Adaptive Measurement of Nuclei Particle Size and Concentration

Airborne particles play a critical role in cloud formation, and climate. Atmospheric nucleation events inject large numbers of ultrafine particles into the air, some of which grow sufficiently large to affect the formation and characteristics of clouds. Yet widespread monitoring of these events is limited by the complexity, cost, and size of available instrumentation. Measurements aloft are especially important to understanding these processes, but are challenging, as instrumentation packages must be small. In turn, this asks for flexibility to adapt hardware to the prevailing atmospheric conditions. This project will develop an adaptive system for physical characterization of newly formed atmospheric aerosol that will be suitable for measurements aboard small drones and tethered balloons, as well as ground sites. This system consists of a “nucleation event trigger” coupled to a compact, multi-size range mobility sizing system, wherein the nucleation event trigger is used to select the size range spanned by the mobility instrument. The nucleation event trigger is a new type of Condensation Particle Counter that combines adiabatic expansion and laminar flow diffusion in a single instrument to give particle number concentrations above two size thresholds, >2 nm and >10nm, with a cycle time of a few seconds. The multi-size range mobility system is based on the compact “Spider” developed previously under DOE sponsorship for rapid (30s scanning) 10-500 nm particle sizing. This will be adapted to measure particles in the 4-20 nm range, while maintaining its larger range capability. The adaptive system will combine measurements from both systems and will adjust the size range of the mobility sizer based on the preponderance of particles in the 2-10 nm size range indicated by the nucleation event trigger. Additionally, both the nucleation event trigger and the mobility analyzer components will be programmed to automatically adapt to their operating environment to ensure consistent performance of over a range of altitudes, from ground level to 6000m. The combined system will be compact, weighing less than 5 kg without battery, and requiring less than 20W. The Phase I project focuses on (1) development of the dual adiabatic expansion, laminar flow condensation particle counter that will act as the nucleation trigger; (2) extension of the capability of our compact mobility sizing system to include the nucleation mode measurements; and (3) development of effective adaptive strategies for controlling the mobility sizing. Building on preliminary success, and guided by modeling and experiment, we will demonstrate the feasibility to rapidly count particles over the >3 nm and >10nm size ranges in a compact, low-power system. Building on the current capabilities of our compact Spider mobility system, we will design and test a system to extend sizing into the nucleation mode while maintaining the larger size capability. We will examine how to adapt measurement protocols to track new particle formation events. The Phase II project will refine these components, and integrate them into a single device, that provides detailed nuclei mode particle sizing during particle formation events over a range of altitudes. This system will aid DOE’s research studies, and atmospheric aerosol research more generally. Beyond atmospheric research, commercial applications include aerosol characterization for nanoparticle fabrication, for the ever-increasing number of industrial processes using nanoparticles, and worker safety.