One-way nested (27km, 9km and 3km) model output of North American atmospheric CO2 simulation (full WRF-chem output)

Synoptic weather systems are a major driver of spatial gradients in atmospheric CO2 mole fractions. During frontal passages air masses from different regions meet at the frontal boundary creating significant gradients in CO2 mole fractions. This study quantitatively describes the atmospheric transport of CO2 mole fractions during a mid-latitude cold front passage and explores the impact of various sources of CO2. We focus here on a cold front passage over Lincoln, Nebraska on August 4th, 2016 observed by aircraft during the Atmospheric Carbon and Transport (ACT)-America campaign. A band of air with elevated CO2 was located along the frontal boundary. Differences in CO2 across the front were as high as 25 ppm. Numerical simulations using WRF-Chem at cloud resolving resolutions (3km) coupled with CO2 surface fluxes and boundary conditions from CarbonTracker (CT-NRTv2017x) were performed to explore atmospheric transport at the front. Model results demonstrate that the frontal CO2 difference in the upper troposphere can be explained largely by inflow from outside of North America. This difference is modified in the atmospheric boundary layer and lower troposphere by continental surface fluxes, dominated in this case by biogenic and fossil fuel fluxes. Horizontal and vertical advection are found to be responsible for the distribution of CO2 mole fractions along the frontal boundary. This study highlights the use of high-resolution simulations in capturing CO2 transport along a frontal boundary.