Scientists at the University of Miami Rosenstiel School of Marine & Atmospheric Science discovered a technique to track urban atmospheric plumes thanks to a unique isotopic signature found in vehicle emissions. Credit: UM/RSMAS |
Scientists
at the University of Miami Rosenstiel School of Marine &
Atmospheric Science have discovered a technique to track urban
atmospheric plumes thanks to a unique isotopic signature found in
vehicle emissions.
Brian
Giebel, a Marine and Atmospheric Chemistry graduate student working
with Drs. Daniel Riemer and Peter Swart discovered that ethanol mixed in
vehicle fuel is not completely burned, and that ethanol released in the
engine’s exhaust has a higher 13C to 12C ratio when compared to natural
emissions from most living plants. In other words, the corn and
sugarcane used to make biofuels impart a unique chemical signature that
is related to the way these plants photosynthesize their nutrients.
The
team suggests that ethanol’s unique chemical signature can be used
during aircraft sampling campaigns to identify and track plumes as they
drift away from urban areas. The results of their efforts, titled “New
Insights to the Use of Ethanol in Automotive Fuels: A Stable Isotopic
Tracer for Fossil- and Bio-Fuel Combustion Inputs to the Atmosphere”
appears in the journal, Environmental Science & Technology.
Giebel
collected and analyzed air from downtown Miami and the Everglades
National Park and found that 75% of ethanol in Miami’s urban air came
from manmade biofuels, while the majority of ethanol in the Everglades
air was emitted from plants, even though a small quantity of city
pollution from a nearby road floats into the park.
Air
samples from the two locations were subjected to a precise scientific
process, first separating the elements using gas chromatography, and
then burning each component. The resulting carbon dioxide was put
through a mass spectrometer, where the researchers were able to measure
the abundance of each carbon isotope.
“According
to global emissions estimates, plants release three times as much
ethanol as manmade sources,” said Giebel. “However, if the amount of
ethanol used in our fuel continues to increase, vehicle emissions should
eventually exceed natural emissions. This is particularly critical in
urban areas because the majority of ethanol in the atmosphere is
converted to acetaldehyde, which is highly reactive and considered to be
a toxin detrimental to human health.”
