Sniffing Out Sulfur Dioxide

They lined up side by side, silent and apprehensive about the task ahead. All seven knew each other, but no small talk broke the tension inside the trailers. They assembled as competitors, and the stakes were high; their reputations would suffer slow-to-heal wounds if they failed.

They weren't athletes. They were chemists, experts on measuring sulfur dioxide in the atmosphere. The National Science Foundation invited the researchers to the University of Delaware, telling them little more than what to bring, which included their best machines for sniffing sulfur dioxide. Fueled by the spirit of competition and the desire for future NSF research funding, they went.

The seven teams were from the National Oceanic and Atmospheric Association and the universities of Washington, Miami, and New Hampshire, Drexel University, J.W. Goethe University in Germany, and representing the University of Alaska, Geophysical Institute chemist Richard Benner and graduate student Jainguo Wu.

The scientists' interest in sulfur dioxide, a colorless gas released when fossil fuels burn, may have been born in the late 1970's with the discovery of acid rain. Sulfuric acid, which forms when sulfur dioxide mixes with moisture, was blamed in part for the acidification and subsequent death of may trout ponds in the northeastern United States and Canada. The source of the sulfur dioxide was hundreds, sometimes thousands of miles away, in the exhaust of Midwest coal-fired power plants.

Today, particularly in Alaska, Benner and other scientists study sulfur dioxide concentrations because sulfuric acid particles are a large ingredient of Arctic Haze, a polluted air mass that settles over the Arctic during late winter and early spring. Researchers say much of this smoggy blanket originates in the smoke stacks of Europe, Asia and the former Soviet Union.

Sulfur dioxide is tough to measure in small quantities, which inspired NSF to bring the heavyweights together. In remote areas away from factories and cities, sulfur dioxide is found in such small concentrations (as low and one-to-two parts per trillion) that it's impossible to measure with commercially available instruments. Such was the case at Poker Flat Research Range north of Fairbanks, where Benner said conventional detectors were ineffective 99 percent of the time. Like a true Alaskan, he built his own.

Benner is co-inventor of the sulfur chemiluminescence detector, a device about the size of a television set. Under Benner's direction, Wu, who has an engineering degree, built from scratch the model they took down to Delaware. Their device burns incoming sulfur dioxide with a hydrogen flame, then adds ozone. These steps combine to produce photons of light. By analyzing the light with a violet filter and a sensitive light detector, Benner and Wu can accurately determine the amount of sulfur dioxide that was sampled.

According to Benner, the machine is so sensitive that if one gram of sulfur were divided into a trillion tiny piles and then one of those piles was divided again into 100 more piles, the chemiluminescence detector would pick it up easily.

Three trailers were set up at the competition, known affectionately as GASIE (Gaseous Sulfur Inter-comparison Experiment). Scientists from the University of Idaho hooked up gas cylinders with undisclosed amounts of sulfur dioxide to a tube that ran between two other trailers. The seven invited scientists tapped into the tube and made measurements all day in relative silence.

"We couldn't talk to each other, and they made us cover up all our displays," Benner said. "It was weird."

It was also tense, Benner said. What if the results showed that a scientist's method for measuring sulfur dioxide in the atmosphere wasn't accurate? Then the scientist would have two major problems: how to defend all previous studies he or she had done with the bogus method, and how to ask for more funding without being laughed at.

Benner knows deep down inside that his sulfur dioxide detector is faster and more accurate than any of the other scientists', but he won't know the outcome of the competition until January, when NSF will publish the results.

"Between now and then I'll be chewing my nails," he said. "I was going to say, pulling out my hair, but those days are gone."