Air quality
The Air You Breathe
Particle matter
What do we breathe?
Particles, or particulate matter (PM), are subdivisions of solid matter that surround us. PM comes in many shapes and sizes and can be solid particles or liquid droplets. It is everywhere: in the atmosphere, at ground level, and even in our homes.
PM floats through the air and, with every breath we take, we breathe it in—even when most of it is not visible to the naked eye.
Particle monitoring
Why monitor particles?
Although too small to see, PM is the air pollution that most commonly affects people’s health. Depending on their size, particles are a leading cause of respiratory and cardiovascular problems. When a person inhales, air contains visible and microscopic particles that can enter through the nose and mouth.
Depending on their size and composition, particles can travel deep into the respiratory system and may be more toxic. Particles smaller than 1 µm are likely to reach the peripheral airways and alveoli or be exhaled; particles from 1–5 µm deposit in the large and conducting airways; and particles larger than 5 µm predominantly deposit in the oropharynx. Effects include asthma, lung cancer, birth defects, and premature death. PM pollution causes around 200,000 deaths per year in Europe.
For example, a person breathes an average of 11,000 litres of air per day. The breakdown of particles breathed per day by particle size is as follows:
| Particle size (µm) | Particles breathed per day |
|---|---|
| 0.1 | 11,000,000,000 |
| 0.2 | 2,607,000,000 |
| 0.5 | 387,200,000 |
Scale
How big is a micron?
Forty microns are the smallest particles that can be seen by the human eye.
Measurement principle
How do particle analyzers work?
A particle counter is an instrument that detects and counts particles. It works on the principle of light scattering, light blocking, or condensation to detect and measure particle size or size distribution. When a particle is illuminated by a light beam, it is redirected (light scattering) or absorbed (obstruction).
The redirected or lost light, depending on the method used, is detected by a photodetector, measured, and the particle is counted and tabulated into standardized counting bins. If direct imaging is used, a halogen light illuminates particles from the back within a cell while a high-definition, high-magnification camera records passing particles. The recorded video is then analyzed by computer software to measure particle attributes.
Sensor anatomy
A particle counter is made up of the following components:
- Light source (bright laser light)
- Reflector
- Light sensor
- Electronic signal-processing circuit
