Configuration and Operation of Marine Aerosol Generator Deployed on R/V Endeavor EN589 during Sept.- Oct. 2016 (NCEI Accession 0278891)

Acquisition Description:
The marine aerosol generator was operated by William Keene (wck@virginia.edu) and John Maben. Please direct any related questions to William Keene.

Description and Operation of the Marine Aerosol Generator: Model primary marine aerosol (mPMA) was produced in a high-capacity generator fabricated from Pyrex and Teflon. See Keene et al. [2007] for a description and schematic of the original configuration of the device and Long et al. [2014] for an explanation of modifications implemented for deployment on ships at sea during the 2010 California Nexis (CalNex) campaign in the eastern North Pacific Ocean and the 2012 Western Atlantic Climate Study (WACS) in the western North Atlantic Ocean. During all previous deployments, bubble plumes were produced using sintered-glass frits and/or plunging seawater jets. During the Endeavor cruise, frits were replaced with force-air Venturis as described below.

Briefly, the 20-cm-diameter generator consisted of a 122-cm-deep seawater reservoir underlying a 97-cm-deep atmosphere. During most periods, fresh seawater drawn from approximately 5-m depth through the ship’s clean seawater line flowed into the base of the seawater reservoir (typically at 4 L min-1) and drained evenly to exhaust over the top annular rim thereby continuously replacing the seawater surface and minimizing formation of standing bubble rafts. During two periods, feed seawater flowing through the generator was transferred from carboys containing seawater that had been collected at a depth of 2500 m, stored in 20 L Teflon lined carboys, and warmed to room temperature. Bubble plumes were generated by two mechanisms. (1) Ultra-pure air and seawater (drawn from the base of the generator’s seawater reservoir) were pumped at adjustable rates of 1 to 5 L min-1 each through one of two force-air Venturi nozzles that were fabricated from Teflon and positioned at depths of 42 (shallow) and 72 cm (deep), respectively, below the air-seawater interface. (2) Bubble plumes were also produced by a seawater jet at flow rates of 1 to 3 L min-1 that impinged on the air-seawater interface. The jet nozzle was 0.32-cm ID and positioned at 50 cm above the interface.

mPMA was emitted to the headspace when bubbles rose to and burst at the air-seawater interface. Ultra-pure sweep air flowed through the headspace above the seawater reservoir at 70 L min-1. During most sampling periods, sweep air was hydrated to a relative humidity (RH) of ~80%. mPMA was sampled for chemical and physical characterization through isokinetic ports at the top of the generator.

The generator was blank tested by measuring mPMA number concentrations in the headspace at typical flow rates of bubble and sweep air but with no seawater in the reservoir. All blank tests yielded undetectable particle number concentrations (less than 2 cm-3) indicating that all particles measured during routine operation originated from seawater.

Bubble-plume void fractions were quantified over ranges of conditions by filling the generator, turning off the flow of feed seawater, incrementally increasing the flow of air through the Venturi, and measuring the volume of displaced water.

Refer to the elated papers below for additional details regarding the design and operation of the marine aerosol generator and associated analytical methods.