The San Joaquin Valley is one of the nation's smoggiest regions and -- not surprisingly -- home to some of the highest childhood asthma rates. But for parents, it can be hard to know when it's safe for their kids to play outside. Air quality activists say that's because local regulators don't issue effective public health warnings.

At a recent outdoor water polo game at Fresno's Sunnyside High, none of the parents seemed to have any idea that their kids were playing while air pollution spiked to levels considered unhealthy for everyone's lungs.

The school district's policy is to cancel games when it gets as bad as it was on that afternoon but the water polo tournament, a football game, and track practice were all in full swing.

Out Of Sight, Out Of Mind

"I don't think there's much harm in it," said Russ Perry, whose daughter has mild asthma. Air quality is pretty low on his list of concerns as the parent of a teenager. Grades and what she's doing on Facebook are bigger worries.

"I guess if I'm not seeing my child gasp, it doesn't strike a reaction with me," said parent Lisa Jones. "It's a fact of living in the Valley."

But here's another fact of living in the Valley: A new study (available as a PDF) from UCSF Fresno and Fresno State University finds that when air pollution spikes, so do visits to the ER. Researchers looked at ground-level ozone, which can scar lung tissue, and particulate matter -- tiny particles, like soot, that can burrow deep into the lungs and cause breathing and heart problems. The effects are more acute in kids, who take in a higher ratio of air for their body weight than adults, especially during exercise.

"What we're trying to do is reduce really vigorous activity when the air quality, even for an hour, is at a high level," said study author Tim Tyner, a researcher in the Department of Medicine at UCSF Fresno. He found that kids with asthma end up in the ER even when air pollution levels are considered moderate--well below the levels reported during the water polo tournament. And when air quality levels get really bad, Tyner said healthy kids should avoid sports or recess, too.

The Parent Trap

Concerned parents can check the air quality forecast in the newspaper or on local TV newscasts. Flags at schools also spell out a rainbow of pollution levels, on a scale from "healthy" green to menacing purple.

But all these sources are predictions of averages for air quality on a given day. They don't take into account the way conditions change throughout the day. On the day of the water polo tournament, for example, schools were flying orange flags, signaling air unhealthy for sensitive groups. But some air monitors near schools registered purple levels by late afternoon.

The San Joaquin Valley Air Pollution Control District boasts the most comprehensive school monitoring network in the country. Schools can go online to check real-time air quality. But many parents don't know about it.

It took some digging for Steve Popenoe to find the real-time data on the Air District website, and he's an environmental engineer.

"It's a lot trickier than I think it needs to be," said Popenoe, whose five-year-old daughter, Zoya, has respiratory problems. The information is useful, especially since he can have it emailed to him each time pollution levels climb in his neighborhood.

He called up a graph, which shows air quality changing dramatically throughout the day; starting off in the "green," or healthy level, but peaking up into the red as ozone levels spike.

"It's just like if there's a big fire, and you see smoke everywhere, you don't want your kids running and breathing that, [whereas] ozone is invisible, and you don't want your kid out there," said Popenoe.

"We have a serious human health crisis," said Kevin Hall, who heads the Central Valley Air Quality Coalition. "Air Board members are failing their mandate as a public health agency. They are not doing an adequate job of educating and warning the public."

"If this were a tornado sweeping across the plains, there would be alerts going out," Hall added. "Broadcasts would be interrupted, sirens would be sounded, people would be told, 'go indoors.' And frankly, that's what needs to happen. People need to be told 'go indoors.' "

Mixed Messages

But since the San Joaquin Valley Air District cancelled its program of "Spare the Air" days a few years ago, its public service announcements have largely downplayed health warnings. Instead, its "Healthy Air Living" campaign emphasizes what people can do to reduce emissions, like walking and riding bikes to school or work, and turning off engines rather than idling at drive-through windows.

This summer, the Air District launched an "air alert" campaign to prevent violations of the one-hour federal ozone standard. But the message was focused more on DMV fines valley drivers could face if the Air District didn't meet that standard than on how to protect health as ozone levels hit red and purple levels.

"The message came out completely backwards," said UCSF's Tyner. "'You want to reduce emissions, so ride your bike and walk when the air quality gets really bad.' They really missed the bigger picture, which is, when the air quality gets worse, you want to reduce activity and protect public health."

Air District communications officer Jaime Holt bristled at that kind of critique. "We're a health agency. That is our goal. But if you have a 15-second sound bite, that may not be the number-one or number-two or number-three message that gets out there into the public," she said.

Holt pointed to the air district's collaboration with schools to develop curricula about the health effects of air pollution, and the agency's outreach to local asthma coalitions, as well as the Real Time Air Quality Network for schools.

"We don't want to scare people. We want to empower people," she said. "How to be healthier on those days when air quality is poor and how to make sure you're not contributing to poor air quality, so we don't have those days when air quality is bad."

"I certainly don't want to create this fear that kids shouldn't be outside doing exercise," agreed Tyner. "Air quality is a health issue. I think obesity and lack of exercise is actually a bigger health issue for children."

On days when the air quality is healthy, Steve Poponoe does encourage his kids to run around. He lives in a largely Spanish-speaking neighborhood and said he thinks it would be tough for many of his neighbors to get online often enough to see how dramatically the air quality changes throughout the day. But he's working on that.

"I've been thinking of building myself a little air quality indictor in my front yard, based on the readings from the website," said Poponoe. My neighbors, at least, can see what the air quality's like."

The nearest playground, by the way, sits under a freeway overpass.