CMAQv5.4+ modeled low background elemental mercury concentrations

[Wunder]

Hello everyone,

I used different versions of CMAQ to simulate elemental mercury concentrations under various conditions in January 2022 (as shown in the figure below, with the format: CMAQ version_initial media mercury concentration_deposition mode_HGBIDI on/off). I found that the simulated concentrations at background sites (<0.5 ng/m³) are much lower than the observed concentrations (1–2 ng/m³). Could you please advise what might be causing this discrepancy? My main configuration information are as follows:

• Meteorological Inputs: WRF v3.9.1
• CMAQ Version: v5.4 / v5.5
• Emission inventory: EDGAR 2022
• DepMod: Stage / m3dry
• Mechanism: cb6r5hap_ae7_aq
• NZ (Vertical Layers): 14
• HGBIDI: Y / N

[Wunder]

CTM_LOG_020.GD_2022022.txt (390.5 KB)

run_HG_D1.csh (43.8 KB)

Here is the run script and log file

[hogrefe.christian]

Concentrations of elemental Hg in regional-scale simulations are heavily influenced by boundary conditions:

Pongprueksa, P., Lin, C. J., Lindberg, S. E., Jang, C., Braverman, T., Bullock, O. R., Jr., et al. (2008). Scientific uncertainties in atmospheric mercury models III: Boundary and initial conditions, model grid resolution, and Hg(II) reduction mechanism. Atmospheric Environment , 42(8), 1828–1845.

Baker, K. R., & Bash, J. O. (2012). Regional scale photochemical model evaluation of total mercury wet deposition and speciated ambient mercury. Atmospheric Environment , 49, 151–162.

In a more recent regional CMAQ Hg modeling study, the authors compared the impacts of default vs. GEOS-Chem derived initial and boundary conditions on simulated Hg concentrations:

Ye, Z., Mao, H., Driscoll, C. T., Wang, Y., Zhang, Y., & Jaeglé, L. (2018). Evaluation of CMAQ coupled with a state-of-the-art mercury chemical mechanism (CMAQ-newHg-Br). Journal of Advances in Modeling Earth Systems , 10, 668–690. https://doi.org/10.1002/2017MS001161