VOA常速英语:Study: Ozone Smog Pollution Expanding

A new study provides the strongest evidence yet that ozone smog, a type of air pollution most often found in big cities, poses a major public health danger. The study found that even at low levels, ozone smog increases the risk of asthma attacks and irritation in the respiratory system; together with air pollution it can also contribute to heart attacks and strokes.

Lorene Alba has suffered from chronic asthma for nearly 20 years. She says living in the city and avoiding asthma attacks is not always easy. "If it is a bad air quality day, I try not to do things in the middle of the day, I try to do them in the early morning or in the evening.  I am really careful about where I walk, away from bus fumes; I try to stay close to the buildings as opposed to closer to the sidewalks," she said.

Alba is not alone.  According to the American Lung Association, more than 20 million people suffer from asthma in the United States - and the number could grow.  "The environment is a huge trigger for me, especially on days of bad air quality. The buses, the smog, the pollution - all of these things can really trigger my asthma," Alba said.

The new study, conducted jointly by the Environmental Protection Agency and the University of North Carolina, found that levels of ozone smog that until now have been considered safe, actually pose a serious public health threat. "The latest study on ozone is telling us that lower levels of ozone can be really dangerous for us to breath," Alba said.

"This study looked at healthy young adults. They looked at levels that we previously thought were pretty safe, and when those healthy young adults were exposed in a clinical setting in a laboratory, that ozone by itself, it caused some real breathing problems for them. It was measurable," said Janice Nolen, with the American Lung Association in Washington.

The ozone damaging the lungs of these young adults is an invisible gas, made of three oxygen atoms.  When it's inhaled, ozone can irritate and inflame the sensitive internal tissues of the respiratory system.  Nolen adds that ozone is usually accompanied by particle pollution such as diesel engine exhaust, which can cause further problems like heart attacks and strokes. 

And while most causes of ozone are found in urban environments, Nolen says ozone smog can be found almost anywhere. "The ozone that is in the atmosphere from the urban centers blows and it goes into other places that may not necessarily be urban, some of the national parks, for example, in tops of mountains in this country have extraordinary high levels of ozone," Nolen said.

Over the past 40 years, a federal law known as the Clean Air Act has enabled many cities and towns to reduce ozone and other forms of urban pollution. But Nolen says the American Lung Association believes much more needs to be done.

"In our last report we had an estimate of over 175 million Americans who live in areas in this country that we gave an F (failing grade) for air pollution," Nolan said.  

The EPA study of ozone smog notes that the people most at risk include children, senior citizens, people with lung diseases such as asthma and those who work or exercise outdoors. Additional studies are underway to measure the long-term health effects of ozone in combination with other forms of air pollution.