Most particle monitors control the flow of air into the monitor with an electric pump or fan. In contrast, a passive particle monitor measures particles that settle out of ambient air. Passive monitors promise to be less expensive and easier to deploy in the field than monitors relying on electrical components. Public Lab is working to replicate and lower the cost of a passive particle monitoring method developed at the University of North Carolina and University of Iowa, known as the UNC Passive Monitor. The system is very simple— a small glass slide sits underneath a screen. Small dust particles pass through the screen and land on the glass slide. The slide is imaged with a microscope, and the particles are counted and sized with the software ImageJ. To collect enough particles to make an accurate estimate, samples are deployed for seven days at a time.
_Deploying samples with Prof. Amber Wise at Chicago State. _
The passive monitors are more accurate than electronic monitors such as the Dylos, and using techniques like scanning electron microscopy (SEM), the types of dust can be distinguished in samples. These advantages are useful in identifying the source of pollution and the risks posed by silica. The two types of systems are complementary. Passive monitors, while accurate, integrate several days into a single sample, rather than the real-time or near-real-time data provided by electronic monitors.
Image of sample deployment in Chicago showing dust and droplets.
Read more on the topic: publiclab.org/passive-pm