusted the AQI scale to reflect this change.  Therefore, the new Code YELLOW to Code ORANGE cutpoint on the AQI was set to 76 ppb.  Here is how this change would have influenced the issuance of Air Quality Action Days over the past 5 years (the number in first column is the year and in the other two columns are the number of days)…

 

	Old AQI	New AQI
2003	4	10
2004	8	16
2005	8	16
2006	3	9
2007	3	17
Average 2003-07	5.2	13.6

 

**Number of days calculated for the ozone monitoring period, from April 1 through October 31.

 

As you can see, this change has increased the number of Air Quality Action Days for Ozone each of the past five years.  Therefore, we expect to be forecasting for more Air Quality Action Days for Ozone starting this year.

 

3.) In addition to the changes in the ozone forecasting, we might see changes in the number of Air Quality Action Days for PM 2.5.  The reason: EPA willeventually be releasing a new PM 2.5 AQI scale.  The history: Back in November 2006, EPA released a new PM 2.5 standard, changing the 24-hour PM 2.5 threshold from 65 ug/m3 to 35 ug/m3 (for more details, seehttp://www.epa.gov/oar/particlepollution/naaqsrev2006.html).  Unlike ozone in 2.) above, EPA did not release a change in the PM 2.5 AQI scale during the time of the announcement of the new PM 2.5 standard.  Therefore, we continue to use the Code YELLOW to Code ORANGE cutpoint in the AQI of 40.5 ug/m3.  The proposed PM 2.5 standard would change the Code YELLOW to Code ORANGE cutpoint in the AQI to 35.5 ug/m3.  Here is how this change would have influenced the issuance of Air Quality Action Days for PM 2.5 over the past 5 years (the table is read the same way as the one for ozone above)…

 

	Old AQI	New AQI
2004	2	7
2005	9	21
2006	11	19
2007	7	16
Average 2004-07	7.3	15.8

 

**Number of days calculated during the entire year, from January 1 through December 31.

 

As I stated above, nothing has officially changed with regards to PM 2.5 cutpoints on the AQI scale.  So as of right now, we will continue to forecast the Code YELLOW to Code ORANGE cutpoint as 40.5 ug/m3.  The change in the AQI is most likely to take effect sometime this summer, though, which is why I wanted to address that item in this email.

 

Thank you for your time.