Notes from the field: Measuring AQI is a troubled affair.
Indoor air quality (IAQ) has been a joke for a long time. Like the weather in New England, everybody complained about it, but nobody did anything about it, until an airborne virus came along and people panicked. And now we are finally doing something about it, but conveniently also, better solutions are now available. In particular of course, I am thinking about the Dexwet Pure Air filter, as well as a couple of other solutions that really help turn the tables on bad indoor air.
The key to it all is to become more aware of indoor air quality, and there seems to be a wide range of choices between $50 and $50K, if you wanted to start a scientific lab. Even between say $50 and $200 the range of choices is overwhelming. The following are just some reflections and recommendations based on field experience. The first distinction that matters is between stationary and hand-held devices.
For Stationary devices, there may be some effort to stabilize the display, so it is not so nervous. I have not been able to document this exactly, but it certainly seems to be the case just from field observation. The Kaiterra Laser Egg series is great choice, because they can be connected through WiFi and you can easily look up the history and even email out a report on the last seven days. They do seem to have some algorithm to stabilize the display, which makes it easier to watch than if it dances around all the time.
The models range from a basic model with AQI, PM 2.5, Temp and Humidity, followed by a model which adds CO2 measurement, and finally a model that includes chemical parameters, Formaldehyde (HCHO) and Total Volatile Organic Compounds (TVOC). The meter that inclues CO2 has been sold out recently, and the others do not include CO2 as a parameter, which is regrettable.
Another favorite for a stationary meter is the BRWISSEN Desktop BR-A18, which does include CO2 and also has the capability of displaying a breakdown of fine dust into PM 0.3, PM 1, PM 2.5 and PM 10. It also has a MicroSD card that comes with it, so you could transfer historical logs to a PC for analysis. The download is a text file (.TXT), which you then have to convert for importing in a spreadsheet. The best route seems to be to convert the text file into a delimited .CSV file first and then import into a spreadsheet.
On the hand held front there are an overwhelming range of choices on the market and most are workable. I have gone crazy over figuring out the differences, but for now, I have come down to some simple observations. There are simply too many choices to cover them all, and for the most part all of them work, with some strange anomalies.
That most important measure, PM2.5
Most of the current batch of meters have the highest level of consistency in the PM2.5 range, which is important in the field of filtration, for fine dust is a significant enemy, as this range in general can be inhaled all the way into the lungs and you will sometimes find toxic particles, such as from brake dust or similar sources, or airborne pathogens and it includes certain popular viruses that fall in this size range.
Many of these meters tend to read low on the PM2.5 range, especially at the low end. I have trouble believing some of the readings. They might be low by about 5-10 points in my experience. To the extent that you are simply trying to ascertain differences, this is not a problem. In a normal house or an apartment it is unlikely that you should meet clean-room conditions, so when I see single digit readings, I tend to want to add 5-10 to the number. Above, I posted a video of a 2nd generation unit, the Temtop M2000C, which may be more accurate in that sense and offers other valuable features besides, such as a download capability of some history, not to mention the ability to set the intervals from 1 min to 5,10, 30 or 60 minutes. This unit is highly recommended. The runner up in this category is the BLATN Smart 128S which also allows you to record history, in 1-minute intervals, but on a MicroSD. It does include TVOC, which the Temtop does not. One other drawback of the 128S is that it’s charge plug is not a standard micro-USB, but a proprietary plug, unlike the desktop unit from the same company which uses standard micro-USB. In the PM2.5 category, it tends to be at the low end by about 10 points compared to the Temtop.
The most difficult reading, TVOC
There are many cheaper options but some can be flaky. Particularly the TVOC can be a difficult value to read accurately and you will see wide variations between meters. I even have two meters from the same manufacturer whose TVoC readings can vary widely, and calibration can be a challenge, depending on your location. Even the differences between meters are not accurate all the time.
Gaining experience with these meters is a work in progress, and we won´t stand still, but the above is a fair summary of the past 8 months of experience. I may update this article from time to time, but for the most part, I will post my favorite meters in the Links, Literature and Tools section of this website.