[ADEQ Forecasts] ADEQ Issues Air Pollution Health Watch for Wed., Jan. 24

[forecasts@lists.azdeq.gov]

For more information, please visit our Web page:
http://www.azdeq.gov/environ/air/ozone/ensemble.pdf

AIR QUALITY FORECAST FOR WEDNESDAY, JANUARY 24, 2007
This report is updated by 1:00 p.m. Sunday thru Friday and is valid
for areas within and bordering Maricopa County in Arizona

Health message for Tuesday, Jan 23: Unusually sensitive people should consider reducing prolonged or heavy exertion. 

Health message for Wednesday, Jan 24: Unusually sensitive people should consider reducing prolonged or heavy exertion. 

Synopsis and Discussion
A PM-2.5 HEALTH WATCH HAS BEEN ISSUED FOR WEDNESDAY JANUARY 24
Tuesday morning ACARS sounding data indicates that stagnation of the local air mass is underway: between 6:30 and 9:30 a.m. the best mixing depth decreased from near 5200’ to near 4300’, dispersion lowered from GOOD to the low end of the FAIR category and may ultimately be MARGINAL, and the mean transport wind speed decreased from over 10 mph to light and variable. During the same period temperatures aloft rose 1-2 deg C in the 5K-10K’ layer.  In addition, a moderate (4-5 deg C) surface-based radiation inversion that formed overnight extends to almost 1700’ and will not break until early afternoon.  Recent rains have settled and stabilized—albeit temporarily—many sources of coarse particles (PM-10), so today’s Valley Brown Cloud is composed almost entirely of fine particles (PM-2.5); monitoring equipment at the Durango and West Phoenix confirm this. An increase in easterly winds is forecast for Wednesday but may only be strong enough to transport particle pollutants from the east valley over the west valley.  Also, strong warming aloft is expected to continue on Wednesday with a steeper inversion and a lower mixing depth the potential outcome.  Due to these factors, a PM-2.5 Health Watch has been issued for tomorrow as a precaution for those with heart or lung disease to limit prolonged or heavy exertion. Another round of easterly winds on Thursday may have a better chance of dispersing the particle pollution then. -Reith     
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