The objective of this project is to collect and analyze airborne and surface data on aerosol and cloud properties in and around Houston, Texas. The goal is to understand how clouds are influenced by the chemical and physical characteristics of the aerosols in the air in which they form. Instruments at a surface site and mounted in a Cheyenne II aircraft will measure size distributions, size-resolved hygroscopic growth, and cloud activation efficiency of the local aerosol. The airplane is also equipped to measure cloud droplet size distributions. The work is motivated by observations that have indicated rainfall and lightning anomalies in the vicinity of Houston and other major cities. Several explanations have been proposed to account for the anomalies, one of which is possible effects of pollution aerosols on cloud microstructure. Large cities are the source of abundant aerosols. Although there is no doubt that increased aerosol loading leads to higher concentrations of cloud droplets than in regions away from the urban influence, it is not clear what effect the increase in droplet concentration has on cloud lifetime, precipitation production, or cloud electrification. To answer these questions requires, as a start, the fundamental information on cloud-forming properties of aerosols that this project will produce. The data collection will be coordinated with a field program in the summers of 2005-06 to study pollution in the Houston area sponsored by the Texas Commission on Environmental Quality. That program (called TexAQS-II) will furnish radar data and other supporting observations to aid in interpreting the cloud and aerosol measurements. A broader impact of the project is the contribution it will make to understanding the influence of anthropogenic emissions on cloud behavior, which ultimately will help quantify the effects of urban aerosol on weather and climate. The project supports a graduate student and provides training opportunities for undergraduates in Dr. Collins's summer field course.
