How Grass Clippings are Helping Cities Gauge Their Carbon Footprints

By analyzing radiocarbon in turfgrasses, researchers at UC Irvine have developed a method for local governments to monitor and potentially reduce their individual municipalities' emissions.

Though cities globally are striving to reduce emissions of greenhouse gases that contribute to climate change, there have been limited methods to assess whether these gases are genuinely declining in specific municipalities. 

Scientists at the University of California, Irvine, have developed an effective new method for measuring gas emissions around cities. Their findings were published in Journal of Geophysical Research: Atmospheres. 

It is hoped that their research will enable local governments to evaluate the effectiveness of their emission-reduction programs. 

Emissions of fossil carbon dioxide are the main driver of climate change. We found that measuring radiocarbon in turfgrasses is a practical and spatially sensitive tool for assessing urban fossil fuel carbon dioxide patterns.

Claudia Czimczik, Study Senior Author and Professor, Department of Earth System Science, University of California, Irvine

The group, headed by former UC Irvine doctoral candidate Cindy Yañez, assessed radiocarbon levels in cultivated turfgrasses across both urban and rural areas of Southern California. In the same locations, they employed a greenhouse gas device supplied by Manvendra Dubey from Los Alamos National Laboratory to measure the overall concentration of carbon dioxide present in the atmosphere.

Czimczik suggests that the team's study demonstrates the potential of radiocarbon analysis of turfgrasses to map 'urban carbon dioxide domes', which can be used to evaluate progress towards decarbonization efforts, especially in areas lacking CO₂ monitoring infrastructure.

This type of plant data provides high-resolution images of greenhouse gas emissions in individual municipalities, enabling cities to assess the effectiveness of their efforts to reduce emissions.

The research is based on a study carried out during the COVID-19 pandemic, in which a collaborative team from UC Irvine and UC Riverside requested that volunteers gather and submit samples of invasive grasses from their local areas to laboratories at UC Irvine.

From this, the team found a significant reduction in fossil fuel emissions during the initial phase of the pandemic, followed by an increase in emissions as restrictions were lifted and individuals returned to driving.

In the current study, the team shifted its focus to sampling managed turfgrasses, allowing for continuous observations throughout the year and collaboration with specialists from the greenhouse gas monitoring sector.

One of the main challenges is understanding exactly how long the plants were recording the carbon dioxide signal. We addressed this by focusing on managed lawns that are mowed regularly, typically every one to two weeks in Southern California.

Claudia Czimczik, Study Senior Author and Professor, Department of Earth System Science, University of California, Irvine

Sampling the tops of frequently mowed grass ensured that the samples represented approximately two weeks of growth, providing the team with a more consistent timeframe for comparison against atmospheric measurements of greenhouse gas concentrations.

“Los Angeles has unique atmospheric conditions, where surrounding mountains trap emissions in a basin. Our method successfully captures these patterns, but we need to test it in other cities with different meteorological conditions to understand if it works as well in places where emissions are subject to more consistent wind transport rather than the mountain and basin situation we see in Los Angeles,” concluded Czimczik.

Journal Reference:

Yañez, C. C., et al. (2025) Quantifying Fossil Fuel CO₂ Enhancements Along an Urban-Rural Gradient With Radiocarbon Analysis of Turfgrasses. JGR Atmospheres. doi.org/10.1029/2025JD043336