RETURN TO NORMAL SMOG SEASON EXPECTED THIS YEAR

June 1, 1999

Fewer Stage 1 Smog Episodes Predicted This Summer

With El Niño 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 Niño’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 Niña’s effect

La Niña, 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 Niño conditions are defined by unusually warm waters in the equatorial Pacific.)

The winter and spring weather systems spawned by La Niña 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 Niña 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 Niña 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.