Editorial: Tank-Barge Vapors Create Ozone, But How Much?

The Memphis Commercial Appeal recently reported that environmental officials are focusing on Mississippi River barges as potential contributors to the creation of excessive smog in the Memphis area. For years, air-quality regulators focused on cars and factories. Further study is needed to evaluate the significance of these emissions, they said.

According to the report, barge emissions are being examined because controls on other pollution sources haven’t produced adequate reductions in ozone levels, officials explained.

About 45 regulators and towing-industry representatives met October 19 in Memphis to review evidence that tank barges routinely discharge vapors known to help create ozone, the Appeal report said.

One Louisiana environmental official said, “…we don’t know if [the] emissions are having a negative impact on air quality.” The tank-barge industry has for years employed practices designed to minimize emissions. They believe it is too early to talk about further controls. Another barge company official said he believes we are “working toward solutions without having quantified the problem.” Still others think barges represent a minor pollution source in the Memphis area because there are few tank barges there.

An Environmental Protection Agency (EPA) spokesman said he hopes the barge industry doesn’t believe the agency is picking on them. Officials said, “Barge emissions alone can’t explain why air-quality monitors—particularly one in Marion, Ark.—continue to show high readings.” Pollution-control regulators are looking everywhere, not just at barges, they said.

The Appeal report said ozone can cause sunburn-like damage to the lungs. It is created when nitrogen oxides react in sunlight with volatile organic compounds, like those released from tank barges hauling petroleum and chemical products.

Well, the regulators have their work cut out for them, and no doubt we will hear from them later on. But the EPA makes no bones about the serious problems with ozone.

First, there is good ozone and bad ozone. Ozone is a gas that forms both in the Earth’s upper atmosphere and at ground level. Depending upon where it is located, ozone is either “good” or “bad” for our health.

Ozone occurs in two layers of the atmosphere: the layer closest to earth (the troposphere), which generally extends to a level about six miles up; and the upper level (the stratosphere), where the good ozone layer extends from six to 30 miles upward and protects life on Earth from the sun’s harmful ultraviolet (UV) rays.

The ozone in the lower level is “bad” ozone. It is a pollutant that is harmful to breathe, and it damages crops, trees and other vegetation. It is a main ingredient of urban smog.

The problem is that the good ozone, which is produced naturally in the stratosphere, is gradually being destroyed by manmade chemicals referred to as ozone-depleting substances, including chlorofluorocarbons, hydrochlorofluorocarbons, halons, methyl bromide, carbon tetrachloride and methyl chloroform. These substances were formerly used—and sometimes still are used—in coolants, foaming agents, fire extinguishers, solvents, pesticides and aerosol propellants.

Once the ozone-depleting substances are released into the air, they are very slow to degrade. They remain intact for years, rising slowly through the troposphere until they reach the stratosphere, where they are broken down by the intensity of the sun’s UV rays and release chlorine and bromine molecules, which destroy the good ozone. According to the EPA, scientists have estimated that one chlorine atom can destroy 100,000 good ozone molecules.

Even though the use of many of these substances has been eliminated, they still can affect the protective ozone layer negatively because of the length of time it takes for them to degrade and because many of them reach the stratosphere.

Research indicates that the good ozone layer is being reduced worldwide. Thinning of the protective ozone layer can be observed using satellite measurements, particularly over the polar regions.

We might say, “That’s a long way up there; what harm can come of it?” But ozone depletion can cause increased amounts of UV radiation to reach the Earth, which can lead to more cases of skin cancer, cataracts and impaired immune systems. Overexposure to UV is believed to be contributing to the increase in melanoma, the most fatal of all skin cancers. Since 1990, the risk of developing skin cancer has more than doubled, the EPA reports.

UV can also damage sensitive crops, such as soybeans, and reduce crop yields. Some scientists suggest that marine phytoplankton, which are the base of the ocean food chain, are already under stress from UV radiation. This stress, says the EPA, could have adverse consequences for human food supplies from the oceans.

The EPA has established regulations to phase out ozone-depleting chemicals in the United States. Over the years, virtually every home and business in the nation has felt the impact of this massive effort. Evaluating tank barge emissions is merely another necessary step in the drive to slow down ozone depletion.

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