Ship Ron Brown Chemistry Atmospheric Ozone, Radon, SO2, UFCN, CN>13 (Johnson)

SO2 Measurements aboard Ronald H. Brown during ACE-Asia
Version 1.1, December 17, 2002
Inlet and Instrument
Air was pulled from 18 m above sea level down the 20 cm ID powder-coated aluminum aerosol sampling mast (6 m) at approximately 1 m3min-1. At the base of the sampling mast a 0.5 Lmin-1 flow was pulled through a 0.32 cm ID, 1m long Teflon tube, a Millipore Fluoropore filter (1.0-um pore size) housed in a Teflon filter holder, a Perma Pure Inc. Nafion Drier (MD-070, stainless steel, 61 cm long) and then through 2 m of Telfon tubing to the Thermo Environmental Instruments Model 43C Trace Level Pulsed Fluorescence Analyzer. The initial 1 m of tubing, filter and drier we located in the humidity controlled (55%) chamber at the base of the mast. Dry zero air (scrubbed with a charcoal trap) was run through the outside of the Nafion Drier at 1 Lmin-1. The analyzer was run with two channels (0-20 ppb full scale and 0-100 ppb full scale) and a 20 sec averaging time. Data were recorded every minute.
Standardization
Zero air was introduced into the sample line upstream of the Fluoropore filter for 10 minutes every hour to establish a zero baseline. An SO2 standard was generated with a permeation tube held at 50?C. The flow over the permeation tube, diluted to 17.7 ppb, was introduced into the sample line upstream of the Fluoropore filter for 10 minutes every 6 hours. The limit of detection for the 1 min data, defined as 2 times the standard deviation of the signal during the zero periods, was 170 ppt. For 30 minute data the limit of detection is reduced to 30 ppt. Uncertainties in the concentrations based on the permeation tube weight and dilution flows is < 5%. The version 2 data have been corrected for losses in the Teflon inlet valve as determined on the NEAQS 2002 field study.

Ozone:
Two ozone uv analyzers were used, a Dasibi 1008 AH and a TECO 49. The TECO 49 analyze was calibrated to a NIST traceable analyzer at NOAA-CMDL prior to the project. One minute averages of the output of each analyzer were recorded on the PMEL data system and plots were made of the raw data. A small portion of the data was deleted (consisting mostly of times that the inlet air was passed through a zero filter - usually when the relative wind was well behind the beam of the ship). After the raw data were cleaned, the Dasibi 1008 AH analyzer was calibrated to the TECO 49 record and 30-minute averages were created. The 30-minute average from each instrument was then averaged together to create the final data file. 30-minute intervals that had no clean ozone data are tagged with a value -999.

Radon:
The PMEL radon instrument is a "dual flow loop, two filtered radon detector". The general features of the instrument are described in Whittlestone and Zahorowski, Baseline radon detectors for shipboard use: Development and deployment in the First Aerosol Characterization Experiment (ACE1), J. Geophys. Res., 103, 16,743-16,751, 1998. The instrument response is due to radon gas, not radon daughters (all of the existing radon daughters are filtered out before entering the decay/counting tank). The instrument registers the total number of decay counts per 30 minute interval on a filter arising from the decay of radon in the tank. The time given in the data file is the time of the start of the counting interval. As the volume of the decay/counting tank was 905 l and the sample flow rate into and out of the tank was typically 70 l/min, the response time of the radon instrument was about 13 minutes. The radon detector was standardized in Honolulu at the beginning of the cruise and in Yokosuka at the end of the cruise using radon emitted from a known source.

Data can be downloaded in ACF format by following the ASCII link, or in binary netCDF file format by following the netCDF link