[ADEQ Forecasts] ADEQ Extends Air Pollution Health Watch for Wed., Apr. 23

[forecasts@lists.azdeq.gov]

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

Health message for Tuesday, Apr 22: Unusually sensitive people should
consider reducing prolonged or heavy exertion outdoors.  

Health message for Wednesday, Apr 23:  Unusually sensitive people should
consider reducing prolonged or heavy exertion outdoors.  

Synopsis and Discussion
TODAY'S OZONE HEALTH WATCH HAS BEEN EXTENDED THRU WEDNESDAY APRIL 23
Monday marked the first day that exceedances of the revised EPA 8-hour
ozone standard (see link below for more information) occurred within the
Phoenix forecast area.  Although elevated ozone levels are not unusual
for this time of year (during the month of April for the period
1996-2007 there were 36 days with concentrations of 76 parts per billion
or higher), only under the new standard are readings at or above that
level considered to be in exceedance of the federal health standard.
(The highest concentration during that interval was 83ppb on April 16
2005).  Since current local weather conditions do not support such high
local ozone formation this time of year, it appears that the continued
transport of additional ozone and/or its precursors from large
California urban centers had a contributing role.  Winds aloft are less
favorable for said transport today, but another major influx is possible
by Wednesday afternoon in the wake of another passing trough from the
west.  In additional, overnight winds on Wednesday night should keep
ozone concentrations levels higher than normal going into Thursday.
Since ozone levels have already reached unhealthy levels at some
downwind sites, a High Pollution Advisory may be issued for Thursday.   

For transportation alternatives:
http://www.valleymetro.org/default.asp

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