Wadleigh: Finding signatures in rain

By Ivan Muzychka

When it rains, most of us see inclement weather. For Dr. Moire Wadleigh however, the rain presents an important research opportunity. Dr. Wadleigh, assistant professor of earth sciences at Memorial, is researching the sulphur content of the atmosphere through the chemical analysis of rain.

It is one thing to know the level of sulphur, quite another to trace where it came from. Sulphur can enter the atmosphere through biological processes, it can come from sea spray, and from industrial sources such as smelting plants and oil refineries. Tracing sulphur levels can be important to the understanding of a serious ecological problem commonly referred to as acid rain.

Dr. Wadleigh sorts the general sulphur content of the atmosphere according to the different sources by examining isotopes, the atoms that make up a given element. Counting and classifying isotopes is critical for mapping and understanding patterns in the sulphur cycle.

"Isotopes are atoms of the same element that have slightly different weights, and so they behave chemically similarly to one another in that they are involved in the same kinds of chemical processes...."

However, each source of sulphur will produce a different kind of isotope. Isotopes tell the story of the sulphur content -- how much of it was formed naturally, how much industrially. In this way isotopes act like identifying signatures. Isotopic composition analysis helps Dr. Wadleigh understand the presence of sulphur in the atmosphere from a wider perspective.

"By using this type of technique, by measuring isotopic compositions, we can look at the signatures that represent the kinds of chemical reactions or processes that the various compounds of the sulphur have been involved in. By sorting out the different sources of sulphur in the atmosphere I try to get some idea of what is and isn't important in the whole sulphur cycle."

The environment is extremely sensitive to sulphur levels. High sulphur content damages vegetation. Acidification generally alters the balance of the ecosystem from fish to anything else that lives which is not acid tolerant.

Dr. Wadleigh needs a large volume of rain for her experiments -- not a problem here in Newfoundland, she noted with a chuckle.

Once rain is collected, the sulphate is extracted and is turned into a solid called barium sulphate. The barium sulphate is then burned and the resulting gases are put through a mass spectrometer so that isotopes can be counted and classified.

Finally, analysis of varying levels of isotopes can point to incipient pollution problems. "It is useful to me to know whether there is much sulphur coming from the oceans, or whether winds are carrying sulphur from somewhere else. Because of wind patterns, we are in the path of pollutants from the mainland. If the sulphate from the sea spray is very low, then that tells me I am getting sulphur from other things."

Dr. Wadleigh feels that in the future earth scientists will be able to use isotopic analysis with more accuracy, something her own research is working towards.

"The ideal thing would be to know the exact isotopic composition of sulphur coming out of the Come-by-Chance refinery, or what generally comes from places like Sudbury, Ontario. We want to know the composition of gases that are emitted from there and be able to pinpoint them."

In the meantime, Newfoundlanders need not worry too much about a sulphur problem. Dr. Wadleigh says that Newfoundland is reasonably pristine as far as sulphur levels are concerned.

"There are various acid monitoring projects going on around the island and there are imposed limits for our type of geology, but there are areas where damage has been done and is being done, such as Hope Brook and Come-by-Chance."

Dr. Wadleigh's research is funded by the Natural Sciences and Engineering Research Council.