By Christopher C. Chang, M.D., Ph.D.

A lot of children experience wheezing in response to weather conditions, allergens, air quality and exercise. For those who live in cities and industrial areas, the prevalence of wheezing and asthma increases. Big cities such as Philadelphia have air quality problems – all one has to do is drive down I-95 flanked by smokestacks with different colored gases pouring out of them to see evidence of air pollution. According to the American Academy of Pediatrics, children and infants are among the most susceptible to many air pollutants.

There are several pollutants that are deemed to be sufficiently hazardous to humans to merit their measurement by the Environmental Protection Agency (EPA). They include ozone, sulfur dioxide, nitrogen dioxides, carbon monoxide, particulate matters, and lead.  Particulate matter varies in size. Those that are less than 2.5 micrometers in diameter are known as fine particles. Scientists have linked fine particle pollution with significant health problems, including aggravated asthma, decreased lung function and difficulty breathing. Although air pollution doesn't necessarily cause asthma (this is still controversial), it can be a factor in making symptoms much worse.

Ultrafine particles are in the nanometer range and are typically less than 100mm in diameter. The aerodynamic properties of smaller particles allow them to penetrate deeper into the respiratory tract. As such, they can be easily inhaled deep into the lungs.  Ultrafine particles can be found in diesel exhaust, ocean spray, cigarette smoke, volcanic lava, and cooking steam. Although some of these particles are not harmful, many components of ultrafine particles are dangerous to health. The well know "freeway studies" in Los Angeles have demonstrated poorer respiratory health in people who live closer to freeways.

Parents of children with asthma who live in areas of poor air quality should make sure the child's asthma is well-controlled, and that they take their medicines as prescribed and as needed. They may find it helpful to close windows and use central heating or air conditioning. Installation of a good ventilation and filtration system may also be helpful in the warmer months. People can also check their daily air quality forecast and limit outdoor activities when an unhealthy air quality index is predicted.

Countries have different standards regarding air pollution, and they are constantly changing. In the U.S., states have varying standards as well, with California, home to the famous "L.A. haze," being stricter than most.  The American Lung Association ranks regional air quality based on ground-level ozone and particulate matter. According to its "State of the Air" report, the Philadelphia region ranks 10th nationally in ozone levels and 16th in the presence of year-round particulate matter. Not the worst, but far from the best.

Before the Bejing Olympics in 2008, officials were understandably worried about air pollution affecting the health of athletes and visitors as well as giving the viewing audience a negative impression of the city.  A city-wide campaign to reduce pollution that included limiting the number of cars on the roads was highly successful in making a positive impact on air quality in Bejing. It shows what can be done if strict policies to limit pollution are followed and enforced. Unfortunately, this was a temporary measure, and from a global standpoint, all countries need to develop standards that will allow for sustainable reductions in harmful air pollution.

Christopher C. Chang, M.D., Ph.D., is division chief of the division of pediatric allergy/immunology at Nemours/Alfred I. duPont Hospital for Children, and clinical professor of pediatrics at Jefferson Medical College.