3.2. Differential Mobility Analyzer

So sometimes you want chemical composition, and you are getting a lot of material. So you are, again, you are looking at composition that composition will give you a lot of clues to where it is coming from just getting mass distribution is not enough.

Understanding the chemical composition of particulate matter (PM) is crucial for identifying its sources and effects. Simply measuring the mass distribution of PM does not provide enough information. In many cases, multiple sources may contribute to the PM in the air, meaning that without knowing its composition, we cannot accurately determine where it originates from. Hence, analyzing the chemical makeup gives essential insights into environmental sources.

Imagine you find a mysterious brown powder at a crime scene. If you only know the weight of the powder, you might still not know what it is or where it came from. However, if you analyze its composition and find traces of cocoa, sugar, and flour, you might deduce it’s cake flour, helping you understand more about the crime context.

What we call a source apportionment, we have source of apportionment and you can do source apportionment as long as you get a very specific signal for a source.

Source apportionment refers to the process of determining the origins of pollutants. It can be conducted effectively when clear and distinguishable signals from different sources are available. If signals overlap or are mixed, it becomes challenging to ascertain the exact source of the particles. Thus, distinct chemical characteristics play a pivotal role in effective source apportionment.

Consider a music concert where many bands play. If you can easily identify the distinct sounds of the drums, guitar, and vocals, you can figure out which band is playing at any moment. However, if bands are overlapping with similar sounds, it becomes harder to tell who is who, just like with mixed pollution sources.

Now the theory is further down we are going further down you are already in the nanometer nanoparticle range is few 100 nanoparticles, very difficult to measure.

Particle classification becomes increasingly challenging as we analyze smaller particles in the nanometer range. For traditional methods that rely on mass and momentum, measuring such tiny particles may be inadequate. Therefore, alternative methods, such as utilizing electrical mobility, become necessary to distinguish and classify these particles effectively.

Think of trying to filter tiny grains of sand from a large batch of water. If the sand pieces are very small, conventional means may not suffice, but using charged electrostatic methods would allow for better separation and identification, similar to how electrical mobility helps with nanoparticles.

So electrical mobility, and the instrument that is used to make is called as a differential mobility analyzer. And this instrument, what it does is it charges all the particles coming in.

A Differential Mobility Analyzer (DMA) is an instrument that uses electrical mobility to classify and analyze particles. It charges incoming particles based on their size, and when a potential difference is applied, the particles experience different forces based on their charge and size, allowing for their separation. This method allows for a specific size particle to be selected and analyzed further.

Imagine a carnival game where you shoot balls through hoops. The hoops are different sizes, and you need to aim differently for each. Similarly, in a DMA, the varying size and charge of particles dictate how they move through an electrical field, allowing precise sorting based on size.

So, that method of measurement called as a condensation particle counter (CPC).

Condensation particle counters are used to measure particles in the nanoparticle range (usually under 0.3 microns). They work by allowing these small particles to grow in size through a saturated atmosphere of vapor, making them easier to detect. This indirect measurement allows the determination of the number of particles present, even when they are initially too small to count directly.

This is similar to watching tiny raindrops form on a window during a rainstorm. At first, you can't see the droplets individually, but as they coalesce into larger drops, they become more visible. The condensation particle counter takes tiny particles and makes them detectable by helping them grow.

So, very complicated instrument, the entire thing is called as a scanning mobility particle sizer or SMPS very expensive instrument cost around 50 lakhs, 60 lakhs as you can imagine.

The Scanning Mobility Particle Sizer (SMPS) is an advanced and costly instrument utilized to measure particle size distributions from 10 nanometers to 10 microns. It integrates various components, including a differential mobility analyzer and condensation particle counter, to provide extensive particle data in a single sweep. Despite its high cost, it offers critical insights into particle characteristics essential for environmental studies.

Think of the SMPS as similar to high-tech weather radar that provides detailed readings of storm systems. Just as the radar gives comprehensive data crucial for understanding and predicting weather patterns, the SMPS delivers vital particle information needed for analyzing air quality.

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