Scientists climb UChicago buildings to study air quality and pollution

Methane and ethane are potent greenhouse gases—even more so than carbon dioxide—and yet scientists have gaps in their knowledge of the sources of these emissions. Luckily, scientists can analyze trace gas signatures to determine whether they’re coming from biological sources—like cows or landfills—or from natural gas sources, like industrial activity or leaks from home heating systems.

Floerchinger is part of a Harvard team that is studying a dozen cities around the United States to catalogue emissions in urban areas, including Chicago. Scientists can pair the data with meteorological records to map wind direction and better understand the sources of the air they are measuring. Floerchinger said they can already see differences in Chicago: south winds that bring emissions from industrial plants to the south, north winds that carry particles from the city of Chicago; and cleaner but rarer east winds off Lake Michigan.

Other things that could show up in the data would be evidence for the spring plant bloom, and natural gas leaks reducing as Chicagoans turn off their winter heating.

The data may be able to inform policy decisions on how to reduce urban greenhouse gas emissions, Floerchinger said.

Testing air for isotopes

On the other side of campus, another instrument went up atop a building—this one the Knapp Center for Biomedical Discovery. Instead of methane, it tests the water vapor in the air.

Water can come in any of several slightly different configurations; for example, a small percentage of water molecules contain hydrogen atoms with an extra neutron.

“You can use these isotopes to get some sense of the origin of the water vapor—whether it evaporated off the lake or was produced in a car tailpipe from combustion,” said Clouser, who modified the instrument to measure at much lower altitudes than their group’s usual airborne missions. “Water that was recently part of a hydrocarbon and then burned has a very different isotopic signature than water that was recently in the lake.”

Scientists don’t have much data on the source of urban water vapor, so the results should be interesting, Clouser said.

Moyer and Clouser also suspect that the current picture of these isotopes that scientists use in their climate models is not as complete as we think. The amount of heavy water is often interpreted to indicate where that water originally evaporated from, but what they’ve seen in the upper atmosphere makes them think it may not be so simple.

“We’d like to see how much this value varies at the ground level and by weather—whether it changes after a thunderstorm, for example,” Moyer said. “If so, that could help us bring a little more realism to the models.”

Funding: National Science Foundation