By Barbara Anderson / The Fresno BeeAcross the San Joaquin Valley, thousands of children start the day by inhaling asthma drugs. Many Valley doctors and parents blame dirty air for an asthma epidemic. [See and hear an animation of pollution's effects on the lungsy]More than one in five Valley children has asthma -- the highest level in the state. And researchers fear more than one in four children could have the chronic lung disease within the next few years.Fresno County is California's asthma capital: Nearly one in three -- or about 75,000 children -- have it, according to a 2005 statewide health survey. The estimate was 50,000 just four years earlier.Easier access to doctors in Fresno, the Valley's biggest city, could explain why so many children in Fresno County are diagnosed.Asthma causes a sufferer's airways to narrow and spasm, sometimes prompting a debilitating wheezing attack.Researchers are not yet ready to say dirty air causes asthma, but they know that dirty air stunts children's lungs and worsens asthma and bronchitis attacks. Ozone, the main ingredient in smog, rubs like sandpaper against delicate lung tissue. And particulates -- tiny bits of soot, chemicals and dust -- irritate and inflame lungs.San Joaquin Valley Air Pollution Control District officials say they aren't convinced air quality can be entirely blamed for the Valley's skyrocketing childhood asthma rates.For one thing, the air is getting cleaner, says air district Executive Director Seyed Sadredin. So why are asthma rates increasing?Sadredin doesn't know, but he said it's possible that indoor air pollution, pollen or some other irritant could be the principal asthma triggers.Air pollution plays a role in asthma, Sadredin says. But "I think you're going to find out at the end of the day that air pollution is not the primary factor in increasing the asthma rates that we've been experiencing."Agriculture, the region's biggest industry, produces pollen by the ton. Allergies to pollen can trigger asthma attacks. But researchers have found hay fever and asthma rates are 16 times greater when people are exposed to pollutants at the same time they're exposed to allergens -- grasses, weeds, cat dander, smoke.And many doctors say there's little doubt that smoggy and sooty air increases the frequency and severity of asthma attacks that send gasping children to doctor offices and emergency rooms throughout the Valley each year. They even have a nickname for their patients' chronic coughs: Valley lung.Car and diesel exhaust, dairy farm waste, agricultural field dust, pesticides and industrial soot provide the raw ingredients for the Valley's dirty air. And geography and weather conspire to trap these lung irritants inside the bowl-shaped, 25,000-square-mile Valley."What we have here is kind of the perfect storm," says Dr. Michael Peterson, a Fresno doctor and president of the California Thoracic Society, the medical arm of the American Lung Association of California.Dr. John D. Gasman, a pulmonologist who treats adults at Kaiser Permanente Medical Center in Fresno, noticed soon after moving from the Bay Area in 2001 that a lot of his patients had persistent coughs not caused by allergies.Breathing constantly irritated their noses, throats and airways."I'm quite certain it has to do with air quality here," Gasman says. "People that were fine elsewhere moved here, and it's this nonspecific, year-round sort of phenomenon."Alicia Bohlke, 41, of Merced has no doubt that dirty air affects her son.Daniel Bohlke, 10, was diagnosed with asthma four years ago after he stumbled into his mother's bedroom choking for air. Daniel's asthma attack came three months after the family moved to Merced from Florida.He had no symptoms prior to the attack, says Bohlke, director of outpatient clinics at Mercy Medical Center in Merced and a volunteer with the Merced/Mariposa County Asthma Coalition.Although complicated by allergies, his condition worsens when pollen counts are lowest, she said."I'm not a rocket scientist, but it doesn't take one to figure out it may be where I'm living that's causing this," Bohlke says.Dr. Alex Sherriffs, a Fowler family practitioner, sees so many patients with asthma who complain about smog and soot worsening their breathing problems that he takes note of smog levels."When I see asthmatics with an exacerbation of their asthma, I'm writing down what the air quality was that day," he says.Air quality has become such a concern of Valley doctors that in the past five years, they've organized to get the word out about the medical dangers."Physicians recognized this is the largest public-health issue that the Valley experiences," says Kim Thompson, who was hired in May 2006 by the Fresno-Madera Medical Society to coordinate air quality education and advocacy programs for doctors.All children are at risk from ozone and particulates. Pound for pound, they inhale more air than adults. And their lungs are developing. But it's children with asthma who suffer the most when the air is dirty.The lungs of young asthmatics are trigger-sensitive. Small amounts of irritants can cause an explosion inside their airways, which swell and tighten. Air trying to get into the lungs backs up. And carbon dioxide that needs to get out can't escape through swollen and congested air passages.Of Valley children taking medication for asthma, more than 60% experienced symptoms more than once a month, according to a 2004 report by the Central California Children's Institute at California State University, Fresno.Asthma medications, such as bronchodilators and corticosteriods, are potent drugs. While considered safe, they can cause heart palpitations, restlessness, headaches and sleeplessness. Long-term use of the steroids can cause brittle bones, cataracts and slow healing of wounds, among other problems.Doctors at Children's Hospital Central California in Madera County see many of the Valley's worst asthma cases in the hospital's pulmonary clinics and emergency room.Last year, doctors at Children's admitted 657 children for asthma treatment and saw 8,011 in the emergency room and clinics. Asthma was the sixth most common reason for emergency room visits, behind colds and the flu, earaches, stomachaches and convulsions.Kevin Hamilton, a Fresno respiratory therapist and asthma educator, says he's looked at poverty and other possible reasons for the Valley's high childhood asthma rate.Studies show poor children nationwide are more likely to have asthma. Nearly one in three Valley children was considered poor last year.But Hamilton says children in other areas of the country where poverty rates are higher than the Valley have lower rates of asthma.The Valley's childhood asthma rates can't be explained without including air pollution, he says."Our blend of pollution -- industrial, auto and agriculture -- is not really found in any other place in the country," Hamilton says.