DOI: 10.6075/j04f1nnx
title: Measurements of Generated and Ambient Marine Aerosol Particles in August 2012 on board the R/V Ronald H. Brown during the Western Atlantic Climate Study (WACS)

description: Measurements of generated primary marine aerosol particles were collected on board the R/V Ronald H. Brown in the Atlantic Ocean at a biologically productive site and a non-productive site from 19 August to 27 August 2012. Generated primary marine aerosol particles (gPMA) were produced with two model ocean systems, the Bubbler and the Sea Sweep. Sea Sweep Description: The Sea Sweep consisted of a raft deployed over the side of the ship in the ambient seawater. Bubbles were created with stainless-steel diffusion frits at 75 cm below the ocean surface, and the resulting aerosol particles were transported onto the ship for characterization. Bubbler Description: Model primary marine aerosol (gPMA) was produced in a high-capacity generator fabricated from Pyrex and Teflon (referred to here as the Bubbler). See Keene et al. [2007] for a detailed description and schematic of the device and Long et al. [2014] for an explanation of modifications implemented for deployment on ships at sea. Briefly, the 20-cm-diameter generator consisted of a 122-cm-deep seawater reservoir underlying a 97-cm-deep atmosphere. 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<sup>-1</sup>) and drained evenly over the top annular rim thereby continuously replacing the seawater surface and minimizing formation of standing bubble rafts. Bubbles were generated by two mechanisms. First, bubble plumes were produced by pumping ultra-pure air through a coarse porosity sintered glass frit (45-mm diameter, 145- to 174-μm pore size) or through 11 fine porosity sintered glass frits (90-mm diameter, 10- to 20-μm pore size) positioned at an average depth of 84 cm below the air-seawater interface, which is within the range of ambient bubble-cloud depths generated by breaking waves on the open-ocean surface. The fine frits were plumbed as two independently regulated sets of 5 and 6 frits each that were positioned at average depths of approximately 60 and 100 cm, respectively. To prevent flooding via backflow of seawater into the bubble-air feed lines, it was necessary to maintain finite positive pressure behind and associated minimal air flow of 0.2 L min<sup>-1</sup> through the course frit and each set of fine frits (total of 0.6 L min<sup>-1</sup>). Second, bubble plumes were also produced by one or two seawater jets at combined flow rates of 1 to 4 L min<sup>-1</sup> that impinged on the air-seawater interface. Jet nozzles were 0.32-cm ID and positioned at 50 cm above the interface. gPMA were 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 48 to 70 L min<sup>-1</sup> (depending on the combined flow rates required to accommodate different sampling devices). During most sampling periods, sweep air was hydrated to a relative humidity (RH) of 80±2%. . 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<sup>-3</sup>) indicating that all particles measured during routine operation originated from seawater. Particle Number Size Distributions: Number size distributions were measured under different configurations of the system. For some characterizations, a diffusion dryer was mounted in line between the generator and the sizing instruments and, for others, no dryer was mounted in line. In addition, for some characterizations, the scanning electrical mobility spectrometer (SEMS, Brechtel Manufacturing, Inc.) was plumbed to use dry room air as sheath air and, for others, humid sample air was used as sheath air. Finally, for some characterizations, the aerodynamic particle sizer (APS, TSI) was configured with the standard brass inlet and, for others, it was configured with a custom plastic inlet, which helped minimize changes in the temperature and relative humidity of the sample air stream. The combined particle sizes measured ranged from 0.01 to 15 µm in diameter. Particle Filter Sampling: Ambient atmospheric submicron particles were sampled through an inlet, dried using diffusion drier, and were sampled on 37 mm Teflon filters. Submicron gPMA from the Sea Sweep the Bubbler were dried with a diffusion drier and collected on 37 mm Teflon filters. These samples were frozen and transported to the laboratory for analysis by Fourier transform infrared (FTIR, Bruker Tensor 27) spectroscopy in a temperature and humidity controlled clean room. The gPMA samples were dehydrated prior to final analysis. The FTIR spectrum for each filter was analyzed with an automated algorithm that baselined the spectra. Absorptivity and molar masses were used to convert peak area at specific wavenumbers to mass for the organic functional groups hydroxyl, alkane, amine, carboxylic acid, and carbonyl. The total organic mass (OM) is calculated as the sum of the concentrations of the organic functional groups. Size-resolved gPMA was sampled from the generator’s head space at 30 L min<sup>-1</sup> with two non-rotating Multi-Orifice Uniform Deposit Impactors (MOUDIs) operated in parallel. Substrates and back filters from one impactor were analyzed for major ions and those for the other impactor were analyzed for water extractable organic carbon (OCwe). The aerodynamic cut diameters for the impactor’s size fractions were 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, and 0.18 µm. Impactors were configured with precombusted 47-mm diameter aluminum substrates and 37-mm diameter quartz backup filters. Bulk gPMA was also sampled in parallel at 30 L min on precombusted 47-mm quartz filters. After recovery, size-resolved samples for analysis of major ions were transferred to precleaned 10-ml HDPE tubes, stored frozen, subsequently extracted in 5 mL deionized water (DIW), and analyzed by high-performance ion chromatography (IC) at the University of Virginia (UVA). One half of each bulk sample was extracted in 5 mL DIW and analyzed for major ions as described above. Size-segregated and bulk samples for analysis of OCwe were transferred to precombusted 10-mL Pyrex centrifuge tubes, extracted immediately after recovery in 5 mL DIW, stored frozen, and analyzed with a Shimadzu Model TOC-V CSH carbon analyzer at the State University of New York (SUNY). Data for gPMA samples were corrected based on median concentrations of analytes measured in dynamic handling blanks (N = 5 for impactor and 4 for bulk samples) that were loaded and unloaded during the campaign and subsequently processed and analyzed using procedures identical to those used for samples. Seawater Sampling: Unfiltered seawater for analysis of major ions was sampled in precleaned 10-ml HDPE tubes, stored frozen, and analyzed by IC at UVA. Seawater for analysis of dissolved organic carbon (DOC) was filtered through 0.2 μm Whatman POLYCAP 75 AS cartridge into precombusted 10-mL Pyrex centrifuge tubes, stored frozen, and analyzed with a Shimadzu Model TOC-V CSH carbon analyzer at SUNY. Other: Size distributions of bubbles produced in the Bubbler were determined using computer enhanced camera images taken 2 to 4 cm below the model ocean surface.
description: Reading data in ICARTT Format (.ict files): Dates and times in file names are in UTC. The date and time in the file name give the date/time at which the data within the file begin. For more information on reading and understanding the data in ICARTT format visit: http://www-air.larc.nasa.gov/missions/etc/IcarttDataFormat.htm If you are using Igor Pro, you should be able to use this software to read the files: http://cires1.colorado.edu/jimenez-group/wiki/index.php/Analysis_Software#ICARTT Alternatively, you can open the .ict files directly using the import data tool in excel. Raw HDF AMS data can be analyzed with SQUIRREL and PIKA, which are available here on AMS wiki site from CU Boulder: http://cires1.colorado.edu/jimenez-group/ToFAMSResources/ToFSoftware/index.html