Ref. No. [UMCES]CBL 2013-014
ACT VS12-01
EXECUTIVE SUMMARY
Instrument performance verification is necessary so that effective existing technologies can
be recognized, and so that promising new technologies can become available to support coastal
science, resource management, and ocean observing systems. The Alliance for Coastal Technologies
(ACT) has therefore completed an evaluation of commercially available in situ hydrocarbon sensors.
This verification included test applications for: (1) controlled laboratory tanks with additions of
various organic, fluorescent compounds, (2) experimental wave tank with additions of two sources of
crude oils with and without dispersants, (3) a moored deployment in Baltimore Harbor, and (4)
hydrocast surveys in the Gulf of Mexico at a site near a submerged leaking oil barge.
In this Verification Statement, we present the performance results of the Chelsea UV
Aquatracka CDOM (UV-CDOM) and Hydrocarbon (UV-HC) fluorometers. It should be noted that
the initial lab trials were performed with the UV-CDOM configuration of the Aquatracka because the
Hydrocarbon unit was not available at the time. Quality assurance (QA) oversight of the verification
was provided by an ACT QA specialist, who conducted technical systems audits and a data quality
audit of the test data.
Response specificity of the UV Aquatracka(s) to a range of organic compounds was
evaluated in a series of lab tests. The UV-CDOM and UV-HC instruments are based on a
logarithmic response photodetector behind the emission optical filters configured to provide a 0-5V
output over its detection range. Instrument response with respect to challenge compound
concentration varied with respect to the inherent fluorescence properties of the challenge compound
as well as sensor optics. The UV-CDOM version exhibited an expected logarithmic voltage response
to concentration for both quinine sulfate (R
2
=0.9998) and carbazole (R
2
=0.9984) over a 0 – 100 ppb
concentration range and was largely insensitive to naphthalene disulfonic acid (NSDA) and Basic
Blue 3. While the UV-HC was not available for this challenge series, it also exhibited the expected
log-response to #2 Diesel Fuel Oil (R
2
=0.9986) in a follow-on lab test. Similar performance was
observed in the Bedford Institute of Oceanography wave tank test using exposures to Arabian Light
and Alaskan North Slope crude oils in the presence of Corexit 9500 (R
2
=0.9326 and 0.9274
respectively). Instrument responses to various challenge compounds converged when compared to
standardized EEMs fluorescence intensity estimated to correspond to the instruments emission
optics.
Field deployments in Baltimore Harbor and northern Gulf of Mexico were equivocal as all
field reference samples were at or below the limit of detection for total petroleum hydrocarbons (≤ 25
ppb), yet the Aquatracka UV-HC output was above the baseline response in deionized water.
Instrument response was consistent with environmental background fluorescence as determined by
EEMs analysis for both moored and hydrocast surveys, indicating that ambient fluorescence
properties need to be accounted for to make quantitative hydrocarbon estimates from these sensors.
During this evaluation, no problems were encountered with the provided software, set-up
functions, or data extraction at any of the test sites. One hundred percent of the data was recovered
from the instrument and no outlier values were observed for any of the laboratory tests, field
deployment tests, or tank exposure tests.
We encourage readers to review the entire document for a comprehensive understanding of
instrument performance.
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