The Shinyei experiment
Real-time Air Quality readings from Beijing

Share: aqicn.org/sensor/shinyei/hk/
For a complete list of all the Air Quality Sensors test on the World Air Quality Index project, check our sensor overview page.

Introduction

For more information about those real-time dylos and BAM monitor PM2.5 and PM10 readings, please refer to our article on the Dylos Air Particule Counter experimentation.


If you want to know about other affordarable Air Quality Sensors such as Shinyei and Samyoung, check our sensor overview page.

Are cheap low-cost air quality sensor really worth?

There are many affordable and low-cost air particule sensor. The most famous one is definitely the Japanese Shinyei sensor, with a cost of around 75 CNY (12 USD), and it's Korean copy, the Samyoung sensor, with a cost of around 35 CNY (5.5 USD).

This objective of this experiement is to provide empiral data about the quality of those sensor, e.g. can they be used to acurately measure Air Quality, especially for outdoor data and polluted countries.

There are many research papers on this topic. The one most up-to-date at the time of writing is from David Holstius. Check it online here: field calibrations of a low cost aerosol sensor ( research paper).

Inside the low-cost sensor

Compared to the Dylos monitor, one could say that low-cost sensors are more like measuring the air opacity rather than individual particles:

The Dylos monitor works by counting individual particles, and classifying them by size (smaller than 0.5 and smaller than 2.5). By doing so, it is able to provide accurate values about the exact amount of dust particles in the air. And by knowing the typical "dust" type that is being measured, is it somewhat straight forward to deduct the total mass of particles.

The low-cost sensor, on the contrary, are not counting individual particles, but instead, counting the amount of time particles are detected by the photo diode sensor. The graph below represents how the Shinyei is "calculating" the air quality: First, it applies a pass band filter to remove very small particles or noise, which is represented by the red line. Then, independently of the intensity (or particle size), it counts the amount of time any particle is seen. This amount of time, also called "Low Pulse Occupancy" (LPO), can be considered as the "opacity percentage" of the air circulating through the sensor. In order to measure the LPO for different particles sizes, the sensor provide a variable input which allows to adjust the pass-band filter.

Shinyei PPD42NS raw diode reading
Shinyei PPD42NS raw diode reading (in volts)

Shinyei PPD42NS raw LPO reading
Shinyei PPD42NS raw LPO reading (in occupancy)

Experiment Setup


The low-cost particule counters used is this experiment are based on: The reference air quality meters are:
For the source code and hardware connectivity information, please refer to this page: aqicn.org/api/shinyei/.

Note (December 18th 2014): Due to a wrong setup, the data is from the Samyoung is currently not available - it will added again later. Also, this experiment has been updated to use both Shinyei output, which are supposed to be able to reflect small and large particles.

Real-time data

Current Dylos readings are: Particules larger than 2.5 is -, larger than 0.5 is -, updated on - - (China time).

Current Shinyei readings are: LPO for particules larger than 1 is -, LPO for 2.5 is -, updated on - - (China time).

Time series graphs

From the previous graph (Shinyei vs. Samyoung), it is clear that the data generated by the Samyoung sensor is not at all reflecting actual air quality. In order to ensure that this issue is not caused by a deficient sensor, the sensor was replaced with a new one, but yet, no improvement were observed. For this reason, the Samyoung data will not be represented in the next plots. It is however interresting to notice that other resarch papers, such as the low-cost coarse airborne particulate matter sensing for indoor occupancy detection study (online ref) shows much better results for the Samyoung sensor, so this this something to be further investigated.

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Shinyei:
PM2.5 based Air quality data:
PM10 based Air quality data:

Initial findings

At first glance, the correlation for the Shinyei sensor seems to be much stronger from PM10 than PM2.5 readings. But, actually, it seems to be even more complicated since during some periods, the correlation to PM10 seems higher while for other periods, correlation to PM2.5 is higher. If this turns out to be true (which will require more data for the confirmation), that would mean that calculating the AQI from a Shinyei sensor could prove to be very arbitratary (see the PM10 vs. PM2.5 analysis).


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For the list of all air quality sensors, check the Sensor Overview page

Read or publish comments (they rely on Disqus)

關於空氣質量與空氣污染指數

本網站採用的污染指數和顏色與EPA是完全相同的。 EPA的指數可以從 AirNow上查到

空气质量指数 空气质量指数级别(状况)及表示颜色 对健康影响情况 建议采取的措施
0 - 50 一级(优) 空气质量令人满意,基本无空气污染 各类人群可正常活动
51 -100 二级(良) 空气质量可接受,但某些污染物可能对极少数异常敏感人群健康有较弱影响 极少数异常敏感人群应减少户外活动
101-150 三级(轻度污染) 易感人群症状有轻度加剧,健康人群出现刺激症状 儿童、老年人及心脏病、呼吸系统疾病患者应减少长时间、高强度的户外锻炼
151-200 四级(中度污染) 进一步加剧易感人群症状,可能对健康人群心脏、呼吸系统有影响 儿童、老年人及心脏病、呼吸系统疾病患者避免长时间、高强度的户外锻炼,一般人群适量减少户外运动
201-300 五级(重度污染) 心脏病和肺病患者症状显著加剧,运动耐受力降低,健康人群普遍出现症状 儿童、老年人及心脏病、肺病患者应停留在室内,停止户外运动,一般人群减少户外运动
300+ 六级(严重污染) 健康人群运动耐受力降低,有明显强烈症状,提前出现某些疾病 儿童、老年人和病人应停留在室内,避免体力消耗,一般人群避免户外活动
(参考详见 http://zh.wikipedia.org/wiki/空气质量指数)

如果你想了解更多有關空氣質量與污染,詳見維基百科或者 AirNow

有關健康建議詳​​見北京的Richard Saint Cyr MD醫生的博客:www.myhealthbeijing.com


注意事項: 所有空氣品質數據在發佈時均未經驗證,且為了確保資料準確性,這些數據可能隨時被修改,恕不另行通知。 世界空氣品質指數專案在編制這些訊息內容時已經謹慎的運用了所有適當的技巧,在任何情況下世界空氣品質指數 在任何情況下,世界空氣品質指數專案團隊或其代理人均不對因提供此數據而直接或間接引起的任何損失、傷害或損害來承擔契約、侵權或其他責任。



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