Performance Verification Statement for the Chelsea UviLux Hydrocarbon and CDOM Fluorometers.

Abstract

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 near a leaking oil barge. In this Verification Statement, we present the performance results of the Chelsea Technologies Group (CTG) UviLux Hydrocarbon (UV-HC) and CDOM (UV-CDOM) fluorometers. 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 two UviLux fluorometers to a range of organic compounds was evaluated in a series of lab tests. The CTG UV-CDOM and UV-HC instruments incorporate a linear response photodetector behind the emission optical filters and are configured to provide a 0-5V analog or RS232 digital output over its detection range and ambient signal overload protection above this 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 robust linear voltage response to concentration for both quinine sulfate (R2=0.9998) and carbazole (R2=0.9999) over a 0 – 1000 ppb and 0-100 ppb concentration range respectively. Diesel Fuel #2 was detected with a 7,750x lower sensitivity (R2=0.8461). This sensor configuration was also generally insensitive to naphthalene disulfonic acid (NSDA, R2=0.8672) and Basic Blue 3 (R2=0.8137) except at challenge concentrations > 500 ppb. In contrast the UV-HC configuration exhibited 9-1000x higher sensitivities to carbazole (R2=0.0.9997), NSDA (R2=0.9975) and #2 Diesel Fuel (R2=0.9865) relative to QS (R2=0.9789) and sensor output was quenched in presence of BB3. Similar performance was observed in the Bedford Institute of Oceanography – COOGER wave tank test using exposures to Arabian Light and Alaskan North Slope crude oils in the presence of Corexit 9500 with the CTG UV-HC exhibit over 10x higher detection sensitivity than the UV-CDOM configuration. Instrument responses to various challenge compounds linearly scaled with 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 UviLux-HC and -CDOM 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. Only storm induced damage to an ACT supplied communication cable resulted in premature termination of the UviLux-CDOM deployment at the Baltimore Harbor deployment. 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.