14. April 2026

Particulate Monitoring Performance Indoors

Within this article we are going to take a factual look at the type indoor air quality monitoring systems currently avaialble on the market. To be more precise, we shall take a look at particulates, the types of sensors avaiable, how they measure and which are more accurate. For our purpose we shall review the sensors in two well regarded products. The Nosmotech BuiltAir and the Air Gradient One

Different indoor environments will behave differently, specifically high humidity environments may provide very different results

Sensor Types

The two sensor types we will review are the Terra Next PM and the PlanTower. Both use laser light scattering and measure the scattered light intensity. The Terra uses multiple channel particle counting. The Plantower uses a single channel:

Comparism Terra PlanTower Size Bins micron 0.3-0.5 0.3 to 1.0 or 1.0 to 2.5 o4 2.5 to 10.0

0.5–1 µm

1–2.5 µm

2.5–5 µm

5–10 µm

To Sumarise

The Plantower measures one optical signal( scattered light) and converts that into PM1/PM2.5/ PM10 using internal assumptions and effectively behaves like a nephelometer (bulk signal device). This means it does not truly resolve particle size independently.

The Tera Sensor Next PM uses multi-channel particle counting, this separates particles into bins. which means it actually measures size distribution, then derives PM1/ PM2.5 and PM1

The means that the Plantower provides good correlation in many studies

• But:
  • Strong dependence on aerosol type
  • Needs calibration
  • Output is still derived from a single signal

NextPM

• Very strong correlation (lab R² > 0.99)
• But:
  • Systematic underestimation vs reference instruments
• Highly stable and consistent

Winner: NextPM (more stable + physically grounded)

Plantower can appear “accurate enough” after calibration but where things really go amiss is on the measurment of larger particles. PM1's can actually appear similar to pm2.5's and PM10's are often unreliable this is because it is estimating distribution not measuring it. Tera Next PM provides clear seperation of particle sizes and bias is consitant because we are actually measuring particle size.

BuiltAir from Nosmotech

Simple Anaology Imagine you are looking into a frosted glass jar containing marbes. You can probably see the quantity of marbles within the jar but cannot define anything further, i.e. how many are small marbles and how many are large marbles, you are guessing This is the Plantower. Next consider sorting the marbles into size buckets and counting each one. This is the Tera Next PM. One further point. The Tera Next PM also has a heated inlet function. This can be used where humdity is high and where the particulate nature may be quite aggressive. This is one more reason to chose the BuiltAir monitor for more accurate measurement where research and for more complex applications.www.nosmotech.com