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Observation and modeling of vertical carbon dioxide distribution in a heavily polluted suburban environment

ABSTRACT The vertical distribution of carbon dioxide (CO2) is important for the calibration and validation of transport models and remote sensing measurements. Due to the large mass and volume of traditional instruments as well as supporting systems, in-situ measurements of the CO2 vertical profile within the boundary layer are rare. This study used a miniaturized CO2 monitoring instrument based on a low-cost non-dispersive infrared (NDIR) sensor to measure the CO2 vertical profile and meteorological parameters of the lower troposphere (0–1000 m) in southwestern Shijiazhuang, Hebei Province, China. The sensors were onboard a tethered balloon with two processes: the ascending process and the descending process. The results showed that the overall trend of CO2 concentration decreased with height. Weather conditions and CO2 emission sources caused fluctuations in CO2 concentrations. The CO2 concentration varied from morning to afternoon due mainly to the faster spread of air mass during daytime, with strong convections and the accumulation of emissions at night. The low-cost sensor produced results consistent with the traditional gas chromatography method. The Weather Research and Forecasting model could not capture the CO2 profiles well due mainly to the bad performances in boundary layer height and the potential outdated fossil fuel emissions around the experimental site. This experiment is the first successful attempt to observe the CO2 vertical distribution in the lower troposphere by using low-cost NDIR sensors. The results help us to understand the vertical structure of CO2 in the boundary layer, and provide data for calibrating and validating transport models. Graphical Abstract