The burning of fossil fuels (coal, oil, and natural gas) for energy production, transportation, and industrial processes releases a range of harmful substances into the atmosphere. Common air pollutants include:
- Sulfur dioxide (SO$_{2}$): Primarily released from the combustion of sulfur-containing fossil fuels, particularly coal, in power plants and industrial facilities. Sulfur dioxide is a major contributor to acid rain and respiratory problems.
- Nitrogen oxides (NO$_{x}$): (e.g., NO, NO$_{2}$) Formed during high-temperature combustion processes in vehicle engines and power plants. Nitrogen oxides also contribute to acid rain, smog formation, and respiratory illnesses.
- Carbon monoxide (CO): A colorless, odorless, and highly toxic gas produced by the incomplete combustion of carbon-containing fuels (e.g., in car exhaust or faulty furnaces). It reduces the oxygen-carrying capacity of blood.
- Particulate matter (PM): Tiny solid particles or liquid droplets suspended in the air, arising from various sources including combustion (soot), industrial processes, and construction. Fine particulate matter can penetrate deep into the lungs, causing respiratory and cardiovascular problems.
- Volatile Organic Compounds (VOCs): A diverse group of carbon-containing compounds that readily evaporate at room temperature. Sources include vehicle exhaust, industrial solvents, paints, and adhesives. VOCs contribute to ground-level ozone formation and smog.

These air pollutants contribute to major environmental problems:
- Acid Rain: Formed when sulfur dioxide and nitrogen oxides react with water, oxygen, and other chemicals in the atmosphere to form sulfuric acid and nitric acid. These acids then fall to Earth as rain, snow, or fog, damaging forests, acidifying lakes (harming aquatic life), eroding buildings, and contaminating drinking water.
- Smog: A type of air pollution characterized by a hazy mixture of fog and smoke, often with a brownish tint. Photochemical smog, prevalent in urban areas, is formed when sunlight reacts with nitrogen oxides and volatile organic compounds from vehicle exhaust and industrial emissions, producing ground-level ozone and other harmful secondary pollutants.
- The Greenhouse Effect and Climate Change: Certain atmospheric gases, known as greenhouse gases (primarily carbon dioxide (CO${2}$), methane (CH${4}$), nitrous oxide (N${2}$O), and water vapor), naturally trap some of the Earth's outgoing heat, keeping the planet warm enough to sustain life. This is the natural greenhouse effect. However, human activities, particularly the extensive burning of fossil fuels and deforestation, have significantly increased the concentrations of these gases in the atmosphere. This enhanced greenhouse effect traps more heat, leading to a rise in global average temperatures, a phenomenon known as global warming, which is a key aspect of climate change. The chemical implications include ocean acidification (as CO${2}$ dissolves in seawater, forming carbonic acid), disruption of ecosystems, more extreme weather events, and rising sea levels.