A stagnant, dry winter has created near-historic soot levels in the San Joaquin Valley and around California, perhaps unraveling years of work on federal air standards, Valley air authorities said Thursday.
The Valley was supposed to achieve a federal standard for such tiny particles, known as PM-2.5, by 2015. But the soot siege during the record-breaking drought probably ends any chance the Valley might have had, air officials said.
Though federal authorities do not grant exceptions based on extremely dry conditions, air officials hinted that it might make sense to make an exception this time.
"We're not the only ones affected," said Seyed Sadredin, executive director of the San Joaquin Valley Air Pollution Control District. "The Bay Area might go into PM-2.5 nonattainment for the first time."
But the U.S. Clean Air Act says there are no exclusions for stagnant air as a result of inversion layers, which act as an atmospheric lid holding pollutants closer to the ground. Such inversions occur in many areas of the West.
Atmospheric layering in winter usually traps cold air beneath warm air. It is a common feature of Valley weather in colder months.
This winter, the lid has been extreme for the Valley and much of California. The last time it rained in Fresno was Dec. 7 when .15 of an inch fell. Dry-year records have fallen all over the state.
"This inversion layer (in the Valley) has lasted longer than any I've seen," said Kerry Drake, an associate director in the EPA's San Francisco office. "But inversion layers are typical in the West. They happen over and over. That's the reason we have air cleanup plans."
In their season update on Thursday, Valley air officials said pollution emissions here are at an all-time low for many reasons, including a wood-burning ban on most days. But the weather has overwhelmed their efforts, they say.
The air district board discussed emergency measures, such as completely banning wood burning in fireplaces and wood stoves during such intense events.
Board member Alex Sherriffs, who is a physician, suggested the district will have to develop new ideas.
"Maybe we need to have no (leaf) blower days, maybe we need no drive-through days," he said.
Such changes would require a public comment process, air leaders said.
This season's problems went out of control in December when the soot level in the Valley was recorded four times higher than the federal health threshold. The levels have backed down since then, but the air continues to exceed the threshold most days.
The microscopic PM-2.5 specks are a serious health problem. They can pass through the lungs into the blood stream and lodge in body organs, such as the heart. They are known to trigger asthma and heart problems. They also cause premature death, according to medical studies.
The specks can be directly emitted from fireplace burning and diesel exhaust, but they also form in the atmosphere when ammonia from dairies and oxides of nitrogen combine.
The Valley has long been one of the country's worst air basins for PM-2.5. But this winter San Francisco's air already has exceeded the threshold 12 times. The Bay Area had zero exceedances last year at this time.
Valley air district experts say the inversion layer is stronger than any since 1999. Sadredin said he thinks it is an exception to the normal in California.
He also said the weather-related air problems won't end after winter. Fire season -- which results in soot -- will start early because of the dry landscape.
"Fire hazard is going to be a big issue this year," he said.
The reporter can be reached at (559) 441-6316, email@example.com or @markgrossi on Twitter.