Kang Sun and fellow researchers from Princeton University drove 2,700 miles across California this winter, but it was no ordinary road trip. Strapped to the roof of their car was a suite of air sensors that might look more at home on the Mars rover than their rented Chevy Impala.
“It is definitely unique,” said Sun, a doctoral student in Princeton’s department of civil and environmental engineering.
Sun traveled with David J. Miller, graduate student, and Lei Tao, post-doctoral research associate. They covered territory in California’s Central Valley, from L.A. to the San Francisco Bay area while collecting data from an array of air quality sensors hooked to their luggage rack. The six gasses they were tracking include carbon dioxide, ammonia and nitrous oxide.
“Some of them are greenhouse gases,” Kang said. “Some of them are precursors to particulate matter. Some are just general air pollutants.”
The data they collected will be contributed to a NASA air quality research mission called DISCOVER-AQ. The mission’s goal is to help scientists make better air quality forecasts using Earth-observing satellites. Such forecasts are a challenge because it can be difficult for satellite instruments to distinguish between air pollution near the surface — where people live and breath — and the upper atmosphere.
The heart of the DISCOVER-AQ campaign is a fleet of sensor-equipped aircraft. The planes were also traveling around California while Sun and his colleagues collected data at the surface.
The car sensor suite includes two custom, laser-based sensors developed by Princeton’s Atmospheric Chemistry Group. The group is led by Mark Zondlo, an assistant professor of civil and environmental engineering. One of the group’s sensors measures ammonia, and the other simultaneously measures nitrous oxide and carbon monoxide.
The car also carries two off-the-shelf sensors from LICOR. One measures methane and the other carbon dioxide and water vapor.
The suite also includes a Vaisala weather station that measures air temperature, atmospheric pressure and wind speed. The temperature and pressure measurements are particularly important for calibrating the data from the gas sensors.
“These two are very important to us,” Sun said. “If we really want to have data with very good quality, we need to have a very good temperature sensor and pressure sensor.”
The Vaisala weather station is particularly well suited for their needs because it’s built for field use. That means it can withstand dusty, windy and bug-splattering conditions that come with cruising down country roads and freeways.