WORK IN PROGRESS

Carbon Dioxide (CO₂)

CO₂ is a natural part of our atmosphere, however it can accumulate indoors and cause health effects, so it’s worth keeping an eye on CO₂ levels.

[X]

Concentration
400 ppm	Approximate ambient level (Outdoors)
600 ppm	Upper limit of normal range
1000 pm	Slightly reduced cognitive function
2500 ppm	Reduced cognitive function
10,000 ppm (1%)	Upper limit before severe health effects
50,000 ppm (5%)	Exhaled breath

The MQ-Z19B CO₂ sensor I chose for my AirNode project has a range of 400ppm - 5000ppm, which covers the range which I consider “healthy”.

It’s interesting to note that in my 1-bedroom Studio apartment the CO₂ concentration easily reached the upper end! (TODO: Find graph of CO₂ data)

Carbon Monoxide (CO)

Carbon monoxide is much more of a danger to health, but isn’t usually present indoors unless you’re burning things (charcoal, gas). It might be interesting to track this, but available sensors are inaccurate and drift significantly over time. You would probably be better covered by a carbon monoxide alarm.

[X]

Concentration
0.1 ppm	Approximate ambient level (outdoors)
9 ppm	Upper limit for living areas
50 ppm	Upper limit for continuous exposure (over 8h period)
200 ppm	Headaches / nausea within 2-3 hours

Oxygen (O₂)

We all know oxygen is essential for survival, but what levels are healthy?

[X]

Concentration
>50%	Toxic
20%	Normal levels
<19%	Adverse effects begin
15-19%	Impaired thinking
<10%	Death

Given that oxygen gas sensors are expensive (~$100), are difficult to calibrate, need annual replacement, and you’re unlikely to run out of oxygen anyway, I don’t think it’s worth measuring O₂.

Ozone (O3)

[X]

TODO

PM 2.5 / PM 10 Concentration

Dust particulates are typically measured by counting dust particles with a laser beam, and are usually grouped into PM 2.5 (<2.5um) & PM 10 (<10um).

PM 2.5 particulates are especially bad for your health, so you should try to keep these down. Typical sources of particulates are smoke, exhaust fumes, cooking, dusting, etc.

[X]

Concentration1
0 - 12.0	Good
12.1 - 35.4	Moderate
35.5 - 55.4	Unhealthy for sensitive groups
55.5 - 150.4	Unhealthy
150.5 - 250.4	Very Unhealthy
250.5 - 500.4	Hazardous
(ug/m3, measured over a 24hr period)

WHO guidelines state that cities with an average annual PM2.5 exposure of >12ugm3 had significant increases in risk of health. WHO also define that the PM2.5 / PM10 ratio should be 0.5 to 0.8 for developed country urban areas.

PM 2.5	PM 10
25 ug/m3	50 ug/m3	Daily average limit2
10 ug/m3	20 ug/m3	Annual average limit2

Temperature & Humidity

Temperature is more personal preference than anything else, and is highly influcenced by humidity, but 21-22C is typically considered to be “room temperature”. [citation needed]

Humidity is generally recommended to be in the range of 30-50% for living, and if it’s too humid things like mold and fungi may start to grow in your home, which can cause many negative health effects

VOCs

It is hard to quantify exactly how VOCs affect your health, as they can include many different types of compounds, including but not limited to: Ethanol, Acetone, Benzene, Natural Gas, “Human Emissions”, Decomposing Fruit, …

So while you can’t use this to determine how healthy the air is, you could probably use it as a signal to activate ventilation. I have personally seen VOCs rise as my rubbish starts to “ripen”, which is a good signal that it’s time to take the rubbish out :)

My Recommended Indoor Levels

Taking the data above, these are the levels I’ve chosen to use to maintain healthy indoor air quality.

CO₂
< 600 ppm	Ideal range
> 2000 ppm	Need ventilation
> 4000 ppm	Dangerous condition

CO
< 2 ppm	Ideal range
> 8 ppm	Need ventilation
> 50 ppm	Dangerous condition

PM 2.5
< 10 ug/m3	Ideal Range
> 30 ug/m3 for 24h	Need ventilation or activate filters
> 200 ug/m3 for 5m	Warning condition - high levels of dust present

References