750 Introduction to Industrial Hygiene

The Criteria Pollutants

The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six common air pollutants.

Criteria Air Pollutants include:

1. Particulate Matter (PM): A complex mixture of tiny solid particles and liquid droplets suspended in the air. When inhaled, these particles can reach deep into the lungs and even enter the bloodstream.

• Examples: Dust, dirt, soot, smoke, ash, pollen.
• Sources: Wildfires, construction activities, unpaved roads, power plants, and vehicle exhaust.
• Health effects: Asthma attacks, lung disease, heart problems, premature death in sensitive groups.
• Environmental impacts: Reduces visibility (haze), damages crops, soils, and water systems.

2. Ground-Level Ozone: A harmful gas formed when sunlight reacts with pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). Unlike the protective ozone layer high in the atmosphere, ground-level ozone is dangerous to breathe.

• Examples: Main component of urban smog.
• Sources: Vehicle emissions, power plants, industrial facilities, and chemical solvents exposed to sunlight.
• Health effects: Coughing, throat irritation, worsened asthma, reduced lung function, breathing difficulties.
• Environmental impacts: Damages crops, forests, and sensitive ecosystems.

3. Carbon Monoxide (CO): A colorless, odorless, tasteless gas created by the incomplete burning of fossil fuels. It prevents oxygen from being carried through the body when inhaled.

• Examples: Vehicle exhaust, faulty heating systems, indoor generators.
• Sources: Cars, trucks, small engines, gas stoves, and furnaces.
• Health effects: Headaches, dizziness, nausea, impaired vision, cardiovascular stress, death in high concentrations.
• Environmental impacts: Contributes to ground-level ozone formation.

4. Sulfur Oxides (SOx): Gases produced when fuels containing sulfur are burned. Sulfur dioxide (SO2) is the most common form and a major contributor to acid rain.

• Examples: Sulfur dioxide from coal-fired power plants.
• Sources: Burning coal and oil, industrial facilities, metal smelters, ships, and locomotives.
• Health effects: Irritates airways, triggers asthma, worsens lung and heart disease.
• Environmental impacts: Causes acid rain, damages crops, soils, lakes, and building materials.

5. Nitrogen Oxides (NOx): Highly reactive gases produced from combustion. They play a major role in the formation of ground-level ozone and smog.

• Examples: Nitric oxide (NO), nitrogen dioxide (NO2).
• Sources: Cars, trucks, power plants, industrial boilers, and agricultural activities.
• Health effects: Irritates lungs, worsens asthma, increases risk of respiratory infections.
• Environmental impacts: Contributes to smog and acid rain, harms ecosystems, reduces visibility.

6. Lead: A toxic metal once widely used in gasoline, paint, and plumbing. Though greatly reduced in the U.S., lead is still released into the air from some industries.

• Examples: Lead-acid batteries, old paint, contaminated soil.
• Sources: Industrial processes, metal smelters, battery recycling, previously from leaded gasoline.
• Health effects: Affects brain and nervous system, slows growth and development, especially harmful to children.
• Environmental impacts: Contaminates soil and water, harms wildlife and plants.

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