To create a more gray-yellow has become a national motto of mutual inspiration

Since last year, "thick Germany to carry fog, self-improvement do not suck, the head of the haze, and then create a gray yellow" has become the motto of the people to inspire each other, look at the local PM 2.5 indicators have become a lot of our daily habits, air quality has become the number one concern for the people. In fact, however, air quality is a very complex issue, and not an index can be summed up simply.

Taking indoor air as an example, there are two major factors affecting indoor air: the first is the external factors, whether indoor temperature or air convection will greatly affect the indoor air environment, a heat convection may make the air quality in the room to completely change; second, the human factors, the cooking when the small solid particles raised, Or the dust from the next door being decorated will greatly affect the indoor environment. The outdoor air environment is more complex, coupled with water, plants, buildings and other factors, a city's air quality is far from the set in a few specific locations of the test equipment given by the data can be reflected.

As a result, Professor Lin of Tsinghua University led his lab team to develop the Pimi air box, trying to construct a real-time air quality monitoring community in a portable air quality monitor that allows everyone to know the air quality anywhere. Pimi's first generation of equipment air box engineering machine has been released, accumulated dozens of cities nationwide more than 100,000 hours of indoor air quality data. The second generation Pimi air box, which is now portable, has been put into production.

There are two difficulties in achieving comprehensive air quality monitoring, the first is the diversity of monitoring sites, the other is the accuracy of the equipment itself, Pimi's technical team is using the calibration method, the use of large calibration equipment, calibration of low-cost air quality monitors to ensure the accuracy of equipment.

At present, the air quality monitoring in the market is almost all using light scattering method to determine air quality. That is, there is a darkroom inside the device, the air through the darkroom when the device will give a light, and then according to the light scattering intensity of the converted pulse signal to calculate the relative mass concentration of dust in the air, and finally converted into a PM 2.5 index. This method is less accurate than the beta-ray attenuation method or the micro-oscillation balance method used in large air quality testing equipment.

However, Pimi team found that the use of light scattering method of equipment has a great improvement in space. Because the light scattering device reading error is positive or negative 10%, however, the difference between inexpensive light scattering air quality monitors and high-priced equipment using the same measurement method is that the error area of a high-priced device is centered on a standard reading, while a low price measurer may be centered over a point in a larger error range. For example, if a region has a PM 2.5 value of 100, the readings for each high-priced light-scattering air monitor are between 90~110, while the low bidder has some readings between 20~30 and 160~70. The end result is that the precision of the advanced equipment is plus or minus 10% while the low priced equipment is positive or negative 60%~70%.

As a result, the Pimi team used ISO standard dust, based on piecewise linear mapping and time domain deconvolution, to calibrate the readings of inexpensive light scattering air monitoring devices so that they read the chatter within the range of the standard readings plus or minus 10%. This process without sacrificing the accuracy of the case, so that hundreds of yuan of air quality detector precision can reach thousands of yuan of air quality monitor accuracy. The technology was awarded the Best System Display award at the International Sensor Network Conference (IPSN) organized by the Institute of Electrical and Electronics Engineers (IEEE). (The following figure is the calibration Air test chamber)

At the same time, Pimi launched a mobile application with an air monitor to display all the information recorded by its paired Pimi air monitor. Also includes a record of relative humidity and temperature, allowing users to view trends in air quality over the past few weeks. These air quality data will be uploaded to the cloud, allowing each user to view the air in every corner in real time to get rid of the air quality monitoring data being "kidnapped" by several air monitoring points. The future Pimi team will also use large cloud data, based on the prediction of user scenarios, to further increase the accuracy of air monitoring.

The air quality monitoring hardware is also interested in air.air! and ink weather. Air.air! is a start-up team from Shenzhen and is also a portable air monitor. Interestingly, air.air! successfully financed the Kickstarter of foreign-funded platforms and failed to raise money on a roll-call date. In fact, this is also a good embodiment of the current domestic consumer mentality, "know what the use of air quality?" Anyway, it's bad enough. "This is also the problem of ink weather." Air quality monitoring may be a good starting point for improving air quality, though the complexity of air purification is more than air detection. Pimi is also considering the failure to provide an air quality automatic air purification scheme based on the current region, as an entrance to an intelligent air quality improvement facility. But whether consumers are interested in a single-sale air monitoring device is still worth observing.