Low-cost, Time-resolved Chemical Characterization of Atmospheric Aerosols

The composition of atmospheric particulate matter (“aerosols”) strongly influences health and environmental impacts, but there exist few time-resolved, long-term records of particle-phase chemical composition due to lack of appropriate monitoring tools. Needed is an instrument that is robust, easy-to-operate, with automated calibrations and data reduction, to provide operationally-inexpensive measurements of particle chemical composition. Our “ChemSpot™” instrument captures airborne particles from 0.005 - 2.5 micrometers in a concentrated “spot” deposit, which is subsequently thermally stepped to desorb for direct analysis by a flame ionization detector and a flame photometric detector coupled to a downstream CO2 detector to provide volatility- resolved organic carbon and its degree of oxygenation, plus total elemental carbon, sulfur and possibly nitrogen. Phase I validated the measurement approach. Measured particle collection efficiency is in excess of 97% for particle sizes from 7 nm to the largest size tested of 900 nm, and transfer of samples to detectors is better than 94%. Limits of detection for sample mass were estimated as 100 ng/m3 for hourly measurements of both organic carbon and total sulfur. Calibration of detectors by gas-phase standards was shown to be equivalent to thermal desorption of known compounds. Fully automated measurements on ambient air demonstrated instrument robustness. Measuring CO2 produced by an FID flame provides a new approach to measure oxygen-to-carbon ratios of individual components and mixtures to within 0.1 units across the range expected for atmospheric aerosol (0 to 1). Phase II will extend the approach to include elemental carbon analyses and nitrogen compounds, will incorporate automated calibrations and on-line “under-the-hood” data processing, to provide simple data streams of volatility binned organic carbon, oxygen-to-carbon ratio of each fraction, total elemental carbon, sulfate and possibly nitrogen. The identification of organic sulfur and nitrogen compounds will be investigated. Instruments will be validated against mass spectrometer and traditional filter measurements in chamber and ambient testing. The goal is an affordable, cost-effective monitoring tool that provides key atmospheric aerosol chemistry. Commercial Applications: Primary targeted application of this research is a monitoring tool to provide long-term, uninterrupted aerosol chemistry data for atmospheric research, for epidemiology studies, and for air quality monitoring.