High levels of smog occur more often in the summer, especially on sunny, hot and humid days. Ground-level ozone is invisible, but particulate matter may give the air a hazy appearance. Nitrogen dioxide gas gives the air a dirty, brown color. Smog advisories include both environmental information, such as a description of the pollution sources that contribute to smog, as well as health information to advise the public on the possible health risks associated with smog exposure. It is now well-known and documented that smog aggravates a wide range of serious cardiorespiratory health problems.
Smog causes irritation of the eyes and throat, cough, and chest tightness.
The harmful effects of greatest concern are aggravation of respiratory problems, including respiratory infections, asthma, chronic bronchitis, and emphysema. Smog is linked to other adverse health outcomes, including increased emergency hospital visits and hospital admissions, and even premature death. While there is no evidence that smog causes increased prevalence of asthma, or other chronic lung conditions, it clearly contributes to episodes of these conditions. Although everyone is affected by smog, some groups are more sensitive or susceptible. These include individuals with cardiac or respiratory diseases such as asthma, emphysema and chronic bronchitis.