How to judge whether the air in your home is good or bad? Highly recommended to collect!

With the recent outbreak of various respiratory diseases, people have paid more and more attention to air quality. Many people have purchased air purifiers. Does installing an air purifier mean that the indoor air quality will be worry-free? How to judge whether the air is good or bad?

In fact, the monitoring levels of indoor and outdoor air are completely different. Apart from using a haze meter to measure indoors and expecting the air purifier to reflect the actual situation, most of them are inaccurate.

We who do scientific research often come into contact with national laboratory equipment. It happens that a friend in Beijing does outdoor air monitoring, which is what everyone usually knows, air pollution forecasts, PM2.5 index released by the state, etc. They use the most advanced and minimally erroneous instruments for measuring air quality. Then I will introduce how to determine whether indoor air is polluted, and at the same time, I will go over the working principles behind the common haze meters and purifier readings, and briefly introduce the scientific research level air monitoring methods.

01 Determine whether the air is polluted - Daily version

You may have seen haze meters from different channels. There are many types of this tool on the market, with prices ranging from hundreds to tens of thousands. There are handheld ones and larger box-like instruments. Ordinary families do not need to buy this specifically to understand the quality of indoor air, but they can also understand its working principle.

The monitoring principles of haze meters are similar, mainly relying on laser sensors and using the light scattering method. The sensor emits light, and if it encounters particulate matter in the air, it will block the propagation of light, resulting in a decrease in the light sensed by the laser sensor, thereby determining pollution. Based on the light sensing data, the scale of pollution can naturally be inferred.

Just like the following picture:

A more straightforward sentence: You are blocking my sight...

Interestingly, different instruments with similar detection principles can read completely different data. Why is this? Because the data collected by the light scattering method must go through a data processing process to become the PM2.5 and PM10 values ​​that ordinary people can understand. This step is very critical. The accuracy of the algorithm directly affects the reliability of the final reading.

Insert a picture, the data collection and processing process of a certain brand of sensor. The first two steps include the process of collecting data and laser scattering, and the third step converts the data collected during the scattering process into a signal, which is then processed by the algorithm of the microcontroller and output as data that the user can understand.

The reason why the algorithm processing process is very important is mainly to eliminate some interfering data, such as the influence of air conditions such as air humidity and temperature on the analysis conclusions. Generally speaking, each manufacturer will set up a series of data collection, testing, and comparison processes to develop an algorithm. Only after the algorithm is processed can data worthy of reference be obtained. This data standard is formulated by the Environmental Protection Agency (EPA) in the United States and NPL in the United Kingdom, but China’s "PM2.5 Mass Concentration Monitoring Calibration Specification" has been soliciting opinions since 2016 and has not yet been officially issued. In other words, as of now, the data results of various domestic monitors on the market have no standard specifications. Isn’t it terrible!

Speaking of the indoor air quality standard that consumers most often refer to - the air quality data from air purifiers, the main reason why purifiers have such digital displays is actually the built-in sensor components. In fact, in the final analysis, many purifier manufacturers have also seen that consumers have this demand, so now many machines will display readings, which means that you can use it clearly. Even if you can't see or smell the indoor air pollution, you can understand the quality of the air in the room through the changes in the numbers on the machine, and then feel the purification effect from the constantly decreasing numbers. Don't think that you are wasting money. From this level, purifier manufacturers will require how accurate this reading is, and you can also judge for yourself.

However, many careful consumers will still refer to the readings to choose the appropriate purification mode. Even in automatic mode, the operation of the machine itself is closely coordinated with the data read by the sensor. Of course, in order to improve the monitoring accuracy of air purifiers, there are still many conscientious manufacturers making more efforts.

for example:

Use more sensors: If one is not enough, add another. Adding more sensors is always the best way. Multiple sensors monitor independently, and then process the data as a whole, which can increase the sensitivity of monitoring and improve the authenticity of data.

More in-depth calibration of the algorithm: The sensitivity of the sensor element itself is naturally important, but as analyzed above, the algorithm may actually play a more decisive role in the accuracy of the final reading. In this regard, continuous calibration between the readings and the readings of national-level professional equipment can help derive a more rigorous algorithm, and the final monitoring results can be closer to scientific research-level monitoring. Of course, the factors that need to be considered in calibration are also very complex, such as different weather conditions, different regional environments, etc., which generally require a longer time, so not many related equipment manufacturers can do this step very thoroughly.

Collecting more detailed air data: This is also the idea of ​​many manufacturers to improve. In the past, air pollution often only gave you a grade index or a comprehensive index. However, as people understand air quality better, attention to various indicators has become a demand.

Most intuitively, air pollution is generally divided into particulate matter pollution and gas pollution. The former includes the familiar PM2.5 and PM10, and the latter includes gaseous substances such as nitrogen oxides.

Different pollutants naturally require different treatment methods. If it is particle pollution, then take measures such as filtration, if it is gas pollution, then use activated carbon adsorption.

In addition, many air purifiers also add options such as air humidity and temperature, making them more comprehensive.

02 Determine whether the air is polluted——Professional version

After all, the above-mentioned household air purifiers are for families, so both the monitoring conditions and monitoring technology are naturally of civilian level and are mainly used for reference.

If you are really concerned about professional testing, then, to be vulgar (sorry), I have to say that compared with professional equipment and technology, the testing of civilian equipment still has a greater placebo effect.

First of all, most of the air purification monitoring in the civilian market actually uses one detector to detect all indicators. Professional monitoring does not do everything at once, but monitors each item separately.

Even though some machines will give more detailed indicators as mentioned before, professional testing is done for specific purposes and is clearly divided.

For example, just to detect PM2.5, you need to use a proprietary device (as shown below)

Two detection methods (oscillating balance method, beta ray method)

Secondly, the detection technology also has various indicators and requirements. The following table is the analysis method of air monitoring formulated by the national standard GB3095-2012 "Ambient Air Quality Standard". You will find that common methods include ultraviolet fluorescence, differential absorption spectroscopy, chemical judge method, other filtrate-related infrared absorption methods and other professional methods, which are much more complicated than the detection methods of haze meters or purifier sensor elements described above.

In addition, professional air monitoring will also distinguish between monitoring locations, such as construction sites, transportation venues, factory areas, and other different places. The types and emphases of monitoring projects are also different.

03 Professional VS Daily

After reading so much, I believe you also understand the technology and difficulty of real professional monitoring. These professional-grade monitoring equipment cost tens of thousands or even hundreds of thousands of dollars, and also take up huge space and places. For ordinary people, it is naturally impossible to hold it and there is no need for it.

But then again, except for newly renovated houses, people are particularly concerned about formaldehyde. Generally speaking, people don't need to have an exact understanding of indoor air quality, so as long as the equipment readings are not particularly outrageous, they can basically be used as a reference.

Of course, it would be best if it could be as accurate as possible, especially the display readings of the purifier. After all, this is a configuration that many purifier manufacturers now have on the machine, and it has gradually become a direct quantitative reference for many people to judge the quality of indoor air. Therefore, for families with children, the elderly or people with allergies, whether the readings are accurate will become more important. Another reason is that the automatic mode of many purifiers itself operates according to the readings calculated by the sensor. If the readings are inaccurate, it will not work when it should, or it will continue to purify strongly when it is not important, which is a bit embarrassing.

Finally, of course, we also hope to see the introduction of national calibration standards as soon as possible to regulate different household detectors and air purifier sensors.