By: Alan Connor
Tar has been known to accumulate in the lungs of smokers; but how does the tar actually get there? Some may say it is because the tar is inhaled or that it somehow evaporates into the lungs, others may not have a reason at all why this is possible. The inability of being able to answer questions like these have been an interesting topic of discussion. This discussion has caused many scientists to throw their hats into the ring to describe how and why it works. In a new paper published through the joint collaboration of the University of Massachusetts and Minnesota, Aerosol Generation by Reactive Boiling Ejection of Molten Cellulose by Andrew Teixeira and colleagues, describes a new mechanism of air pollution. This new mechanism, accurately named “reactive boiling ejection,” may finally explain how heavy compounds become airborne.
Reactive boiling ejection.
Aerosols are a solid or liquid substance that forms a cloud within a gas, and is often characterized as being as light as air itself. During experimentation, when cellulose was superheated it degraded forming aerosols. Cellulose is an organic substance that is found in all plants, and is also used in the creation of bio fuels. Organic material is known to be any material that is composed only of carbon, oxygen, hydrogen, and nitrogen. Inorganic material pertains to compounds that contain a metal. Many organic and inorganic materials were also formed through the degradation of cellulose and were found to be trapped within the aerosol.
After enough aerosols had accumulated within the molten cellulose, it formed a bubble. The aerosol bubble then worked its way to the surface of the cellulose where it was ejected and became airborne. The ejection of the aerosol bubble from the molten cellulose is an extremely fast reaction that takes place over the course of several milliseconds. Interestingly enough organic and inorganic products that had been caught within the aerosol were also forced airborne due to their entrapment within the aerosol. Another interesting part about this experiment was that the products that were trapped within the aerosol were usually nonvolatile, which means these products could not form vapors easily unless they heated to extremely high temperatures. Through continuous reactions these trapped compounds are hypothesized to become soot, organic gases like oxygen and carbon dioxide, and can also become heavier aerosol compounds.
Impact in the world.
In their paper, researchers describe:
“As much as 30% of degrading biomass can be converted to aerosols… as much as 60% of the inorganic content in the condensable products of biomass pyrolysis results from the generation of aerosols.”
Biomass is plant and animal matter that can be found within a given area. If that area were to be engulfed in flames, 30% of all that matter has the possibility of becoming aerosols. Then 60% of the inorganic content found could essentially have come from content that was trapped within these aerosols. As an example, if a pile of dry leaves was burned, 30% of the weight of the leaves would become aerosols and 60% of any inorganic content found within the air came from being carried by the original 30% of aerosols. This shows that a large percentage of air pollutants that comes from burning plant or animal matter is pulled into the air by these aerosols.
Wildfires are good examples of how an area can be engulfed in flames. These fires can essentially heat up plants to a point where cellulose, found within biomass, can become molten. Through chemical shifts within the heated biomass aerosol jets of large quantities are ejected into the air from the burning plant matter. The ejected aerosols make their way into the atmosphere causing alterations within high altitude chemistry, which could be the cause of various environmental conditions like acid rain.
Since aerosols can be formed from burning plant matter, even small things like smoking can cause their formation. This may also be why tar has been found in smokers lungs. The tar formed from a burning cigarette can be trapped within aerosols. Since the person is inhaling at the same time the cigarette is burning, the aerosols are forced into the persons lungs. The aerosol may be broken apart within the lungs before exhaling, causing tar and other substances to be left within in the lungs.
Aerosols may also be capable of depositing substances in areas other than their origin. If the atmosphere is cold enough the aerosols may condense, which could cause whatever was caught within the aerosol to be released. This may be a reason why high levels of inorganic content have been found in areas of little to no human contact. It is important to note that aerosols themselves may not be seriously dangerous but the substances that are trapped within them can be.
Improving mechanisms and future implications.
The process of reactive boiling ejection is still being conducted since many mechanisms of the transport and degradation of various substances are not well understood. Further research is being conducted on these mechanisms and how they may interact with one another. To complete this understanding would mean the increase in predictability of these phenomena. This information could also lead to the formation of processes that can reduce the amount or purity of aerosols that are being released.
Broad implications of these advances include the decrease of pollutants caused by cars, reduction of pollutants from burning waste, and the reduction of pollutants that end up into lakes, streams, and rivers as a result of rainfall.
Energy Environ. Sci., 2011, 4, 4306