v2.1
JAN 16 2025 4:52PM UTC−08:00
AQI
The Air Quality Index refers to an aggregate value of data points that measures:
- Ground-level ozone
- Particle pollution (including PM2.5 and PM10)
- Carbon monoxide
- Sulfur dioxide
- Nitrogen dioxide
- It does not include volatile organic compounds (VOCs)
- Large particulate is not included in AQI
Do you need to know the individual values for the data points?
No. The way the overall value is calculated means that if any one data point is out of the normal bounds, the overall value will reflect that.
Why might I want to know the individual values?
Different pollutants require different precautions. For example, PM2.5 suggests using masks, while high ozone means avoiding outdoor exercise. Individual values also help identify pollution sources (like nearby fires vs urban smog) and are especially relevant if you're sensitive to specific pollutants.
What is “PM”?
Particulate Matter. It’s a broad term and can refer to hundreds of different chemical sources. Via the EPA website, they are broken down into categories like:
- PM10: inhalable particles, with diameters that are generally 10 microns (micrometers) and smaller; and
- PM2.5: fine inhalable particles, with diameters that are generally 2.5 microns and smaller.
- How small is 2.5 microns? Think about a single hair from your head. The average human hair is about 70 microns in diameter – making it 30 times larger than the largest PM2.5 particle.
- In the right light you can see a PM10 particle. You cannot see PM2.5 unless they are highly concentrated, like when smog collects over a large area.
Is AQI a good indicator of air quality?
Yes! In general it is. But since it does NOT account for VOCs, it doesn’t tell the whole story. If you are in or around a burn zone, VOCs can reach hazardous levels; this is why evacuation zones and perimeters are set up.
What is “VOC”?
Volatile Organic Compound. Like particulate matter, VOCs are present in thousands of products (paint, varnish, wax, cleaning products, degreasers, cosmetics, gasoline, fuels, solvents, pesticides, aerosol sprays, etc.). They are invisible, often bind to other particles, can be soluble, and pose a health hazard to anyone who inhales them. This sounds scary, but exposure is generally avoidable with proper precautions.
Do I need to be worried about VOCs?
Are you digging around in ash? Are you cleaning off belongings that have been burned in a fire? Are you actively fighting a fire? Are your clothes covered in ash? Is there wind-blown ash present? Then yes. If you are in an area that was burned, you should consult authorities about the level of VOCs still present; they take time to dissipate. VOCs are why you work with paint in well ventilated areas. Read more about them.
What about benzene or formaldehyde?
These VOCs can indirectly contribute to the formation of ground-level ozone, so their secondary effects still influence AQI indirectly.
Must/should I wear a mask in my neighborhood when the AQI is good?
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.
Must/should I wear a mask in my neighborhood when the AQI is moderate?
Do you suffer from breathing conditions? Then yes. And of course, it won’t hurt even if you’re healthy. Otherwise, see above.
What kind of environmental warnings are issued around air quality?
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.
How far is far enough from a burn zone?
We cannot specify a distance that is safe; it's incredibly hard to say, 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.
I’m still worried. What can I do?
If you still have concerns about your safety, limit your time outside until VOC levels have demonstrably returned to safe levels. A high quality consumer-level VOC monitor like the Atmotube Pro can be used to track local outdoor VOCs. Check out the Research & FAQs section below to really get into it.
Leaf Blowers & Gardens
Do not use leaf blowers. Period. There is a temporary ban on them in LA County. Lawn and garden maintenance after an urban wildfire poses unique challenges. Please be careful. There is an expectation that soil and ground water will be affected, but the extent is as yet unknown.
Home Filtration
If you have central heating or central heat and air, you likely have an air filter. These should be changed every three months — or sooner, in the case of an events like the Palisades and Eaton fires.
Generally, a MERV11 filter is good enough for your home, but a MERV13+ filter is recommended during a wildfire. Be aware that at MERV13 filter may damage your HVAC system due to increased air resistance, so consult the manual for your HVAC when installing one.
HVACs and ACs (even your window units) are air recyclers: they draw air from inside your apartment, and recycle it. Some have the ability to draw in fresh air — make sure this feature is not active.
Additional measures:
- Do not leave your windows open.
- Make sure your carbon monoxide monitors are functional.
- Don’t use your fireplace.
- Use high quality air purifiers (preferably with a charcoal filter along with HEPA) to help with indoor air.
Masks
The mask practices we learned during COVID aren't sufficient for wildfire smoke. While a casually worn N95 or KN95 might have provided adequate protection against virus particles, wildfire smoke requires a properly fitted N95 mask with a complete seal at minimum, with a VOC filtering P100 being preferable. This means performing a fit test and ensuring there are no gaps around the edges of the mask. Without this proper seal, ash and PM2.5 particles from wildfires can easily leak around the sides.
Masks are either “N” (not oil resistant), “R” (resistant to oil), or “P” (oil proof).
The number refers to the mask’s efficiency at 0.3 microns.
- N95: not oil resistant, 95% effective at 0.3 microns.
- R99: resistant to oil, 99% effective at 0.3 microns.
- P100: oil proof, 99.7% effective at 0.3 microns.
Why oil proof?
Because some particulates bind to oil and the oil, when airborne, can find its way through an N-designated mask. This makes a big difference when dealing with VOCs, and it’s why N-designated masks don’t work that well at protecting against VOCs.
Do I need eye protection?
In burn zones or active fires, or if there is a lot of ash in the air, yes you do. These should be tight-fitting safety goggles.
Mask Types
N95
These are protection against common particulates down to and including PM2.5. They come in all kinds of shapes and sizes, but for very basic protection against wildfire-related air quality issues, you want a dual-strap fitted N95 mask. These will not filter out VOCs, and they are not rated for asbestos or lead. Some may be rated for silica dust (OSHA has a guide for this). While effective and useful as baseline protection, they can provide a false sense of security.
P100
These are the “gold standard” as designated by NIOSH (National Institute for Occupational Safety and Health). They provide the most suitable protection for anyone in or near a burn zone, but you must have the right filter.
The filters to look for are:
- 3M 60926
- Very good VOC protection
- Protects against: asbestos and silica
- Protects against: certain organic vapors, chlorine, chlorine dioxide, formaldehyde, hydrogen chloride, hydrogen fluoride, hydrogen sulfide, methylamine, ammonia, sulfur dioxide
- Suitable for burn zones
- Expensive
- 3M 60923
- Good VOC protection
- Protects against: asbestos and silica
- Protects against: certain organic vapors, chlorine, hydrogen chloride, hydrogen fluoride, hydrogen sulfide, sulfur dioxide
- Marginal for burn zones, so limit your exposure
- Suitable for emergencies so you can make a quick, safe exit
- Less expensive
Per the manufacturer data sheet, while the 3M 60921 filter has the same form factor as the 60926 and 60923, it does not protect against: acid gases, ammonia, formaldehyde, other chemicals commonly released in building fires.
P3? P1?
Other countries have other standards. If you hear someone mention “P3” masks, they’re probably from Europe, Australia or New Zealand. There was a post floating around saying, “P100 is insufficient, you need P3” — this was likely written by someone who wasn’t familiar with American standards. P3 is the equivalent of P100 under U.S. standards.
Resources
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.