休斯顿是如何治理空气污染的？

RENEE MONTAGNE, HOST: NPR aired a series last year called Poisoned Places about regions living with industrial pollution. We're reviving that series this week, but the news isn't all grim. This morning we take a look at a city that has cleaned up its air: Houston.

DAVID GREENE, HOST: That metropolitan area is home to hundreds of petrochemical plants. They produce about a quarter of the nation's gasoline and about a third of the plastics that are in our cars, cupboards and just about everywhere else. In the last decade, Houston's air has improved dramatically.

MONTAGNE: How that happened is a tale of new technology and a Texas law that prompted companies to disclose what they were emitting. NPR's Richard Harris has the story.

RICHARD HARRIS, BYLINE: If you want to get to the heart of Houston's petrochemical industry, take a trip out onto the Houston ship channel. It's a muddy brown body of water that's surrounded by refineries, tank farms and petrochemical companies as it winds inland from Galveston Bay toward downtown. Dana Blume is standing on the deck of a fireboat plying the channel. She's been monitoring the air and water for the Port of Houston Authority for the past 14 years. And she says you sure notice those smoggy summer days.

DANA BLUME: It's hot. It's harder to breathe. I mean I'm fortunate. I don't have respiratory issues. But I do worry about my child and other children who play on days that it's a high ozone day.

HARRIS: In recent years, those high ozone days have come less often, and they're less intense when they do strike.

BLUME: I can look out of my office window now and almost every single day see downtown. And that wasn't the case 10 years ago.

HARRIS: To get the surprising back story about how Houston's air got cleaner, it's worth a visit to Harvey Jeffries at the University of North Carolina's School of Public Health in Chapel Hill. As this retired professor tells the story, air pollution regulators were on the verge of making a multibillion dollar mistake. This involves a little chemistry. Ozone is created in the air when one kind of pollution - nitrogen oxide - reacts in sunlight with chemicals called volatile organic compounds. Regulators were focusing their efforts overwhelmingly on nitrogen oxides, cranking down on them so hard, compliance would cost $4 billion a year. Jeffries says big mistake.

HARVEY JEFFRIES: If you spent the $4 billion, if you did all the cleanup, they were controlling the wrong thing and they wouldn't do anything to actually prevent the true cause of the highest ozone.

HARRIS: Jeffries says, sure, you need to control nitrogen oxides, but the most bang for the buck would come from cutting back on volatile organic compounds like ethylene, which is used to make polyethylene plastic. Chemicals like these are produced in abundance along the ship channel.

JEFFRIES: You're talking about billions of pounds of fluids and liquids a day being produced in Houston. And if you only lose .001 percent of that, it's a massive amount of material, and that was being ignored, totally, completely.

HARRIS: Jeffries pointed to a massive scientific study the state of Texas had funded in the year 2000. Results from that showed that volatile chemicals were a big culprit, and happily for industry cheaper to fix. And it wasn't just the day-to-day emissions but big unexpected releases. For instance, sometimes plants released potent chemicals like ethylene in order to prevent a catastrophe.

JEFFRIES: Ethylene is more explosive than hydrogen, and they're making billions of pounds of ethylene. And so it's not something that you want to sort of fool around with. And if there's likely to be a big back-pressure or something like this, you want a safety valve to go off.

HARRIS: And when a valve goes off, tens of thousands of pounds of these chemicals can vent into the air all at once. If the sun is beating down and the wind is blowing in the right direction, a narrow plume of smog can form. Because smog forms over the course of a few hours, often these plumes appear in the suburbs, miles from the ship channel. Typically now, a bad air day in Houston is caused by one of these narrow plumes, not a citywide miasma, as you find in Los Angeles or Dallas. Scientists link those plumes of smog to these chemical burps thanks to a Texas law that required industry to report unexpected events in a public database.

JEFFRIES: And as soon as all of this became visible, voila, it got cleaned up.

HARRIS: Just a few years after Houston had won the title of the worst air in the country, residents finally tasted success.

JEFFRIES: Beginning in 2005, '6, '7, the peak ozone concentration dropped in a straight line, until in 2009 Houston achieved - for the first time in 35 years - the ambient ozone standard that was in effect at that time.

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HARRIS: It's not only that scientists had finally identified he problem; they also had a new technology to help them address it. That's a camera that can see what the human eye cannot. It looks at infrared light. And when a chemical like ethylene is in the air, it appears in the infrared camera like a dark cloud. Jason Harris from the Texas Commission on Environmental Quality was on the side of the road just north of the Houston Ship Channel one winter morning, looking out at tank farms for signs of leaks.

JASON HARRIS: We look at any and all sources we can see from roadways or other public areas. You know, we're looking for those unrecognized or unauthorized emission sources.

HARRIS: And in a typical day, do you see a leak or do you not see a leak?

HARRIS: I'd say more often than not we don't find anything, which is good news.

HARRIS: But in the early days of this technology, it was quite a different story.

HARRIS: We did some flyovers of the ship channel. We attached a similar camera to a helicopter and flew over the industrial areas and saw some pretty eye-opening things.

HARRIS: Barges carting chemicals up and down the channel turned out to be leaking this stuff into the air. And some types of storage tanks turned out to leak as well. Steve Smith from the chemical giant LiondellBassell says his company didn't want to lose its products into the air, so they bought nine of the infrared cameras, at about $100,000 apiece, to find their own leaks.

STEVE SMITH: And we are able to fix things sooner and we are able to fix the right things as opposed to thinking that it might be one problem when in fact the camera shows us something different. And therefore we can do the right thing sooner and obviously have lower emissions and a cleaner environment.

HARRIS: And, of course, save the company money by reducing its pollution taxes and avoiding potential fines. Larry Soward was one of the commissioners on the Texas environmental board during those critical years when Houston's air improved. He says getting industry to this point wasn't quite as painless as you hear tell these days.

LARRY SOWARD: Well, early on they came kicking and screaming because it meant either major investments for technology or it meant major operational changes.

HARRIS: But change they did, and gradually many companies came to realize that tightening up their leaks and reducing their accidental releases gave them a competitive advantage.

SOWARD: At least you're leading industry, you're, you know, some of your ExxonMobils, your LiondellBassells, those type of industries really began to see that it was in their economic benefit to not only comply but to get ahead of the curve.

HARRIS: The question now for these industries - in fact for all of Houston - is what next? Despite all the improvement, the air quality still falls short of increasingly stringent federal health standards. Richard Harris, NPR News.

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MONTAGNE: Tomorrow, we'll hear how getting that next big improvement could be tough. Poisoned Places is a collaboration with the Center for Public Integrity.