Night air quality monitor for child respiratory issues (at high RH)

[Guilherme]

Hello all,

Yesterday I received my AirGradient One, and yesterday night I put it to test in our bedroom first to see how things look like. Below I share initial impressions and collected data from the night as extracted from AirGradient dashboard.

Please note that I haven’t yet had the chance to fine tune the CO2 and PM2.5 measures, so these may be affected by the lack of altitude compensation and / or relative humidity, but I think the overall trend can still be useful here.

Firstly, I was a bit concerned about the lights on the monitor (as I like to sleep on dark rooms), but by simply putting it underneath my bedside table did the trick for me to sleep well.

Before going to bed (at 9:30PM), I intentionally closed both my bedroom’s window and door, as I wanted to simulate an environment in which we slept quite often in the past (also with my daughter when she was younger, when she presented many times her nocturnal cough episodes) - back then I was unaware of CO2 issues.

So in the middle of the night I woke up having trouble sleeping and decided to open the window a little bit. At some point later on in the night, I also heard rain and strong wind. Unfortunately, I did not write down the timestamps for either case… I only know that I woke up just before 6AM and closed the window again (as my wife was still sleeping).

Below is the CO2 graph:

So looking at this, I would believe that I opened the window between 1AM and 2AM, when the CO2 curve stopped to increase. It still decreased slowly likely because of the window shutter - it has just tiny holes, so it doesn’t let much air come through. And I would guess that at around 3:30 the wind picked up and made the CO2 decrease quite quickly.

Anyway, maybe the timestamps and hypothesis are not right and it’s difficult to know now, but I was impressed to see how quickly the CO2 increased (and likely it was 16% higher due to altitude), and how it can potentially have affected so often our sleep quality in the past.

Below is now the PM2.5 graph:

I found also quite interesting to observe the opposite pattern here. In the closed and controlled environment, the PM2.5 readings decreased over time until reaching some plateau in the middle of the night. And likely when the CO2 mostly decreased (air coming in), we also observe the PM2.5 increasing. I believe the outdoor air quality was poorer than the indoor one, leading to such behavior. And this may be tricky for us to balance (although I believe in this particular case the impact of CO2 was worse than the moderate PM2.5).

Below now is the TVOC graph:

This for me was the most intriguing behavior… I have not yet read about TVOC other than it’s a relative metric. But I was not expecting it to positively correlate with the CO2 in that way, and I would like to hear your thoughts on this But one thing I started to consider is whether there is some source of VOCs in my bedroom that would lead to increased TVOC numbers while it’s closed… We have painted the apartment one year ago, not sure if it could (still) be related.

Finally, as a reference, below the RH readings throughout the night (I forgot to extract temperature, but it was always around 21.5ºC):

All in all, I’m very happy to have the AirGradient One at home and will keep exploring, learning and trying new things with it! And soon enough will also move it to my daughter’s bedroom. It’s definitely a great tool to better understand the environment we live in.

[Guilherme]

As a follow up here, to add on the first point I mentioned:

Firstly, I was a bit concerned about the lights on the monitor (as I like to sleep on dark rooms), but by simply putting it underneath my bedside table did the trick for me to sleep well.

The AirGradient dashboard actually had nice features to control the light intensity of the LEDs and the display, and turn them off if desired. Quite handy.

And regarding the TVOC I’m still puzzled… this night I observed the same behavior. Then I tried to turn on the air purifier in the room in the morning, but TVOC stayed quite high regardless. Only solution was to indeed open the windows, then it decreased rapidly.

Another experiment I tried was during the day to just close the bedroom window and door again, but this time without anyone in. But the TVOC didn’t increase then. I’m not sure whether it could be potentially impacted by the CO2 concentration itself, or even by some other physiological source… I tried to look it up but couldn’t find an explanation yet, other than that it seems to be indeed tricky to understand it.

[Ethan]

Hi @Guilherme,

Thanks for the update!

@Guilherme

The AirGradient dashboard actually had nice features to control the light intensity of the LEDs and the display, and turn them off if desired. Quite handy.

I’m glad you found this! Yes, they can be dimmed or even disabled if you want.

@Guilherme

So looking at this, I would believe that I opened the window between 1AM and 2AM, when the CO2 curve stopped to increase. It still decreased slowly likely because of the window shutter - it has just tiny holes, so it doesn’t let much air come through. And I would guess that at around 3:30 the wind picked up and made the CO2 decrease quite quickly.

Interesting findings! I am surprised, however, that the CO2 concentration really didn’t decrease much at all until around 3:30 am. However, it makes sense if there are only tiny holes in the shutter.

@Guilherme

Anyway, maybe the timestamps and hypothesis are not right and it’s difficult to know now, but I was impressed to see how quickly the CO2 increased (and likely it was 16% higher due to altitude), and how it can potentially have affected so often our sleep quality in the past.

I know how hard it is to balance outdoor pollution and conditions (like temperature), but this is the reason I almost always sleep with at least one window open (even if just slightly) now. I’ve found that decreasing the CO2 concentration from < 2000 ppm to less than 1000 has vastly improved my sleep quality. However, this isn’t always possible if you’re running AC or heating due to outdoor conditions. My wife has also noticed a massive difference in sleep quality (and cognitive performance) so now she will also insist we always have a window at least slightly open.

@Guilherme

I found also quite interesting to observe the opposite pattern here. In the closed and controlled environment, the PM2.5 readings decreased over time until reaching some plateau in the middle of the night. And likely when the CO2 mostly decreased (air coming in), we also observe the PM2.5 increasing. I believe the outdoor air quality was poorer than the indoor one, leading to such behavior. And this may be tricky for us to balance (although I believe in this particular case the impact of CO2 was worse than the moderate PM2.5).

I would love to hear more about this once you receive the outdoor air quality monitor, as I wonder how bad (or good) outdoor air quality is where you live. Based on how this graph is inverse to the CO2 graph, I believe your conclusion that the outdoor PM2.5 concentration is worse is spot on.

I think this is where having an outdoor monitor will really help you. It makes it much clearer to know when opening a window is a benefit or detriment.

@Guilherme

This for me was the most intriguing behavior… I have not yet read about TVOC other than it’s a relative metric. But I was not expecting it to positively correlate with the CO2 in that way, and I would like to hear your thoughts on this But one thing I started to consider is whether there is some source of VOCs in my bedroom that would lead to increased TVOC numbers while it’s closed… We have painted the apartment one year ago, not sure if it could (still) be related.

This is particularly interesting. You are right in that VOCs can influence CO2 measurements from NDIR sensors, however, CO2 should not greatly impact metal-oxide semiconductor readings (which the SGP40 is). Also, the NDIR sensor should not be impacted much at all unless the VOC concentration is very high. In fact, from what I’ve read, the S8 should have little to no sensitivity to VOCs, and the SGP40 should not be significantly influenced by CO2. As such, I would say that you do actually have a source of VOCs in the room.

It sounds like you’re already very aware of the relative nature of VOC sensors, but this post explains the Sensirion index in more detail:

Air Quality Monitors for VOCs

When it comes to indoor air quality monitors, there are generally three pollutants that people care about: Particulate matter (PM0.3-PM10) VOCs (volatile organic compounds) CO2 (carbon dioxide) For some, CO and radon sensors are also important, but I’ve found that most readers ask me to recommend a monitor with the above three sensors. While I’ve discussed CO2 and PM sensors at length, I thought it would be interesting to discuss VOC sensors in air quality monitors because they have a few cav…

Luckily, on AirGradient monitors you can change the baseline calibration period to 720 hours (look under ‘place’ settings), meaning it is far more useful than a sensor that adjusts every 24 hours.

One thing to consider here is that humans exhale trace amounts of VOCs. While a very small amount, they can accumulate over time, and this could explain the increase if no other VOC sources are present. While the increase would be relatively small (I would think), it may be that your usual VOC levels are so low that a 500 index reading is possible. To test this, I would try putting the monitor in the room (without people) and completely close the room so there is no ventilation. Does the VOC index still increase? If so, there is another source that you might want to look into - if there is nothing obvious, I would guess it is off-gassing.

@Guilherme

And regarding the TVOC I’m still puzzled… this night I observed the same behavior. Then I tried to turn on the air purifier in the room in the morning, but TVOC stayed quite high regardless. Only solution was to indeed open the windows, then it decreased rapidly.

Does your purifier have a carbon filter? If not, it won’t decrease VOCs, only particles.

@Guilherme

Another experiment I tried was during the day to just close the bedroom window and door again, but this time without anyone in. But the TVOC didn’t increase then. I’m not sure whether it could be potentially impacted by the CO2 concentration itself, or even by some other physiological source… I tried to look it up but couldn’t find an explanation yet, other than that it seems to be indeed tricky to understand it.

I only just read this now, but I think what I mentioned above may be the case. Humans can exhale some VOCs. For example, we exhale acetone and isoprene (among others) and this could build up enough to trigger the SGP40 if there is no ventilation. Since you’ve already tried the empty room experiment, I think this is likely the reason for your increasing VOCs at night.

These are all really interesting findings. Thanks so much for sharing!

[Guilherme]

Hello,

So it’s been a week since my last post, and have a few updates to share here.

After a couple of nights, we decided to move the monitor from our bedroom to our daughter’s room.

The first interesting finding there is that TVOC readings are always increasing whenever windows are closed, even if no one is in the apartment.

The figure above illustrates that: at 4PM we left the apartment, and the readings are still increasing. I know this would be the expected behavior in case of a VOC source in the apartment / room, but it’s just to indicate a different observation than in my previous post (in our room, it only seemed to happen when someone was in). The difference here might be due to furniture, but I still need some time to investigate this hypothesis, e.g. to move things out of the room.

Nevertheless, I followed your suggestion Ethan, and in the last few days I’m always leaving one window slightly open during the night, even if it’s cold outside. Likely I end up paying a bit more for the AC I n heat mode, but this way I see the CO2 and VOC readings are well controlled during the whole night.

The graph above illustrates the CO2 level during last night, which looks better than the one in my previous post I would say.

Additionally, we have that air purifier running in her room, so potentially being able to reduce PM concentrations in case the outdoor levels are high.

As previously mentioned, for VOC the air purifier doesn’t seem to change anything. Checking its user manual, they don’t mention specifically activated carbon, but rather a “deodorizing” filter (https://www.daikin.com.sg/resources/ck/files/manual/MC40UVM6.pdf). When I purchased it I thought it would be the same, but I’m not sure now, or maybe it’s only effective to filter out some specific VOCs.

To sum up, I think the air quality monitor has been quite educational for me in this first week. When I have some time, I’ll try to run more experiments for VOCs, and will post here if I find anything new.

[Guilherme]

Well, just to contradict myself, last night PM readings went through the roof.

As the air purifier is completely manual and doesn’t have an app interface, I cannot know how it actually behaved during the night. For example, if its auto mode was unable to recognize the high PM concentration for a while, and didn’t work in it properly.

Also, I wonder if that was all caused by outdoor pollution alone, or even indoor as well. If the latter could show such pattern for example when the wind picks up, resulting on the particulates that were stable on the floor to start fluctuating in the air, thus impacting the monitor PM readings.

Ideas for these theories are: (a) switch air purifier from auto mode to constantly active; (b) assess outdoor air quality with a dedicated monitor (luckily will get one soon too, it was just shipped from AirGradient ); (c) vacuum our apartment more often. We usually vacuum once a week, but not sure if the quite dry+cold weather from the previous days rather requires us to do it at least twice a week then.

[Ethan]

Hi @Guilherme, thanks a lot for yet another update! It’s fascinating to hear about your findings. Sorry for the late reply; it’s been a super busy week for me.

@Guilherme

The figure above illustrates that: at 4PM we left the apartment, and the readings are still increasing. I know this would be the expected behavior in case of a VOC source in the apartment / room, but it’s just to indicate a different observation than in my previous post (in our room, it only seemed to happen when someone was in). The difference here might be due to furniture, but I still need some time to investigate this hypothesis, e.g. to move things out of the room.

This, in particular, is quite interesting. Outside of any apparent sources, it would seem to indicate off-gassing furniture, as you’ve mentioned. Out of curiosity, what period do you have your adjusting VOC baseline set to? I would be curious to see how significant the off-gassing is by placing the monitor outdoors and then comparing (with the baseline set to something like 720 hours) the indoor values. If the off-gassing goes to 200, it’s not as severe as 500, for example. Alternatively, you could use the ind30 index on the analytics page for a more ‘absolute’ reading.

@Guilherme

Nevertheless, I followed your suggestion Ethan, and in the last few days I’m always leaving one window slightly open during the night, even if it’s cold outside. Likely I end up paying a bit more for the AC I n heat mode, but this way I see the CO2 and VOC readings are well controlled during the whole night.

These are far better levels! It’s hard to tell if it’s worth it with the likely increased electricity/gas prices, but have you noticed a significant (or just noticeable) improvement in your sleep or general feeling in the morning?

@Guilherme

Also, I wonder if that was all caused by outdoor pollution alone, or even indoor as well. If the latter could show such pattern for example when the wind picks up, resulting on the particulates that were stable on the floor to start fluctuating in the air, thus impacting the monitor PM readings.

I’m wondering this, too. Surely, it’s outdoor pollution entering through the window you said you were now leaving open slightly? It seems too high for indoors unless you are cooking (which seems unlikely at 1 am!) or have another PM source like a candle.

@Guilherme

Ideas for these theories are: (a) switch air purifier from auto mode to constantly active; (b) assess outdoor air quality with a dedicated monitor (luckily will get one soon too, it was just shipped from AirGradient ); (c) vacuum our apartment more often. We usually vacuum once a week, but not sure if the quite dry+cold weather from the previous days rather requires us to do it at least twice a week then.

A and B sound great! C, I’m not sure about. I would imagine the particles would settle overnight and only be disturbed (and, therefore, become airborne) when there is movement around the house. I’m not sure when you normally sleep, but it seems odd that those particles would suddenly become airborne at around 12-1 am. I am leaning towards these particles being from outdoors (assuming the window was indeed open).

Super excited to hear your findings with an outdoor monitor! You’ve also inspired me to do some around-the-house tests too!

[Guilherme]

Hi Ethan, thanks again for your input here! This time I’m the one rather late on responding…

I’ve been a bit busy with the other forum (AirGradient), as in the past couple of weeks I incorporated the altitude compensation formula for CO2 (Altitude compensation for CO2 - Components - AirGradient Forum) as well as the alternative corrections for the PM 2.5 estimation (PMS5003 : CF=1 or CF=ATM data? - Components - AirGradient Forum), and then have been exploring these results

Out of curiosity, what period do you have your adjusting VOC baseline set to?

You’re right there! Up until my previous message, I still hadn’t changed the default baseline (which I think was 12 hours). But then I did change it to 720 hours and started to see less of a roller coaster in the readings.

Nevertheless, I still find it a bit difficult to interpret the results and have not yet identified potential sources. Although in the meantime I did change my pillow - which was new, but seemed to have some fabric with synthetic odor - and that seems to have improved my sleep too.

Surely, it’s outdoor pollution entering through the window you said you were now leaving open slightly?

I think that is indeed the case. What I’m doing is to leave two windows open, one facing north and the other one facing south. So even there are very small passage to the air, it can create some wind current during the night due to the opposite opening.

And more interestingly what I also discovered is that those high PM readings seem to be caused by a very specific condition we have in Brazil: many wildfires across the whole country (Brazil wildfires worsened by 'mega drought,' extreme heat – DW – 08/30/2024)

Even though there is none close to me, our local media reported several times that our city is being influenced by that too. For the past two weeks, we can see the sun rather orange on the horizon, and it’s been quite dry as well (unusual for our region).

So I did switch the air purifier to be constantly active in the past few weeks. And last night’s trend is quite interesting - we can clearly see when the PM 2.5 start to be a bit more over control exactly in the period when the purifier is on:

On this note, just to conclude on one of my hypothesis:

(c) vacuum our apartment more often

Here I think you were right as well - vacuuming didn’t seem to have an impact on the readings from the monitor. But, again, after discovering the wildfires context, that became a clear candidate to explain it.

So, once I receive the outdoor monitor, will still explore it indoor side-by-side with the other monitor to learn more, but then once it’s out up and running I will share more insights here!

[Ethan]

Hi @Guilherme,

I saw your posts over there; they’ve been very informative (I’ve learnt a lot researching the topics you’re bringing up!). I wish I had a bit more time to reply, but I’ve been keeping up with all of the conversations.

@Guilherme

You’re right there! Up until my previous message, I still hadn’t changed the default baseline (which I think was 12 hours). But then I did change it to 720 hours and started to see less of a roller coaster in the readings.

Aha! I had a feeling this might be the case, and it makes a lot of sense.

@Guilherme

Nevertheless, I still find it a bit difficult to interpret the results and have not yet identified potential sources. Although in the meantime I did change my pillow - which was new, but seemed to have some fabric with synthetic odor - and that seems to have improved my sleep too.

I can relate to this! I’ve been trying to look more into VOCs (and the low-cost sensors we use to monitor them) myself recently, and I’ve come to the conclusion that, at least to me, they aren’t particularly useful. Even the ‘absolute’ values are very hard to interpret due to how many chemicals can influence them. I’m also in a similar situation where I’ve been having odd VOC spikes in some areas of the house that I simply can’t explain. I am considering trying out some more specialised VOC sensors to see if they make a difference, but I think the issues inherent with VOC sensors may make this a challenge.

@Guilherme

And more interestingly what I also discovered is that those high PM readings seem to be caused by a very specific condition we have in Brazil: many wildfires across the whole country (Brazil wildfires worsened by ‘mega drought,’ extreme heat – DW – 08/30/2024)

Even though there is none close to me, our local media reported several times that our city is being influenced by that too. For the past two weeks, we can see the sun rather orange on the horizon, and it’s been quite dry as well (unusual for our region).

So I did switch the air purifier to be constantly active in the past few weeks. And last night’s trend is quite interesting - we can clearly see when the PM 2.5 start to be a bit more over control exactly in the period when the purifier is on:

This is very interesting!

One question - is your air purifier suited to the room it’s in (regarding CADR)? There is a significant drop when it’s on, but over a period of almost 12 hours, I would expect to see much more of a drop. Alternatively, are there potential gaps around windows/doors or extraction fans that could act as an entry point for outdoor pollution when the purifiers are running?

I’m very much looking forward to hearing more when you have the outdoor monitor setup. In the meantime, I would recommend looking into the purifier performance and/or potential particulate matter entry points around your house, as it seems like some may still be getting in.

[Guilherme]

Hi all,

One interesting note I’d like to add on tVOC readings.

I’m currently travelling and checking the AG dashboard while no one is in the apartment. Now that I 've got an outdoor monitor as well, I can see how the indoor and outdoor readings are associated.

Below is the tVOC from the last 48 hours. Blue bars are from indoor monitor, and grey trace is from the outdoor one.

I would say there is some association between those readings. And most likely the indoor one is picking up the same measures / fluctuations as the outdoor one.

Now, I have no idea what could be causing the outdoor to behave like that. But at least I start to better think on a potential cause why in the past I saw all those fluctuations in the indoor monitor.

Note: both monitors are set to the 720 days baseline. And I left a few windows slightly open to circulate air in our home while we’re away.

[Guilherme]

Oh and I had forgot to address this:

One question - is your air purifier suited to the room it’s in (regarding CADR)? There is a significant drop when it’s on, but over a period of almost 12 hours

I’m under the impression there is something wrong with my PM sensor in the indoor monitor. After inspecting different date points and conditions, I think it is capable of picking up high PM levels (i.e. to follow outdoor monitor trends during wildfire smoke), but it doesn’t go below a certain minimum baseline.

The last 8 hours illustrate this behavior. The indoor average is around 10, whereas the outdoor has been constantly been below that.

As mentioned on my previous post, this is in an empty apartment with windows slightly open.

And I’ve also reported and briefly discussed the issue here: Mounting instructions - indoor and outdoor? - #5 by Guilherme - AirGradient Forum

I’m not sure if there is something that got into the sensor after a while (for a few weeks it was standing directly on the floor) that could explain that.

But so far I have not had the time (or courage) to try to open the PM sensor and examine that. I’m also afraid of breaking it.

And such behavior doesn’t harm much either for now.

[Ethan]

Hi @Guilherme,

Thanks for the update! The correlation between indoor and outdoor VOC readings is very odd, and I’ve never seen such a direct example before. I would expect some similarities in certain situations, but these are so closely related that it seems (like you said) that the same VOCs are impacting both monitors.

How close are these monitors? I know they’re in entirely different locations indoors and out, but are they located near the same window, perhaps?

I’ve also been intending to do some of my own testing regarding the AirGradient ONE and use it on a desk as I’ve had a couple of other customers reach out about similar situations. In those two cases, both customers noticed far lower PM readings when the device was sitting on a solid, flat object (like a table) and much higher readings when the device was either wall-mounted or sitting on a vented/grated surface. It’s led to me being very curious, and I want to test this further. I will let you know if I discover anything!

If you open them, PM sensors can be quite easy to damage, so my first suggestion would be to try swapping the sensor with your outdoor monitor for a while and see if that exhibits the same behaviour. It’s still a bit arduous and you won’t get outdoor readings for a while, but it should allow you to assess if the sensor currently in the AG ONE is performing as expected or has something inside.

[Guilherme]

Hey Ethan, thanks for your response!

The outdoor monitor is on the balcony ceiling. The living room facing the balcony had the door closed while we were away. Also, the indoor unit is in another room (bedroom). Due to these, I would rule out the possibility of the outdoor monitor receiving some wind flow from indoor with VOCs.

That’s why I rather thought it could be the other way around, i.e. the bedroom window slightly open could have led the outdoor VOCs enter the room and therefore show such association between monitors readings. And that could only be observed while the house was completely empty and with everything off.

After observing that, I kept inspecting the outdoor monitor traces in particular and found and even more intriguing pattern (at least for me), as I described here: Outdoor tVOC values - AirGradient Forum

I thought on writing in the AG forum to see if any other people with AG outdoor monitors would also observe such pattern. Let’s see if someone responds.

[Ethan]

The post on the AirGradient forum is fascinating! I just checked my monitor (which has only been set up for a couple of days, as I just moved into a different apartment), and I have trends similar to yours.

While it’s too early to draw conclusions, I see a significant VOC increase at around 3 pm daily. Interestingly, I am currently located on the 15th floor of an apartment building, so I think VOCs (caused by people) would not have a big impact at this height as opposed to at street-level. I also have a 720-hour average period set for my ind40 readings, but even my ind30 readings show a similar trend.

Like you, I was curious if the temperature or RH could explain the intensity of these peaks (I had a theory the second and third peaks might be on days of higher temperature/relative humidity), but this doesn’t appear to be the case, as you can see below. The temperature was higher during the first (smaller) VOC peak than during the second day! The RH readings are similar.

I will keep these monitors collecting data over the coming days, but I think your theory about photochemical reactions could definitely be impacting the monitors. However, I don’t know how we could measure this without having a device to capture sunlight, as it would be based on that instead of temperature. While not ideal, perhaps a cheap solar panel could be purchased and placed next to the monitor? The output could then be measured, which would be an indication of sunlight levels throughout the day. I’m not sure if this would work, but that’s the first idea that comes to mind.

Interestingly, on the days I have data for so far, I also see another, smaller spike at just after 6 a.m. The apartment I am currently in is east-facing, and the current sunrise time here is 5:30 a.m. I’m looking forward to collecting some more data and seeing the results!

[Ethan]

After continuing to collect data, I now see data that is much harder to interpret. While my VOC levels throughout the day still tend to be higher, I am also seeing some spikes throughout the night and the trend that was there earlier (a significant increase during the afternoon), so longer seems to be the case. I checked both the ind30 and ind40 indexes and both now appear quite different.

I have one potential explanation, but I won’t be able to test it until next week, unfortunately. Has your monitor kept following the same trend?

[Guilherme]

Hey Ethan, thanks for investigating your own outdoor VOC measures, it’s quite nice to have someone’s else perspective on this as well.

I’ve just checked again my outdoor VOC readings for the last 7 days, and it shows a similar pattern:

However it’s also nice to see in this case that two days had rather small increase during the day.

In one of the days, temperature indeed didn’t increase that much, but for the other it actually did:

And Ive just tried to also check the sunlight in a public database and I don’t see a clear pattern for that yet. But I’m on my phone now and it was a very quick visual inspection of the table numbers.

It remains a puzzle for me…

[Ethan]

Hi @Guilherme,

It’s interesting how much more obvious the trends are in your data than in mine. I just got back to New Zealand, and I plan to set up my outdoor monitors as soon as the rain stops (it’s been raining constantly since I got back so far!). I have four with me, so I also want to see if the results are consistent across monitors - especially as the temperatures here are less extreme.

I will let you know what I come across!