Particulate Matter (PM2.5 and PM10) Explained

What is Particulate Matter?

Particulate matter (PM), also known as particle pollution, is a complex mixture of extremely small particles and liquid droplets suspended in the air. These particles vary widely in size, composition, and origin. Unlike gaseous pollutants, particulate matter is a physical substance that can be inhaled deep into the respiratory system.

The EPA regulates two categories of particulate matter based on size, as particle size directly determines how deeply particles can penetrate the body and the resulting health effects.

PM2.5 vs PM10: Understanding the Difference

The numbers in PM2.5 and PM10 refer to the particle diameter in micrometers (also called microns). To understand how small these particles are, consider that a human hair is approximately 50-70 micrometers in diameter.

PM10 (Coarse Particles)

• Size: 10 micrometers or smaller in diameter (but larger than 2.5 micrometers)
• Visibility: Generally visible as dust or haze
• Penetration: Can reach the upper respiratory tract (nose, throat, and large airways)
• Common sources: Dust from roads and construction, pollen, mold spores, windblown dust, grinding operations

PM2.5 (Fine Particles)

• Size: 2.5 micrometers or smaller in diameter (about 30 times smaller than a human hair)
• Visibility: Invisible to the naked eye individually, but creates haze when concentrated
• Penetration: Can reach deep into the lungs and enter the bloodstream
• Common sources: Combustion (vehicles, power plants, wildfires), industrial processes, secondary formation from chemical reactions

PM2.5 is generally considered more dangerous than PM10 because its smaller size allows it to bypass the body's natural defenses and penetrate deeper into the respiratory system. These fine particles can even cross into the bloodstream and affect organs throughout the body.

Sources of Particulate Matter

Particle pollution comes from both natural and human-made sources:

Primary Sources (Direct Emissions)

• Vehicle exhaust: Cars, trucks, buses, and diesel engines emit fine particles directly
• Industrial operations: Factories, refineries, and manufacturing facilities
• Power generation: Coal-fired power plants and other fuel combustion
• Construction and demolition: Dust from building activities
• Wildfires and prescribed burns: Major seasonal source of PM2.5
• Residential heating: Wood stoves, fireplaces, and oil furnaces
• Agriculture: Tilling, harvesting, and animal operations

Secondary Formation

Some particles form in the atmosphere through chemical reactions between other pollutants:

• Sulfur dioxide from power plants can transform into sulfate particles
• Nitrogen oxides from vehicles can become nitrate particles
• Volatile organic compounds can react to form organic particles

Health Effects of Particulate Matter

According to EPA research, particle pollution is one of the most harmful forms of air pollution. Health effects depend on particle size, concentration, duration of exposure, and individual sensitivity.

Short-Term Exposure Effects

• Irritation of eyes, nose, and throat
• Coughing, sneezing, and runny nose
• Shortness of breath and difficulty breathing
• Aggravated asthma with increased attacks
• Decreased lung function
• Irregular heartbeat in susceptible individuals
• Heart attacks in people with existing heart disease

Long-Term Exposure Effects

• Reduced lung function and lung development in children
• Development of chronic bronchitis
• Increased risk of lung cancer
• Cardiovascular disease and stroke
• Premature death from heart or lung disease
• Potential neurological effects including cognitive decline

AQI Readings for Particulate Matter

The Air Quality Index (AQI) translates PM2.5 and PM10 concentrations into a standardized scale from 0 to 500:

Protection Strategies

When particulate matter levels are elevated, take these precautions:

Monitoring and Planning

• Check the AQI daily, especially during wildfire season or high pollution periods
• Sign up for air quality alerts from AirNow.gov
• Plan outdoor activities when PM levels are lowest (often early morning)

Reducing Outdoor Exposure

• Limit time outdoors when AQI exceeds 100
• Avoid strenuous outdoor exercise during high PM days
• Avoid areas with heavy traffic or industrial activity
• Wear N95 or KN95 masks when you must be outside during poor air quality

Protecting Indoor Air

• Keep windows and doors closed during high pollution periods
• Use HEPA air purifiers in main living areas and bedrooms
• Run HVAC systems on recirculate mode with quality filters (MERV 13 or higher)
• Avoid indoor pollution sources like smoking, candles, and frying foods
• Create a "clean room" during extended poor air quality events