Aerosol Chemistry Field Calibration System

The Department of Energy’s Office of Biological and Environmental Research has identified a programmatic need for increasing the utility and reliability of field deployed instruments currently in use and under development. Reliably quantifying measurement uncertainties is fundamentally important for scientific measurements and DOE has identified a need for improved field portable calibration systems. The calibration of aerosol mass spectrometers that respond to chemically specific aerosol mass require introduction of known calibrant aerosol levels. Currently there is no way to provide fixed mass delivery of aerosols but instead rely on sampling distributions of generated calibration particles that are sized and counted to estimate the delivered mass to the recipient instrument. This approach has multiple sources of uncertainty related to physical properties unrelated to mass. The proposed device builds on the well-established method of drug delivery- the meter dose inhaler or atomizer- that was developed specifically to deliver fixed mass doses. The proposed aerosol chemical calibration device will use decoupled reservoirs for increased flexibility so different calibrants can be used. It will also 1) deliver scalable quantities of solute with high mass precision, 2) minimize consumption of solvents and standards, 3) remain sufficiently clean to handle mass spectrometer level sensitivities without contaminant interference and 4) be packaged in a fully automated compact, field portable system. In the Phase I effort, a self-contained, fixed mass atomizer will be developed and tested for efficiency and reliability of delivering aerosol. A working prototype using a range of calibrants will be tested directly on a mass spectrometer based aerosol instrument for validation of the working principle. The proposed aerosol calibrator will improve quantification accuracy in measuring a wide range of chemically resolved aerosols. Many atmospheric aerosol properties of interest currently measured e.g. optical scattering and absorption, cloud or ice formation potential) depend on chemical composition. Therefore, indirect benefits would be obtained by reducing measurement uncertainties with mass spectrometer based instruments. This new calibration approach could additionally serve as a new benchmark standard by which to evaluate a wide spectrum of aerosol instrumentation. The three broad technology classes of aerosol samplers, generators or control systems would all potentially benefit from such an improved means of standardized delivery of calibration aerosol.