1.7. Sampling of PM

So, today we will quickly go over the method for sampling and processing of air. We already covered sampling of water and processing of soil. We will do sampling of soil today we’ll finish that also. But for sampling and processing of air, you may have two sampling objectives, one you are interested in looking at the composition and concentration of the vapor phase. In other words, we are looking at concentration of different components then we are looking at composition of the PM, the particulate matter associated with air.

In air sampling, there are two main objectives: measuring the composition of vapors in the air and assessing the composition and concentration of particulate matter (PM). Understanding these objectives helps in determining the best sampling methods and instruments to use for effective analysis.

Think of air sampling like going to a buffet. You first decide if you want to taste different dishes (vapor phase) or focus on specific food items like meat or vegetables (particulate matter). Depending on your preference, you will choose different plates and utensils to sample effectively.

So, when you say sampling of PM, we know that PM is classified again as PM 10, PM 2.5, and a whole bunch of things, and ultra-fine particles and so on, so you need to know what it is that you are looking for.

Particulate Matter (PM) is categorized based on size, with common classifications being PM 10 (particles less than 10 micrometers) and PM 2.5 (particles less than 2.5 micrometers). Knowing which type of PM you need to sample is crucial, as it dictates the sampling method and equipment.

Imagine trying to catch different sizes of fish in a lake. You need to use specific nets designed for the size of the fish you want to catch. Similarly, for PM sampling, the equipment must be suited for the specific particle size to ensure accurate results.

So, let us say that you are interested in sampling PM 10. The general design of PM 10 sampling, which means that PM 10 as the definition is everything all PM with less than the aerodynamic diameter of 10 microns which means you need a classifier.

To sample PM 10 effectively, a classifier is used to separate particles larger than 10 microns from those smaller. The sampling method involves an impactor that utilizes principles such as inertial impaction and Brownian motion to filter out unwanted larger particles.

Think of this like sieving flour to remove lumps. You pass flour through a sift, allowing the fine particles to fall through while keeping the large lumps behind. In PM sampling, the impactor acts similarly, letting smaller particles pass while catching the larger ones.

So a PM impactor, let us say you have an impactor. So, what will happen in the impactor is let us say that this is the flow of air and I have an impactor or something and what goes through the impactor or what is retained on impactor is anything greater than PM 10...

The PM impactor captures larger particles while allowing smaller ones (PM 10 and below) to pass through. This is achieved through a flow of air directed through the impactor, where large particles lose momentum and get trapped. The collected particles can then be weighed for analysis.

Imagine a basketball hoop with varying netting. Large basketballs (big particles) get stuck in the net, while smaller balls (small particles) drop through unhindered. The impactor works similarly, collecting larger particles while allowing smaller ones to continue flowing.

So, whatever I say now, may not be applicable 2 years later, so, it is always evolving depending on what you want. But the PM 10, PM 2.5 methods are fairly well established, and we will just go over that once.

Gravimetric measurement involves weighing the collected particles using a balance after they have been trapped by a filter. This method remains standard practice for quantifying PM, despite advancements in technology. Sampling duration affects the mass collected, and thus the measurements.

This is akin to measuring ingredients for baking. If you're making a cake and need a specific amount of flour, you can't just scoop a little; you need a substantial quantity to achieve accurate results. Similarly, longer sampling times ensure ample mass collection for reliable measurements.

So when we report PM, we report PM as concentration. If you are doing 8-hour sampling, it gives you an 8-hour average you are not able to say that the concentration is higher at this point within 8 hours...

PM concentrations are reported based on the volume of air sampled over a certain duration, often 8 or 24 hours. This provides an average concentration, but it may miss short-term spikes in pollution. Therefore, understanding the timing and duration of sampling is critical for accurate reporting.

Consider monitoring your heart rate. If you check it only once a day, you might miss moments of high activity or stress. Continuous or more frequent checks give a better overall picture of your health. Similarly, continuous air quality monitoring is essential to capture fluctuations in PM concentrations.

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