Evaluating Urban Surface Emissions of Coarse-Mode Particles Using Lidar Retrievals and Large Eddy Simulations

Description

Accurately measuring the particle exchange rate between the surface and the atmosphere is key to understanding the particles’ role in atmospheric processes such as radiative transport, cloud dynamics, and climate change. Particulate matter is important for cloud formation, yet its emissions are poorly understood. A new method has recently been proposed: surface emissions of particle number larger than 0.5 μm in dry diameter are obtained using the eddy covariance method applied to Doppler lidar elastic backscatter and Doppler lidar velocity measurements. This analysis was based on the TRACER campaign at an urban site near Houston, TX, USA during the summer of 2022. Here, we extend the considered emission flux to the time period from October 2021 to August 2022 to account for annual and seasonal effects. In addition, we performed large eddy simulations (LES) as a testbed to evaluate the efficacy of the analysis approach vis-a-vis known surface emissions. Our results show that all retrieved fluxes were upward, indicating surface emissions. Fluxes exhibit a diurnal pattern peaking around noon local lime. Fluxes varied widely in intensity over the study period. Emission fluxes reached ∼100-200 cm⁻² s⁻¹ and correlated with the surface friction velocity. Seasonal and annual analyses reveal long-term trends, refining models for future predictions. For example, the highest  flux was observed in the spring for this area. Our evaluation of flux in the context of LES provides further insight into the quantitativeness of the technique. These results demonstrate the significant contribution of the urban environment to the boundary layer coarse particle budgets and provide important data for improving aerosol-cloud interaction models by improving underlying aerosol forecasting schemes.