High-resolution greenhouse gas modeling for the Los Angeles megacity

Abstract:

A high-resolution greenhouse gas modeling framework was developed on top of the WRF-Chem model version 3.5.1 (coupled the VPRM model) for the Los Angeles megacity. One-way two-nested domains with horizontal resolutions of 12- and 4-km were used. All domains used 51 vertical levels, with 25 vertical layers below 2 km. The 32-km North American Regional Reanalysis (NARR) data were used to provide the initial and boundary conditions for meteorological fields, and an urban canopy model was used for an accurate representation of the urban environment. Other than that, the model system also takes into account anthropogenic and biogenic CO₂ fluxes and initial and boundary conditions for CO₂ from the GEOS-Chem model, which aims at disentangling atmospheric CO₂ signals from different sources. The purpose of the model configuration is to present realistic greenhouse gas transport with respect to the complex meteorology of the Los Angeles basin: terrain induced mesoscale phenomena such as sea-land-breeze circulation, mountain-valley circulations, urban heat islands, etc.

Simulated meteorological fields and CO₂ are compared against in-situ and CLARS-FTS measurements. The comparison shows that the model is able to capture the main observed features in the CO₂ distribution reasonable well. The simulations show that the diurnal variations of CO₂ over Los Angeles basin can be strongly affected by the complex terrain and the land-water contract. The evolution of urban CO₂ dome over the Los Angeles basin is analyzed as well. Such high-resolution model outputs are also valuable to regional inverse modeling.