Understanding Outdoor Air Pollution
A practical guide to what is in the air, why it matters, and how to use air quality information to protect your health.
Clean air is essential for good health. Most of the time we do not think about the air around us, but every breath can carry tiny particles and gases from traffic, smoke, dust, industry, agriculture, and natural sources. Air quality can change from hour to hour, and understanding those changes helps people make everyday decisions.
What is outdoor air pollution?
Outdoor air pollution is a mixture of small particles and gases in the air we breathe. Some pollutants are released directly from sources, while others form in the atmosphere when emissions react with sunlight and other chemicals. Pollution may be visible as smoke, haze, or dust, but it can also be invisible and odorless.
Transportation
Cars, trucks, buses, and equipment can release exhaust and particles.
Wildfire and wood smoke
Smoke contains fine particles and gases that can travel long distances.
Industry and energy
Facilities and power generation can release gases and particle-forming emissions.
Agriculture
Dust, burning, equipment, and ammonia emissions can affect local air quality.
Dust and wind
Wind can lift soil, road dust, construction dust, and other particles into the air.
Atmospheric chemistry
Sunlight and weather can help form pollutants such as ozone and secondary particles.
What is PM2.5?
Particulate matter, often called PM, is made up of tiny solid particles and liquid droplets floating in the air. PM2.5 means fine particulate matter that is 2.5 micrometers or smaller in diameter. These particles are so small that they can travel deep into the lungs. Some particles may enter the bloodstream and contribute to effects beyond the lungs.
Why does air pollution matter?
Air pollution can affect how people feel right away and can also contribute to long-term health risks. Short-term exposure may irritate the eyes, nose, throat, and lungs. It can cause coughing, wheezing, shortness of breath, chest tightness, or make it harder to be active outdoors.
Lung health
Fine particles can irritate the airways and worsen asthma, bronchitis, and other lung diseases.
Heart health
Particle pollution is linked with cardiovascular stress and can increase risk for people with heart disease.
Children
Children breathe more air relative to body size, spend time outdoors, and have developing lungs.
Older adults
Older adults and people with chronic illness may be more sensitive to poor air quality.
Pregnancy
Pregnant people may be more vulnerable during episodes of high pollution or smoke.
Outdoor workers
People who work or exercise outdoors can receive higher exposure when pollution levels are elevated.
Understanding the Air Quality Index (AQI)
The Air Quality Index, or AQI, is a color-coded scale used to describe how clean or polluted the air is and what that means for health. Green and yellow days are generally lower concern. Orange and higher indicate increasing health concern, especially for sensitive groups such as children, older adults, people with asthma, and people with heart or lung disease.
- Good (0-50): Air quality is satisfactory for most people.
- Moderate (51-100): Acceptable for most people; unusually sensitive people may notice symptoms.
- Unhealthy for Sensitive Groups (101-150): Sensitive groups should consider reducing prolonged or strenuous outdoor activity.
- Unhealthy (151-200): Everyone should reduce prolonged or strenuous outdoor activity.
- Very Unhealthy (201-300): Health alert; everyone should take steps to reduce exposure.
- Hazardous (301+): Emergency conditions; follow public health guidance.
What can you do when air quality is poor?
Check conditions
Look at the AQI before long outdoor activity, especially during smoke, dust, or stagnant weather.
Adjust activity
Move strenuous exercise indoors, shorten outdoor activity, or take more breaks when AQI is elevated.
Reduce indoor smoke
Avoid burning candles, wood, or incense and avoid smoking or vaping indoors during poor air quality events.
Close up when needed
During wildfire smoke, close windows and doors and use recirculate mode in vehicles.
Filter indoor air
Use a portable HEPA air cleaner or a properly built box-fan filter when appropriate.
Follow health advice
People with asthma or heart/lung disease should follow their action plan and contact a health care provider if symptoms worsen.
How is air quality measured?
Air quality is measured in several ways. No single tool tells the whole story. Regulatory monitors provide highly accurate information used for official decisions, while community sensors can show more neighborhood-level variation. Weather information helps explain how pollution moves, builds up, or clears out.
Regulatory monitors
High-quality instruments operated under strict requirements. These data are used for official air quality decisions and long-term trends.
Community sensors
Lower-cost devices that can provide useful local information. They help communities see patterns, but may be affected by calibration, humidity, or local conditions.
Weather data
Wind, temperature, humidity, and inversions help explain when pollution spreads out or stays near the ground.
Forecasts and advisories
Forecasts combine measurements, weather, and models to help people plan ahead.
The big picture
Air quality is not just an environmental issue. It is a public health issue that affects families, schools, workplaces, and communities. Learning what the colors mean, checking conditions, and taking simple steps during high-pollution events can reduce exposure while helping people continue to enjoy outdoor activities when conditions are favorable.