Atmospheric aerosols have at least two important implications for the environment: The acid rain it produces harms both terrestrial and marine life, and they alter the earth's climate by reflecting solar radiation and thereby cooling the part of the earth beneath the haze. Aerosols combine with heat-trapping green house gases to induce climatic change. Greenhouse gases tend to warm the earth while aerosols tend to cool some regions. Greenhouse gases tend to remain in the atmosphere for decades or even centuries while aerosols can rain out of the atmosphere in a few days.
One way to discriminate between natural sources of aerosols and human made sources is to look at the location of aerosol plumes. Natural aerosols like salt particles from sea spray are typically widespread over larger areas and not particularly concentrated downwind of urban areas. Or they are particularly concentrated downwind of obviously natural sources, such as the streams of dust originating from the Sahara Desert. Another clue to a plume's origin can be found in the size of the aerosol particles it carries. In general, smaller particles are more likely to be produced by human activities, while larger particles are more likely to have natural origins.
Aerosols produced by humans appear in punctuated bursts of thick and concentrated plumes comprised of small particles. They can also be found concentrated downwind of regions altered by human activities, such as deforested regions. Plumes of smoke and regional pollution are distinguished by their large concentrations of small particles (less than one micrometer) downwind of biomass burning sites and urban areas. These particles are important because, depending upon the type of particles produced, human pollution can either have a warming or cooling influence on climate, and they can either increase or decrease regional rainfall.
Examining global satellite images in concert with global scale models and globally distributed ground based pollution measurements gives scientists the best tools they have ever had to estimate the effects of aerosols on climate and weather patterns around the world. The next step is to quantify more precisely the roles human aerosol pollution plays in Earth's weather and climate systems. NASA plans to further expand global aerosol research with the launch of satellite based light imaging radars, known as lidars, that send bursts of light to Earth and, like a radar signal, provide a measure of the altitude and vertical structure of aerosol plumes and clouds.