[ADEQ Forecasts] ADEQ AIR QUALITY FORECAST FOR FRIDAY, APRIL 18, 2008

[forecasts@lists.azdeq.gov]

http://www.azdeq.gov/environ/air/ozone/ensemble.pdf

Health message for Thursday, Apr 17:  Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 
 
Health message for Friday, Apr 18:  Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors. 
 
Synopsis and Discussion
All those who are tired of windy days here in the Valley, raise their hands!  The peak wind gust on Wednesday at Phoenix Sky Harbor was 43 mph out of the northwest with sustained winds ranging from 15-25 mph between 12pm yesterday through early this morning.  It had a significant affect on air quality, too.  As you would expected, Particulate levels climbed well into the "Moderate" range at most sites with West 43rd barely exceeding the federal health standard at 101 AQI (155µg/m3).  One might scratch his or her head, noticing that all but four Ozone monitors were in the "Moderate" range, some in the upper part of that category.  Question: Aren't strong winds supposed to mix that atmosphere enough so that Ozone levels are low?  Answer: Most of the time.  In this case, there was a significant amount of Ozone and precursors transported into the forecast area during the day before the strongest winds kicked in.  In fact, concentrations never really dropped off overnight as they normally do.  As a result, we are starting out higher at most sites today than we did 24 hours ago!  With much lighter winds Thursday afternoon, it could be and active day for ozone formation.  We'll see.  High pressure will allow suspended particulates to settle the next couple of days before, yes, another wind-producing trough pushes into the area on Saturday afternoon (sigh...).  Next week looks much less dynamic, so hopefully the air quality will be able to recover then.  Check back tomorrow for a better look at your weekend weather and air quality.  Have a good day!  -J.Paul

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