COI Funded Project: Semiconductor Sensors: Faster, Cheaper, Better for the Trace Gas Biogeochemistry in High-Spatiotemporal Variability Coastal Environments? A Scientific -Technical Reconnaissance


Project Duration: 7/18/01-7/17/02

Proposed Research

In response to the need for more and better affordable, high-performance chemical sensors, we propose to acquire a new commercial device (GC/SCD) based on tin oxide semi-conductor sensor technology for measuring carbon monoxide (and possibly methane and hydrogen) in seawater.   We will evaluate its potential for use in coastal waters (A) with and (B) without gas chromatographic separation before CO detection.   Success with option (B) would show that very rapid development of sensor arrays using these devices is feasible. Initial field measurements will delineate the range and difficulty of the scientific questions that may first be tackled locally.   Assuming that Martha's Vineyard Observatory (MVO) is the best site for initial work, we will make concentration, optical, and process rate measurements using the GC-SCD on R/V Mytilus on related local transects (Woods Hole- MVO; Vineyard Sound and Buzzards Bay).   The results will reduce uncertainties about technology, science, and site feasibility to acceptable levels for a proposal (NSF/OCE/ Instrumentation) to continue development/ science.   The best feasible initial science will probably be to study near-surface vertical mixing and gas exchange at MVO using CO as a process tracer.   Ultimately, we hope the large-scale coastal transport and transformation of Colored Dissolved Organic Matter (CDOM) from rivers and estuaries and its export into offshore blue-waters can be explored using sensor arrays.

Final Report

Keywords: instrument development, remote sensing, CO flux, gas exchange, Marthas Vineyard Observatory (MVO)

Summary Report: Semiconductor Sensors: Faster, Cheaper, Better for the Trace Gas Biogeochemistry in High-Spatiotemporal Variability Coastal Environments? A Scientific –Technical Reconnaissance

Revised goals were to: (1) lab test the FISInc GS-19 instrument for measuring carbon monoxide (CO) in marine situations, (2) to field-test it at sea in Delaware Bay after interfacing it with our automated system for CO in surface waters. These ests showed that the GS-19 is suited to our ultimate goal, autonomous use at Martha's Vineyard Coastal Observatory (MVCO). Three mini-cruises to MVCO also verified that CO-related physical, chemical, and biological dynamics there are suited for CO studies.   Prof. K. Takeda of Hiroshima University worked on sabbatical on this project about half time. He was very productive, and we could not have supported his visit without COI funding.

Our original approach of testing cheap, versatile FIS sensors (separately from the FIS instrument incorporating them) proved impossible. Their semiconductor trace gas sensors (carbon monoxide, hydrogen, and methane) are available only as a part of the GS-19 analytical system, although the sensors are on their web site as a product. After much waffling, FISinc finally admitted that they do not sell the sensors and drivers separately!

We borrowed and tested a GS-19 from Prof. Gary King (Umaine). Initial lab tests by Zafiriou showed it to be stable to motion, power fluctuations, and vibration, but sensitive to drafts (due to remediable bad design). We then interfaced it to our automated CO system via a new valve system/software (with assistance from T. Donoghue and W. Wang). Lab tests also succeeded, so we sent it on a 21-day coastal-offshore cruise with Profs. Takeda and Xie (see photograph), where it was used for several days. (Figure).

It worked OK, was adaquately sensitive, and survived all the associated shipping and travel, convincing us that it has good potential as a field instrument for MVCO and other seagoing work. As a plus, Prof. Takeda and H. Xie using our "old" analytical system (after the GS-19 had to be shipped Prog. King in Hawaii it to study lava gases) also obtained an excellent, unique data on CO variability and process rates in the Delaware estuary (to be published).

At MVCO, COI-supported fieldwork also showed the expected strong, very shallow (1-2m) mid-day thermal layering on summer low-wind days. Also, the water-column distribution of "CDOM" –the precursor of CO – was fairly uniform between WH and MVCO. (Strong gradients, if frequent, would pose problems in interpreting CO cycling.) Based on these initial data, MVCO seems highly suitable for CO studies using a GS-19.

Based largely on these results:

(1) Dr. Eric Hintsa of MC&G/WHOI has obtained WHOI internal funds to acquire a GS-19. It will be buoy-mounted to measure CO in air at moorings.

(2) We expect to collaborate in generating a proposal to work on CO in air and water at MVCO