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Abstract

Common transport models use the mixing height (MH) to determine turbulent coefficients and to obtain tracer concentrations in the planetary boundary layer (PBL). We conducted a pseudo data experiment to elucidate the impact of assimilating MHs to improve CO2 transport within the Stochastic Time-Inverted Lagrangian Transport model (STILT). Transport of CO2 was simulated for August 2006 with a receptor located at Bialystok, Poland. STILT was driven by meteorology obtained from the Weather Research and Forecasting (WRF) model, using the Yonsei University (YSU) and Mellor-Yamada-Janjić (MYJ) PBL parameterizations, which differ substantially in the produced MHs. To quantify model-data mismatch in CO2 to errors in vertical mixing, we defined the WRF-YSU simulation as known truth. Pseudo MH observations were sampled from WRF-YSU at locations of real radiosonde stations. These point observations were interpolated in space-time to the entire WRF domain using kriging with an external drift, which combines observed and modeled MHs to create a “best guess” MH field. We prescribed MHs in STILT driven by WRF-MYJ winds with the best guess to study the impact on CO2 concentrations. Differences in CO2 between the STILT simulations were on the order of ~0–1 and ~1–10 ppm on average (i.e., bias), with standard deviations of ~1–3 and ~4–14 ppm (random error) during day (12 UTC) and nighttime (0 UTC), respectively. These were reduced when using STILT with the best guess (~50%–80% of the bias, ~10%–20% of the random error). Simulated CO2 concentrations and MHs were also compared to measurements made at the Bialystok tall tower.