Ground-Level Ozone
Introduction
Ground-level ozone, also known as tropospheric ozone, is a harmful air pollutant and a significant component of smog. It is not emitted directly into the air but is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs). This reaction occurs when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight.
Formation and Chemical Reactions
Ground-level ozone formation involves a series of complex chemical reactions. The primary precursors, NOx and VOCs, react in the presence of sunlight to produce ozone. This process is facilitated by the presence of hydroxyl radicals (OH), which are formed from the reaction of sunlight with water vapor and other compounds in the air.
The formation of ground-level ozone can be summarized by the following reactions:
1. NO2 + sunlight → NO + O 2. O + O2 → O3 3. NO + O3 → NO2 + O2
In the first step, nitrogen dioxide (NO2) absorbs sunlight and splits into nitric oxide (NO) and a single oxygen atom (O). This oxygen atom then quickly reacts with an oxygen molecule (O2) to form ozone (O3). However, the newly formed ozone can react with nitric oxide (NO) to form nitrogen dioxide (NO2) and oxygen (O2), thereby reducing the ozone concentration.
Health Effects
Exposure to ground-level ozone can have several harmful effects on health. It can cause respiratory problems, trigger asthma, reduce lung function, and cause lung diseases. According to the World Health Organization (WHO), exposure to ozone can also lead to premature death due to respiratory conditions.
In the respiratory system, ozone reacts with biological molecules, leading to oxidative stress and inflammation. This can cause symptoms such as coughing, throat irritation, and chest pain. Long-term exposure to ozone can lead to chronic obstructive pulmonary disease (COPD), a serious lung condition that includes diseases such as emphysema and chronic bronchitis.
Environmental Impact
Ground-level ozone is not only harmful to human health but also has detrimental effects on the environment. It can cause damage to vegetation, including crops and forests, and can negatively impact sensitive ecosystems.
Ozone exposure can lead to reduced photosynthesis in plants, which can affect crop yield and forest growth. It can also cause visible injury to the leaves of sensitive plant species. According to the United Nations Environment Programme (UNEP), ground-level ozone is one of the most significant air pollutants causing damage to crops worldwide.