Frequently Asked Questions: (2) What & Why to Monitor for Particulate Pollution?

PM is generally measured in terms of the mass concentration of particles within certain size classes:

• Total suspended particulates (TSP, with aerodynamic diameter <~30 microns (μm)
• PM10 (with an aerodynamic diameter of less than 10 μm, also referred to as coarse)
• PM2.5 (with an aerodynamic diameter of less than 2.5 μm, also referred to as fine)
• Ultrafine PM are those with a diameter of less than 0.1 micron

These size distinctions result because coarse and fine particles come from different sources or formation mechanisms, which lead to variation in composition and properties. The range of sizes also affects the atmospheric lifetime, spatial distribution, indoor-outdoor ratios, temporal variability, and health impacts of particles.

To date, most measurements are conducted for PM10 and most of the developing country cities still monitor PM10 as an indicator. Slowly, with the growing knowledge on the higher importance of PM2.5 and finer fractions on human health, the new regulations are prescribing a focus change and make the PM2.5 the new criteria indicator.

What to monitor is a tricky question. Depending on the purpose of the experiment, the monitoring equipment and the monitoring scales change. For example, for a regulatory body, it is important to know the ambient levels of criteria pollutants only, at various designated locations, along with some meteorological parameters. However, for a research body, it is important to measure more than the criteria pollutants, to better understand the chemical mechanisms leading up to the measured ambient levels and also to study the evolution of the pollution.

What to monitor also depends on the financial status of the city or concerned institution. It is important that as many monitoring stations are established as possible, to better map the city or the area of interest, for each of the pollutant in concern, and this is highly dependent on the local institutional capacity, not only from procuring it, but also to operate and maintain the same.

Since the PM pollution is of the concern for most of the growing cities, effort should be made to monitor the same. With the growing advances in technology, there is a wide array of monitors, in size, precision, and cost, available to the users, and an informed decision will help make the most of what is available.

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