Nanoparticles at the World Trade Center

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay

Nanoparticles are particles about the size of a wavelength of light, with dimensions measured in nanometers, or billionths of a meter. A millimeter is 1/1000 of a meter or about 0.04 inches (1/25 inch), a micron is 1/1000 of a millimeter and a nanometer is 1/1000 of a micron. Nanoparticles are of interest to health because they are tiny enough to get into the most remote parts of the lungs and even into the bloodstream. Internal combustion engines produce lots of nanoparticles and so do combustion processes of many types. Welding, for example, vaporizes small amounts of metal, which then oxidizes to form nanoparticles.

So after a barrage of four abusive phone calls in ten minutes from someone claiming to be with the Physics Department of 9-11 University, I visited the department's page and found this claim:

Analyses of air samples from the 9/11 WTC (""Ground Zero"") particle plume reveal the unexpected presence of many particles smaller than 1 micron (ie, nanoparticles). Among the smaller GZ particles, the distribution of their sizes clearly indicates that they were caused not by pulverization but by widespread molecular dissociation, which occurs only at energy levels higher than what could result from a collapse or even what can be achieved through the use of conventional weapons technology.

When matter is elevated to temperatures hotter than the surface of the Sun, molecular dissociation results. Disintegration chambers based upon this principle are available; other forms of energy can also break down molecules. When molecular dissociation occurs, covalent molecular bonds are broken, but atomic bonds survive. The resulting particles -- loose component atoms and fragmented molecules -- are far tinier than what occur in any conventional explosive event, including the most violent volcanic eruptions:

There are numerous links to a legitimate group called DELTA (Detection and Evaluation of the Long-Range Transport of Aerosols) that monitored aerosols after 9-11. A centerpiece of the 9-11 University page is this graph from the DELTA Web site:

The lower graph shows typical particle size distributions for typical aerosols, and the top graph is the size distribution from the World Trade Center. There's more fine material from the World Trade Center than we find from typical pulverization.

Maybe. The two graphs aren't saying precisely the same thing. What we really need is data on concentrations of nanoparticles in the air after pulverizing a mass of thousands of tons and letting the particles disperse. We can assume the coarser particles will settle out faster so a dust plume from a volcanic eruption or large landslide might not have exactly the same particle size distribution as static pulverized debris.

However, it turns out that pulverization is a red herring, because the chemical analysis of the WTC nanoparticles points to a different mechanism. The particles are anomalously rich in metals. And the DELTA group has a slide show that discusses the nanoparticles at length. It's at

A few excerpts from the slide show (emphases mine):

The surface and near sub-surface debris pile was hot enough to melt aluminum, make steel red hot, and burned until Dec. 19.

But this is still much cooler than typical sources of very fine particle metals such as power plants, smelters, and diesels.

We see organic species in the very fine mode that would not survive high temperatures

Explanation: The hot collapse piles are converting some [molecular] species to gasses that can escape to the surface of the piles and then form aerosols, a process that yields very fine particles.

In other words, the organic nanoparticles show that not only did we not have "temperatures hotter than the surface of the Sun," we didn't even reach the temperatures typical of normal sources of nanoparticles. So how did we form the nanoparticles? A process called "anaerobic combustion" or combustion under oxygen poor conditions. It happens all the time. Coal seams can burn for decades underground. Peat bogs can burn right through the winter under snow cover. Materials either react with oxygen to form partly oxidized compounds (carbon monoxide is a familiar example) or react with other elements like sulfur or chlorine (both readily available in any industrial setting). Volatile combustion products escape to the surface, oxidize completely, and create nanoparticles. The chemical data show that generally the most abundant metals in the nanoparticles are those that form the most volatile combustion compounds.

How Many Nanoparticles?

The chemical analyses show that a very large portion of the nanoparticles are organics. Concentrations of metals in the aerosols are typically in nanograms per cubic meter. In other words, in a cubic kilometer of air there would be one gram of that metal.

The graph above shows that nanoparticles are present at concentrations of a few micrograms per cubic meter of air. The total amount, even counting sulfates, in the particles smaller than one micron is 55 micrograms per cubic meter. In a cubic kilometer of air (a billion cubic meters) that would be 55 billion micrograms or 55 kilograms. For a size comparison that's roughly equivalent to a hiker on the top of Half Dome in Yosemite.

So let's be lavishly generous. Let's assume the nanoparticles are spread through a volume 10 kilometers on a side and a kilometer high (100 cubic kilometers). Let's assume steady winds of 20 kilometers per hour so that volume of air is cleared away and replaced every half hour, and let's assume it goes on for 100 days (three months). We have 55 kilograms per cubic kilometer or 5500 kilograms in our volume of air. That's 5.5 tons, replaced 48 times a day for a total of 264 tons a day, times 100 days = 26,400 tons. Since the towers weighed over a million tons, we can see that claims of exotic weapons turning most of the towers to nanoparticles are just plain ridiculous.

Ant the estimate above is wildly, insanely generous. The particles weren't dispersed through such a huge volume of air, the winds wouldn't have been that strong at street level, and the particle output dropped off rapidly after 9-11. But even if we're as insanely generous as the used-car salesmen claim to be, we just don't get enough nanoparticles.

By the way, the nanoparticles here should not be confused with the dust created by the collapse itself. The nanoparticles formed by combustion in oxygen poor conditions in the rubble after the collapse.

Bottom Line

Nutty 9-11 Physics
Really Nutty 9-11 Physics
Vaporizing the World Trade Center

Return to Pseudoscience Index
Return to Professor Dutch's Home Page

Created 30 January, 2006;  Last Update 24 May, 2020

Not an official UW Green Bay site