Adaptive Measurement of Nuclei Particle Size and Concentration

C53-26a-271115The extent, persistence and microphysical properties of clouds influence Earth’s climate and hydrologic cycles. A critical factor affecting cloud characteristics is the concentration of airborne particles around which cloud droplets form. A significant contributor to these particles is atmospheric nucleation, which injects large numbers of small particles into the atmosphere. Once formed, these particles grow quickly. It is estimated that these nucleation processes and the subsequent particle growth are significant contributors to the number of cloud condensation nuclei, and subsequent cloud formation. Characterizing particle nucleation events, and the dynamics of the evolution of the particle size distribution, is important to improving our understanding of global climate. Yet current observations are limited by size, cost, and the relatively slow pace of the measurement. This is due, in part, to the low charging efficiency in the sub-10nm regime, which leads to long measurement times to obtain sufficient counting statistics. Needed is a compact, rapid-response instrument that can accurately track the evolution in size and concentration of newly formed particles. This project will develop a new measurement system to provide the tools needed to better characterize the physical dynamics associated with these new particle formation events. This system consists of two coupled instruments, one which is quick to sense an atmospheric nucleation event, and one that has the precision to characterize it. The rapidly responding instrument is a Nano-Particle Counter which continuously reports particle concentrations in two nanoparticle size ranges, approximately 2nm-10nm, and 10nm and larger. The precise instrument is an “adaptable” differential mobility analyzer that measures aerosol size distributions based on electrical mobility. This adaptable differential mobility analyzer has several modes of operation, with the capability, in one instrument, to measure freshly nucleated, nanometer sized particles as well as the larger pre-existing aerosol with which these newly formed particles interact. Its “adaptability” is the capacity to readily switch among these size ranges. These two components are coupled through common control, whereby an abundance of 2-10 nm particles that is characteristic of an atmospheric nucleation event triggers the mobility sizing system to direct its measurements to this important nucleation mode. Having demonstrated the efficacy of each of these two approaches, the effort of this project focuses on extending these capabilities, with refinement based on modeling and experimental verification. The instruments will be coupled with common control to provide a single, adaptive measurement system. Adaptive protocols, as well as the instrument components, will be further refined under field testing in conjunction with another air quality measurement program. In addition to the automated adaptive system for studying atmospheric nucleation events, this SBIR project will produce two new instruments, a flexible differential mobility analyzer and a dual size range nanoparticle counter, both of which will see broad application within, and outside of, atmospheric aerosol research.