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    San Diego skyline under thick orange wildfire haze with a dim sun and silhouetted palms

    San Diego Air Quality & Wildfire Smoke

    Why the air turns orange some autumns, and what to actually do about it.

    Last updated

    Quick answer

    San Diego's coastal air is usually good, kept clean by onshore ocean breezes. The exceptions are predictable: Santa Ana wind events in autumn, which push hot dry air from the interior toward the coast and both raise wildfire risk and carry smoke; inland valleys in summer, where heat and stagnant air build ozone; and smoke transported from fires elsewhere in California. Inland East County and North County valleys routinely record worse air than the coast. Check AirNow.gov or PurpleAir for real-time AQI, and treat anything above 150 as a day to stay indoors, close windows, run recirculated air conditioning and use a HEPA filter. N95 respirators help outdoors; cloth and surgical masks do not filter smoke particulate.

    AQI, in practical terms

    AQICategoryWhat to do
    0–50GoodNormal activity — this is most San Diego days
    51–100ModerateUnusually sensitive people may notice; everyone else is fine
    101–150Unhealthy for sensitive groupsAsthma, heart conditions, kids and seniors should ease up outdoors
    151–200UnhealthyEveryone should limit outdoor exertion; close windows
    201–300Very unhealthyStay indoors, run filtration, N95 if you must go out
    300+HazardousAvoid all outdoor activity

    The three things that wreck San Diego air

    Santa Ana winds

    Hot, dry offshore winds that blow from the interior toward the coast, most commonly from autumn into winter. They reverse the normal onshore flow, drop humidity into single digits, and turn any ignition into a fast-moving fire. Historically the biggest San Diego County wildfires — the 2003 Cedar Fire and 2007 Witch Creek Fire — were Santa Ana driven.

    Local tip: When a red flag warning is issued, that's your cue to charge devices, fuel the car and know your evacuation route — not to plan a hike in the back country.

    Wildfire smoke, local and transported

    Smoke doesn't need a local fire. Plumes from fires in Los Angeles, the Central Valley or even Northern California can settle over the county for days depending on the wind pattern.

    Summer ozone inland

    East County valleys and the inland North County corridor build ground-level ozone on hot, still summer afternoons. This is invisible and routinely worse than the coast, where the sea breeze keeps things clean.

    Where to check

    AirNow.gov

    The EPA's official AQI source, aggregating regulatory monitors. The most authoritative number, but the monitor network is sparse — your neighborhood may differ.

    PurpleAir

    A dense network of low-cost citizen sensors, giving far better neighborhood-level resolution during a smoke event. Readings run high during smoke unless you apply the conversion setting.

    Local tip: During a smoke event, cross-check both: AirNow for the official call, PurpleAir for what's happening on your block.

    San Diego County Air Pollution Control District

    Issues local forecasts, advisories and burn-day information for the county.

    Watch Duty and CAL FIRE

    For the fire itself rather than the air — incident maps, containment and evacuation orders.

    What actually helps on a smoke day

    Close up and recirculate

    Shut windows and doors, and switch your car and home HVAC to recirculate so you're not pulling smoke inside.

    HEPA air purifier, correctly sized

    A purifier rated for the room's square footage makes a genuine, measurable difference. Run it on high during the worst hours.

    A box fan filter works

    A MERV-13 furnace filter taped to a box fan — the Corsi-Rosenthal design — is a cheap and surprisingly effective DIY substitute when purifiers sell out.

    N95 only

    Cloth and surgical masks don't filter fine smoke particulate. A properly fitted N95 or P100 does.

    Skip the workout

    Exercise multiplies how much air you pull into your lungs. Move the run indoors or take the day off.

    Escape to the coast

    During an inland smoke or ozone event, the immediate coastline is frequently many AQI points better. Sometimes the best filtration strategy is driving ten miles west.

    If you live in a fire zone

    • • Much of East County and inland North County sits in a designated high fire hazard severity zone — know yours before you rent or buy.
    • • Sign up for AlertSanDiego emergency notifications and keep a go-bag during Santa Ana season.
    • • Defensible space requirements around structures are enforced and matter for insurance.

    Frequently asked

    Is air quality good in San Diego?

    Coastal San Diego generally has good air, kept clean by onshore ocean breezes. Inland valleys in East County and North County record worse air, especially summer ozone on hot still days and smoke during Santa Ana wind events.

    When is wildfire season in San Diego?

    Risk is highest from late summer through autumn and into early winter, peaking during Santa Ana wind events when hot dry offshore winds drop humidity and drive fast-moving fires. Historically the county's largest fires have come during these events.

    What are Santa Ana winds?

    Hot, dry winds that blow from the interior deserts toward the coast, reversing San Diego's normal onshore flow. They bring high temperatures, single-digit humidity and extreme fire danger, most commonly in autumn and winter.

    Where can I check San Diego air quality right now?

    AirNow.gov for the official EPA AQI, PurpleAir for neighborhood-level sensor readings, and the San Diego County Air Pollution Control District for local forecasts and advisories.

    What AQI is unhealthy?

    Above 100 is unhealthy for sensitive groups; above 150 is unhealthy for everyone and a good threshold for staying indoors, closing windows and running filtration. Above 200, avoid outdoor activity entirely.

    Do masks help with wildfire smoke?

    A properly fitted N95 or P100 respirator filters fine smoke particulate. Cloth and surgical masks do not meaningfully help against smoke.

    Keep reading

    Earthquake Risk

    The other natural hazard people ask about.

    Heat Wave Guide

    What to do when it's 105 inland.

    Weather by Month

    What the climate actually does here.

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    About this guide

    Written and fact-checked by the Sandi Spots Editorial team — San Diego residents publishing under Sleep Coast LLC. Every place we recommend has been visited in person or verified against an official source, and no business can pay for inclusion or a higher ranking. Last updated .

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