Five carbon dioxide sensors monitor the air at sites on the Salt Lake Valley floor of Utah, marking the only multisite urban CO₂ network in the world with more than a decade of continuous measurements. Analysis of data collected since 2001 shows that suburban sprawl increases CO₂ emissions more than similar population growth in a developed urban core. The sensors require resource-intensive maintenance and calibration, factors that may explain why few other cities have multisite networks.

One sensor was installed in the southwest corner of the valley, intended to represent rural areas. That Growth and development in the southwest Salt Lake Valley since 1984. Source: Google Earth Engineinstrument is located in what is now the Daybreak community and has yielded some of the most interesting results. Although the area consisted of open fields when the sensor was first placed in 2004, it’s now a bustling, developed area home to more than 13,000 people.

The Daybreak sensor provided an opportunity to directly compare the effect of population growth on emissions in different land-use areas. Over the same time that population in the southern part of the Salt Lake Valley and neighboring Utah Valley exploded, Salt Lake City grew by around 10,000 people. But the growth in CO₂ emissions wasn’t comparable with the growth associated with suburban expansion in the southern end of Salt Lake Valley.

The researchers concluded that population growth does not directly correlate with growth in CO₂ emissions. Other factors, specifically the types of neighborhoods where population is growing, are much bigger factors.

The data were compared to four inventories of global carbon emissions to see if the same trend held. These inventories also showed that population growth was not directly correlated to emissions growth but posted a constant rate of emissions over the Salt Lake Valley, failing to capture the high CO₂ growth rate in suburban areas.

The researchers are now leading a project called CO₂-USA (CO₂-Urban Synthesis & Analysis network) to link CO₂ monitoring networks in urban areas across the U.S.