EarthTalk: What is 'Acid Rain' and What Causes It?

Dear EarthTalk: What is "acid rain" and what causes it?
-- Jeff Ohmberger, Lincoln, NE

"Acid rain," also known as acid precipitation and acid deposition, is a broad term used to describe the nitric and sulfuric acids that fall to Earth during rain, snow or fog. These chemicals form in our atmosphere to begin with when pollutants released into the air through the burning of fossil fuels blend with other substances, including water vapor. When it storms, these substances return to the Earths surface where they get into rivers, streams and groundwater, literally making these waters more acidic.

This acidity, in turn, damages trees and other plant life and makes it difficult for wildlife--especially aquatic life--to thrive and reproduce. The consequences of acid rain can also be seen in the cracks and discoloration on some building surfaces and on the smoothed and faded facial features on outdoor statues.

Emissions of sulfur dioxide (SO2) and nitrogen oxide (NOx) are primarily to blame. While volcanoes and other natural sources produce these chemicals, too, as much as 95 percent of the SO2 and NOx emitted in North America comes from industrial sources and the tailpipes of cars and trucks.

According to the U.S. Environmental Protection Agencys (EPA) Acid Rain Program, the highest concentrations of acid rain in the U.S. are in western Pennsylvania and West Virginia. Prevailing winds move large masses of pollutants there from the smokestacks of the many coal-fired and other kinds of power plants dotting the banks of the Ohio River.

Meanwhile, the National Atmospheric Deposition Program (NADP), which monitors the chemistry of precipitation at some 200 locations around the United States, reports high levels of acid rain throughout the entire Northeast, extending from Indiana all the way to the Atlantic coast. NADPs website features interactive maps detailing acid rain concentrations nationwide.

During the 1980s, public outcry over acid rain resulted in Congress amending the Clean Air Act to impose limits on industrial emissions of SO2 and NOx. While the regulations have helped, many environmentalists think more needs to be done in order to protect plants, wildlife and water throughout the northeastern U.S. and southeastern Canada. A growing body of evidence shows that without significant additional cuts in acid rain-forming emissions, many of the problems associated with acid rain will persist for many decades, says Ellen Baum, ecosystem expert at the Boston-based nonprofit organization, Clean Air Task Force.

Since the burning of fossil fuels accounts for most of the troublesome SO2 and NOx emissions, individuals can make a difference by reducing their energy consumption at home and by driving fewer miles in their internal combustion vehicles. Businesses can take similar steps by increasing energy efficiency at the workplace and encouraging employees to carpool or take public transit.

Dear EarthTalk: How can I recycle my old propane gas tank that can no longer be refilled?
-- Bruce Krasnow, Santa Fe, NM

If you have an older propane gas tank that has been denied refilling by a retailer, it is probably because it lacks an Overfilling Prevention Device (OPD). As of April 2002, the National Fire Protection Agencys (NFPA) safety code requires an OPD on every propane tank that holds between four and 40 pounds of the gas, which includes tanks normally used for grills, RVs and other devices. An OPD is part of the valve and is designed to prevent the release of gas from overfilling which can lead to fires and injuries.

The NFPA says you can easily check to see if your tank has an OPD by examining the shape of the valve wheel. Most cylinders with a triangular valve wheel have an OPD, and will be marked accordingly. Cylinders with a round or star-shaped valve wheel usually do not have an OPD.

For a fee, you can take your old tank to a local propane dealer for retrofitting with a new valve. You can also sometimes pay a fee and exchange your old tank for a newer model. If youve already purchased a new unit, or dont need to use propane anymore, many dealers will take them, usually for a small fee, repaint them, re-certify them, install an OPD and resell them.

If you have a 20-pound propane cylinder, the Blue Rhino Company, which claims thousand of retailers nationwide, will accept your old tank and provide an upgrade, usually for an upgrade fee and provided your old tank can be refurbished. Then that upgrade can be repeatedly returned empty and exchanged for a full tank. The company reuses and refills the tanks, so this arrangement both eliminates the wait of refilling and maintains a pattern of re-use.

If Blue Rhino cannot refurbish your tank and all else fails, propane cylinders can be recycled at household hazardous waste collection sites. The website Earth911.org provides a free zip code-based directory with information on where to recycle old propane tanks, among other household items, in your local region. Most state departments of environmental protection also include lists of locations that will refurbish or recycle old tanks.

Homeowners should keep in mind that old propane tanks pose an environmental hazard if simply abandoned outside and an explosion risk if thrown into a dumpster or garbage truck trash compactor. Also, cylinders should always be stored and transported upright to prevent potentially dangerous leakage, even if they are on their way to the recycling center or the refill station.

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