Imagine walking through a room filled with millions of tiny, nearly invisible specks floating in the air. Your eyes might not see them, and the total weight of these particles might seem insignificant, like dust barely registering on a scale. But these tiny invaders are not harmless—they are stealthy agents of pollution, small enough to slip through the cracks of your body’s defences and cause real damage.
Traditional mass measurement methods (µg/m³), like weighing the dust on a scale, can give you a rough idea of how dirty the air is. This works well for PM10 and PM2.5 but it can be misleading when it comes to understanding the real danger posed by sub-micron particles.
These tiny particles might not weigh much, but they exist in enormous numbers, creating a swarm of potential health hazards.
Source: See The Air - Particulate Matter (PM2.5) Mega Guide
Instead of focusing on how heavy the dust is, particle counting measures the actual number of particles in the air. This method is like counting every single bee in the swarm, giving you a clearer picture of the threat level. When we start counting these particles, the numbers can be staggering, revealing a much more accurate story about the air we breathe.
Focusing on PM2.5 can lull us into a false sense of security
In countries with high outdoor pollution levels, the difference an air purifier makes to indoor PM2.5 levels is staggering both at home and in the workplace. However in the UK, levels tend to be much lower indoors except when cooking or wood-burning is taking place. What about in a work environment where these daily spikes are less likely to be seen?
The table below shows PM2.5 and PM5 data in a 60m² hospital lab, before and after our Blast Mini was switched on at top speed:
| Before | After* | |
| Mean 2.5u | 382.2 | 477.82 |
| Mean 5u | 213.39 | 498.15 |
* This is a one hour snapshot with 3 people in the lab 'before', 6 people 'after' so the tiny increase in larger particles is likely linked to people entering and leaving the lab
The PM2.5 and PM5 data shown here are actually 'particle counts'. If we convert this into the widely familiar 'mass concentration' (µg/m³), both before and after PM2.5 data readings are below 5 µg/m³, the threshold set by the World Health Organisation in 2022.
So if levels are below W.H.O. guidelines without an air purifier, you could argue against the benefit of air filtration in this hospital.
However when we look at the PM0.3 data, we get a very different picture:
| Before | After | |
| Mean 0.3u | 531345.5 | 219665.8 |
Over 99% of the hospital PM2.5 reading is actually PM0.3 (or smaller)
When you focus on the PM0.3 data, which we know is the most harmful, the Blast Mini actually reduced sub-micron particles by almost 60%!
If we look at the hospital particle count data above, 99% of PM2.5 data is actually PM0.3, which correlates with the chart below:
Mass concentration measurements (weight) can miss the bigger picture as sub-micron particles don't weigh much. Measuring particle number by size distribution (particle count) provides a more accurate representation of the potential health risk.
The case for particle counting vs mass measurement
Particle counting is especially crucial in environments where mass-based measurements might show low levels of pollution. For instance, in a seemingly 'clean' urban area, the mass of PM2.5 might be within 'safe' limits, but a closer look with particle counting could actually reveal millions of ultrafine particles from car exhaust or other industrial processes.
Car manufacturers can meet PM2.5 limits imposed on them by reducing PM2.5 emissions while increasing ultrafine particles, which are not currently measured! Yet it is these particles, though small, that are numerous and can have serious health impacts.
We need more low-cost air quality monitors that use real measurements, not extrapolation of data taken from larger particles. The last time we checked, Dylos was the only true particle counter under £500 but even this only goes down to PM0.5 for the DC1700 model (PM1 for the DC1100 model).
Just focusing on PM2.5 in countries with lower levels of air pollution can give the impression that HEPA filters add little value to the indoor environment.
HEPA filters trap virtually 100% of nano-particles including viruses and bacteria. But unless we start monitoring at a sub-micron level, the health benefits of cleaning the air might not be so obvious.
