Air and Breathing
Suspended particles in the air create aerosols that are important to the behavior of whole atmosphere and play a role in determining human disease. Natural sources of atmospheric particles are volcanoes, dust storms, spontaneous forest fires, tornadoes and hurricanes. Clouds are a product of aerosols that seed the formation of water droplets. Human air pollution now dominates aerosol production over cities with negative health effects. Thick aerosols are obvious as haze and contain a complex system of particles with adherent toxic gases such as sulphur dioxide. NASA’s earth observatory information states:
Aerosol particles may be solid or liquid; they range in size from 0.01 microns to several tens of microns. For example, cigarette smoke particles are in the middle of this size range and typical cloud drops are 10 or more microns in diameter. The majority of aerosols form a thin haze in the lower atmosphere (troposphere), where they are washed out of the air by rain within about a week. Aerosols are also found in a part of the atmosphere just above the troposphere (stratosphere). A severe volcanic eruption, such as Mount Pinatubo in the Philippines in 1991, can put large amounts of aerosol into the stratosphere that remain there for many months, producing beautiful sunsets around the globe, and causing summer temperatures to be cooler than normal. Mount Pinatubo injected about 20 million tons of sulfur dioxide into the atmosphere, cooling average global temperatures over the following year by about half a degree.”
Aerosol particles from factories and power plants increase the number of droplets in clouds that reflect more sunlight, retain water and do not produce rain. Man made aerosols change local weather systems. The effect of greenhouse gases such as carbon dioxide is warming the planet. The effect of aerosols is cooling the planet. The net effect of air pollution depends on the ratio of warming gases to cooling particles.
Over land up to a quarter of the total airborne particulates are pollens, fungal spores, bacteria, viruses, plant and animal matter. Air inside buildings contains local aerosols that are sometimes more concentrated and more toxic than outdoor air. The term dust refers to the larger particles in the aerosol that settle on walls and furniture.
A smoker in the living room of a house produces a toxic aerosol that permeates the rest of the house. Smoke particles settle on walls and every object in a room so that a smoker leaves a trail of contamination that non-smokers smell as soon as they enter the room.
Indoor air contains a living aerosol of microorganisms that infect or trigger allergic reactions. Spores of bacteria and fungi are microscopic and may persist for months or years. You can see the indoor aerosol under the right lighting conditions, such a sunlight streaming through a window. The abundance of microorganisms, even in a very clean house, surprises most people who have tests done to assess air quality.
NASA Earth Observatory. Scientific Studies of Aerosols. Online http://earthobservatory.nasa.gov/Library/Aerosols