Observation of Particulate Matter as a Proxy for Cloud Condensation Nuclei

The analysis of coincident observations of aerosols, clouds and the associated meteorological conditions is an important step towards understanding the interactions between convective systems and the spectrum of aerosol effects on the environment. The TRacking Aerosol Convection interactions ExpeRiment (TRACER) took place in the Houston, Texas region during the period from October 2021 through September 2022 with a goal to understand the interactions between isolated convective cells and aerosols. The TRACER measurements include detailed quantification of aerosol size, number, composition and hygroscopicity, from which cloud condensation nuclei (CCN) concentrations are calculated, at two sampling sites. At the same time, the Texas Commission on Environmental Quality (TCEQ) operates an environmental monitoring network that measures the mass concentration of particulate matter with sizes less than 2.5 microns (PM2.5). For cloud-aerosol interaction studies, CCN concentration in the inflow regions of convective clouds are needed. To estimate the regional variability of CCN concentrations, we investigate the correlation of CCN and PM2.5 concentrations at the TRACER site towards developing a simple proxy for CCN concentrations. We find strong correlations of CCN and PM2.5 concentrations that show dependence on the surface wind direction. For southerly wind directions, a bimodal relationship is found where one mode is found to correspond with local dust or biomass burning events. The developed relationships are applied to the TCEQ network measurements to estimate gradients in CCN concentrations across the southeastern Texas region.