Microscope Images of Dust

Ever wonder what blown dust looks like under a microscope? No, you haven’t? Well then this post isn’t for you. Here we’re going to look at collected dust particles under extreme magnification, by way of the scanning electron microscope at the material science department at Stony Brook. If you’re interested in learning more about the machine check out the wikipedia page on how scanning electron microscropes work and then check out the gallery of images taken from the scanning electron microscope at Stony Brook, maintained by Jim Quinn. Some very cool shots over there.

The images we’re about to look at are taken at a very high magnification. The particles we are looking at are in actuality tiny, but here will appear to be quite large. From these images we get an idea of how big the dust is, how it is shaped, how dense it is on the filter and what the dust particles are made of (by mass spectroscopy).

The filter we are looking at is from Pensacola, Florida. We chose Florida because it is apt to be impacted by dust from North Africa (the Sahara Desert) and possibly from Asia too. This filter is from a particularly dusty period. The sample was shared with us by Atmospheric Research Inc, and we are grateful for their assistance.

The unit of length is measured in microns, or to be technical micro-meters. The human eye can detect objects down to about 40 microns in size. A grain of salt is about 60 microns in size. A human hair is 70 to 100 microns in diameter. The objects we are looking at are between 1 and 10 microns generally, so much smaller than what the naked eye can detect.

Image #1:

The spider-like dark grey strands are Teflon filbers. They interconnect in a weave to form the filter on which particles in the atmosphere are collected. I was quite surprised that the filter looked like this. I expected it to be much more solid, but as you can see it is quite porous, well at least on a particle level.

On the filter we see three flakes of dust one in the top left, one in the top right and one in the center. The dust appears to be white on the image. The brighter the color on the image the higher the atomic weight of the particle. Thus, heavier elements appear to be bright white, and light elements appear to be dark grey. The dust particles are well rounded and look to be quite physically weathered.

On the bottom of the image, on the footer, you can see the scale bar. Using the scale bar at the bottom we can estimate the dust particles to be about 2 microns in length.

From the spectral analysis, we see that this particle is composed mainly of silicon and oxygen, suggesting that this is likely sand. (Note if you are looking at the spectral analysis, that the fluorine peak is from the Teflon filter itself).

Image #7:

This is a much larger particle, coming in at about 5 microns in width and 10 microns in length. It has much sharper edges, suggesting it has not been weathered much.

Spectral analysis shows that this particle is composed of iron, nickel, chromium, calcium and aluminum; as well as silicon and oxygen. This suggests it is an iron oxide of some variety.

Image #10:

Again this is a very large particle, coming in at 7.5 microns in width and nearly 15 microns in length. The larger the particle the more likely it is from local sources. Large particles tend to be heavier and thus fall out of the atmosphere quicker. Thus we expect particles from distant sources like Africa and Asia to be small.

Spectral analysis suggests that this particle is composed of iron, chromium, calcium, and aluminum; as well as silicon and oxygen. This is likely an iron oxide as well.

Image #11:

This mammoth particle is over 20 microns in width and 15 microns in length. Note how smooth it looks, with rounded edges. There appear to be little deposits growing on top of the particle.

Spectral analysis shows that this particle is rich is calcium, oxygen, aluminum and silicon. It is likely calcium carbonate – with some sort mineral contained in the matrix.

Image #12:

Now we are looking at the type of particles that make up windblown dust, small and spherical, ready for flight. This particle weighs in at less than 1 micron in diameter.

Spectral analysis shows that it is composed of nearly pure lead!

Image #13:

Here is another small fellow (bright spot, center of image). He is composed of iron, zinc and sulphur.

Image #15:

Look in the center of the image for a small grey, box like image. The particle is about 1.5 microns by 1.5 microns. This is a crystal of pure sulphur. It has nearly perfectly squared edges.

Image #21:

Soil, dirt and sand aren’t the only particles in the atmosphere. Here we see signs of living material in the atmosphere. Take a look at the honey comb like particles in the middle of the image. I’m not a marine biologist, but those appear to be diatoms (a type of plankton from marine environments) or diatom like cells on top of a dust particle. It’s hard to tell but the strand of diatoms seem to continue downward over the dust particle, before their signal is subsumed.

I hope you enjoyed your fun science pictures of the day!

A link between dust and hurricanes?

At right, Hurricane Floyd in the late summer of 1999 before it made its northward turn up the eastern seaboard of the United States. Image from NCDC.

Hurricanes capture the human imagination. Hurricanes are the perfect natural disaster for the 21st century. Unlike their brethren disasters, hurricanes are somewhat predictable, their massive symmetric swirl can be seen on satellite images days before the hurricanes reach the short of a tropical island or the coastline of a massive continent. Best yet, hurricanes are beamed into your livingroom via satellite. Whether you are watching a panting weatherman on CNN yelling barely coherent words about how this is the worst hurricane to hit since the last one, or you are watching on the Weather Channel as some slightly idiotic meteorologists stations themselves 15 feet from the ocean as 95 mile per hour winds batter their highly makeuped faces, hurricanes are something that everyone can understand, successfully visualize and ultimately relate to.

At right, dust blows off the Sahara Desert over Western Africa on it’s way across the Atlantic. The presence of dust can be seen as a gentle haze over much of the left 1/3 of the picture. The image was taken by MODIS satellite June 6, 2008.



So, maybe it’s more surprising that it ought to be that hurricanes can be impacted by the presence of tiny earthen particles in the atmosphere, known as mineral dust. Mineral dust is picked up by the wind from dirt, dust and sand on the Earth’s surface and blown hundreds or thousands of miles, sailing across oceans on rivers of air high above, often landing on differing continents. When the wind direction and speed are just right and the soil conditions just so, lots of dust can be picked up at once, and the sky darkened as dust obscures the sun’s rays. These impressive massive floating storms of dust are known as dust storms, and recent findings suggest that these dust storms makes hurricanes less likely to form or thrive in their presence.

Recently, this topic was discussed on all things considered on NPR. Follow this link and click on the red button with a speaker icon to take a listen to the report.

Dust seems to oppose hurricane formation in two ways, first by absorbing sunlight it cools the ocean beneath it. Hurricanes rely on warm waters to gather the energy and moisture necessary for them to develop into intense storms. Secondly, dust tends to be found in a dry, hot airmass lofted between 1 and 5 kilometers above the surface. This dry, hot layer tends to choke the hurricane by stealing moisture from the storm, and interfering with the convection that provides the heat engine for the hurricane.



Interestingly enough, dust storms are maximized each year during the summer, coincident with hurricane season. This coincidental timing increases possibility that there are meaningful dust – hurricane interactions each season. The figure to the right if from research we have done here at Stony Brook, showing the average amount of absorbing aerosols, including dust, that are found in the atmosphere each season. As you can see there are a lot of these aerosols over Africa, and as you head westward it slowly decreases. This suggests that dust plumes pick up large quantities of dust, which gets transported long distances, increasing the likelihood that it has a chance to interact with tropical systems.

Dust is what I study, and this finding is quite exciting. I am working hard to find ways to anticipate the quantity of dust storms that will occur each year based on meteorological conditions. If said forecasts help to further predict how many hurricanes each year, I will have made a lasting contribution to humanity, which is always the goal of a research scientist.