Estimation of Urban Biospheric and Anthropogenic CO<sub>2</sub> Atmospheric Signals Using CO Tracer Technique

Abstract

Although the continued world urban population growth is responsible for the increasing anthropogenic CO2 emissions, accurate accounting of the partitioning between urban anthropogenic and biospheric CO2 signals is key to effective emission reduction strategies. Furthermore, the partitioning of urban anthropogenic and biospheric CO2 emissions, estimated from ground-based atmospheric measurements can contribute to an independent reporting of local, regional and national CO2 emission inventories. In this study, between the years 2017 to 2019, daily and seasonal ground-based cavity-ring down spectroscopic (CRDS) CO2 measurements were recorded in Cookeville, a medium sized city located within the Eastern highland rim region of the United States (36.1628° N, 85.5016° W). The obtained CO2 signals were partitioned into anthropogenic and biospheric dry mole fractions, utilizing CO as a tracer. The average winter biospheric CO2 dry mole fraction values ranged from -0.65 ± 3.44 ppm to -9.80 ± 8.99 ppm. On the other hand, anthropogenic dry mole fraction CO2 values varied from 10.01 ± 6.53 ppm to 22.88 ± 9.96 during the winter season. During the winter season, the percentage contribution of the oxidation reaction between the OH radical and isoprene (CH2=C(CH3)−CH=CH2 + OH) to the total CO budget in Cookeville is negligible. However, during the summertime, the CO from isoprene oxidation was estimated to be significant, although less than 50%, implying that any summertime study based on the CO as a tracer of combustion emission should account for its photochemical production through biogenic volatile organic compounds (VOCs).