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. This project will develop an aerosol chemical calibration device to (1) deliver scalable quantities of aerosol of known composition with high mass precision, (2) be suitable for organic and inorganic species and for compound mixtures, (3) minimize consumption of solvents and standards, (4) remain sufficiently clean to handle mass spectrometer level sensitivities without contaminant interference and (5) be packaged in a fully automated compact, field portable system. In the Phase I effort, a prototype system was developed and tested for efficiency and reliability of delivering ammonium nitrate, the primary calibrant compound for the most common aerosol mass spectrometer instruments. The prototype demonstrated near 100% mass delivery efficiency with a variability under 10%. During Phase II, the calibration system will be tested on commercial grade aerosol mass spectrometers and the range of calibration compounds will be extended to include all major chemical classes of atmospheric aerosols. 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.