June 5, 2005

What is in the Air?

A hosted post from Dr. J. Vanderlei Martins ? JCET/UMBC - NASA GSFC

The air that we breath every day is primarily composed of gas molecules, but it also contains a large variety of suspended solid and liquid particles. These particles in suspension in the atmosphere are called aerosols. Aerosols are present in many aspects of our daily life. When we see smoke from a fire, truck exhaust, cigarette, etc., we are usually observing the effects of light being scattered and absorbed by aerosol particles rather than gas molecules. Similarly, aerosol particles interact with solar radiation scattering and absorbing energy that contributes to the heating or cooling of our planet. Aerosols are also essential for the formation of clouds droplets on Earth, acting as condensation nuclei for the water vapor molecules.

This figure below

shows some examples of aerosol particles collected on filters and analyzed under the scanning electron microscope in collaboration with the Institute of Physics of the University of Sao Paulo, Brazil. Generally, aerosols cover a broad range of sizes from a few nanometers all the way to hundreds of micrometers, and all sorts of shapes. Here we show a) particles from the Sahara desert that traveled in the atmosphere all the way to the Virginian Coast in the US, b) particles from biomass burning fires in the Amazon during smoldering phase emissions (low temperature emissions after the fire), c) a large cluster aggregate of biomass burning particles from the Amazon emitted during flaming phase (high temperature) and collected near the fire, and d) an example of air pollution particles from China.

The black circles showed in each figure correspond to filter pores, while the aerosol particles are showed in white or gray tones. The scale on the bottom of each image shows a 1 micrometer reference for the particle size. The mineral dust particles in a) are irregular and relatively large compared to the remarkably spherical and relatively small smoldering particles from biomass burning. The biomass burning particles are primarily composed by transparent organic material with a smaller fraction (5-20%) of an efficient light absorbing material called “black carbon”. The cluster aggregate can reach several tens of micrometers near the fire but they usually won't last very long in the atmosphere, usually breaking in smaller pieces or condensing in more compact particles. Particularly in the Amazon, these large clusters have not been observed more than a few miles downwind from the fire. The China pollution particles, collected by in collaboration with the University of Maryland Baltimore County and College Park, are composed of a blend of spherical particles and irregular and complex cluster aggregates.

Posted by Ray Hoff at June 5, 2005 7:07 PM