Pollution (environmental pollution) refers to the introduction of substances or forms of energy into the environment that can cause harmful effects to ecosystems, wildlife, or human health. Pollution can be caused by human activities as well as natural processes. Even when there is no immediate visible harm, environmental contamination can have harmful long-term effects. For example, nitrogen oxides released into the atmosphere can contribute to the formation of ground-level ozone and other components of photochemical smog when they react with other pollutants in the presence of sunlight.

Pollution occurs on both regional and global scales. In the past, attention was focused primarily on regional pollution. For example, burning coal produces particulate matter and sulfur dioxide, which can harm human health and contribute to acid rain. However, scientific research has shown that pollution can also have effects across national borders and around the world. Burning coal also produces carbon dioxide, a greenhouse gas that contributes to climate change when emitted in large quantities.

Whether something constitutes pollution depends on its effects on the environment and human health. For example, excess nitrogen and phosphorus from agriculture, wastewater, and other human activities can enter rivers, lakes, and coastal waters. Excess nutrients can promote abnormal algae growth, resulting in harmful algal blooms and reduced oxygen levels that can damage aquatic ecosystems.

Pollution is generally classified into air pollution, water pollution, soil or land pollution, and pollution from chemicals and waste. Other forms, including marine pollution, noise pollution, light pollution, and thermal pollution, can also affect human health and ecosystems.

Major sources of pollution include industrial facilities, the improper disposal of hazardous and radioactive waste, excessive or inappropriate use of pesticides and fertilizers, industrial and domestic wastewater, motor-vehicle emissions, fuel combustion, and various forms of commercial and transportation-related activity. Accidents involving industrial facilities, nuclear power plants, oil pipelines, and other infrastructure can also cause severe localized pollution incidents.

作者：Michael Chiu，MWS，CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026