Air pollution analyzer. Devices for measuring the quality of the environment. Intuitive interface

The level of human comfort and safety depends on the microclimate where people spend most of their lives, namely: in the home, office and office. Air pollution, reduction of green spaces, the use of synthetic materials impairs the composition and properties of the inhaled air mixture. In our country there are regulations which the responsible owners of industries and companies must adhere to. In order to have an idea of ​​the composition of the air mixture, devices and detectors have been developed that determine the state of the atmosphere for the presence of dust, the content of harmful substances, and the deviation of the parameters of the air mixture from the standard characteristics.

Scope of gas analyzers

A very important area of ​​application of gas analyzers is the control of air purity in the offices of the building, which is understandable, because the owner of a small company, office or cinema will not be able to influence the city air. In the office, taking into account modern possibilities, you can create an acceptable atmosphere by installing a ventilation system that will work in the desired mode, taking into account the state of the air mixture, which allows you to create an optimal atmosphere in the office premises. Sanitary standards establish special characteristics of air, which include temperature, humidity, concentration carbon dioxide, ozone, volatile organic compounds, smoke and dust. The efficiency and speed of measurement depends on the accuracy of the air quality sensor. When there are many people in the building, the gas analyzer must quickly measure the state of the air mixture, according to its commands, the supply of clean air must be carried out more intensively. If there are few or no people at all, the feed should be reduced until it stops completely.

Indoor Carbon Dioxide Analyzers

One of the main parameters that characterize the optimal air composition is the concentration of carbon dioxide. When a person walks into an office and notes that it is stuffy, this most likely indicates an increased content of carbon dioxide. When the air is inhaled, where the carbon dioxide content is higher than the recommended values, the body feels discomfort, the person feels tired, becomes inattentive and distracted. When a significant number of people are in the office, when they all exhale carbon dioxide, the room becomes stuffy, therefore, the main criterion for a poor composition of the air mixture is the content of carbon dioxide in it, which indicates the need to ventilate the office. Tracking the carbon dioxide content in the air allows you to monitor the state of the atmosphere in the building. For this, air quality sensors that monitor the level of carbon dioxide are used, they are produced by various companies, there are many models that differ in price and characteristics, and are offered different options their placement.

Room detectors

Arduino indoor air quality sensors monitor carbon dioxide content by attenuating infrared radiation as the amount of carbon dioxide increases. The measurement is carried out with an infrared analyzer. Room analyzers of the state of the air mixture give the possibility of individual adjustment of the supply of external air when it is necessary to refresh the room, ensure the state of the air that meets the standards, and reduce energy costs, since the supply is carried out at the right time. There are many models of indoor air quality sensors available, and there are many types of wall-mounted devices. Of the room detectors for monitoring the air condition, two types are most used:

1. Carbon dioxide detector with relay output, ventilation system control buttons, LED indication.
2. Detector without indication and control buttons. Analyzers show the content of carbon dioxide in the room, if its concentration is exceeded, the employee independently turns on the ventilation and provides an inflow of clean outside air. All detectors can measure the amount of carbon dioxide, tracking the boundary indicators, measurements usually have the following ranges:

• 0 to 0.02%.
• 0 to 0.03%.
• 0 to 0.05%.
• 0 to 0.1%.

The received data is converted into active output signals to the monitor, it is possible to use an analog data output that carries information about the concentration of carbon dioxide. State standards regulate the permissible concentration of carbon dioxide in the air and the performance of the ventilation system, which depends on the number of people. According to the standard, one employee must have at least thirty cubic meters of fresh air per hour. The room air quality sensor must be installed in accordance with the standards at a distance exceeding one meter from the permanent location of people, but not closer than one meter to the supply ventilation.

Automatic sensors for ventilation

Air quality sensors for ventilation are used to automate the operation of the supply and cleaning system. These devices are connected to ventilation control devices and, if the parameters deviate from the set ones, they automatically regulate the oxygen flow. Automation of ventilation systems makes it possible to maintain the air condition in the room at an optimal level, eliminating the human factor. Air quality sensors built into the ventilation also save energy, since air conditioners and ventilation systems do not work constantly, but only at the time specified by the program. The analyzers can be connected to humidification or ozonation systems. The technology of the device operation consists in the fact that through the relay the sensor turns on the ventilation system only when an excess of the concentration of carbon dioxide is noticed.

Gas analyzer SQA

In addition to carbon dioxide, other gases and odors can float in the house. In order to monitor the quality of inhaled oxygen and the increase in the concentration of some gases, gas analyzers have been developed. They are able to control the characteristics of the air mixture. The SQA air quality sensor monitors the concentration of a non-separate element of the atmosphere, carbon dioxide or other separate gas, it turns on ventilation when it detects organic substances that change the composition of the atmosphere depending on the parameters set in the device. After the parameters of the microclimate of the office reach the norm, and the air mixture acquires the necessary characteristics, the supply of air from the outside will continue for some time, set by the timer, up to twenty-five minutes. The control device can set the preset air parameters, if deviating from them, it turns on the forced supply of the air mixture until the optimal composition is achieved.

Arduino Air Pollution Control Detector

Protection organization environment the main five air pollutants have been identified, including nitrogen oxide, sulfur dioxide, carbon monoxide, ozone, and particulate matter. The Arduino Air Quality Sensor is an optimal and very cost-effective way to monitor air quality, it can detect pollution from major harmful agents other than sulfur dioxide. The device also has a detector for particulate matter, humidity, temperature and an analyzer for detecting the presence of household gas, which makes it possible to determine leaks and the presence of other combustible hydrocarbons in the air. Air quality sensors automatically start ventilation to clean the building. This happens if there is an excess for any given parameter.

Air quality sensors VOC

VOC stands for Volatile Organic Compounds. The VOC air quality sensor evaluates the composition of the mixed air with a mixed gas analyzer. It monitors the concentration of the existing mixture determines the state of the air, allows you to quantify its saturation with various gases, cigarette smoke, gasoline vapors, solvent, paint. This sensor is self-calibrated, controlled by a microprocessor, exceeding the concentration of harmful impurities is detected using a chemical sensitive element, which reacts with organic impurities of air pollutants, which leads to a change in its electrical conductivity. It is measured by instruments and converted into digital form. A sensitive chemical element is consumed during the operation of the device, its service life depends on the type of pollutants and their concentration.

KNX air condition detectors

KNX is an automated comprehensive building management system that is standardized and uses a single software... Automation of home control using the system makes it possible to significantly save energy resources, for example, the use of integrated building services for ventilation control can provide energy savings of up to forty-five percent. With the KNX system, air quality sensors control the ventilation of the building as a whole. Detectors of other functions, heating, blinds, lighting are also connected to the control devices of these systems. The essence of the microclimate control scheme in a building is to measure air quality control sensors, record current readings and transfer them to the microclimate control system, which regulates the supply or termination of the supply of fresh air to a particular room.

Pollen Detection Devices

There are now a whole line of indoor air quality sensors that can detect the presence of pollen in the air. Such devices determine the degree of pollution of the atmosphere with particulate matter. Manufacturing companies have developed and are selling dust and pollen quantification devices capable of distinguishing particles as small as 2.5 microns using optical methods and using a laser beam. Particles of this size are considered serious and hazardous air pollutants, and in Japan and China they are considered an important factor in the growth of diseases. Pollen and dust are especially dangerous for those suffering from asthma, chronic pneumonia, cardiovascular diseases during seasonal flowering of plants. The optical method consists in the fact that the light scattered from the particles is collected by a system of mirrors. The sensor developers believe that the device is able to distinguish dust particles from pollen by analyzing characteristics scattered light. Detectors that use an optical method to monitor the concentration of dust and pollen in the air show the amount of particles suspended in the air. A device that uses a laser beam to determine the amount of particulate matter in the air uses the method of directing the laser beam into the air, and the concentration of particulate matter suspended in the air is determined from the scattering of the returned beam.

Air purifiers for pollen

People could not stop at determining the degree of pollution and developed devices for cleaning the air from impurities. Good inventions for air purification need to perform at least two tasks: to maintain optimal air condition by ventilation, to clean it from suspended particles, as well as harmful gases. These devices must be equipped with filters that must trap dust, pollen and other solid contaminants. The principle of cleaning consists in running the air mixture by the fan of the device through a set of filters, which allows for quick cleaning of large-volume rooms.

Many models are equipped with carbon filters, which capture most of the carcinogenic substances, gases, eliminate odors, tobacco smoke, sometimes the models are additionally equipped with air ionizers. There are also instruments for measuring air quality with pollen sensors. According to the cleaning methods, the following types of cleaners can be distinguished:

• The electrostatic cleaner cleans with ionized air. It effectively traps dust, soot and tobacco smoke. Equipping with an ozonizer helps to regulate the number of germs and bacteria. The device is easy to maintain, consumes little electricity, is inexpensive, does not require consumables, you just need to periodically remove the accumulated dust.
• Replacement filter cleaners are very effective against dust. They are inexpensive, but filters need to be changed periodically.
• Photocatalytic purifiers are considered to be the most effective, and are purified by the decomposition of solid matter in the air under the action of ultraviolet rays and a catalyst. Also effective against odors and smoke. These devices do not need consumables, but they are quite expensive.
• Purifiers using water. Appliances of this type usually combine a humidifier and an air purifier at the same time.

Often, a manufacturer has to fit a whole combination of different ways cleaning, which increases the efficiency of the device. The choice of such a device should be made taking into account the area of ​​the house, the amount of dust, the presence of smokers, as well as the price and manufacturer. Man has invented many ways to detect pollutants and monitor the condition of indoor air, and even more will be invented. However, nevertheless, do not forget about the elementary, centuries-proven methods of dealing with dust, dirt and odors, this is a systematic wet cleaning and cleaning from dust.

In modern living quarters, complex automated monitoring of the state of conditions of stay in office premises is used, which automatically allows you to respond to changes in the characteristics of the microclimate in buildings. But in old buildings, ventilation is rarely equipped with at least coarse filters to clean the incoming air from large dust particles. In order not to jeopardize the health of personnel, experts recommend installing local systems for maintaining a microclimate in the premises. The air quality relay sensor can help with this.

I recently purchased another AirVisual air quality measurement station and decided to donate the first for the benefit of the community. Moreover, since September 2017, under unknown circumstances, the Mosecomonitoring website has been closed. And residents of the city have lost the opportunity to observe the level of air pollution in different parts cities.

I installed a station in my area, not far from the Universitet metro station. And the data on the number of microparticles of dust PM2.5 is now available to everyone. Ideally, you can announce crowdfunding and create your own network of stations throughout the city, but first things first. Go!

The photo below is my second AirVisual Pro monitoring station from IQAir Corporation. You should already be familiar with this unparalleled device on the market. I was the first AirVisual customer from Russia exactly one year ago. Then the station was called AirVisual Node and cost only $ 209 (now the updated version costs $ 269). The Pro version differs in a different, better screen, advanced settings and another PM2.5 laser particle detector of its own design. The sensor for the concentration of carbon dioxide CO2 in both devices is the same - SenseAir S8 Extended Range (measuring range up to 10,000 ppm). The device is also equipped with Wi-Fi, a 5-inch screen and a battery for autonomous operation (its charge is enough for 3-4 hours of operation, if you wish, you can connect an external power supply from a powerbank - so I took measurements in transport).

Surprisingly, there are no analogues to this device in the world in terms of its characteristics. It is worth noting that the station uses industrial-grade accuracy sensors (you can google tests in which the PM2.5 particle detector from AirVisual shows an accuracy comparable to professional equipment costing several thousand dollars).

As I noted earlier, on September 11, 2017, the Mosecomonitoring website stopped working. In Moscow, more than 10 stations were installed in different parts of the city, data from which were successfully picked up both by the AirVisual device itself and by the mobile application (it is convenient to use even if you do not have your own station).

Okay, so we will monitor the pollution of the street air on our own. Moreover, these measurements clearly show us that HEPA filtration of the supply air really works. On the screen on the left, you can see the level of PM2.5 particles in the bedroom (in fact, it is lower, the ultrasonic humidifier simply introduces an error, although it runs on reverse osmosis water with 9 ppm - I will write a separate article about this). That is, in reality, the concentration of PM2.5 in the bedroom is on average 2-3 μg / m3. While on the street at this very moment the concentration is 17 μg / m3. It is almost safe for healthy people, but sensitive people should avoid long walks and sports outside at this point. Allergy sufferers should also avoid prolonged outdoor exposure if the AQI air quality index exceeds 50.

I installed the station on the balcony, next to constantly open window. It only transfers data via PM2.5 to the public. You can monitor the state of the outdoor air either from the official website (https://airvisual.com/russia/moscow/universitet) or via the AirVisual mobile app. Of course, it is a pity that the device in this form is not used for all 100. In fact, there is a battery, a screen, a CO2 sensor, temperature and humidity sensors idle. But, unfortunately, there are no other options on the market (in fact, there are, but costing several thousand dollars).

Here's another screenshot from my admin area. Here you can see the very data on CO2, temperature and humidity from the street station, which are not publicly available. And at the same time appreciate highest quality air in our apartment. As I noted above, if you remove the humidifier, then PM2.5 will be 2-3 μg / m3. Well, 640 ppm in terms of CO2 is simply the highest air quality, which guarantees, among other things, the absence of formaldehydes and other pollutants.

If you want to know in more detail what PM2.5 microparticles are, then I highly recommend reading this one. I see no reason to repeat myself and retell it again.

I will only note a very important point, why it is necessary to monitor the PM2.5 particles. In fact, one of the best air quality detectors we all have is our nose. If you feel bad smell then it is obvious that you need to take measures not to breathe this. Likewise, your eyes will not let you down if you see a dense cloud of dust and quickly leave the place of pollution. The problem with PM2.5 particles is that they cannot be seen or felt in advance. Due to their microscopic size, they easily overcome biological barriers (nasal mucosa) and settle in your lungs. And after that, with great difficulty, they are removed from there. Regular exposure of the body to PM2.5 particles lowers immunity, increases the risk of chronic lung disease, and ultimately shortens life expectancy.

And now I have a very important question, first of all for the residents of Moscow. There is a proposal to make our own network for monitoring the quality of urban air on the basis of such stations (last year such a project was implemented by enthusiasts in Krasnoyarsk - http://krasnoyarsknebo.ru). As I noted above, the station costs $ 270 with delivery to Russia. We need volunteers who will agree to install stations on their balconies and provide connection to the network (USB 5V 1A is enough) and the Internet (via Wi-Fi). And also people who are ready to donate a small amount of money for the development of the project (purchase of stations, creation of a website and a mobile application, support of performance). Of course, the air in Moscow is not as dirty as in other megacities of the planet (look at the AQI index in India and China, for example -.

ADDITION FROM AUGUST 20, 2018:
The station has been dismantled, monitoring of the air condition in the area is not carried out.

Still have questions? Ask them in the comments!

And don't forget to subscribe to my blog so you don't miss out on new articles!

Such a device can help monitor air quality, as well as warn the owner of a gas leak or the presence of flammable gases. For additional functionality, the detector includes a humidity and temperature sensor. This mini-station will be able to determine all the main air pollutants (carbon monoxide, nitrogen oxide, sulfur dioxide, ozone and particulate matter), except for sulfur dioxide.

Due to the fact that the sensors used have different prices and their parameters differ from one another, their calibration took place at the concentration of gases known to the author.

Materials:
- Arduino Uno
- 5V power supply
- LCD shield RGB 16x2 LCD shield
- Gas sensor MiSC-2614 (Ozone)
- Gas sensor MQ-9
- Sensor for measuring humidity and temperature Keyes DHT11
- Particulate matter sensor Shinyei PPD42
- Gas sensor MQ-2
- Gas sensor MiCS-2714 (NO2)
- Access to a 3D printer (for the case, you can use the existing plastic or wooden box)
- Bread board
- Fan 5V
- Conductors of caliber 24 (0.511 mm) 10 - 15 pieces

Electrical diagram:

This diagram shows general scheme the operation of the device to represent what this detector is. The author asks you to pay attention to the fact that most of the ports with sensors can be changed, but then you will need to change the program code.

Step one. Particle sensor.
Two Shinyei PPD42 sensors are used to collect particulate matter data.
Each of them has two outputs: the left yellow one for small solid particles, and the second one for large particles. The outputs will be connected to a 5V Ardiuno as shown in the general diagram.

Each of the sensors uses an LED and a photodiode to measure the concentration of airborne particles.

Step two. Gas sensor board.
Shown below is a circuit diagram of a printed circuit board for gas and temperature sensors with humidity. The author made a printed circuit board on his own and recommends doing it also for those who will be engaged in this project, and notes that the board may differ physically from the one indicated in the diagram.

Step three. NO2 and ozone sensors.
The DIY uses the surface mount sensors MiCS-2614 and MiCS-2714 to detect ozone and ozone dioxide in the air.

Each sensor uses an internal resistor in its sensor element. The diagram shows the location of the measuring resistor between terminals K and G. To determine their correct location, an ohmmeter was used. The resistance of the resistor is within kOhm. Also the sensors have a heating element between terminals H and A, which maintains the temperature of the sensor element. The heating element has a resistance of 50-60 kOhm.

Step four. Gas sensors.
The author uses gas sensors MQ-2 and MQ-9, which measure toxic gases. The sensors use a gas sensing resistor to detect toxic gases, and use their heating element to set and maintain the required sensor temperature.

The sensors are installed according to the breadboard diagram. The MQ-2 sensor is connected with the A pin to the 5V supply, the G pin to the ground, the S pin to the ground through a 47 kΩ resistor. The MQ-9 sensor is connected a little differently: pin A to the transistor, B to the 5V supply, pin G to ground and pin S to ground through a 10 kΩ resistor.

Step five. Humidity and temperature sensor.
This sensor is a must, as the control of humidity and temperature is a very important part in determining the concentration of gases. Higher humidity and temperature values ​​will greatly affect the measurement accuracy, both of these parameters can be monitored with one sensor. Its connection is as follows: the left terminal is connected to power, the middle terminal is the signal output, and the right terminal is connected to ground. The signal from this sensor will go to the digital port of the Arduino.

Step six. Fan and power supply.
If you look at the diagram of the entire project, you will notice that only one input voltage of 5V is used. This homemade product uses a regular network adapter. For proper operation of the device, and to prevent overheating, a 5V case fan is used.

Step seven. Frame.
The body can be made from scrap materials such as wood, metal, plastic. The author used a 3D printer, at the bottom of the article there is a file for printing.

I present to your attention a review of 12 gadgets that will let you know the quality of the air you breathe. Basically, these are devices that allow you to measure the concentration of carbon dioxide and the amount of micro-dust particles PM2.5. But some of the devices presented in the review can also measure the concentration of carbon monoxide, ozone and noise levels (as well as temperature, humidity and pressure).

But first things first. Go!

So, today we will focus on the following devices:

Masterkit MT8057
Awair
TION MagicAir
AirVisual Node / Pro
iCeeO2-500 (-700)
AZ Instruments AZ-7798/7788/7787
HT-2000
NetAtmo Weather Station
uHoo Air Sensor
Specialized CO2 relays
CleanSpace Tag
Xiaomi PM2.5 Detector
WP-6910/6912

From this list, I use everything except: AZ-7798, NetAtmo Weather Station, uHoo Air Sensor and HT-2000. This is largely because these devices have less functionality than their counterparts. All monitored devices (except one, but not in this list) have a true NDIR CO2 detector and / or a quality PM2.5 sensor. We will also consider specialized CO2 relays that allow you to automate the control of supply ventilation.

I made a table in which I collected the main characteristics of the devices:

<

	AirVisual Node / Pro	Masterkit MT8057	Awair	TION MagicAir	iCeeO2-500 (-700)		HT-2000	NetAtmo Weather Station	uHoo Air Sensor	Xiaomi PM2.5 Detector	WP-6910/6912
CO2 sensor	Yes (SenseAir S8 Extended Range)	Yes (Zyaura ZG07)	There is	Yes (SenseAir S8)	Yes (NDIR dual channel)	Yes (SenseAir K30)	Yes (SenseAir S8 LP)	There is	There is	No	No
Particle detector PM2.5	Yes (Laser)	No	Yes (IR)	No	No	No	No	No	Yes (IR)	Yes (Laser)	Yes (Laser)
Volatile Organic Sensor VOC	No	No	There is	No	No	No	No	No	There is	No	There is
Screen	5 "color	LCD + LED	LED matrix	LED matrix	LCD	LCD	LCD	LED	LED	OLED	LCD
Temperature and humidity sensor	There is	Temperature only	There is	There is	Yes (in the -500 model, only temperature)	There is	There is	There is	There is	No	No
Measurement memory	There is	No	No	No	No	Yes (in AZ-7798)	There is	No	No	No	No
Built-in rechargeable battery	There is	No	No	No	No	No	4xAA	No	No	There is	There is
Nutrition	USB 5V	USB 5V	12V DC	USB 5V	USB 5V	5V DC	6V DC	USB 5V	USB 5V	USB 5V	USB 5V
Wi-Fi	There is	No	Yes (+ Bluetooth)	There is	No	No	No	There is	There is	There is	No
Smartphone app	There is	No	There is	There is	No	No	No	There is	There is	There is	No
PC connection	Yes (via Wi-Fi)	There is	No	No	No	There is	There is	No	No	No	No
API	There is	No	There is	No	No	No	No	There is	There is	No	No
Notes (edit)						Relay in version AZ-7788		Noise and Pressure Sensor	CO, NO2, O3 sensors		Formal Dehyde Sensor
Cost (excluding delivery)	$240	$100	$170	$180	$60	$170-240	$80	$220	$300	$50	$40-60

© site

Masterkit MT8057

I'll start with the very first CO2 measuring device that I got 4 years ago. This is the simplest compact meter of CO2 concentration and temperature from the ZyAura company (model ZGm053U), sold in Russia under the Masterkit MT-8057 trademark (Dadget). The inexpensive meter, which has three color indicators (thresholds can be configured), is powered by USB, and also has the ability to connect to a computer to record measurement statistics. A good option if you only need to measure the concentration of carbon dioxide CO2 at stationary conditions. The device uses a proprietary NDIR sensor, which shows high measurement accuracy and has an automatic calibration (ABC) function. You can buy the device in Russia (at one time it was cheaper than on aliexpress).

TION MagicAir

The MagicAir base station measures the temperature, humidity and carbon dioxide concentration in a room. It is powered by USB, has Wi-Fi on board for connecting to the network and a radio module for communication with fresh air breathers. All measurements are stored in the cloud service. The main task of the device is to automate the operation of the supply ventilation TION. The device is equipped with a high quality SenseAir S8 carbon dioxide sensor. The base station is only suitable for stationary measurements. requires a permanent internet connection. Ideal for work in conjunction with a breather. The mobile app does not have push notifications yet. An ideal device if you want to automate the supply ventilation in your apartment. You can buy it on the official website of Tion.

Detailed overview about TION MagicAir you can see.

Awair

The Awair air quality meter has a stylish design (body made of natural wood) and quite good functionality, including a mobile app with push notifications. Among the shortcomings, it is worth noting the infrared particle matter detector, which cannot accurately determine the particle size, which leads to a sufficiently large measurement error. But the device has a volatile organic matter (VOC) sensor, which, in my opinion, is completely unnecessary in a domestic environment (more on that later). All measurements are stored on the server, so the device is only suitable for stationary measurements. Also, the data cannot be obtained in text form for independent analysis (this also applies to the TION MagicAir station). In addition, the 12-volt power supply will not allow the use of an external battery for wearable measurements. You can buy the device on Amazon with delivery to Russia through an intermediary.

A detailed review about Awair can be viewed.

AirVisual Node

In my opinion it is best device on the market that has no analogues. Measures CO2 and PM2.5 (as well as temperature and humidity). It has a huge color screen, built-in memory (4 GB) and a battery for autonomous operation. There is also a mobile application with an air quality map and push notifications (the application can be used without a station). The device can work both offline and connected to a network via Wi-Fi. Access from a computer is possible via the Samba protocol (as on any network drive). It has a SenseAir S8 Extended Range carbon dioxide sensor and a high-precision industrial grade PM2.5 detector (confirmed by numerous tests, the results are available on the Internet), the company's own development.

A detailed overview of the AirVisual Node can be viewed.

I regularly use this device to assess the air quality in residential and office premises, and also with the help of it, I conducted research on air quality in public transport. At the moment, this device is a public station for monitoring air quality in Moscow (area of ​​the University metro station). You can read more about this in more detail.

IQAir AirVisual Pro

Since the first AirVisual Node is now used for outdoor observation, I bought a second one. This is an updated version, with a better glossy screen, an improved PM2.5 particle sensor (with a completely silent fan) and advanced functionality (the ability to turn off Wi-Fi and adjust the measurement interval, for example). Now the brand belongs to the world famous IQAir company. Again, this is the best device that can be used to monitor indoor air quality (CO2) and outdoor (PM2.5). You can buy the device on the official website (the price on the website is indicated with delivery).

iCeeO2-500

A very interesting and inexpensive carbon dioxide meter from China. It stands out against the background of competitors in that it has a two-channel CO2 sensor (allows for more accurate automatic calibration). Designed not only for CO2 control in residential buildings, but also in greenhouses. If it is critical for a person high level CO2 in the inhaled air, then for plants CO2, on the contrary, is needed for more productive growth. The manufacturer assumes that it can be used in conjunction with an external battery. Also in the assortment, the manufacturer has advanced and more expensive modifications that have a logger function (for a separately installed micro sd memory card). I believe this is the best device for the lowest cost if you only need to measure CO2. You can buy the device on TaoBao through an intermediary.

There are 4 more devices worth mentioning, but I personally don't own them.

AZ Instruments AZ-7798/7788/7787
This is one of the first mainstream CO2 sensors that could be bought on Aliexpress. For several years, the price for it has dropped. There are 3 modifications of the device: without measurement memory and without relay, only with memory, only with relay. It copes well with the task of observing CO2. The design is outdated, the functionality is limited, and it is inconvenient to carry with you. You can buy on Aliexpress.

HT-2000
Probably the cheapest CO2 logger on the market. Equipped with either a SenseAir S8 LP sensor or an MH-Z19 (if you're lucky). Has problems with automatic calibration, can be connected to a computer. A good option if you need the cheapest CO2 logger. You can buy on Aliexpress.

NetAtmo Weather Station
Personal weather station equipped with a CO2 sensor of our own design. Also measures pressure and noise level. There is a nice mobile app with push notifications. At the same time, it reacts very slowly to changes in CO2 concentration. You can buy it in Russia.

uHoo Air Sensor
A device with a huge number of sensors compared to competitors. In addition to the generally accepted air quality indicators CO2 and PM2.5, this device can measure the concentration of carbon monoxide (CO), nitrogen dioxide (NO2) and ozone (O3). For the same reason, this is the most expensive device in the review. But at the same time, it does not have a screen (only a mobile application), a battery (for autonomous operation) and memory. Also, in my opinion, the device has a redundant set of sensors. Objectively, one carbon dioxide sensor is sufficient for indoor measurements. You can buy the device on the official website, delivery will cost another $ 30.

ADDITION: I purchased this device and returned it back, disappointed. Unfortunately, it was not possible to get any accurate readings from him for CO2, and even less for PM2.5 (especially since he does not have a laser detector). Plus there were problems with the Wi-Fi connection. I do not recommend it.

Specialized devices: CO2 relays
These devices are needed to automate the work of supply ventilation in residential and office premises. They are equipped with a CO2 sensor and a power relay that controls the switching on / off of the supply ventilation when a certain value is reached (the response threshold and hysteresis are set by the user).

In this photo there are two such CO2 relays from the manufacturer. Tongdy, they are sold worldwide and under other brands. The device on the left uses a SenseAir K-30 sensor and is powered by 24 volts. On the right is a device with a color screen and powered by 220 volts. It uses a GE Telaire T6500 sensor. It is impossible to buy these devices in Russia, I bought them directly from the manufacturer, having paid, among other things, for expensive delivery. The device on the left cost 8 thousand rubles, on the right - 11 thousand. By the way, I'm ready to sell the relay on the right. for their tasks in country house I decided to choose the first option (I'll make a separate article about this).

An affordable alternative for the tasks of automating the work of supply ventilation can be considered devices from AZ Instrument. it AZ-7722/7721(the latter does not have a humidity sensor). It didn't suit me because of its size and old-fashioned appearance. Such a device costs about 10 thousand rubles, you can buy it on Aliexpress.

Since we touched on the CO2 relay, it is naturally worth mentioning this device, which caused a lot of noise on the Internet last fall. it Hessway KF-900F(pictured on the left). The problem is that the seller who placed the lot on Aliexpress mentioned not only VOC, but also CO2 in the text. Freebie lovers immediately jumped at the device, which was selling for less than $ 50, although it is obvious to any sane person that for this money it is impossible to buy a device with a real NDIR CO2 sensor.

And what actually happened? No, this is not a CO2 relay for supply ventilation. This is a VOC relay for control EXHAUST ventilation... First of all, this is clearly written in the instructions. And secondly, it is obvious from the principle of operation. The device has 4 relays on board: 3 of which are used to turn on the fan at different speeds, and another one is used to control the bypass valve for supply ventilation (an icon is even visible on the screen). Consequently, this device is designed to be installed on the hood of the working area (in the kitchen, for example). Bypass control is necessary because as we know cooker hood not "friendly" with supply and exhaust ventilation. And in a dirty area, there is no need to measure CO2 specifically. The task is more global - to remove odors. Therefore, the device uses the Winsen MG-812 VOC sensor. It will not work to use this device as a CO2 meter or a relay to control supply ventilation.

It is also worth noting the various homemade devices what people are trying to do with Ardiuno / Raspberry and the cheapest NDIR CO2 sensor Winsen MH-Z19 (B)... First, the cost of the device will still turn out to be around $ 100 (which means what's the point of doing this if you can buy a ready-made device?). Secondly, the reliability and accuracy of a homemade meter will be much lower than the factory solution (all homemade products usually fail the automatic calibration).

CleanSpace Tag

This device with a "perpetual" battery stands out from the review in that it measures neither CO2 nor PM2.5. But it can measure the concentration of carbon monoxide (CO), which is deadly to humans. It is relevant only for measurements on the street (in traffic jams) or in underground parking lots. Carbon monoxide usually does not get into apartments (especially on high floors). Despite the fact that the device itself is charged from a GSM and Wi-Fi radio signal, its mobile application requires GPS to be turned on for full operation, which has an extremely negative effect on the operating time of your smartphone. But I would like to note one interesting point that came to light during operation - a bluetooth connection with a smartphone is maintained at a distance of at least 20 meters. The device is produced in England and is not officially sold in Russia, but I managed to negotiate a sale to Russia.

Xiaomi PM2.5 Detector

As the name suggests, this is a PM2.5 particle detector from Xiaomi. Equipped with Wi-Fi (can be controlled via the proprietary Mi Home application). Has a battery that can work for about 2-3 hours. Designed for the Chinese market with a wired time zone that cannot be changed (all of China uses one time zone) - it will not work as a night light / clock. A very compact and handy device that you can take with you. You can buy in Russia or on Aliexpress.

WP-6910/6912 (pictured left and right)

The two most affordable portable PM2.5 and VOC detectors on the market. The models differ only in screens (more expensive with a color screen). They have a built-in rechargeable battery and allow for mobile measurements of PM2.5 particles, formaldehyde and VOC. They cope with their functions perfectly. You can buy on Aliexpress.

So what should you choose?

First, you need to decide what exactly you want to measure and what problem to solve.

If you are worried about dirty air outside, then you need a PM2.5 particle detector. That is, it is obvious that any PM2.5 particle detector must be mobile. The PM2.5 particle sensor will also be very useful to you if you use a stove / fireplace. I recommend Xiaomi PM2.5 Detector.

If the apartment / office is stuffy and you want to track the moment when you need to open the window for ventilation, you need a CO2 sensor. I recommend the iCeeO2-500.

But in fact, measurements of indoor air quality are limited by the fact that inside living quarters, an automated supply air supply is required. ventilation system with filtration.

It turns out a vicious circle: the room became stuffy (high concentration of CO2) - you opened a window to feed into the room Fresh air and there is dirty air outside (PM2.5 particles) - the window must be closed again.

Of course, you can fight the consequence (PM2.5 particles that got into the apartment through the window from the street) and install an air washer, but in fact you need to deal with the source of pollution (street) and use filtered ventilation. And do not forget that if you do not have supply ventilation, then the window will actually have to be constantly kept open (or open for 5 minutes every 30 minutes and do so around the clock - I published the measurements earlier).

The same applies to formaldehyde and VOC. They are in any apartment and office. Emission of harmful substances from finishing materials and furniture has been taking place during the entire service life. This is the same smell that you feel when you enter an apartment in which there were no people and the windows were closed (it seems not stuffy, but there is some kind of smell). But all these air pollutants are simply removed using forced ventilation. And if you have a forced forced ventilation, it turns out that you do not need a CO2 sensor (except to track when the filter is replaced).

If you want to measure both CO2 and PM2.5, the AirVisual Pro has no alternatives. Since neither the Awair nor the uHoo Air Sensor can be taken with you. And AirVisual is actually the only device that has built-in measurement memory.

Take care of your health and the health of your loved ones.
And do not forget: one thing is short-term exposure to pollutants (traffic jam in the street, stuffy carriage), quite another - regular exposure (your apartment, in which you spend half of your life).

Self-study literature:
How much air does a person need for comfort?
On the issue of standardizing air exchange in terms of CO2 content in outdoor and indoor air
Indoor air quality in buildings built in cold climates
Particles PM2.5: what is it, where and why is everyone talking about it

Still have questions? Ask them in the comments!

And don't forget to subscribe to my blog so you don't miss out on new articles!

This device will provide users with an economical solution for air quality monitoring. Environmental organizations have identified five main air pollutants: ozone, particulate matter in the air, carbon monoxide, sulfur dioxide and nitrogen oxide. This device can detect all these pollutants except sulfur dioxide. In addition, the device includes a domestic gas detector to alert users of gas leaks or the presence of flammable gases. Also included is a temperature and humidity sensor.

We calibrated the device according to the sensor datasheet for a preliminary assessment of the overall performance of the device. Since the sensors used are quite cheap and their parameters vary significantly from component to component, their calibration was carried out with a previously known concentration of harmful gases.

Step 1: Materials

Management and nutrition

• Arduino Uno microcontroller
• 5V power supply
• RGB 16x2 LCD shield

Sensors

• Particulate Sensor Shinyei PPD42
• Gas sensor MQ-2
• Gas sensor MQ-9
• Gas sensor MiCS-2714 (NO2)
• Gas sensor MiSC-2614 (Ozone)
• Temperature and humidity sensor Keyes DHT11

Additional materials for assembly

• Access to a 3D printer
• Bread board
• 5V fan
• 10 - 15 conductors of 24 gauge (0.511 mm)

Step 2: General electrical diagram

The above wiring diagram is a general diagram showing the operation of the hazardous gas detector. A detailed circuit diagram for the breadboard will be presented below. Please note that you can change most of the digital and analog ports that the sensors are connected to if necessary (for any reason); to do this, you need to make changes to the provided program code.

Step 3: Particulate Sensor

We used two Shinyei PPD42 dust sensors to collect data on the concentration of particulate matter in the air.

Each Shinyei sensor has two signal outputs, one for fine particulate matter (left yellow wire in the image above) and one for large particulate matter. These outputs are connected to the digital inputs of the Ardiuno. The sensor ports require + 5V supply and ground. See general electrical circuit.

Each sensor uses an infrared LED and a photodiode to measure the concentration of particulate matter in the air. An internal circuitry converts the output of the photodiode into digital signals. Typically, the sensor outputs a + 5V signal, and when the sensor detects particles, it sends out a low voltage pulse. The time period when the output signal is low or "low-pulse occupancy percentage" is proportional to the concentration of particulate matter in the air.

For a detailed analysis of the reverse decoding of the Shinyei PPD42 sensor, refer to teaching material Tracy Allen

Step 4: Gas sensor PCB

Above is the wiring diagram for the printed circuit board. gas sensors and a temperature / humidity sensor. The details for installing each component are shown below in the following steps. Please note that your PCB may differ physically from the one shown in the image. In fact, it is recommended that you make your own PCB for your surface mount components instead of using a breadboard.

Step 5: Ozone and NO2 sensors

We used surface mount sensors MiCS-2614 and MiCS-2714 which can detect ozone and nitrogen dioxide in the air, respectively.

Both of these sensors use an internal resistor in their sensor element. In the diagram above, the measuring resistor is located between terminals (G) and (K). Use an ohmmeter to make sure correct location conclusions. The resistance of the resistor should be between 10-20 kΩ.

In addition, both sensors are equipped with a heating element between terminals (A) and (H). This heating element maintains the required temperature of the sensor element. The resistance of the heating element is 50-60Ω.

Ideally, both sensors should be surface mounted on the PCB. However, in the absence of a printed circuit board, you should carefully solder to the outputs of these sensors using low temperature solder and take extra care.

As shown in the wiring diagram for the breadboard, we installed 82Ω and 131Ω resistors in series with the heating elements of the MiCS-2614 and MiCS-2714 sensors, respectively. This ensures that the heating elements receive the required power level. If you do not have a 131Ω resistor (this is a non-standard value) then use 120Ω and 12Ω resistors in series.

We have placed measuring resistors in both sensors in series with the 22kΩ resistors in order to create a voltage divider. From the voltage at the output of the voltage divider, we were able to calculate the measuring resistance of the sensor.

Rsenor = 22kΩ * (5V / Vout - 1)

Step 6: MQ Toxic Gas Sensors

We used gas sensors to measure toxic gases including propane, butane, LPG and carbon monoxide MQ-2 and MQ-9.

The MQ-2 and MQ-9 are very similar to the MiCS sensors. They use a gas sensitive resistor (SnO2) to detect toxic gas concentrations and have a heating element to maintain the required sensor temperature. The circuits used for these sensors are similar to those for the MiCS sensors, except that we used a transistor instead of a resistor to regulate the heating power in the MQ-9.

Refer to the breadboard wiring diagram for details on wiring. For the MQ-2 sensor, connect the A pin to the 5V supply, the G pin to ground, and the S pin to ground with a 47kΩ resistor. For the MQ-9 gas sensor, connect the A pin to the transistor, the B pin to the 5V supply, the G pin to ground, and the S pin to ground with a 10 kΩ resistor.

Step 7: temperature and humidity sensor

This sensor must be used because temperature and humidity control plays an important role in determining the concentration of gases. High humidity and temperature significantly affect the measurement accuracy. Therefore, it is very important to control these changing parameters. Temperature and humidity can be monitored simultaneously with one sensor. As shown in the picture above, the left pin is connected to power, the middle pin is the signal output, and the right pin is connected to ground. The output from this sensor goes to the digital port of the Arduino. Our code assumes that the temperature signal goes to digital port 2. If necessary, you can change to another digital port; just make the appropriate corrections in the program code depending on the selected port. For proper use of this component, refer to the breadboard wiring diagram.

Step 8: power supply and fan

If you look at the wiring diagram for the entire project, you will see that you only need one input voltage of 5V. For this project, you can use the normal network adapter shown above. You also need a case fan to help keep your device from overheating. A standard 5V fan of the required size can be used.

Step 9: case

The body can be manufactured in many ways. We used an UP 3D printer. We have attached the STL file that we used for the final print.

Step 10: program code

The code for extracting raw data from the device is attached above. This code prints the sensor resistance values, the Shinyei PPD42 low pulse busy rate, and the temperature and humidity readings on a computer via a serial monitor. Also, the raw data can be viewed on the LCD display.

For the code to work correctly, you first need to load the libraries for the LCD shield, and the temperature and humidity sensors. Libraries can be found on the following websites:

Step 11: Interpreting the data

We used David Holstius to determine the particulate matter concentration. In the article for the Shinyei PPD42 dust sensor, the ratios of the sensor outputs to the measurements taken by the Environmental Protection Agency were determined. The charts in the app indicate the most appropriate charts for the data. We used plots to perform an approximation of PM2.5 particulate matter concentration in micrograms per cubic meter as follows:

PM2.5 = 5 + 5 * (a small percentage of the time during which the output of the photodiode is low voltage).

To estimate gas concentration from MiCS gas sensors, we used datasheet plots (NO2 and) to extract functions related to sensor resistance versus gas concentration.

For the MQ sensors, we used graphs from the sensor datasheets to qualitatively evaluate the data. When the resistance value falls below half the resistance in air, it is likely that the sensor is detecting target gases. When resistance drops by a factor of 10, target gas levels will be around 1000ppm, close to the required safe limit.