All Americans should be able to breathe clean air. But pollution from power plants and vehicles puts the health of our nation’s children and families at risk. Ground-level ozone, the main component of smog, is one of the most harmful and one of the most pervasive air pollutants. According to the American Lung Association, nearly half of all Americans – 48 percent – still live in areas with unhealthy levels of smog pollution. Studies show that on days with high concentrations of smog pollution in the air, children and adults suffer more asthma attacks, increased respiratory difficulty, and reduced lung function. Exposure to smog pollution can exacerbate respiratory illness and even cause premature death. Sensitive populations including children, the elderly, and people with respiratory illness are particularly at risk of the adverse health effects of air pollution.