We strongly recommend reading the full Los Angeles Wildfire Primer.

AQI (Air Quality Index)

• Measures multiple pollutants but doesn't include VOCs (Volatile Organic Compounds)
• Individual pollutant levels matter because they require different precautions
• PM2.5 (fine particles) and PM10 (larger particles) are key concerns
• Very large particulate is not included in AQI

Particulate Matter (PM)

• PM10: Inhalable particles 10 microns or smaller
• PM2.5: Fine particles 2.5 microns or smaller
• Visibility: PM10 can be visible in right light; PM2.5 only visible when highly concentrated (like smog)
• Size reference: Human hair is 70 microns - 30x larger than the largest PM2.5 particle

Volatile Organic Compounds (VOCs)

• Found in many products: paint, varnish, cleaning products, gasoline, cosmetics, etc.
• Invisible and can bind to other particles
• Can be soluble and pose health hazards when inhaled
• Not included in AQI measurements
• Main concern in burn zones or when handling fire-damaged items
• Take time to dissipate after fires
• Generally avoidable with proper precautions in normal conditions

Home Filtration

• Change HVAC filters every 3 months (sooner after fires)
• Use MERV13+ filters during wildfires if your system can handle it
• Keep windows closed, disable fresh air intake
• Use air purifiers with HEPA and charcoal filters

Masks

• Need proper fit testing and complete seal
• N95: Limited protection, won't filter VOCs
• P100 (with 60923 filter): Average protection, filters some VOCs and other chemicals
• P100 (with 60926 filter): Better protection, filters more VOCs and other chemicals
• Use fitted safety goggles if ash is present

Mask Choice

• Regular conditions, dependent on AQI: Properly fitted N95
• Near burn zones/heavy smoke, and when under advisories (i.e. wind-blown ash warnings): P100 with 3M 60923 or 60926 filters
• Do not become overconfident in your safety when wearing an N95 mask

When To Wear A Mask

Is your neighborhood a recent burn zone or close to one? Is there a specific public safety warning? If not, the AQI is good, and the VOC levels are low, then wearing a mask is probably unnecessary. You can still wear a mask; it won’t hurt, and it’s your own choice. Keep tabs on weather conditions since ash and particulate can travel hundreds of miles. Remember that ash may be present on the ground in sufficient quantities to pose a risk even with a good AQI, especially if it’s disturbed, and that N95 masks do not protect you against VOCs.

We cannot specify a distance that is safe from a burn zone; it's incredibly hard to calculate, and we can't in good conscience give a specific number. The VOC FAQ has information about why it’s so hard to make generalized assessments on air quality after urban wildfires. Things change — fast.

Public Warnings

LA County Department of Public Health and the South Coast Air Quality Management District will both provide specific warnings. For example, from January 15-16, 2025, there was a wind-blown ash advisory, during which wearing a mask was recommended even at considerable distances from burn zones. Use this primer to educate yourself, but always keep up-to-date on the latest guidance for where you live.

Use this information at your own risk. Please consult with local agencies regarding laws and regulations. This information is provided without warranty or guarantee. Your safety comes first. Be careful, be empathetic, and please don’t be an asshole.