When our laser hits the PM, light scattering occurs. The 3443 collects the amount of scattering light and calculates the mass concentration in proportion to the luminescence. The mass concentration is based on the density of PM, thus gravimetric sampling is required if the density is unknown.
PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. Particle pollution includes:
- PM10: inhalable particles, with diameters that are generally 10 micrometers and smaller; and
- PM2.5: fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller.
- How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter – making it 30 times larger than the largest fine particle.
Sources of PM
These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Most particles form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries and automobiles.
A dust monitor measures the mass concentration of particulates in the air. This is typically expressed in milligrams of particulates per cubic meter of air. This makes the dust monitor very useful for monitoring substances that could negatively impact a person’s health.
We have two different types: a light-scattering monitor model 3443 (the industry standard) and a piezobalance monitor model 3521.
There are two key differences between the units. The first is that the light scattering model 3443 requires a K-factor to accurately report the mass concentration of particulates, while the piezobalance model 3521 does not. The second key difference is that model 3443 is suitable for long-term monitoring while the piezobalance model 3521 needs to be cleaned every hour to function correctly. The piezobalance monitor is also capable of measuring oil mist for specialized applications.
In order to accurately report on the mass concentration of particulates that it has measured a light-scattering particle counter needs to know the density of the particulates at the measuring site. Without this the unit will still count particulates, but it cannot accurately gauge the concentration in the air. To obtain the factor it is necessary to obtain a gravimetric sampling of the particulates at the measurement site. This is done by collecting particulates in a special sample container and then sending it to a lab for analysis.
Yes, all our instruments come with a NIST TRACEABLE CALIBRATION certificate.
Annual calibration is recommended to ensure accuracy. However, this can vary based on how often the dust monitor is used and the environments it’s used it. Also, some companies have an SOP in place that specifies how often the instrument will need to be serviced. More specifically, regulatory compliances may dictate the calibration interval.