Volatile particles are a major component of atmospheric aerosols and by-products of atmospheric transformation from precursors generated by aircraft engines and many other sources of anthropogenic and natural origins. Volatile particles do not present themselves as “particles” as in a condensed or particulate state, but they will emerge and be detectable as particles when they are downstream of an aircraft engine exhaust nozzle. The knowledge about the contribution of military aircraft to the formation of volatile components in the atmospheric aerosol is inadequate and currently subject to great uncertainty. One of the major uncertainties is related to the quality of volatile particle data that currently exist.

The objectives of this project were: to improve understandings of volatile particles in military aircraft engines and other type of fossil fuel combustions, to develop a new sampling system that resolves current sampling difficulty of using a tip-dilution probe, and to develop a novel instrument for precision measurement of engine particulate volatility.

Understanding the contribution of aircraft emissions to atmospheric particles starts with accurate measurement of volatile particles in the engine exhaust. This research program focused on development of a new sampling and measurement system to be deployed at the engine exhaust plane where negligible influence of ambient influence exists.  The new system consisted of a dilution chamber (DC) and vapor-particle separator (VPS). The goal of this program was for this system to be deployable to field use replacing the emission measurement system currently for nonvolatile engine particles. The new system was designed with the idea in mind that it can be used for measurement of nonvolatile particles as well as volatile particles by simply dialing in required conditions.

Volatile particles are currently challenging to sample and measure. These particles and their precursor species are highly transitional in nature, which render its quantitative determination highly difficult if not impossible. The partition of the volatile components depends on the properties of the condensing molecules and quantity of the active particle surface, which is a function of temperature and pressure. Through this project, prototype devices have been developed and tested in laboratory and field conditions using synthetic and engine emitted particles. Most importantly this project has determined the fundamental behavior of nanoparticles that consist of pure and mixed material properties in dry and wet states. The knowledge helps interpret the data produced by the new instruments (DC and VPS) developed in this project.

The prototype devices developed in this project delivered useful data for advancing the science of engine emissions measurement and aerosol volatility. The results will become the foundation for future work in sampling and measurement of volatile engine particles. An improved ability to characterize non-volatile particles from aircraft emissions will also be useful to regulatory agencies in the design of air quality control strategies for military bases and surrounding areas.