Weeks of dry weather and smoke from a pair of major fires Tuesday cooked up one of the Bay Area's worst soups of air pollution in years -- but with more wind in the forecast, residents may finally get to catch their breath.
Concentrations of soot, dust and other tiny airborne debris were worst in downtown San Jose, where particulate pollution levels at noon reached nearly three times the federal health standard -- the highest reading in the city since June 2008, when forest fires in the North Bay blanketed the region with soot.
Similarly, San Francisco hit its highest level in two years Tuesday. And Oakland reached a level not seen since December 2011, except for one other day -- July 4 this year -- when smoke from a fireworks show at the Oakland Coliseum temporarily sent air pollution monitors spiking.
Tuesday's bad air combined smoke from the unseasonable wildfire raging 75 miles south in Big Sur and an early morning blaze at a Redwood City recycling company that sent a pungent scent of burning plastic across the region.
"It's so strong I had to stop walking my dogs and go back inside," said Leslie Stainton, who took cover in Gilroy about 10 a.m.
San Jose's air was so bad Tuesday that it ranked second-worst in air quality in the United States for a few hours, behind Bakersfield. Bay Area health and air pollution officials recommended that people limit their time outside, particularly residents with asthma and other respiratory problems.
"It was a good day to stay inside and write holiday cards," said Dr. Sarah Cody, Santa Clara County's public health officer. "Don't burn wood. And don't train for any marathons."
State air quality officials said conditions should begin to improve Wednesday and Thursday, as the forecast calls for an increase in wind that will dissipate much of the smoggy mess eastward.
The main factor in the poor air quality, they said, is the relentless dry weather. Normally, particle haze in the Bay Area increases in the winter as residents burn wood in fireplaces. But those fine particles, which can lodge deep into people's lungs, causing respiratory ailments and heart problems, typically are washed out of the air every few days as winter rains come and go.
This year, however, Northern California is on pace for the driest calendar year since 1850, when records were first kept. So smoke from fire places, combined with road dust, soot from buses, trucks and construction equipment, along with other particles from industrial pollution, all build up, growing worse with every passing hour.
Making things even smoggier, wind levels have been low in recent days.
"It's like living in a terrarium. There's no rain and no winds. So we aren't having the normal cleansing effect," said Lisa Fasano, spokeswoman for the Bay Area Air Quality Management District in San Francisco.
The agency issued a record 11th straight "Spare the Air" alert for Wednesday, making it illegal to burn wood, manufactured logs or other solid fuel indoors or outdoors in any of the nine Bay Area counties.
Overall, smog levels in the Bay Area have declined dramatically over the past 50 years as cleaner-burning gasoline, tough regulations on factories and power plants, and other rules have cut pollution levels. A new car today emits less than 2 percent of the air pollution that a car built in the 1980s produced. So even as the population rises, overall smog levels have fallen as older cars cycle off the roads.
But certain weather conditions -- heat waves in the summer that exacerbate ozone pollution, or cold, dry winter stretches that allow particles to build up -- can trigger unhealthy air. The fire that burned piles of appliances at Sims Metal Recycling in Redwood City and the Pfeiffer Fire in Big Sur brought more haze across Monterey Bay and into the Bay Area.
Proximity to those fires, along with topography and Santa Clara County's large population, gave San Jose a reading of 94 micrograms per cubic meter for particle pollution at noon Tuesday. The federal health standard is 35. Oakland peaked at 68 and San Francisco peaked at 70.
"Everything sort of pooled in the South Bay," said Fasano.
It's not all bad news. So far this year, the Bay Area has exceeded federal health standards for particle pollution five days. But there were 11 such days in 2009, 12 in 2008 and 14 in 2007.
What changed? This year the air district has altered its standards to call winter no-burn days more often -- 25 so far in 2013, compared with nine in 2011, six in 2008 and 23 in 2007. That public relations campaign has reduced wood burning, and as a result, the number of unhealthy days, district officials say.
Staff writer Mark Gomez contributed to this report. Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN