June 1, 1999
Fewer Stage 1 Smog Episodes Predicted This Summer
With El Niņo now history and last summer’s unusually hot summer not expected to
recur this year, meteorologists forecast a more normal smog season this summer compared to
the wide swings of 1997 and 1998.
"We should see a return to more normal weather patterns, and as a result, fewer
Stage 1 ozone episodes this summer than last," said Joe Cassmassi, senior
meteorologist for the South Coast Air Quality Management District.
A Stage 1 episode occurs when ozone levels reach 0.20 parts per million or 200 on the
Pollutants Standard Index (PSI). Air quality then is considered very unhealthful and
everyone is urged to avoid vigorous outdoor exercise.
"Our air quality this summer may not be as good as it was in 1997, when El
Niņo’s cooler temperatures and unsettled conditions brought unusually clean
conditions," Cassmassi said. "But we should see a return to the long-term trend
toward reduced peak levels of ozone and fewer days violating federal health standards for
the pollutant."
In 1997 there was only one Stage 1 episode, while in 1998 there were 12, predominantly
in the central San Bernardino Mountains.
So far this year there have been two violations of the federal standard for ozone, on
April 18 in downtown Los Angeles and in the central San Bernardino Mountains, and on May
28 in the central San Bernardino Mountains. The federal ozone standard is exceeded, and
air quality is considered unhealthy, when ozone rises above 0.12 parts per million or 100
PSI.
La Niņa’s effect
 La Niņa, a global weather
phenomena featuring unusually cool waters in the equatorial Pacific Ocean, has brought
winter-type weather into spring and resulted in relatively good air quality so far this
year. (In contrast, El
Niņo conditions are defined by unusually warm waters in the equatorial
Pacific.)
The winter and spring weather systems spawned by La Niņa also have created high winds
in the Coachella Valley, causing two unusual Stage 1 episodes for particulate matter this
year on Jan. 21 and April 22. A Stage 1 episode for PM10 is declared when
levels exceed 350 micrograms per cubic meter (200 PSI). High winds are less prevalent in
the desert during summer and additional Stage 1 particulate episodes are not expected
there this summer, Cassmassi said.
During last July and August, La Niņa was given credit for extremely strong
high-pressure systems and stagnant atmospheric conditions across the region and an
increase in Stage 1 episodes in the central San Bernardino Mountains. Climate data appears
to show that La Niņa has reached its peak or is weakening, which should result in more
normal weather conditions by mid-June, Cassmassi said.
AQMD is the air pollution control agency for the urban portions of Los Angeles, San
Bernardino and Riverside counties and all of Orange County.
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