Dangerous soot levels continued Wednesday morning in the San Joaquin Valley with the highest readings in Fresno, Tulare, Kings and Kern counties.
At 8 a.m., Visalia's monitor showed 130 parts of soot per cubic meter of air -- the threshold is 35 parts per cubic meter averaged over a full day.
Fresno, Hanford and Bakersfield had readings higher than 100 parts per cubic meter.
Such soot levels are considered very unhealthy, even for adults with no lung problems. Children, senior citizens and those with sensitive lungs are more vulnerable to the pollution.
The tiny specks of pollution come from fireplaces, diesel engines, cars and other sources. The pollution has been building in the stagnant Valley air for more than a week.
The San Joaquin Valley Air Pollution Control District continues to urge the public to check its hourly updates online and stay indoors as much as possible.
"This is related to the dry winter we're having," said air district executive director Seyed Sadredin. "For the last eight days, we've had no cleansing wind or storms. This is affecting the whole Valley."
A storm is expected to provide some relief on Thursday.
Soot pollution spiked more than two times the federal health threshold Tuesday.
The Valley on Tuesday had the nation's worst particle pollution, known as PM-2.5, according to the U.S. Environmental Protection Agency's website.
Doctors in Fresno are seeing patients with complaints of coughing, wheezing and shortness of breath because of the bad air. Dr. John Gasman, a pulmonologist at Kaiser Permanent Medical Center-Fresno, said people with asthma, chronic pulmonary obstructive disease (COPD) and other lung diseases are showing up in increasing numbers as the pollution siege continues.
Over the last several days, air district leaders have been prohibiting wood burning in fireplaces for many parts of the Valley. Holt said this is among the more intense PM-2.5 episodes in the last few years.
People who violate the no-burn orders could be cited and fined. More than 125 notices of violation have been written Valleywide this year through Tuesday, compared to 78 at this point last year. The fine for violating the no-burn order is $50.
Air district officials are responding to phone calls from residents who report neighbors burning in violation of the burning ban.
The federal fine-particle standard has been breached each day for the last week in at least one of the eight Valley counties. This week, the exceedances are happening in most cities.
On Tuesday, the district's air monitors showed spikes more than twice the federal standard for PM-2.5 in Clovis, Fresno, Merced and Visalia.
Hanford was more than three times the standard at midday -- 120 parts per cubic meter of air. The federal threshold for PM-2.5 is a daily average of 35 parts per cubic meter of air.
Particle pollution comes from diesel exhaust, dust and other sources, too. It also forms in the atmosphere by combining oxides of nitrogen from cars and ammonia plumes from such sources as dairies.
The tiny particles can penetrate deep into the lungs, triggering asthma and heart problems. The particles are considered more dangerous than summertime ozone.
Even people with healthy lungs can have a burning throat, shortness of breath, coughing and burning eyes, said Gasman of Kaiser.
"If this were to continue for a week, the asthma and COPD patients will be in the ER and the healthy patients will be in the doctors' offices," he said.
The reporter can be reached at (559) 441-6330, email@example.com. Staff writer Barbara Anderson contributed to this report.