Andreas Markwitz

UV and humidity sensing properties of ZnO nanorods prepared by the arc discharge method

The UV and humidity sensing properties of ZnO nanorods prepared by arc discharge have been studied. Scanning electron microscopy and photoluminescence spectroscopy were carried out to analyze the morphology and optical properties of the as-synthesized ZnO nanorods. Proton induced x-ray emission was used to probe the impurities in the ZnO nanorods. A large quantity of high purity ZnO nanorod structures were obtained with lengths of 0.5-1 microm. The diameters of the as-synthesized ZnO nanorods were found to be between 40 and 400 nm. The nanorods interlace with each other, forming 3D networks which make them suitable for sensing application. The addition of a polymeric film-forming agent (BASF LUVISKOL VA 64) improved the conductivity, as it facilitates the construction of conducting networks. Ultrasonication helped to separate the ZnO nanorods and disperse them evenly through the polymeric agent. Improved photoconductivity was measured for a ZnO nanorod sensor annealed in air at 200 degrees C for 30 min. The ZnO nanorod sensors showed a UV-sensitive photoconduction, where the photocurrent increased by nearly four orders of magnitude from 2.7 x 10(-10) to 1.0 x 10(-6) A at 18 V under 340 nm UV illumination. High humidity sensitivity and good stability were also measured. The resistance of the ZnO nanorod sensor decreased almost linearly with increasing relative humidity (RH). The resistance of the ZnO nanorods changed by approximately five orders of magnitude from 4.35 x 10(11) Omega in dry air (7% RH) to about 4.95 x 10(6) Omega in 95% RH air. It is experimentally demonstrated that ZnO nanorods obtained by the arc discharge method show excellent performance and promise for applications in both UV and humidity sensors.

Urban air quality in the Asian region

Over the past decade, member states of the Regional Co-operation Agreement (RCA), an intergovernmental agreement for the East Asia and Pacific region under the auspices of the IAEA with the assistance of international organizations and financial institutions such as the World Bank and the Asian Development Bank, have started to set in place policies and legislation for air pollution abatement. To support planning and evaluate the effectiveness of control programs, data are needed that characterizes urban air quality. The focus of this measurement program describe in this report is on size segregated particulate air pollution. Such airborne particulate matter can have a significant impact on human health and urban visibility. These data provide the input to receptor models that may permit the mitigation of these impacts by identification and quantitative apportionment of the particle sources. The aim of this report is to provide an overview of the measurements of concentrations and composition of particulate air pollution in two size fractions across the participating countries. For many of the large cities in this region, the measured particulate matter concentrations are greater than air quality standards or guidelines that have been adopted in developed countries.

Fabrication of surface magnetic nanoclusters using low energy ion implantation and electron beam annealing

Magnetic nanoclusters have novel applications as magnetic sensors, spintronic and biomedical devices, as well as applications in more traditional materials such as high-density magnetic storage media and high performance permanent magnets. We describe a new synthesis protocol which combines the advantages of ion implantation and electron beam annealing (EBA) to produce surface iron nanoclusters. We compare the structure, composition and magnetic properties of iron nanoclusters fabricated by low dose 15 keV Fe implantation into SiO(2) followed by 1000 °C EBA or furnace annealing. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) images together with superconducting quantum interference device (SQUID) magnetometry measurements show that only EBA leads to the rapid formation of surface crystalline Fe spherical nanoclusters, showing magnetic moments per Fe atom comparable to that of bulk bcc Fe and superparamagnetic properties. We propose a fabrication mechanism which includes e-beam enhanced desorption of SiO(2). This method has potential for fabricating nanoscale magnetic sensors integrated in microelectronic devices.

Non‐diadromous recruitment in coastal populations of common bully (Gobiomorphus cotidianus)

Abstract Otolith microchemistry of common bullies (Gobiomorphus cotidianus) collected from the lower reaches of the Mataura, Clutha, and Taieri/Waipori River systems of New Zealand was examined using particle induced X‐ray emission (PIXE). High strontium:calcium (Sr:Ca) ratios in otolith cores relative to otolith edges suggested either diadromous or estuarine‐reared common bullies are present in all three systems, including fish collected from Clydevale (50 km inland) on the Clutha River. However, constant or slightly variable Sr:Ca ratios from otolith core to edge, suggesting a non‐diadromous life history, were also observed in fish from the lower Mataura and Taieri/Waipori systems, even where access to the sea was continuously available. The results suggest that diadromy in common bully may be facultative, and that a proportion of the common bully population may be non‐diadromous in river systems where suitable larval/juvenile rearing habitat is present.

Air pollution by fine particulate matter in Bangladesh

Abstract In Dhaka, Bangladesh, particular matter (PM) is the air pollutant that is most harmful to public health and the environment when compared to other measured criteria pollutants. During recent years, the Government of Bangladesh has tried to control PM emissions coming from anthropogenic sources. About 30–50% of the PM 10 mass in Dhaka (depending on location) is in fine particles with aerodynamic diameter less than 2.2 µm. These particles are mainly of anthropogenic origin and predominately from transport–related sources. However, the combination of meteorological conditions, long–range transport during the winter and local sources results in PM concentrations remaining much higher than the Bangladesh National Ambient Air Quality Standard (BNAAQS). It has been found that black carbon accounted for about 50% of the total fine PM mass before the adoption of control policies. As a result, the PM emission as well as BC has not increased in proportion to the increase in the number of combustion sources like motor vehicles, diesel power generator or brick kiln. Positive Matrix Factorization (PMF) was applied to fine particle composition data from January 2007 to February 2009. It was found that motor vehicles contribute less BC with respect to brick kiln industry. This result demonstrates the effectiveness of the government’s policy interventions since previously vehicles represented the major contributors of BC. BC is also transported over long distances, mixing with other particles along the way as demonstrated by a potential source contribution function analysis. Transboundary transport of air pollution in the South Asian region has become an issue of increasing importance over the past several decades. The relative amounts of local and long–range transported pollutants are currently unknown.

Air particulate matter pollution in Ulaanbaatar, Mongolia: determination of composition, source contributions and source locations

Ulaanbaatar, the capital city of Mongolia is subject to high air particulate matter pollution episodes during winter and during dust storm events in spring and autumn that have severe implications for the health of the exposed population. This paper presents the results of fine (PM2.5) and coarse (PM10–2.5) particulate matter monitoring in Ulaanbaatar from 2004 to 2008 and receptor modelling to determine the sources contributing to particulate matter pollution. Ion Beam Analysis was used to determine elemental concentrations in the two size fractions and black carbon was measured with a light reflectance device. Mass contributions to ambient particle concentrations from emission sources were estimated by positive matrix factorisation and air mass back–trajectory analysis was used to assess probable source locations. The results show that crustal matter sources are the primary contributors to the coarse particle fraction. Combustion sources (coal combustion, biomass burning, and motor vehicles) dominate the fine fraction of particulate matter in the Ulaanbaatar airshed, primarily from local emission sources but forest fires to the north can be a significant contributor to biomass burning concentrations at times. Analysis of seasonal differences showed that coal combustion processes were largely responsible for fine particle air pollution episodes during winter. Temporal trends show an increase in the coal combustion contributions over the monitoring period. We suggest that this is linked to the increase in the Ulaanbaatar population and a consequent increase in the use of coal for power generation and domestic heating purposes.

Long-range transport of soil dust and smoke pollution in the South Asian region

Transboundary transport of air pollution in the South Asian region has been an issue of increasing importance over the past several decades. Long–range transport of anthropogenic pollution is contrasted with that of pollution produced by natural processes such as dust storms or natural forest fires. Airborne particulate matter datasets covering the period from 2002 to 2007 from the neighboring countries like Bangladesh, India, Pakistan and Sri Lanka were used to find the source areas that are primarily responsible for long range transported pollutants. All four countries collected samples with the same type of sampler and follow the same technique for mass and BC measurements. It was found that high fine soil contributions were from dust storms. On the other hand, smoke in this region mainly comes from northern India where agricultural waste is often burned.

Identification of Particulate Matter Sources on an Hourly Time-Scale in a Wood Burning Community

Particulate matter (PM) sources at two different sites in a rural town in New Zealand were investigated on an hourly time-scale. Streaker samplers were used to collect hourly, size-segregated PM(10-2.5) and PM(2.5) samples that were analyzed for elemental content using ion beam analysis techniques. Black carbon concentrations were determined using light reflection and PM(10) concentrations were recorded using colocated continuous PM monitors. PM(10) concentrations at both sites displayed a diurnal pattern, with hourly PM(10) concentration maxima in the evening (7 pm-midnight) and in the morning (7-9 am). One of the monitoring sites experienced consistently higher average PM(10) concentrations during every hour and analysis indicated that katabatic flows across the urban area contributed to the increased concentrations observed. Source apportionment using positive matrix factorization on the hourly data revealed four primary PM(10) sources for each site: biomass burning, motor vehicles, marine aerosol and crustal matter. Biomass burning was the most dominant source at both sites and was responsible for both the evening and morning PM(10) concentration peaks. The use of elemental speciation combined with PM(10) concentrations for source apportionment on an hourly time-scale has never been reported and provides unique and useful information on PM sources for air quality management.

Effect of substrate hardness on splat morphology in high-velocity thermal spray coatings

In this study, Ni-chrome alloy particles were thermally sprayed onto a variety of substrate materials using the high-velocity air fuel (HVAF) technique. Although the various substrate materials were sprayed using identical powder material and thermal spray conditions, the type and variation of splat morphologies were strongly dependent on the substrate material. Predominantly solid splats are observed penetrating deeply into softer substrates, such as aluminum, whereas molten splats were observed on harder substrates, which resisted particle penetration. The observed correlation between molten splats and substrate hardness could be due a dependency of deposition efficiencies of solid and molten splats on the substrate material. However, it was found that conversion of particle kinetic energy into plastic deformation and heat, dependent on substrate hardness, can make a significant contribution towards explaining the observed behavior.

AIR PARTICULATE RESEARCH CAPABILITY AT THE NEW ZEALAND ION BEAM ANALYSIS FACILITY USING PIXE AND IBA TECHNIQUES

PIXE and Ion Beam Analysis are one of the few techniques that can be used to identify the elemental composition of air particulates without destroying the filter sample. They are key tools for identifying the sources and determining the relative contribution of biogenic and anthropogenic sources of air particulate matter pollution in our environment. Over the last 8 years, specialised equipment has been designed and built at the New Zealand Ion Beam Analysis facility in Lower Hutt for semi automated analysis of air filters. The equipment and experimental techniques have been refined to improve sensitivities for many of the elements in the periodic table. At GNS, sensitivities have recently been further improved by using two X-ray detectors simultaneously with different amounts of X-ray filtering and collimation. The average limit of detection is improved from 66 ng/cm2 (typical for a setup using a single detector) to 35 ng/cm2 using two detectors simultaneously. The New Zealand Ion Beam Analysis facility now routinely analyses air particulate matter collected on filters from several locations around New Zealand. In this paper, results of air particulate studies from several locations in the Wellington region are presented.