Frequently Asked Questions
Find answers to common questions about air quality, the AQI, pollutants, and protecting your health.
Air Quality Index (AQI)
What is the Air Quality Index?
The Air Quality Index (AQI) is a standardized indicator used by government agencies to communicate how polluted the air is. It runs from 0 to 500, with higher values indicating worse air quality and greater health concerns.
How often is the AQI updated?
The AQI is updated hourly for current conditions. Forecasts are typically issued twice daily - once in the morning and once in the afternoon. During significant pollution events, updates may be more frequent.
What AQI level is safe?
An AQI of 0-50 (Green) is considered good air quality with little or no risk. An AQI of 51-100 (Yellow) is moderate and acceptable, though sensitive individuals may experience minor effects. Levels above 100 are considered unhealthy for sensitive groups.
Can air quality vary within a city?
Yes, air quality can vary significantly within a city due to local sources of pollution, traffic patterns, topography, and weather conditions. Areas near busy roads or industrial sites typically have worse air quality.
Why does the AQI change throughout the day?
The AQI changes due to varying emissions (like rush hour traffic), meteorological conditions (temperature, wind, sunlight), and chemical reactions in the atmosphere. Ozone, for example, typically peaks in the afternoon on sunny days.
Pollutants
What is PM2.5?
PM2.5 refers to fine particulate matter with a diameter of 2.5 micrometers or smaller. These tiny particles can penetrate deep into your lungs and even enter your bloodstream, making them the most dangerous form of air pollution.
What is the difference between PM2.5 and PM10?
PM2.5 particles are 2.5 micrometers or smaller, while PM10 particles are 10 micrometers or smaller. PM2.5 is more dangerous because it can penetrate deeper into your lungs and has greater health impacts.
What causes ozone pollution?
Ground-level ozone forms when nitrogen oxides (from cars and power plants) and volatile organic compounds react in the presence of sunlight. This is why ozone pollution is worse on hot, sunny days and why it's called "smog season" in summer.
Is wildfire smoke worse than regular pollution?
Wildfire smoke contains very high levels of PM2.5 and other harmful substances. During major wildfire events, smoke can cause AQI levels to spike into the "Hazardous" range (300+), making it far worse than typical urban pollution.
What pollutant is usually responsible for poor air quality?
PM2.5 and ground-level ozone are the most common pollutants causing poor air quality. PM2.5 is often the culprit in winter and during wildfire season, while ozone is typically responsible for summer air quality issues.
Health & Protection
Who is most affected by air pollution?
Sensitive groups include children, older adults, pregnant women, and people with lung diseases (asthma, COPD) or heart disease. People who work or exercise outdoors also face higher exposure.
Can air pollution affect healthy people?
Yes. While sensitive groups are most at risk, healthy people can experience health effects from air pollution, especially at higher levels or with prolonged exposure. Anyone can develop symptoms like throat irritation or reduced lung function.
Do face masks protect against air pollution?
N95 and KN95 masks are highly effective at filtering PM2.5 and other particles if worn properly. Surgical masks and cloth masks provide minimal to no protection against air pollution. The mask must fit snugly with no gaps.
Do air purifiers really work?
Yes, air purifiers with HEPA filters are very effective at removing PM2.5 and other particles from indoor air. They must be properly sized for the room and run continuously. They don't remove gases like ozone or carbon monoxide.
Should I exercise outdoors when air quality is moderate?
If you're in a sensitive group, consider reducing prolonged outdoor exertion when the AQI is 51-100 (Moderate). Healthy individuals can usually exercise normally. It's best to exercise early morning when air quality is typically better.
What should I do if I have asthma and air quality is poor?
Stay indoors with windows closed, use air conditioning, run air purifiers, and keep your rescue inhaler handy. Follow your asthma action plan, and if symptoms worsen despite precautions, seek medical attention.
Indoor Air Quality
Is indoor air quality better than outdoor?
Not necessarily. Indoor air can be 2-5 times more polluted than outdoor air due to sources like cooking, cleaning products, mold, and poor ventilation. However, during poor outdoor air quality, staying indoors with proper measures is safer.
Should I open windows to improve air quality?
Only when outdoor air quality is good (AQI 0-50). When outdoor air quality is moderate to unhealthy, keep windows closed and use air purifiers and air conditioning instead.
What HVAC filter should I use?
Use filters rated MERV-13 or higher if your system can handle it. These filters remove PM2.5 and other fine particles. Standard fiberglass filters (MERV 1-4) provide minimal air quality benefits.
Do houseplants improve indoor air quality?
While plants can remove small amounts of certain pollutants, research shows they don't significantly improve indoor air quality in real-world conditions. A single air purifier is far more effective than dozens of plants.
Monitoring & Forecasts
Where does air quality data come from?
Air quality data comes from networks of monitoring stations operated by local, state, and federal agencies. These stations measure pollutant concentrations continuously using specialized equipment.
How accurate are air quality forecasts?
Air quality forecasts are generally reliable for predicting whether air quality will be good, moderate, or unhealthy. However, exact AQI values may vary. Unexpected events like wildfires can make forecasting more difficult.
Can I measure air quality myself?
Yes, consumer air quality monitors can measure PM2.5 and other pollutants. However, their accuracy varies. Look for monitors that have been validated against EPA reference monitors.
Why doesn't my area have air quality data?
Not all areas have monitoring stations due to cost and logistics. Rural areas and small towns often lack coverage. Nearby stations can provide a general idea, though local conditions may differ.
Regional & Seasonal
Why is air quality worse in summer?
Summer brings higher temperatures and more sunlight, which create ideal conditions for ozone formation. Additionally, increased air conditioning and vehicle traffic in summer can contribute to pollution.
What is a temperature inversion?
A temperature inversion occurs when warm air traps cooler air near the ground, preventing pollutants from dispersing. This commonly happens in winter and can cause pollution to accumulate to unhealthy levels.
Why does California have bad air quality?
California faces multiple challenges: geography (valleys that trap pollution), large population, vehicle emissions, wildfires, and agricultural activities. However, air quality has improved significantly over past decades due to regulations.
Does rain improve air quality?
Yes, rain can "wash" particles out of the air, temporarily improving air quality. However, rain doesn't significantly affect gases like ozone. The improvement is usually short-lived once rain stops.
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