While you can download apps to find out the quality of the air outside, these apps won’t complete the picture because the air quality indoors is different. In fact, according to the EPA, indoor pollution can be 2-5 times worse than outside.
Poor air quality can lead to dizziness, headaches and fatigue in the short term — all of which can lead to respiratory diseases, cancer, and heart disease in the long term. That is why monitoring the air quality indoors matters.
Since 2020, I have tested over 100 air purifiers, and along the way, I have used nearly 20 air quality sensors as part of our air purifier testing process. In this article, I will share my findings and highlight the best air quality monitors on the market right now.
If you want to know the air quality in your area, many free apps can provide this data. For those in the U.S., the EPA has an app called AirNow, and even Google Maps now provides air quality data. For those outside the U.S., the IQAir AirVisual app is straightforward and, more importantly, free.
These tools can help you get local information on air quality without spending money, which you can then use to mitigate the problem, such as investing in an air purifier. If you only have $150, you are better off investing the entire budget in a good performing (and affordable) air purifier instead of buying a cheap sensor and a cheap air purifier.
If you want to start monitoring the quality of your air indoors, then keep reading.
Staff picks: The air quality monitors we recommend
| BEST PORTABLE MONITOR | BEST VALUE FOR MOST PEOPLE | MOST ACCURATE MONITOR | BEST UNDER $100 | |
|---|---|---|---|---|
| Aranet4 HOME | QP Pro | PurpleAir Zen | QP Lite | |
 |  |  |  | |
| Measurements: | CO2, temp, RH and pressure | CO2, PM2.5, PM10, tVOC, temp, RH and sound | PM1, PM2.5, PM10, tVOC, temp, RH and pressure | CO2, PM2.5, PM10, temp and RH |
| Power source: | 2 AA batteries | 5V, USB-C | 5V, USB Micro | 5V, USB-C |
| Mounting type: | Indoors table top or wall mounted | Indoors table top | Outdoors wall mounted and indoors table top | Indoors table top |
| Sensor type: | Nondispersive infrared sensor (NDIR sensor) | Grandway P5500 optical particle counter | Plantower PMS6003 optical particle counter + Bosch BME688 gas sensor | Grandway 7500 optical particle counter |
| Dimensions: | 7.01 x 7.01 x 2.38 cm | 8.5 x 7.5 x 8.6 cm | 8.5 x 8.5 x 10 cm | 6.36 × 4.6 × 5.46 cm |
| List price | $199.00 | $149.99 | $299.00 | $76.00 |
If you are short on time and can’t ready my full article, then you can watch my YouTube video below where I share some more info on the best air quality sensors we tested since 2020:
Since the start of the COVID-19 pandemic, there has been an increasing number of people who are interested in understanding the air quality in their home. The problem is that most of the cheap sensors you’ll find online are nothing more than random number machines.
Read on to learn more about the only air quality monitors we recommend here at HouseFresh.
1. Best portable monitor: Aranet4 HOME
A battery-powered CO2 monitor that you can bring with you wherever you go.
While you might be tempted to go straight for a particle sensor, many people will find a CO2 sensor way more useful as a first step towards understanding indoor air quality. High levels of CO2 have been linked to poor decision-making, slower reaction times, and increased tiredness. Plus, a study from 2021 showed that the level of CO2 can reflect risks of COVID as it can be a proxy of how well ventilated a room is.
The Aranet4 HOME is small, portable CO2 monitor that you can bring with you wherever you go. I highly recommend this CO2 monitor for those who want a device that can quickly assess the need for better ventilation in a space.
What we really like
What we think could be better
I bought the Aranet4 HOME back in 2022, when it was selling for $250. However, you can now find it for around $170. This is still a significant investment but you will be buying an air quality monitor that can last up to four (4) years on one set of batteries thanks to its e-ink screen — and battery life can be extended to up to seven (7!) years if you set it to record CO2 readings every 10 minutes.
| Measurements: | CO2, temperature, relative humidity and atmospheric pressure |
| Sensor type: | Grandway P5500 optical particle counter (non-FEM) |
| CO2 concentration accuracy: | ± 30 ppm (+ 3% of reading) |
| Mounting type: | Indoors table top or wall mounted (with this wall mount bracket) |
| Power source: | Two AA alkaline batteries (included) |
| Dimensions (in inches / in cm): | 2.76 x 2.76 x 0.94 in (7.01 x 7.01 x 2.38 cm) |
| Weight (in pounds / in kg): | 0.23 lbs (104 g) |
| App connectivity: | Yes |
| Manufacturer’s warranty: | 1 year |
The Aranet4 HOME uses a highly accurate NDIR (nondispersive infrared sensor) and this is a big reason why it has a high price tag. However, you can find cheaper (and smaller) CO2 sensors that use photo-acoustic sensors. These sensors have been shown to work well indoors but are not as useful outside, according to a study by AirGradient, but they can be found for less than $50.
I have also tested the Qingping CO2 Monitor from Smart Air that can be found for less than $70. It uses an NDIR sensor and is very accurate but it has a much shorter battery life compared to the Aranet4 (around 30 days).
While CO2 monitors are very useful for triggering important actions like improving ventilation, there will be times when you want to know exactly what particles are in your air and, for this, you will need a monitor with a particle sensor.
2. Best value for most people: Qingping Pro (Gen 2)
A good looking air quality monitor with a touch screen and a high quality optical particle counter that will set you back $149.99.
The QP Pro 2 is the second release of the Qingping Pro model. Similarly to the first generation, the QP Pro 2 not only measures CO2 levels but also PM2.5 and PM10 (particulate matter) levels. And, according to AQMD’s Air Quality Sensor Performance Evaluation Center, the Qingping series from Smart Air has been shown to perform as accurately as much higher-priced devices.
What we really like
What we think could be better
On top of CO2 and PM, the QP Pro 2 also measures temperature, relative humidity and noise levels. It also detects VOCs, which is rare as VOC sensors are expensive and are hardly ever included in budget air quality monitors. Plus, the QP Pro also functions as a clock (with alarms) and it displays the weather, air quality index and UV index in your area.
And the thing about the QP Pro is that it looks GREAT thanks to the combination of a high quality aluminium outer casing that houses a replaceable sensor and a 4-inch touchscreen display.
| Measurements: | CO2, PM2.5, PM10, tVOC, temperature, relative humidity and sound levels |
| Sensor type: | Grandway P5500 optical particle counter (non-FEM) |
| CO2 concentration accuracy: | ±15% |
| PM2.5 concentration accuracy: | ±10% |
| Mounting type: | Indoors table top |
| Power source: | 5V, USB-C |
| Dimensions (in inches / in cm): | 3.35 x 2.69 x 3.4 in (8.5 x 7.5 x 8.6 cm) |
| Weight (in pounds / in kg): | 0.23 lbs (104 g) |
| App connectivity: | Yes |
| Manufacturer’s warranty: | 1 year |
The internal battery of the QingPing Pro Gen 2 will only last a few hours so be sure to keep the sensor plugged into a battery pack or the well with a USB-C cable if you are pulling regular readings.
3. The most accurate monitor: PurpleAir Zen
The PurpleAir Zen is the very sensor we use here at HouseFresh to test the particle removal speed of every air purifier we review.
I first heard about PurpleAir sensors from a report from the South Coast Air Quality Management District (AQMD), which tests air quality monitors and compares their performance against that of reference devices that cost upwards of $20K. Inside the Zen, you will get a replaceable dual laser particle counter and a gas sensor — the most powerful combo of any of the sensors on my list.
It doesn’t come with a fancy screen but you do get an in-built color-coded LED ring that ranges from green (good) to purple (hazardous). allowing you to quickly see the overall quality of your air at a glance. This sensor can be used indoors (with the table top mount) and also outdoors (with the use of cable ties).
We use the PurpleAir Zen as our main sensor for our hands-on air purifier tests, as it allows us to track PM1, PM2.5, and PM10 every few seconds. What I love about the Zen (and one of the reasons why we use it for our testing) is that it allows you to export all your data, which is something you don’t get with many sensors.
What we really like
What we think could be better
If accuracy is your core concern, then the PurpleAir Zen sensor is the best you can get without investing tens of thousands of dollars in reference instruments like the GRIMM EDM 180 or the Teledyne API T640.
| Measurements: | PM1, PM2.5, PM10, tVOC, temperature, relative humidity and atmospheric pressure |
| Sensor type: | Plantower PMS6003 optical particle counter (non-FEM) + Bosch BME688 gas sensor |
| PM2.5 concentration accuracy: | ±10% at 100 to 500μg/m³ ±10μg/m³ at 0 to 100μg/m³ |
| Mounting type: | Indoors table top or wall mounted |
| Power source: | 5V USB Micro, 0.18A continuous, 600mA peak |
| Dimensions (in inches / in cm): | 3.5 x 3.5 x 4 in (8.5 x 8.5 x 10 cm) |
| Weight (in pounds / in kg): | 0.78 lb (357 g) |
| App connectivity: | No |
| Manufacturer’s warranty: | 1 year |
If you like the sound of a PurpleAir sensor but you can’t justify the $200+ price tag of the Touch or the Zen sensors then check out the new PurpleAir PIXEL. It is small, portable and powered by USB. Plus, it also has an LED color coded light to show the quality of the air at a glance.
4. The best monitor under $100: Qingping Lite
Retailing at $76, the QP Lite is the most reliable air quality sensor you can buy for less than 100 bucks.
The smaller sibling of the Qingping Pro, the QP Lite is a small cube with a big OLED screen that houses a Grandway 7500 optical particle counter (non-FEM) sensor that can measure CO2, PM2.5, PM10, relative humidity and temperature.
The QP Lite can detect CO2, PM2.5, PM10, relative humidity and temperature. You can rotate through each of the measurements by tapping or sliding the touch bar on the top of the device.
What we really like
What we think could be better
If you don’t need to take this monitor with you, I recommend you plug it in USB power all the time as it will ensure you have constant air quality readings. That said, the QP Lite has a 2000mAh lithium battery built-in, so you will be able to use it unplugged for up to seven (7) hours.
| Measurements: | CO2, PM2.5, PM10, temperature and relative humidity. |
| Sensor type: | Grandway 7500 optical particle counter (non-FEM) |
| CO2 concentration accuracy: | ±15% |
| PM2.5 concentration accuracy: | ±10% |
| Mounting type: | Indoors table top |
| Power source: | 5V, USB-C |
| Dimensions (in inches / in cm): | 3.35 x 2.69 x 3.4 in (8.5 x 7.5 x 8.6 cm) |
| Weight (in pounds / in kg): | 0.31 lbs (143 g) |
| App connectivity: | Yes |
| Manufacturer’s warranty: | 1 year |
5. The best formaldehyde sensor: Elitech Temtop LKC-1000S+
This is the only monitor on this list that can detect HCHO (formaldehyde) molecules.
The Temtop LKC-1000S+ is a handheld air quality monitor that measures PM2.5, PM10, formaldehyde (HCHO), tVOC, temperature and relative humidity. It comes with a little stand at the back so you can place it on surfaces without the need to be holding it all the time.
Something I really like about this monitor is that it has a function that shows the changes of PM2.5 levels for the last 12 hours represented as a histogram chart, which makes it easy to digest the data as a bar chart compared to a simple line chart. However, I know this is a subjective thing because I am a sucker for data visualization 🙂
What we really like
What we think could be better
At the bottom of the screen, you get a color-coded air quality indicator light that ranges from green (good) to maroon (hazardous) so you can quickly see what the quality of your air is at a glance.
| Measurements: | PM2.5, PM10, HCHO (formaldehyde), tVOC, temperature and relative humidity |
| Sensor type: | Dart electrochemical HCHO sensor + Temptop laser PM2.5 sensor + Sensirion temp & humidity sensor |
| PM2.5 concentration accuracy: | ±10μg/m3 (0-100μg/m3) ±10%(100-500μg/m3) |
| Mounting type: | Indoors handheld and table top |
| Power source: | 5V |
| Dimensions (in inches / in cm): | 6.9 x 2.6 x 1.2 in (17.7 x 6.5 x 3.2 cm) |
| Weight (in pounds / in kg): | 0.48 lbs (219 g) |
| App connectivity: | No |
| Manufacturer’s warranty: | 1 year |
6. The best radon detector: Airthings View Plus
The only air quality sensor on our list capable of detecting radioactive gas.
The Airthings View Plus is not cheap at just under $300, but it can detect CO2, PM2.5, tVOCs, temperature, humidity, pressure AND radon. Similarly to the Aranet4 HOME, it comes with an eInk display that can be customized to show the air quality values you want to always have on show.
This monitor integrates with IFTTT, Alexa and Google Assistant, and it also connects to the Airthings app, where you can see historical data visualized in easy-to-digest charts. It runs with six AA batteries and you can also plug it in with a USB-C cable.
What we really like
What we think could be better
| Measurements: | Radon, CO2, PM2.5, tVOC, temperature, relative humidity and atmospheric pressure |
| Sensor type: | Alpha-spectrometer for radon + NDIR sensor for CO2 + Laser scattering based optical particle counter |
| CO2 concentration accuracy: | ±50ppm ±3% within 10–35°C (50-95°F) and 0–80% RH |
| PM2.5 concentration accuracy: | 0 ~100μg/m3, ±10μg/m3,100 ~200 μg/m3, ±10% |
| Mounting type: | Table top or wall mounted |
| Power source: | 6 AA batteries or USB-C |
| Dimensions (in inches / in cm): | 6.6 x 3.5 x 1.3 in (17 x 9 x 3.3 cm) |
| Weight (in pounds / in kg): | 0.79 lbs (360 g) |
| App connectivity: | Yes |
| Manufacturer’s warranty: | 5 years |
7. The best open-source DIY sensors: AirGradient ONE & AirGradient Open Air
Two sensors with open-source hardware and firmware that you can assemble yourself with replaceable parts.
AirGradient devices are the best alternative to PurpleAir monitors due to the use of high-end replaceable sensors from industry leaders like Plantower, Sensirion and SenseAir. And unlike PurpleAir, AirGradient follows an open-source model for the data whereas the terms and conditions from PurpleAir make it clear that they own all the data.
Another unique aspect of these sensors from AirGradient is that both of them are available as build-it-yourself kits. If you go for the kit version, you will get everything you need to build the monitor at home, including detailed instructions that are clear and easy to follow. And if you have any problems, you can drop a question in the AirGradient Forum and someone from the community will get back to you with their advice.
What we really like
What we think could be better
Indoor monitor: AirGradient ONE
The AirGradient ONE is an indoor air quality monitor that measures CO2, PM2.5, tVOC, NOX, temperature and humidity. It has a color-coded LED bar and small 1.3-inch OLED display at the front that show the current air quality in the room. Even though it’s an indoor sensor, it comes in a plastic, UV resistant and weather proof enclosure.
| Measurements: | CO2, PM2.5, tVOC, NOX, temperature and relative humidity |
| Sensor type: | SenseAir S8/S88 CO2 NDIR sensor + Plantower PMS5003 laser particle counter + Sensirion SGP41 TVOC/NOX sensor + Sensirion SHT3x/4x temperature & humidity sensors |
| CO2 concentration accuracy: | ±40 ppm ±3% of reading at 5 to 30°C, 0-85% RH (400 – 2000ppm range) |
| PM2.5 concentration accuracy: | ±10%@100-500μg/m³, ±10μg/m³@0~100μg/m³ |
| tVOC/NOX concentration accuracy: | tVOC <±15 @ 0 to 500 VOC Index NOX <±50 @ 0 – 500 NOX Index |
| Mounting type: | Table top (with clip-on stand) or wall mounted |
| Power source: | 2A 5V USB-C |
| Dimensions (in inches / in cm): | 5.1 x 5.1 x 1.3 in (13 x 13 x 3.5 cm) |
| Weight (in pounds / in kg): | 0.77 lbs (350 g) |
| App connectivity: | Yes |
| Manufacturer’s warranty: | 1 year |
Outdoor monitor: AirGradient Open Air
The AirGradient Open Air is an outdoor air quality monitor. Similarly to the ONE, the Open Air monitor detects CO2, PM2.5, tVOC, NOX, temperature and relative humidity. At the back of the device, you get zip tie holders you can use for pole mounting and you also get screw holes for wall mounting. There is also a small hole at the back that you can use with a secure screw to prevent the monitor from being stolen.
| Measurements: | CO2, PM2.5, tVOC, NOX, temperature and relative humidity |
| Sensor type: | SenseAir S8/S88 CO2 NDIR sensor + Plantower PMS5003T laser particle counter + Sensirion SGP41 TVOC/NOX sensor + ScioSense ENS210 temperature & humidity sensor |
| CO2 concentration accuracy: | ±40 ppm ±3% of reading at 5 to 30°C, 0-85% RH (400 – 2000ppm range) |
| PM2.5 concentration accuracy: | ±10%@100-500μg/m³, ±10μg/m³@0~100μg/m³ |
| tVOC/NOX concentration accuracy: | tVOC <±15 @ 0 to 500 VOC Index NOX <±50 @ 0 – 500 NOX Index |
| Mounting type: | Pole or wall mounted |
| Power source: | 2A 5V USB-C |
| Dimensions (in inches / in cm): | 3.60 x 3.41 x 3.34 in (9.1 x 8.6 x 8.5 cm) |
| Weight (in pounds / in kg): | 0.38 lbs (180 g) |
| App connectivity: | Yes |
| Manufacturer’s warranty: | 1 year |
Common questions about air quality monitors
The air quality sensors available to consumers estimate particulate matter or gaseous pollution in the air, often based on a reading of a different but easier-to-measure substance related to the pollutant. For instance, a sensor may be designed to measure the amount of light that particulate matter scatters, which, more often than not, increases as the levels of pollution rise. These results are then interpreted by the device and shown on a scale of low to high, sometimes with associated colored bars or LEDs.
The most basic air quality monitor is one you probably already have in your home—a smoke detector, which uses a binary scale and signals whether smoke is present.
Air quality is measured by the EPA using the U.S. Air Quality Index (AQI), and it has six categories corresponding to different levels of health concerns. Each of the six categories has its own color to make it easier for the public to know if the air quality is approaching unhealthy levels. The colors and categories are:
- Green – Good
- Yellow – Moderate
- Orange – Unhealthy for sensitive groups
- Red – Unhealthy
- Purple – Very unhealthy
- Maroon – Hazardous
According to the CDC, “The EPA has identified six pollutants as “criteria” air pollutants”. These six air pollutants are:
- Carbon Monoxide. Breathing in high levels of CO can cause confusion, unconsciousness, and death.
- Lead. Lead in the air may have an adverse effect on the nervous system, kidneys, immune system, and cardiovascular system.
- Nitrogen Oxides (NO2). Breathing air with high levels of NO2 can lead to respiratory problems such as asthma and can become severe.
- Ozone. Increased ozone levels can cause coughing, damage your airways, and make the lungs more vulnerable to infections.
- Particulate Matter. This pollutant contains solids or liquid droplets so small they can only be seen under a microscope and if inhaled, can cause serious health problems, getting into your lungs, and even into your bloodstream.
- Sulfur Dioxide (SO2). Exposure to SO2 can cause harm to your respiratory system and make it difficult to breathe. Asthmatics and young children are at particular risk.
You’ve probably heard that the air inside your home can contain up to five times more pollutants than the outside air. The only way to accurately monitor the air quality in your home is to invest in a suitable quality air quality monitoring device.
An indoor air quality monitor, by definition, does precisely what the name implies: it monitors the quality of the air inside your home, continuously or periodically, depending on the type of monitor.
If you are concerned about the air quality in your home, get a monitor that tests for nearly all the pollutants found indoors such as the QP Pro.
It all depends on the technology the sensors use, the type of sensor, and lastly, the incorporated display method. Many middle- to high-end air purifiers have at least one integrated sensor. The most commonly found sensor is a PM2.5 sensor, capable of detecting particle matter up to 2.5 micrometers. They are normally the cheapest to manufacture and provide only basic readings and results. PM2.5 sensors found in air purifiers mostly use infrared technology, and while they do what they are supposed to do, the measurements are not very accurate. On the other hand, laser beam technology gives more precise air quality readings.
The display method used by the air purifier to show the quality of the air is also an important factor in determining the accuracy of the sensors. Most of them use a color scale to show the quality of the air—green for good, up to red for bad—which may look appealing, but it doesn’t tell you much. A display that shows the air quality index as a number, or a series of numbers, is more accurate.
PM2.5 is the measurement given to fine particulate matter (PM) with a thickness of fewer than 2.5 micrometers. To put that number in perspective, a grain of sand has a diameter of 90 micrometers, and a human hair measures 50-70 micrometers.
A PM2.5 sensor works by counting these fine particles suspended in the air. As air is sucked into an air quality monitoring device, particles in the air stream pass through a laser beam, which causes the light to diffract. The diffracted light will land on the sensor, placed at a right angle to the laser beam. The changes in the light intensity that the sensor picks up mean that individual particles can be counted.
VOC is an acronym for Volatile Organic Compounds and is an extremely broad classification of carbon-based chemicals. Consumer-related devices with integrated VOC sensors have become more and more available in the past few years, but they are relatively low-cost sensors that can only give a general reading as to the total amount of VOCs in the air and cannot pinpoint with any accuracy exactly what VOC it is detecting. They cannot differentiate between VOCs that are harmful and those that are not. There are some sensors on the market specifically designed to detect particular VOCs. For example, you can get a sensor that will detect formaldehyde, one for Carbon Monoxide, another for Radon, and some high-end devices have multiple sensors built-in to cover all major VOC detections with some degree of accuracy. Still, they tend to be a bit pricey.
Depending on your smartphone’s operating system, two of the best air quality apps are:
- For Android users, the IQAir AirVisual app gives you historical, real-time, and forecast air quality data for your area. It provides live information on the six “criteria” for air pollutants, with health recommendations.
- For Apple users, then the Air Quality Reader is an excellent choice. With this app, you can switch between the air quality data from the EPA and the air quality index readings provided by PurpleAir on their website.
So… Is it worth getting an air quality monitor?
The short answer is ‘yes’.
Whether you are getting a single-pollutant monitor (such as carbon monoxide or radon) or a sensor that can detect multiple pollutants (like particle matter or tVOCs), getting a sense of the quality of the air in your home will help you take the right precautions when needed — from simply opening a window to setting your air purifier to full speed.
If you have decided to buy your first air quality monitor, I recommend choosing a device that can detect several types of pollutants with an easy-to-understand display screen, such as the Qingping Pro or the Airthings View Plus.
Now, if you are a more technical person and/or care about getting the most accurate results possible, then you should look into the PurpleAir Zen sensor and the open-source AirGradient ONE sensor.
Once you have introduced an air quality monitor to your space, make sure to calibrate it regularly to get the most accurate results possible.
