Question: Are there any methods to distinguish where particulate matter in the air comes from?

stevie asked on May 17, 2017 16:08
140 views | 3 answers | #14204


I'm wondering if there are any methods to tell where particulate matter in the air is coming from. For example, can you distinguish between particulate matter that would come off a road verses a farm or a frac sand mining site?



4 Comments

There is no clear way to conclusively prove PM came from a facility, but there are several inferences that can be drawn.

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I am trying to figure out the same question. So far, I have decided that the most accessible method seems to be using mapping technology to correlate data to GPS locations, then look for hot spots/concentrated areas. The downside is that a wider net would have to be cast to find source areas, or multiple source areas. Also, contacting local regulatory agencies who may already have data that will aid in site selection, potential source areas, etc. is sure to turn up something useful.

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There are a few methods but like most scientific work it isn't always conclusive.

Wind direction. A locally sited meteorological station with wind speed and direction would be your best clue. Otherwise a nearby met station from an airport or site like weather underground might help. More sophisticated would be a back trajectory, which NOAA has a free tool you can use online but it takes some effort to learn:

http://ready.arl.noaa.gov/HYSPLIT.php

Similarly upwind and downwind sampling. Setup in multiple locations around a suspected source and see if results correlate with wind direction.

Other pollutants. If you happen to have a complete set of air quality instruments at your site then looking at the other pollutant concentrations can be another clue. Likewise you can speciate the PM itself by using a x-ray scanning microscope. Other test are available like digestions with atomic absorption for metals, elemental carbon (burning to CO2) testing, etc. Then you need to look at what is nearby and what you would expect to see from the various potential sources. for example if you find X it COULD be from Y:

black carbon - burning wood, forest fires, agricultural burning

silica, minerals - natural sand/dirt/rocks, quarries, sandstorms

sulfur - coal, refineries, volcanoes

nitrates - diesel, mobile sources

Pollution source to receptor timing correlations. Timing the samples to be collected based on the suspected source operation schedule is another method. For example, if you know a quarry operates only Mon to Fri 7 am to 3 pm take samples when it's operating and also when it's not operating to measure operations vs. background. This is where real time instruments have a big advantage.

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As Mathew and David pointed out, there aren't readily available low-cost techniques for distinguishing among potential sources of particulate matter. Many atmospheric chemists will use Principal Components Analysis (PCA) to discern likely sources, and this approach involves a variety of chemical analysis (generally non-metals, alkali, alkali earth, and transition metals; sometimes organic compounds too) and significant modeling of source inputs and atmospheric transformations. Interpreting the PCA results often involves meteorological back trajectories (which David noted) too. It's a powerful tool.

For more accessible methods that could indicate some plausibility of a source of particulate matter, the upwind/downwind and receptor timing strategies David mentioned are key. Here is a wiki with more information about very basic study design for those different questions: https://publiclab.org/wiki/general-environmental-monitoring-study-strategies. The sections of interest for this question are probably "influence of specific mine" and "influence of specific process."

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