Study of CO2 Emissions from Traffic and CO2 Sequestration by Vegetation Based on Eddy Covariance Flux Measurements in Suburb of Beijing, China

Many studies have shown that urban forests function as important carbon (C) sinks by sequestering carbon dioxide (CO2), and there are a great deal of scientific data on their potential to fix CO2 through photosynthesis, including variations among vegetation types and temporal dynamics. However, although vehicle traffic is one of the main anthropogenic sources of CO2, the relationship between these emissions and sequestration by vegetation is unclear. Here, we use the eddy covariance technique to directly measure the net CO2 flux to: (1) quantitatively validate C emissions from transportation and C sequestration by vegetation at the spatio-temporal resolution of 1 km and 30 min and (2) select tree species that best sequester C by photosynthesis and identify the major controlling factors. During the daytime monitoring period (7:00-17:00) of the plant-growing season (May-October), the net photosynthetic C sequestration per tree was used to measure the C fixation capacity of different tree species, and the order was Mono maple > Amur cork tree > Goldenrain > Chinese ash > Chinese pine > Ginkgo. In the study, C sequestration by trees was primarily controlled by photosynthetically active radiation, traffic volume and relative humidity, which together explained 92.3% of the total C sequestration by trees during the monitoring period in the growing season, and C sequestration was positively correlated with photosynthetically active radiation and traffic flow, but negatively correlated with relative humidity. Furthermore, vehicle CO2 emissions significantly increased the amount of photosynthetic C sequestration due to a fertilization effect. Therefore, it is necessary to improve the accuracy of micro-scale regional C flux measurements in order to more accurately determine CO2 sources and sinks and inform the selection of vegetation that can maximize the sequestration of traffic CO2 emissions.