San Marcos, TX Air Quality Today
Sunday, September 20, 2026 · Data: WeatherAPI • EPA
Air quality in San Marcos is Good today, September 20. No pollutant is high enough today to change anyone's plans. Open the windows and keep your plans outside.
Level 1 of 6 on the EPA scale
What's in San Marcos's Air Right Now
PM2.5 (fine particles): 8 µg/m³. Anything under 12 µg/m³ counts as clean, so fine particles aren't a concern right now. These particles come from exhaust and smoke and are small enough to reach deep into your lungs.
PM10 (coarse dust): 11 µg/m³. Readings under 54 µg/m³ rate Good. Dust and pollen fragments ride in this size range and irritate your nose and throat.
Ozone: 102 µg/m³. Ozone forms when sunlight cooks car exhaust, so hot afternoons read worst, usually between 2 PM and 7 PM. Mornings stay cleanest.
Nitrogen dioxide: 1.3 µg/m³. NO2 comes almost entirely from traffic and feeds afternoon ozone. Readings run highest near busy roads during the morning and evening commutes.
Is It Safe to Go Outside in San Marcos Today?
Yes. The air in San Marcos is clean today. Open the windows and keep your run outside. Kids can stay out as long as they want.
Days like this are worth using. If a long walk or a hard workout is on your list this week, today is the day for it.
Air Quality This Week in San Marcos
Air quality in San Marcos holds at Good every day through Thursday.
Each row is that day's average. Single hours run higher or lower, and the reading at the top of this page is a current measurement rather than an average.
Air Quality and Pollen Are Two Different Numbers
The air quality index tracks pollution: ozone, dust, smoke, and exhaust. Pollen isn't part of the score, so a Good air day in San Marcos can still be a rough allergy day.
Right now the biggest pollen load in San Marcos is grass pollen, rated Low. If your eyes itch while the air reads clean, pollen is the likely culprit.
Check today's San Marcos, TX pollen count →Frequently Asked Questions
What is the AQI in San Marcos right now?
Today's air in San Marcos is rated Good, level 1 of 6 on the EPA scale. That's the cleanest category, with no limits on outdoor plans. The reading updates daily, so check back before you head out.
Is it safe to exercise outside in San Marcos today?
Yes. Clean air puts no limit on outdoor exercise today. Morning is still the best window in summer, since ozone builds through hot afternoons.
What will the air quality be tomorrow in San Marcos?
Tomorrow in San Marcos the forecast averages Good, level 1 of 6 on the EPA scale, with fine particles (PM2.5) near 6 µg/m³. That figure is a daily average, so a few hours can run higher or lower than the number here.
Does San Marcos have an air quality alert today?
Official alerts come from AirNow.gov and your state air agency, and MyPollenPal doesn't track them directly. Today's EPA category in San Marcos is Good. Days rated Unhealthy for Sensitive Groups or worse usually line up with an official alert.
Sources
- U.S. Environmental Protection Agency / AirNow. "AQI Basics." airnow.gov
- U.S. Environmental Protection Agency. "Particulate Matter (PM) Basics." epa.gov
- U.S. Environmental Protection Agency. "Ground-level Ozone Basics." epa.gov
Air Quality Is Half the Picture
Pollen fills in the rest. See today's tree, grass, and weed levels for San Marcos, or sign up for a morning email on days when pollen runs High or Very High.