Indoor Air Quality: 2. The importance of indoor AQ Monitors

  • Indoor AQ sensors: sensors that measure the Quality of the Air inside your home, school, office, etc.

This post follows our first post about external AQ monitors and deals with indoor AQ monitors. What are they and why are they as important (if not more) as external AQ monitors ?

Knowing the quality of the air outside our home/office/school etc. is very important for our long-term health, and, as we saw in the first post, we can get really useful real-time data of Air Pollution only by using independent AQ monitors. In fact, Official Governmental AQ Monitoring Stations don’t really help us knowing the air right outside our place because they can be very far away (and air pollution is often a localized issue) and/or don’t publish the data in real-time. Similarly, they can’t tell us anything about the Air Quality that we have inside our home. And believe it or not, indoor Air Quality can be much worse than outdoor AQ, without us even knowing it. In fact, the concentrations of some pollutants can often be 2 to 5 times higher than typical outdoor concentrations. And knowing that we spend approximately 90 percent of our time indoors, this is something that we should start investigating and take measures against if needed.

Where is indoor Air pollution coming from?

Not surprisingly, here in Greece outdoor Air Pollution is a significant source of indoor Air Pollution, because the majority of us still lives in older houses or apartments whose doors and windows are not well insulated. Polluted outdoor Air, be it in form of Particulate Matter and/or dangerous gases such as NO2 or Ozone and which is especially hazardous in winter when it is filled with the smoke of thousands of wood stoves and fireplaces, readily leaks into the house and severely lowers indoor Air Quality.

Add to the recipe indoor-generated pollution such as tobacco smoke, candle smoke (yes, this is a major source of particulate matter too), cleaning and maintaining products (including the excessive alcohol products that we must now use against COVID-19), cooking (if you don’t use a kitchen vent your indoor AQ plummets very quickly, especially when frying and using the oven), and the indoor air quality of our homes becomes a serious issue. Gas kitchens are actually way worse than electric ones because they release dangerous amounts of NO2, among other gases, and Particulate Matter. But there are more pollutant sources in a house, and even new furniture made of low quality wood with melamine releases dangerous gases such as formaldehyde. And some of the worse indoor air polluters are, once again, the big felons wood stoves and fireplaces!

The more scientists study the health effects of Air Pollution, the more worrying facts they find. A study just published reveals that “Exposure to household air pollution over 10 years is related to asthma and lung function decline”: long-term exposure to indoor air pollution (gas, wood smoke, tobacco smoke and their combinations) is linked to adverse respiratory health in middle age, particularly for those living in poorly ventilated houses.

Luckily we can rely on Indoor AQ monitors to help us understanding if we do have a problem of air pollution in our house and where its sources might be. By playing around with some of the AQ Monitors listed below (and there are many more brands on the market now, but all offer about the same features) you can really make the difference and end up improving your indoor AQ dramatically.

But before moving to the description of some of the reliable AQ Monitors that we use daily, we want to remind that :

Adequate ventilation is the key to improve Indoor AQ

With low to absent air exchange with the outdoor world (technically called a low air exchange rate) pollutant levels increase, and, once they pass a certain threshold, we can start feeling the negative result even on the short term: our concentration decreases, we start yawning too often feeling tired when otherwise we should feel fine, we might even get a headache, etc. This is usually the result of high levels of CO2 and VOCs (Volatile Organic Compounds), which can be considered the canary in the mine of Indoor AQ.

High levels of CO2 and VOCs = stagnant Air = inadequate ventilation

Hence an Indoor AQ Monitor that measures CO2 and VOCs is a good start in order to improving indoor AQ. The aim is to maintain CO2 levels lower than 1000 ppm (parts per million). VOCs are less reliable on their own because they can be influenced by many chemicals and they can get very high even when CO2 remains low – for example when you use alcohol to clean your hands or your groceries to be safe from COVID-19, VOCs increase dramatically while CO2 is not affected.

In order to improve indoor ventilation – and lower the chances of getting infected by COVID-19 or any other airborne pathogen, the thing to do is open the windows. Experts say that this should be done up to 6 times per hour, a few minutes each time.

Nothing better than fresh air from outside to clear out stale indoor air. But what if the Air outside is too polluted and we can’t open the windows, otherwise we let even more pollution get into our house? Well, this is a major problem in our Greek cities and villages, especially in winter. And here is where we feel the need of an indoor AQ Monitor to tell us also the concentration of Particulate Matter (PM2,5) inside our house.

If the outdoor Air is almost always polluted like in Athens, Thessaloniki, Patras and many other smaller cities of our country (remember, Greece has a mean yearly PM2,5 Air Pollution that is double than the accepted EU safety value of 25 μg/m3 and five times bigger than the even safer WHO limit of 10 μg/m3) opening the windows can really make thing worse. And now that the government imposes schools to keep the windows open in the classrooms against COVID-19, kids will be exposed to too high pollution levels and this is worrying. They tell kids to bring a blanket along to school (!), but no one warns and protects them from breathing large amounts of PM2,5 and pollution gases, which are known to actually reduce their very cognitive functions and ability to concentrate (see a paper here for example: higher annual PM and Ozone levels are clearly associated with a reduction in test scores)! This measure will probably protect kids from the spread of COVID-19 in schools, but it will open up another Pandora’s box, and the kids will likely pay for it later on in their lives.

An indoor AQ Monitor that measures both Particulate Matter PM2,5 and CO2 would be a solution to help classrooms find the right balance between closed and opened windows. And this is the same solution to look for at your home or office: when CO2 has become too high, you open the windows for a while and make sure that PM2,5 doesn’t raise too high, then you close them.

In practical terms, this open-close procedure, again and again over the day, can become an annoying and stressful routine. But what else can we do to protect ourselves from both indoor and outdoor air pollution? You just need to do what best suits you without getting crazy. Even if you forget a window open for too long or let the CO2 get too high for a while it is not a real problem, as long as along the course of the day the air pollution doesn’t get too high inside. The WHO suggest that the safety level of PM2,5 is 25 μg/m3 per day and 10 μg/m3 per year, meaning that if you make sure that you breathe PM less than 10 μg/m3 in average over the whole year, and 25 μg/m3 in a day, you should be fine.

In my practical experience, I manage to maintain indoor PM2,5 between 0 and 5 μg/m3 daily over the whole year, which is well below the WHO recommendation. And I manage to maintain CO2 and VOCs low as well, even when I must stay closed inside the house feeling like a scared little mouse in its burrow because outside is the wood smoke deluge… How did I manage to do that? Well, I like DIY and I tried out various simple systems until I have learned how to balance the way fresh air gets inside the house and the stale air gets out. This system works great and I will discuss about it in a future post. Just a hint: I use HEPA air filters that clean the indoor air from the PM, and vents that throw out the CO2-laden air.

But the best solution would be to have an automated ventilation and heating system (HVAC – Heating, ventilation, and air conditioning) that also filters the air. Unfortunately this is something that is expensive and not very common yet, because there is not much demand for it at a household level. Yet, HVAC systems will become common in the near future when houses will become green and will be energetically as well as Air Quality efficient. We will discuss about these systems in another post.

Some indoor AQ Monitors

Five reliable indoor AQ monitors, see the descriptions for each one here below

We start with the one we like the most:

  1. IQAir AirVisual Pro: This is advertised as the “World’s smartest AQ monitor”, and in fact it is smart. It has a screen on which you can visualize both Indoor AQ and Outdoor AQ. Indoor AQ is measured by sensors within the monitor, while Outside AQ is taken by a choice of outdoor AQ monitors spread allover the world. You can just select an outdoor AQ sensor from a list, and then it will be shown on your screen. In our case we set the PurpleAir sensor on our balcony, how convenient is that?

The sensors of the IQAir AirVisual Pro measure PM2,5 and CO2, plus temperature and humidity, which are right the minimum we need in order to maintain our Indoor Air under control.

It offers smart features that include:

  • Home monitoring on the go with a phone/tablet App and a desktop platform,
  • Alerts when your air becomes unhealthy,
  • Hourly weather & air pollution forecasts,
  • Community news & educational resources,
  • Air quality data for all of your favorite locations, indoors & out

We really like this AQ Monitor and we find that the Air Pollution forecasts are quite reliable in order to know what kind of Air we will breathe tomorrow for example. Yet, it fails to make a good forecasts for events that can’t be really predicted, like how much wood smoke there will be in the air tonight for example. The Airly sensors are more precise at that.


2. Uhoo: This interesting indoor AQ Monitor is packed with many sensors that measure all sorts of PM and gases that can pollute your indoor Air: PM2,5, CO2, NO2, Ozone, CO, and VOCs, plus Temperature, Pressure and Humidity. It even features a Virus Index, which is meant to tell us if our environment is favorable or not to the spread of viruses at any given time. This is surely a plus during a COVID-19 pandemic!

The Uhoo AQ Monitor has a dedicated phone App that allows you to keep your home AQ under control on the go, and it sends you notifications if some of the pollutants increase above a threshold that you can set yourself.

Uhoo has the disadvantage of not having an in-built screen, so that you must use your phone every time you want to check your indoor AQ.


3. Awair: This AQ Monitor has both a simple screen and a dedicated phone App, and has a nice design that make it to look nice on your desk! It measures PM2,5, CO2 and VOCs plus Temperature and Humidity. The screen visualizes an AQ Index and simplified AQ values for each sensor. The proper values can be seen on the phone App.


4. This is a simple no-name Chinese monitor that I had bought on eBay when I first started controlling AQ in our home several years ago. After all this time it is still working greatly! It doesn’t have any smart feature, no WIFI connection, nor bluetooth. Yet, it measures the right air pollutants, which can be easily kept under control in a well visible screen, and, believe me, it is the one that I look at all the time (along with the IQAIR Visual Pro). Why is that? Because its simplicity makes it very handy. It’s just the right numbers on a single screen. No phones nor computer to be connected to. Just a the important numbers on a nice screen. Plus, this is cheaper than the monitors described above. And, because it has an in-built battery, it can be used anywhere and can be taken around with you. But in practice it is a bit bulky to be kept in your bag, and for this purpose the AQ Monitor here below is just perfect.


5. Talking about simplicity, the Xiaomi Smartmi PM2.5 Air Detector is the simplest AQ Monitor around. Yet, it is very very useful. On its small screen it shows only the values for PM2,5, which is by far the most important pollutant to keep under control. It is also cheap, very accurate, and most interestingly, it can be taken around with you so that you can control the PM2,5 everywhere you go. I have one with me all the time.


There are many more Indoor AQ Monitors around, and every now and then there is a new one coming out. Some are more expensive, some are cheaper, and they are more or less accurate depending on the sensors they feature. You can check the blog of our fellow Greek Air Quality expert Sotirios Papathanasiou who is doing many reviews on AQ equipment; he even wrote several books on Air Quality that are well worth reading.

Published by cleanairingreece

CleanAir in Greece is an independent site meant to inform the public about the day to day Air Quality in Greece, with advice on how to protect ourselves from the dangers of Air Pollution

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