California Air Resources Board

What are particle pollutants?

Particle pollutants, also called particulate matter, or PM, are a complex mixture of small solid particles and liquid droplets found in the air. Particle pollutants differ greatly in chemical composition, shape and size. Particles that are 10 micrometers1  in diameter or smaller, called PM10, are a concern because they can pass through the throat and nose and enter the lungs. Particles that are 2.5 micrometers in diameter or smaller are called PM2.5, or fine particles. Fine particles can penetrate deeper into the lungs than PM10. 

Where do particle pollutants come from?

Particle pollutants are produced naturally from wild fires, dust storms, volcanic eruptions and sea spray. Naturally generated particles also include components from biological sources, many of which are known allergens, such as pollens, mold spores, dust mites and cockroaches. The burning of gas and oil in motor vehicle engines, industrial processes and power generators emit large amounts of particles. Activities such as smoking, cooking and burning wood, candles and incense can emit many particles indoors. Particles also can form from complex reactions of gaseous pollutants emitted from motor vehicles and industrial plants.

Why should I be concerned about particle pollutants?

Inhalation of particle pollutants, especially PM2.5, increases the risk for a number of adverse health effects. Long-term exposure to elevated levels of PM2.5 is associated with premature death in older adults with heart or lung diseases, and with reduced lung growth in children. Short-term exposures to elevated levels of PM2.5 also have been linked to premature death, primarily in people who already have heart or lung disease, as well as hospitalization for cardiovascular causes, including stroke, heart attacks and congestive heart failure, and chronic obstructive disease and asthma. PM2.5 exposure also has been associated with emergency room visits for asthma and increased asthma symptoms, while PM10 exposure has been associated with premature death and hospitalization for respiratory causes in people who have chronic lung disease. Children, the elderly and people with heart or lung diseases are more likely to be affected than healthy adults.

What can I do to reduce my exposure to particle pollutants?

CARB has active programs to reduce particle emissions from sources such as cars, buses, trucks and industrial plants. There are many actions you can take to reduce your and your family’s exposure to particle pollutants in different environments. These are listed below.

Reduce Exposure to Particle Pollutants in Vehicles

The combustion of gasoline and diesel fuel in motor vehicles contributes the majority of particle pollutants in the air in California, especially in urban environments. Due to the close proximity to the emission sources (vehicles), the highest exposure to particles outdoors usually occurs when driving on the road. You can take the following actions to reduce your exposure to particles in vehicles:

• Buy an electric, hybrid (gasoline-electric) or other low-emitting vehicle when you buy your next vehicle
• Avoid using uncertified electronic air cleaners in vehicles because some produce ozone, which may harm your health 
• Most vehicles have a pleated air filter in the outside-air intake for the passenger compartment. Follow the manufacturer’s instructions to change the cabin filter regularly. Install a HEPA filter if available
• Close windows and use the air recirculation setting (close vents) in heavy traffic, but air out the vehicle periodically to avoid drowsiness from build-up of exhaled carbon dioxide
• Avoid long warm-ups (especially in an enclosed space) and unnecessary idling, especially near schools and hospitals
• Keep your vehicle properly tuned and maintained

Reduce Particle Pollution in Indoor Air  

• Use exhaust fans that vent to the outdoors when cooking. If an exhaust fan is not present or it does not vent outdoors, open windows to increase ventilation. Indoor Air Pollution from Cooking 
• Use a high-efficiency portable air cleaner to remove particles. Be aware that in-duct, whole-house electronic air cleaners may produce ozone but are not currently regulated by CARB for ozone emissions. Select Safe Air Cleaners
• Do not allow smoking in your home
• Use an electric or gas heater instead of a wood stove or fireplace. If you do burn wood, use “seasoned” (dry) wood, and make sure that your fireplace or woodstove drafts properly. Information about Wood Burning
• Have gas heaters and stoves checked annually by a professional before the heating season to assure that they are functioning properly and vented to the outdoors
• Never use hibachis, charcoal grills, unvented space heaters or power generators indoors
• Limit burning of candles and incense indoors, and use them only with good outdoor air ventilation
• Avoid use of air fresheners, cleaning products and fragrances that have a pine or citrus scent because they can react with ozone to form particles and formaldehyde. Information about Cleaning Products 
• Assure adequate ventilation during activities that generate moisture indoors, such as showering, cooking and dishwashing. Moisture encourages the growth of molds and dust mites, which can trigger asthma and allergies in people who are sensitive to these allergens

Reduce the Entry of Outdoor Particles into your Home

• Use door mats and remove shoes at the doorway
• Close windows and doors when the outdoor particle level is high. Check the current and forecasted air quality levels for your city at AirNow
• Keep your house clean to avoid re-suspension of particles from carpets and floors such as soil, pollens, cockroach allergens and animal dander. Use a high-efficiency vacuum cleaner or a central (whole-house) vacuum cleaner, and damp mop hard floors often
• Use a medium- or high-efficiency filter in your HVAC system, if your system can accept such a filter. If your home does not have a central system, use high-efficiency portable air cleaners that don’t emit ozone. Follow the manufacturer’s instructions to change filters. Information about Filters and Air Cleaning Devices

Reduce Exposure to Particle Pollutants Outdoors

• Wear a N95 particle mask in smoky or dusty conditions, such as when using a leaf blower or lawn mower
• Avoid activity outdoors when outdoor pollution levels are high. Check the current and forecasted air quality levels for your city at AirNow
• When walking, jogging, biking and doing other outdoor activities, avoid areas close to sources of harmful particle pollution such as busy roads or freeways
• Use electric instead of gas-powered lawn and garden equipment

More Information

Contact CARB's Public Information Office at (916) 322-2990, or CARB’s Indoor Air Quality Program staff at (916) 445-0753.

• 1One micrometer is one millionth of a meter