Low-cost, time-resolved chemical characterization of atmospheric aerosols
SIGNIFICANCE OF THE PROBLEM: The composition of atmospheric particulate matter (“aerosols”) strongly influences its health and environmental impacts, but there exist few time-resolved, long-term records of particle-phase chemical composition. Currently, the composition is measured either by off-line analyses of time-integrated filter samples, or by in-situ instruments requiring near-constant operator oversight, resulting in sparse or limited data coverage. New measurement approaches are needed that are robust, easy-to-operate, and suitable for DOE ARM and other atmospheric monitoring facilities for operationally-inexpensive measurements of particle composition. TECHNICAL APPROACH: In the proposed “ChemSpot™” instrument, airborne particles from 0.005 - 2.5 micron are captured as a concentrated “spot” deposit using a unique moderate-temperature, water-based condensation method that allows efficient sampling of small particles onto a passivated surface at near-atmospheric pressure. The collection surface is then heated to desorb samples for direct analysis by a suite of proven, robust, field-deployable detectors. A flame ionization detector (FID) coupled to a downstream CO2 detector provides organic carbon concentration as well as a novel measurement of oxygen content. In addition, sulfur-containing compounds are detected using a flame photometric detector (FPD). This approach is flexible, allowing easy expansion to include additional detectors to target other elements. Rapid and precise temperature stepping provides volatility-resolution by controlled desorption. RESULTS: Validation of the measurement approach consisted of extensive laboratory testing. Particle collection efficiency exceeded 97% for particle sizes from 7 nm to the largest size tested of 900 nm, and transfer of samples to detectors was 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; both organic and inorganic sulfur were measured. Calibration of detectors by gas-phase standards was shown to be equivalent to thermal desorption of known compounds. Measuring CO2 produced by an FID flame was shown to provide 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). Sample transfer was achieved in rapid temperature steps (20 °C/s) up to 400 °C, with feasible volatility-resolution into 3-4 bins. A complete prototype instrument was also demonstrated in Phase I that interfaced ambient sample collection, thermal transfer to detectors, and analysis, all automated for continuous operation. Ambient samples were autonomously collected for 4 consecutive days, with measured mass concentrations and oxygen content within the range of expectations. Sampling a laboratory source of aerosol verified effective sample collection and analysis. Desorption temperatures of ambient samples also indicate the feasibility of volatility resolution. APPLICATIONS IN RESEARCH: The novel measurement approaches and prototype instrument developed in Phase I will offer a robust and straightforward method for the on-line measurement of particle composition, providing basic chemical and volatility information with hourly time-resolution and little operator effort. Autonomous measurements of volatility-resolved particle-phase carbon and oxygen-to-carbon ratio, as well as inorganic sulfur will represent a substantial improvement to current routine monitoring capabilities. Furthermore, calibration can rely primarily on stable gas-phase standards, allowing simple automated calibration systems conducive to remote deployment and robust operation. The simple data streams produced by these detectors enable automated data processing without the need for complex data analysis. With the additional optimization, research, and validation proposed in Phase II, this instrument will allow hourly measurements of the composition of atmospheric particulate matter, with capital and operational costs that will allow substantially increased spatial and temporal extent of available data.
- Research Organization:
- Aerosol Devices Inc.
- Sponsoring Organization:
- Office of Science (SC), Biological and Environmental Research (BER). Earth and Environmental Systems Science Division
- DOE Contract Number:
- SC0018462
- OSTI ID:
- 1507935
- Type / Phase:
- STTR (Phase I)
- Report Number(s):
- DOE-ADev-18462-1
- Country of Publication:
- United States
- Language:
- English
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