Quantifying sub-grid variability of trace gases and aerosols

Poster PDF

Description

Sub-grid treatments exist for meteorological processes in atmospheric models, such as clouds and turbulence. However, little effort has gone into understanding the impact of sub-grid processes on trace gases and aerosols. In addition to the impact of sub-grid meteorological conditions on aerosol mixing, there are also trace gas and aerosol-specific processes that could contribute to errors in simulated values if these processes are neglected. Two examples are the spatial variability of emissions and the nonlinearity of chemical rate constants with concentration. Using a series of model simulations with varying resolution, we have quantified the amount of variability present for meteorology, trace gases, and aerosols in and around Mexico City during the 2006 MILAGRO field campaign. Our results indicate that the amount of sub-grid variability is greater for trace gases and aerosols than for meteorological variables due to the large gradients in the former. We find distinct differences between the sub-grid variability of trace gases and aerosols that are mostly inert versus those that are secondary in origin. And, as intuitively expected, the sub-grid variability is less for locations remote from large emission regions. Emissions can account for up to 50% of the sub-grid variability over urban areas, and the variability is stronger during daytime than nighttime.