[ADEQ Forecasts] ADEQ Issues an Ozone High Pollution Advisory for the Phoenix Metro Area for Thursday, August 04, 2011

[forecasts@lists.azdeq.gov]

Health message for Wednesday, August 03:  Unusually sensitive people
should consider reducing prolonged or heavy exertion outdoors. 

Health message for Thursday, August 04:  Active children and adults, and
persons with lung disease such as asthma, should reduce prolonged or
heavy exertion outdoors.  


Synopsis and Discussion
OZONE: AN OZONE HEALTH WATCH REMAINS IN EFFECT FOR TODAY 
AN OZONE HIGH POLLUTION ADVISORY HAS BEEN ISSUED FOR THURSDAY AUGUST 04
After nearly a month (July 8) since the last local ozone exceedance,
three Valley monitoring sites recorded unhealthy ozone levels on
Tuesday.  Of special interest was the fact that the highest hourly
concentration of 102 parts per billion at the South Phoenix site was the
second highest of the 2011 season...surpassed only by the 104 ppb
reading at Blue Point on June 9.  Metro area ozone levels have risen
precipitously since July 28; one explanation is that during that evening
a strong outflow boundary from the north and northeast ushered in a
flush of ozone precursors in the form of biogenic VOC's - a situation
that has been observed during previous monsoon episodes.  This was
followed by similar outflows on the 29th, 30th, and 1st.  At the same
time afternoon wind speeds have remained below average and daytime high
temperatures reached record levels on Tuesday.  Since little change in
this current situation is expected, today's Ozone Health Watch has been
heightened to an Ozone High Pollution Advisory for Thursday.     
PARTICLES:  A relatively weak (~25 mph) thunderstorm outflow boundary
arrived over the metro area from the southeast early this morning that
still managed to generate a thick dust wall and resulted in visibilities
as low as 11/4 miles and hourly PM-10 concentrations as high as
3,404.6ug/m3 at the West Chandler monitoring site.  (It remains to be
seen whether this will result in a 24-hour average exceedance).  Nine
other sites had readings above 1,000ug/m3.  The peak of the advertised
break in the summer monsoon circulation pattern for the Phoenix metro
area is now expected to begin on Thursday due to lingering low-level
moisture today.  By then dry southwesterly flow aloft is forecast to
become firmly established due to an encroaching upper level trough from
the west.  


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

For transportation alternatives:
www.valleymetro.org 


If you have any questions or comments regarding this forecast please
contact:

Arizona Department of Environmental Quality
Office of Communications
1110 W. Washington St., Phoenix, AZ 85007
(602) 771-2215
ms15@azdeq.gov