Determination of oceanic ozone deposition by ship-borne eddy covariance flux measurements

Abstract

A fast response ozone analyzer based on the ozone-nitric oxide chemiluminescence method was integrated into the NOAA-ESRL flux system to achieve the first ship-borne, direct ozone flux measurements over the open ocean. Air was collected from an inlet at 18 m height over the ocean surface mounted to the bow-jackstaff and via a 30 m-long sampling line to the ozone instrument on the ship deck. A "puff" system was used for accurate and regular determination of the sample transport time (lag) between the inlet and the chemical analyzer. A Nafion-membrane dryer facilitated removal of fast water vapor fluctuations, which eliminated the need for quenching and density correction of the ozone signal. The sampling-analyzer system was found to have a ~0.25–0.40 s response time at a sensitivity of ~2800 counts s^&minus;1 per ppbv of ozone. Quality control and data filtering procedures for eliminating data that did not meet measurement requirements were critically evaluated. The new ozone flux system was deployed aboard the NOAA Ship <i>Ronald H. Brown</i>, and evaluated using results obtained during several research cruises off the coasts of the North and South America continents, yielding ozone deposition velocities (mean &plusmn; standard error) ranging from 0.009&plusmn;0.001 cm s^&minus;1 to 0.24&plusmn;0.020 cm s^&minus;1.