TITLE: RADON_MLO_2001_ACEASIA_IOP AUTHOR: Dr Wlodek ZAHOROWSKI Australian Nuclear Science and Technology Organisation (ANSTO) PMB 1, Menai, NSW 2234, Australia Phone: +61 2 9717 3804 Fax: +61 2 9717 9260 Email: wza@ansto.gov.au 1.0 DATA SET OVERVIEW: Introduction or abstract: 222Rn has been measured with a dual-flow loop two-filter detector [1]. Four radon detectors have been deployed in Southeast Asia and the Pacific Ocean to record hourly radon concentration in air at selected ACE-Asia ground stations. This includes an instrument at Mauna Loa (19deg28min N, 155deg36min W). The lower limit of detection for a one hour radon count is about 40 mBq m-3. The response time, defined as the time to reach 50% of maximum count rate after step increase in radon concentration, is about 45 minutes. Typically, sample air is drawn continuously at a rate of at least 80 L/min from the site intake mast. Calibration of the detectors is performed periodically by injecting radon from a radon source calibrated by the source's manufacturer (Pylon) against a NIST certified radium liquid standard. The typical data recovery rate is about 90%. Time period covered by the dataset: 1 Mar 2001 - 31 May 2001. Physical location (including lat/lon/elev) of the measurement or platform: Mauna Loa Observatory (19deg28min N, 155deg36min W). Data source: ANSTO 2.0 INSTRUMENT DESCRIPTION: The design is based on the two-filter method which relies on the sampled air being drawn continuously through one filter which removes all radon decay products, then through a delay chamber in which some new progeny are produced. Finally air passes through a second filter which collects the progeny at a rate proportional to the radon concentration. There are two air flows: the external flow takes the sampled air through an inlet filter where existing radon progeny are filtered from the sample; the internal flow rate is high to maximise the likelihood of the progeny plating out on the wire mesh filter rather than on the walls of the chamber. The collected progeny decay by alpha decay which is detected in a scintillator/photomultiplier assembly. Dual flow loop wire screen radon detector can measure radon concentration in air down to 20 mBq m-3 with a time response of about 45 minutes to 50% of the maximum after a step increase in radon concentration. 3.0 DATA COLLECTION AND PROCESSING: Continuous air sampling at 80L/min. Hourly counts converted to concentrations using calibrated source as a reference. Monthly calibrations and annual (or more frequent) evaluation of instrument background. 4.0 DATA FORMAT: Data file structure: header and column delimited ASCII, Data format and layout: PI/DATA CONTACT= Zahorowski, Wlodek DATA COVERAGE = START: 0301000000; STOP: 0531140000 UTC PLATFORM/SITE = Mauna Loa Observatory INSTRUMENT = Dual flow loop, two filtered radon detector LOCATION = MLO, Hawaii DATA VERSION = 3.0 (30 Sep 2001) REMARKS = ANSTO, ACE-Asia REMARKS = Missing data = -9999 REMARKS = Hourly radon concentrations are continuously detected DATE/TIME RADON UTC mBq m-3 5.0 DATA REMARKS: The time stamp refers to the end of one hour counting period 6.0 REFERENCES: [1] Whittlestone S. and Zahorowski, W. Baseline radon detectors for shipboard use: Development and deployment in the First Aerosol Characterisation experiment (ACE 1). J. Geophys. Res. 103, 16,743-16,751, 1998.