### PM2.5 low-cost sensors and calibration data for SDS011 and PMS7003

#### 2. What is laser-scattering method

Three popular models of low-cost sensors for PM2.5 in 2019 are Plantower PMS7003, Nova Fitness SDS011 and Honeywell HPMA115S0. Plantower has other older models such as PMS5003, and PMS3003. The fourth version is not low-cost by a developing country standard, Dylos DC1100 Pro.

Laser-scattering method is mentioned in low-cost sensors with different nuances such as based on the principle of laser scattering (SDS011, PMS7003), laser-based sensor (HPM), and true laser particle counter (DC1100). The distinction is needed because laser emits a narrow region of wavelengths, created a perception of a higher accurate device. Light scattering is used interchangeably in this article. In a true technical term, light scattering referred to a lower accuracy, less expensive LED as the light source. The laser is used in laboratory-grade equipment such as Met One E-Sampler or GRIMM EDM 180.

What I learned from the Internet about laser-scattering method is shining a laser beam onto a particle, light can be scattered, diffracted, absorped or extincted. Measuring size of a particle and how many particle in that size is based Mie Theory with inelastic scattering. To read more about laser-scattering, refer to this 7-page write-up.

# PMS7003 SDS011 HPMA115S0 DC1100 Pro
Price ~13$~$19 ~$19 ~$290
Range (µg/m3 0-500 (1000)* 0-999 0-1000 N/A
Error 10% and ±10µg/m3 15% and ±10µg/m3 15% and ±10µg/m N/A
Lifespan (h) 8,000 8,000 20,000 several years
Communication Serial with headers, baudrate 9600
Mode Continuous or passive query by Serial input 1-minute or 1-hour sampling
Output PM1,PM2.5,PM10, counts with size of 0.3, 0.5, 10, 2.5, 5, 10 µm PM2.5, PM10 in float PM2.5, PM10 in integer small (> 0.5µm) and large (>2.5µm) for Pro model
Software Arduino, Python libraries Data logger (Windows), customized Python script
*: effective and maximum ranges

If we only look at the specifications, PMS7003 is very promising with the lowest cost, smallest footprint, available third-party library for DIY. Particle counting with 0.3 µm at 50% and 0.5µm at 98% efficiency making this sensor stands out for its wealth of outputs. The SDS011 has a sampling hose that can draw sample upto 1m. This is convenient for a setup with no fan installed. HPMA115S0's datasheet is pleasant compared to the first and the brand name brings some ease as well. DC1100 has been used as a middle-device and has shown a good correlation to lab-grade equipment.