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Aerosol Basics

:: Section 1

What is an aerosol?

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An aerosol can be defined as a system of solid or liquid particles suspended in air or other gaseous environment. Aerosols vary in size and composition, they can be naturally or manmade generated, and thus there are a wide range of them, from flame synthesized nanoparticles and nanomaterials (good aerosols), with fundamentally new properties and functions because of their small size (<100 nm) to airborne particulate matter resulted from the industrial production of nanomaterials, and viruses that have a negative effect in visibility and human health (bad aerosols).




Transmittance electron microscope (TEM) image showing titanium dioxide (TiO2) nanoparticles synthesized using an aerosol flame reactor, in which the nanoparticles are produced by combustion of a vaporizable precursor (e.g. TiCl4). Two important issues in the production of TiO2 nanoparticles by this method include the control of size and crystallinity of the resulted particles, and their biological impact. There are several methods reported for the production of TiO2 nanoparticles, however flame synthesis provide good control of the production process and it is relatively easy to scale up for industrial purposes. TiO2 nanoparticles are widely used in applications such as photocatlysts, pigments and cosmetics additives.



Scanning electron microscope (SEM) image of silica (SiO2) nanoparticles. Among the various methods to produce SiO2 particles, flame synthesis and spray pyrolysis -in which the nanoparticle formation occurs by evaporation of the droplets of a precursor solution (e. g. Tetraethyl orthosilicate, TEOS) in a furnace- seem to be the most suitable industrial approaches for gas-phase synthesis of SiO2 nanoparticles. A novel application of silica nanoparticles is as electrochemical immunosensor for the detection of cancer.

Iron oxide


Transmittance electron microscope (TEM) image of iron oxide nanoparticles synthesized in a flame aerosol reactor using iron penta-carbonyl as the precursor. Iron oxide nanoparticles have drawn considerable attention due to interesting magnetic properties with a wide range of applications, including recording media, pigments, and magnetic fluids; in the medical field, for example in drug delivery, cell separation, hyperthermia, and cancer therapy.

              Carbon nanotube                        


TEM image showing carbon nanotubes. Carbon nanotubes are a new form of pure carbon visualized as rolled hexagonal carbon networks that are capped by pentagonal carbon rings, they are of interest because of their high strength, electrical conductivity, electron affinity, and structure. Carbon nanotubes can be produced by a number of methods that include gas phase process such as electric arc-discharge, laser vaporization, electrolysis, and hydrocarbon pyrolysis over metal catalyst (typically iron or nickel). Carbon nanotubes have plenty of applications in electronic devices, polymer additives, and as catalyst support materials.



Micrograph of Electromelia Virus, commonly used to model infection from variola virus, the causative agent of smallpox; it has a length of 200 nm to 400 nm. Virus aerosol are a great health concern because of easily propagation, moreover aerosol transmission of viral diseases could result from a deliberate release in an act of bioterrorism. Thus, efficient, cost-effective control technology is necessary for the removal and inactivation of biological aerosols. Currently research on the inactivation of virus aerosols is carried on.

Ambient aerosol


SEM images of ambient aerosols with different shapes; (A, B) aggregated; (C, D) spherical; (E, F) fibrous; and (G, H) other. Ambient aerosols have a potential role in causing various harmful health effects. There are several characteristics of the ambient particulate matter that may be responsible for specific health effects. Not only are the mass concentration of particles but also particle size, shape, and chemical composition important to determine such effects. Despite the morphology of ambient aerosols plays a significant role in identifying the physical characteristics of that aerosol, not much is known about the morphology.


Nanoparticles: particles with diameter below 100nm that show novel properties due to their small size. They are industrially produced by aerosol methods


Environmental Engineers American Academy of Environmental Engineers
Chemical Engineers American Institute of Chemical Engineers
AGU American Geophysical Union (Atmospheric Sciences Section)
NIEHS National Institute of Environmental Health Sciences

Valuable Reading:

  • W. C. Hinds, Aerosol Technology, 2nd Edition, Wiley Interscience
  • S. Pandis and J. H. Seinfeld, Atmospheric Chemistry and Physics: Form Air Pollution to Climate Change, 2nd Edition, John Wiley & Sons
  • Finlayson-Pitts, B. J. and Pitts, J. N. J. Chemistry of the Upper and Lower Atmosphere. Academic Press: New York, 2000