Airgradient outdoor monitor comes with CO2 and PM2.5 sensors.
But why do we need to check CO2 values outside? Isn’t it always ~400ppm?
I have about 2 years history of data from my outside CO2 sensor and all the time it is ~400ppm with no significant changes.
What other sensors can be useful to measure outside instead of CO2 besides PM2.5, temperature & humidity?
Can we use other sensors in AirGradient devices like CO or SO2 etc?
CO2 in an outdoor monitor allows you to accurately compare the relative increase of CO2 indoors vs outdoors at your location. I would think that this is the primary driver for why AirGradient has opted to keep similar sensors in both indoor and outdoor units, to have a direct reference point comparison of all of the parameters being observed.
CO2 levels can also vary outdoors. They will be, as an example, higher on average in a city than in the country. They can also vary between one part of a city, and another.
They will also show an increase year-over-year as tends have shown
https://www.co2.earth/daily-co2
Having this as a reference point has its uses. There’s a surprising lack of crowdsourced datapoints on localized CO2 levels available.
Air gradient is the only map I’ve seen available that actually answers this question, and you can absoluely see small hotspots of CO2 ppm over 500 over all the US
https://www.airgradient.com/map/?zoom=5&lat=15.093&long=105.064&org=ag&meas=rco2
and even more pronounced in Thailand, as an example
So I applaud the inclusion in the outdoor unit!
Why do we need to track CO2 value outdoor at all since even WHO does not count CO2 as air pollutant for outdoor?
There is only 20% difference in CO2min & CO2max during a year: around 400 vs 500ppm. It does not affect humans health like other significant outdoor pollutant like CO, SO2, NO2, O3.
It’s a reference point. Ambient CO2 can be used as a proxy for other problems. CO/O3 would be nice additions, but I wouldn’t want them in leiu of CO2, I’d want them in addition to.
I understand your point but differant strokes, I suppose.
This blog post gives a real world use case for measuring co2 outdoors.
We do actually see higher CO2 levels in rural areas in the night.
See the chart here:
https://www.airgradient.com/blog/performance-of-low-cost-co2-sensors-outdoors/
Thats really interesting! I guess decomposing organic matter is a large contributer.
Thank you for the answer.
Placing a CO2 sensor near a busy road before and after a speed limit
Detecting idling cars or buses at car parks or in front of schools
Identifying local CO2 impacts from decomposition and wildfires
All these pollutants give significant increase in PM2.5 and can be detected using that sensor. CO2 measurements are not that useful here. Do you agree?
Identify local emission sources (e.g. power plants)
Not sure about that. Why doesn’t WHO use these measurements for that, but use CO, SO2, NO2, O3 instead?
We do actually see higher CO2 levels in rural areas in the night.
How does it affect human health?
As far as CO2 and human health, there absolutely is evidence which directly associates high levels of CO2 with human health concerns.
https://www.sciencedirect.com/science/article/pii/S036013232300358X
CO2 concentrations below 5000 ppm had no significant effect on the performance of simple cognitive tasks. However, the complex cognitive task performance showed a significant decrease at CO2 concentrations of 1000–1500 ppm and was also negatively impacted at 1500–3000 ppm. In addition, physiological responses (e.g., heart rate, HRV, and ETCO2) and psychological states (e.g., emotion, fatigue and sleepiness, and perceived air quality) were likely to be adversely affected by CO2 concentrations higher than 3000 ppm.
Now, these numbers are obviously higher than one would expect to see outdoors (thankfully). But as @Achim_AirGradient blog post he linked shows, we do see periods of time in places where CO2 levels outdoors are twice that of what you would normally expect. Example:
Lets not worry too much about the absolute values here and just use some round numbers. If you, as an example, have an outdoor CO2 level in your area of 450 ppm as measured by your AirGradient sensor. And you, as an example, also have an indoor reading of your other AirGradient sensor of 700ppm.This is within safe ranges. Your delta is about ~350ppm.
If the outdoor CO2 reading suddenly doubled to 900 ppm for several hours, the current ventilation systems you have in place in your house would no longer be able to keep up. Asuming the same ~350ppm delta here. You could begin seeing readings in your home closer to ~1200ppm, which would put you in the territory where you could begin to have health impacts.
All these CO2 values are about indoor air. But the questiong is about why do we need that in outdoor monitor since it is not affects human health because you will not find such CO2 values even close to 1000ppm
Modern cars actually do not emit much PM2.5 anymore as they can be filtered much more easily than gases. The CO2 can be a good proxy about other gases as well like NO2, SO2, etc.
Having both PM and CO2 can also allow source attrbution, e.g. to determine if the PM is from fossil fuels burning or from biogenic organic compounds / secondary compounds.
I’m not sure you and I are reading the same thing. While obviously, the study itself is focused on indoor air in a classroom, you didn’t seem to address any of the points I just made in my last post?
Did you ever see CO2 outdoor with that kind of values as you posted above?
You can open Airgradient map with CO2 values and make sure that 500ppm is already marked as high red value and this is the highest values you can see there.
That’s why I am not sure why you operates to
If the outdoor CO2 reading suddenly doubled to 900 ppm
This case can be 1 in a million and because of that it does not make sense to install CO2 sensors in every outdoor user device. You do not install Geiger counter in every outdoor monitor because it’s pretty useless as well.
Even government’s Ministry of Environment monitors and WHO tracks different most significant pollutant, why don’t we install that kind of sensor there as well instead of spending money on pretty useless CO2 outdoor measurements?
Yes this can be used for research, but people do not buy this outdoor monitor because of possible participation in research.
Can be, but why don’t we install those NO2, SO2 etc sensors to get accurate values instead of unknown correlation proxy
You don’t know that, because without tools to observe this we don’t have the information. The lack of commonly available tools to crowdsource this information is THE problem. The AirGradient solves this, because its cheap. Reference grade CO2 outdoor monitoring systems are more than an order of magnitude more expensive, so no one except government entities and large universities were really looking.
Here’s another example
And another
You are making an assumption that CO2 outdoors is always <500PPM. Your assumption is false. Knowing what the outdoor measurements are allow you to better understand what the needs are indoors. If your outdoor CO2 levels are locally high, then the importance of an increase in ventilation in your building becomes greater. More Air Changes Per Hour are needed to prevent even higher levels from accumulating.
And this can be easily tracked by indoor CO2 sensor, because ventilation will drop your CO2 indoor faster if CO2 outdoor is lower. There is no need to track CO2 outside for that. You can do nothing with this information comparing with PM values where you can enable air purifier to make it lower when PM outside is high.
No, because then you do not fully understand the problem. Knowing that you need to compensate for the outside being vastly higher than you would expect will have a strong impact on how you should be solving the problem inside.
But you have already made up your mind, so have a good day!
Do you know any other way regular people make CO2 lower indoor besides opening window (ventilation)?
When your CO2 indoor is high you have only one option to decrease it: to open a window.
If your indoor sensor does not change after that then there is an issue with the CO2 outside, no need to have CO2 outdoor sensor here. I do not understand what problem you see here and what problem this outdoor CO2 sensor can resolve for regular user
Opening a window is sufficent when the ambient CO2 levels are low enough to allow it to be sufficent. Opening a window relies on convection currents to drive this primarily. The amount of air changes per hour is limited.
In a situation like we discussed, an HRV system may be required which evacuates the indoor air faster.
You will never get lower concentrations than are outside, but if outside consentrations are very high, it would not be unimaginable for indoor concentrations to push 2000-3000ppm.
Even in my current situation, if I shut the door to my bedroom at night with my wife, myself, my dog and my cat, levels will get to that range. If I keep the door open, it comes down much lower. But the act of opening the door would not be enough if the ambient CO2 in the rest of my house was not more sane. And the ambient CO2 in my house is only as low as it is because I’m not a crazed efficiency person sealing all of my windows and doors with plastic or blowing insulation in my attic.
Yes, and that’s OK and this is why you need CO2 sensor indoor and not outdoor where it is redundant when there are more important outdoor air parameters to track.
