Quartz-Enhanced Photoacoustic Spectroscopy for Field Calibration of Atmospheric Aerosol Absorption Properties
For atmospheric research and environmental monitoring, there is a great need for accurate measurements of light-absorbing aerosols in the atmosphere. To address this need, we developed and built a compact and rugged field instrument for measuring light-absorbing aerosols using a variation of photoacoustic spectroscopy (PAS) called intracavity quartz-enhanced photoacoustic spectroscopy (intracavity QEPAS). It uses a quartz tuning fork as the sensing element instead of the microphone typically used in conventional PAS, enabling a high level of immunity to background noise. An additional benefit is a reduction in size since the tuning fork also serves as a resonator, so the acoustic resonance chamber typically used in conventional PAS is not needed, therefore leading to a significantly smaller sample volume and a more compact overall footprint. In this Phase I effort, feasibility was demonstrated by constructing a breadboard intracavity QEPAS system and using it to measure aerosol concentrations from soot over a large range of concentrations. The breadboard sensor was able to detect soot particles and accurately monitor changes in concentration in real time with very good agreement with a reference instrument. The response of the sensor was found to be linearly dependent on the soot particle mass concentration. From the sensitivity relationship obtained and the observed noise minimum, the minimum detectable soot mass concentration of the feasibility breadboard was determined to be 9.8 μg/m3 in a 20-s measurement time and is expected to improve to about 0.14 μg/m3 after optimization in the next stage of development during a potential Phase II effort. Thus, an optimized version would have at least as good a measurement sensitivity as the best state-of-the-art instruments, while being able to operate in a significantly noisier environment and with a smaller footprint. The feasibility breadboard system showed immunity to background noise levels of up 75 dB and showed promise of being able to operate at even higher noise levels with modifications. Based on the promising results from this effort, we recommend that a follow-on experimental study be conducted to determine the optimum intracavity configuration for providing the highest measurement sensitivity and lowest susceptibility to acoustic background noise. Further, we also recommend that a prototype instrument be designed, constructed, and tested in a noisy environment, such as mounted to a ground vehicle or aircraft. The goal will be to demonstrate measurements of light-absorbing aerosols with a sensitivity of better than 1 Mm-1 under challenging field conditions. The instrument would benefit efforts to model climate change by enabling widespread data on light-absorbing aerosols, which is a critical need identified by the Intergovernmental Panel on Climate Change.
- Research Organization:
- MetroLaser, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC), Engineering & Technology. Office of Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) Programs
- DOE Contract Number:
- SC0020526
- OSTI ID:
- 1760279
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- TDE09TJ01F_F; DE09
- Country of Publication:
- United States
- Language:
- English
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