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2 22.In addition to gases, the atmosphere contains solid and liquid particles that are suspended in the air. These particles are referred to as aerosols or particulate matter (PM).

3 They are removed when rain or snow carries them out of the atmosphere or when larger particles settle out of suspension due to gravity Size of aerosols. between 0.01 and 10 micrometers in diameter Aerosols are found where? in the lower troposphere How long do they reside here? a few days State the (2) ways by which they are removed.

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5 24. Complete the table to distinguish between large aerosol particles and small aerosol particles. Type of Aerosol Particle Size Generated/Produced - Examples Large usually 1 to 10 micrometers in diameter generated when winds blow sea salt, dust, and other debris into the atmosphere Examples: sea salt, dust Small (fine) diameters less than 1 micrometer produced when precursor gases condense in the atmosphere Major components of fine aerosols are sulfate, nitrate, organic carbon, and elemental carbon. Examples: black carbon, soot

6 25. High concentrations of aerosols are thought to be a major cause of what? cardiovascular disease and are also suspected to cause cancer

26.U.S. Environmental Protection Agency (EPA) set limits to the size of aerosol particles in 1987 and tighten them again in What were the limits? What was the reasoning behind these acts? Scientific research into the negative health effects of fine particulate air pollution spurred the U.S. EPA to set limits in 1987 for exposure to particles with a diameter of 10 micrometers or less, and in 1997 for particles with a diameter of 2.5 micrometers or less.

27.Explain the important radiative effects aerosols have in the atmosphere Aerosol particles are efficient scatterers of radiation (light) because their sizes are orders of magnitude larger than the wavelengths of visible radiation (0.4 to 0.7 micrometers.

Haze pollution, Acadia National Park, Maine Courtesy NESCAUM, from hazecam.net.

When relative humidity is high, aerosols absorb water, which causes them to swell and increases their cross-sectional area for scattering, creating haze.

29.Without aerosol pollution our visual range would typically be about 200 miles, but haze can reduce visibility significantly. 30. Aerosols have a cooling effect on Earth's climate when they scatter solar radiation because some of the scattered light is reflected back into space. In contrast, some aerosol particles such as soot absorb radiation and have a warming effect.

31.List (3) ways aerosol particles influence Earth's climate indirectly. they serve as condensation nuclei for cloud droplets they serve as condensation nuclei for cloud droplets increase the amount of radiation reflected back into space by clouds increase the amount of radiation reflected back into space by clouds modify the ability of clouds to precipitate modify the ability of clouds to precipitate

32. What is “cloud seeding"? This is where specific kinds of mineral aerosol particles that promote ice formation are injected into a cloud to make it precipitate This is where specific kinds of mineral aerosol particles that promote ice formation are injected into a cloud to make it precipitate.

Craig Funke's job entails firing chemicals into clouds in an ambitious attempt to modify the weather. He is, quite literally, a rain maker. Cloud seeders in Pleasanton, Texas, artificially prime thunderstorms to deliver extra rain over drought-stricken farmland.

33. List (4) major sources of organic aerosols which are emitted to the atmosphere directly by inefficient combustion in the United States. automobiles, wood stoves, agricultural fires, wildfires

34. What is smog? Smog is often used as a generic term for any kind of air pollution that reduces visibility, especially in urban areas. Click to view slideshow of worst smog cities

35.Distinguish between the two broad types of smog. Industrial smog – also called gray or black smog—develops under cold and humid conditions. Photochemical - forms when NOx and VOCs react in the presence of solar radiation to form ozone - typically developing in summer

36.What are the two main health hazards of photochemical smog? Ozone and Aerosols Ozone and Aerosols