Shinyei PPD42NS[1] 做的粉塵感應器 (Dust sensor)[0] 是透過計算一定時間的脈衝次數,紀錄大於 1um 小於 2.5um 的微粒,測量結果單位是 pcs/0.01cf,必須要經過轉換,才能符合常見的細懸浮微粒 (PM2.5) 的 ug/m3 單位,然後透過 ug/m3 才能再算出 AQI[2]。
參考這篇論文 – Preliminary Screening System for Ambient Air Quality in Southeast Philadelphia[3],文中提供了一些公式可用來轉換。
 
為了方便用 node.js 兜起來用,順手改了一版 upm[4][5] 出來。不過由於濕度會影響微粒計算[6],必須配合溼度計,套用雨天或晴天不等的濕度矯正參數公式才會比較準確。
 
[0] Grove – Dust Sensor – Wiki – http://www.seeedstudio.com/wiki/index.php?title=Grove_-_Dust_Sensor&uselang=en
[1] Data sheet of PPD42NS http://www.seeedstudio.com/wiki/images/4/4c/Grove_-_Dust_sensor.pdf
[2] Air Quality Index (AQI) Basics – https://airnow.gov/index.cfm?action=aqibasics.aqi
[3] Preliminary Screening System for Ambient Air Quality in Southeast Philadelphia – http://www.cleanair.org/sites/default/files/Drexel%20Air%20Monitoring_-_Final_Report_-_Team_19_0.pdf
[4] ppd42ns: convert pcs/0.01cf to μg/m3 to aqi by chihchun · Pull Request #409 · intel-iot-devkit/upm – https://github.com/intel-iot-devkit/upm/pull/409/commits/ad31559281bb5522511b26309a1ee73cd1fe208a
[5] upm_0.3.2.bb – https://gist.github.com/chihchun/438625062886f8a53c0c532d22281baf
[6] Seasonal variation of particle size distributions of PAHs at Seoul, Korea | SpringerLink – http://link.springer.com/article/10.1007/s11869-008-0002-2