Measuring Submicron-Sized Fractionated Particulate Matter on Aluminum Impactor Disks

Sub-micron sized airborne particulate matter (PM) is not collected well on regular quartz or glass fiber filter papers. We used a micro-orifice uniform deposit impactor (MOUDI) to fractionate PM into six size fractions and deposit it on specially designed high purity thin aluminum disks. The MOUDI separated PM into fractions 56-100 nm, 100-180 nm, 180-320 nm, 320-560 nm, 560-1000 nm, and 1000-1800 nm. Since the MOUDI has a low flow rate (30 L/min), it takes several days to collect sufficient carbon on 47 mm foil disks. The small carbon mass (20-200 microgram C) and large aluminum substrate (~25 mg Al) present several challenges to production of graphite targets for accelerator mass spectrometry (AMS) analysis. The Al foil consumes large amounts of oxygen as it is heated and tends to melt into quartz combustion tubes, causing gas leaks. We describe sample processing techniques to reliably produce graphitic targets for (14)C-AMS analysis of PM deposited on Al impact foils.     

Input of 129I into the western Pacific Ocean resulting from the Fukushima nuclear event

We present an initial characterization of the input of ¹²⁹I into the Pacific Ocean resulting from the 2011 Fukushima nuclear accident. This characterization is based primarily on ¹²⁹I measurements on samples collected from a research cruise conducted in waters off the eastern coast of Japan in June 2011. These measurements were compared with samples intended to reflect pre-Fukushima background that were collected during a May 2011 transect of the Pacific by a commercial container vessel. In surface waters, we observed peak ¹²⁹I concentrations of ~300 μBq/m³ which represents an elevation of nearly three orders of magnitude compared to pre-Fukushima backgrounds. We coupled our ¹²⁹I results with ¹³⁷Cs measurements from the same cruise and derived an average ¹²⁹I/¹³⁷Cs activity ratio of 0.442 × 10^?6 for the effluent from Fukushima. Finally, we present ¹²⁹I depth profiles from five stations from this cruise which form the basis for future studies of ocean transport and mixing process as well as estimations of the total budget of ¹²⁹I released into the Pacific.