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High concentrations of ozone near ground level can be harmful to people, animals, crops, and other materials. Ozone can irritate your respiratory system, causing you to start coughing, feel an irritation in your throat and/or experience an uncomfortable sensation in your chest. Ozone can aggravate asthma, and can inflame and damage cells that line your lungs. Ozone may also aggravate chronic lung diseases such as emphysema and bronchitis and reduce the immune system’s ability to fight off bacterial infections in the respiratory system. Lastly, ozone may cause permanent lung damage. These effects can be worse in children and exercising adults.
Unlike stratospheric ozone, which forms naturally in the upper atmosphere and protects us from the sun's harmful ultraviolet rays, ground-level (or tropospheric) ozone is created through the interactions of man-made (and natural) emissions of volatile organic compounds and nitrogen oxides in the presence of heat and sunlight. Cars and gasoline-burning engines are large sources of volatile organic compounds (VOCs). VOCs also come from consumer products such as paints, insecticides, and cleaners as well as industrial solvents and chemical manufacturing. Nitrogen oxides (NOx), the other chemical precursor of ozone, are produced whenever fossil fuels are burned and are primarily produced by motor vehicles and power plants.
The sun's direct ultraviolet rays convert these emissions into ground-level ozone, which is unhealthy to breathe.
Many factors impact ground-level ozone development, including temperature, wind speed and direction, time of day, and driving patterns. Due to its dependence on weather conditions, ozone is typically a summertime pollutant and a chief component of summertime smog.
