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Fang F.,Institute of Geological & Nuclear Sciences | Kennedy J.,Institute of Geological & Nuclear Sciences | Futter J.,Institute of Geological & Nuclear Sciences | Hopf T.,Institute of Geological & Nuclear Sciences | And 3 more authors.
Nanotechnology | Year: 2011

Several different synthetic methods have been developed to fabricate tungsten oxide (WO3) nanostructures, but most of them require exotic reagents or are unsuitable for mass production. In this paper, we present a systematic investigation demonstrating that arc discharge is a fast and inexpensive synthesis method which can be used to produce high quality tungsten oxide nanostructures for NO2 gas sensing measurements. The as-synthesized WO3 nanostructures are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), finger-print Raman spectroscopy and proton induced x-ray emission (PIXE). The analysis shows that spheroidal-shaped monoclinic WO 3 crystal nanostructures were produced with an average diameter of 30nm (range 10-100nm) at an arc discharge current of 110A and 300Torr oxygen partial pressure. It is found that the morphology is controlled by the arc discharge parameters of current and oxygen partial pressure, e.g.a high arc discharge current combined with a low oxygen partial pressure results in small WO3 nanostructures with improved conductivity. Sensors produced from the WO3 nanostructures show a strong response to NO2 gas at 325 °C. The ability to tune the morphology of the WO3 nanostructures makes this method ideal for the fabrication of gas sensing materials. © 2011 IOP Publishing Ltd.

Todd M.C.,University of Sussex | Todd M.C.,Aeroqual Ltd | Allen C.J.T.,University of Oxford | Bart M.,University of Leeds | And 25 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

The climate of the Sahara is relatively poorly observed and understood, leading to errors in forecast model simulations. We describe observations from the Fennec Supersite-2 (SS2) at Zouerate, Mauritania during the June 2011 Fennec Intensive Observation Period. These provide an improved basis for understanding and evaluating processes, models, and remote sensing. Conditions during June 2011 show a marked distinction between: (i) a "Maritime phase" during the early part of the month when the western sector of the Sahara experienced cool northwesterly maritime flow throughout the lower troposphere with shallow daytime boundary layers, very little dust uplift/transport or cloud cover. (ii) A subsequent "heat low" phase which coincided with a marked and rapid westward shift in the Saharan heat low towards its mid-summer climatological position and advection of a deep hot, dusty air layer from the central Sahara (the "Saharan residual layer"). This transition affected the entire western-central Sahara. Dust advected over SS2 was primarily from episodic low-level jet (LLJ)-generated emission in the northeasterly flow around surface troughs. Unlike Fennec SS1, SS2 does not often experience cold pools from moist convection and associated dust emissions. The diurnal evolution at SS2 is strongly influenced by the Atlantic inflow (AI), a northwesterly flow of shallow, cool and moist air propagating overnight from coastal West Africa to reach SS2 in the early hours. The AI cools and moistens the western Saharan and weakens the nocturnal LLJ, limiting its dust-raising potential. We quantify the ventilation and moistening of the western flank of the Sahara by (i) the large-scale flow and (ii) the regular nocturnal AI and LLJ mesoscale processes. Key Points First detailed observations from western Sahara sector Intraseasonal shift in Saharan heat low drives meteorological/aerosol conditions Atlantic Inflow interaction with low level jet ©2013. American Geophysical Union. All Rights Reserved.

Salmond J.A.,University of Auckland | Williams D.E.,University of Auckland | Laing G.,Aeroqual Ltd | Kingham S.,University of Canterbury | And 3 more authors.
Science of the Total Environment | Year: 2013

Space constraints in cities mean that there are only limited opportunities for increasing tree density within existing urban fabric and it is unclear whether the net effect of increased vegetation in street canyons is beneficial or detrimental to urban air quality at local scales. This paper presents data from a field study undertaken in Auckland, New Zealand designed to determine the local impact of a deciduous tree canopy on the distribution of the oxides of nitrogen within a street canyon. The results showed that the presence of leaves on the trees had a marked impact on the transport of pollutants and led to a net accumulation of pollutants in the canyon below the tree tops. The incidence and magnitude of temporally localised spikes in pollutant concentration were reduced within the tree canopy itself. A significant difference in pollutant concentrations with height was not observed when leaves were absent. Analysis of the trends in concentration associated with different wind directions showed a smaller difference between windward and leeward sides when leaves were on the trees. A small relative increase in concentrations on the leeward side was observed during leaf-on relative to leaf-off conditions as predicted by previous modelling studies. However the expected reduction in concentrations on the windward side was not observed. The results suggest that the presence of leaves on the trees reduces the upwards transport of fresh vehicle emissions, increases the storage of pollutants within the canopy space and reduces the penetration of clean air downwards from aloft. Differences observed between NO and NO2 concentrations could not be accounted for by dispersion processes alone, suggesting that there may also be some changes in the chemistry of the atmosphere associated with the presence of leaves on the trees. © 2012 Elsevier B.V.

Marsham J.H.,University of Leeds | Hobby M.,University of Leeds | Allen C.J.T.,University of Oxford | Banks J.R.,Imperial College London | And 17 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

We describe observations from the Fennec supersite at Bordj Badji Mokhtar (BBM) made during the June 2011 Fennec Intensive Observation Period. These are the first detailed in situ observations of meteorology and dust from the central Sahara, close to the center of the Saharan heat low and the summertime dust maximum. Historically, a shortage of such Saharan observations has created problems for evaluating processes, models, and remote sensing. There was a monsoon influence at BBM before 8 June and after 12 June, with dry Harmattan winds in between. A split boundary layer, generated by ventilation from the Atlantic, persisted during the drier phase. Extensive cold pools (haboobs) and microburst-type events were regularly observed. Moisture reached BBM at night from the monsoon and the embedded haboobs. As well as the regularly occurring nocturnal low-level jet (LLJ), a Saharan upper boundary layer (650 hPa) jet was observed, where winds feel drag from dry convection in the afternoon. This jet is linked to the diurnal cycles of moisture and cloud. Most dust was observed in the cloudier monsoon-affected periods, and covarying dust and cloud amounts explain most of the variations in shortwave radiation that control the surface sensible flux. Dustiness is related to a standard parameterization of uplift using 10 m winds ("uplift potential"), and this is used to estimate uplift. Around 50% of uplift is nocturnal. Around 30% is from the LLJ, and 50% is from haboobs, which are mainly nocturnal. This demonstrates, for the first time from observations, the key role of haboobs, which are problematic for models. Key PointsFirst detailed observations from the central Sahara (upper BL jet observed)Most dust in moist air. Together, dust & cloud control surface energy balance~50% of dust uplift is nocturnal. ~30% from the LLJ and ~50% from haboobs ©2013. American Geophysical Union. All Rights Reserved.

Ryder C.L.,University of Reading | Highwood E.J.,University of Reading | Rosenberg P.D.,University of Leeds | Trembath J.,Airborne | And 12 more authors.
Atmospheric Chemistry and Physics | Year: 2013

New in-situ aircraft measurements of Saharan dust originating from Mali, Mauritania and Algeria taken during the Fennec 2011 aircraft campaign over a remote part of the Sahara Desert are presented. Size distributions extending to 300 μm are shown, representing measurements extending further into the coarse mode than previously published for airborne Saharan dust. A significant coarse mode was present in the size distribution measurements with effective diameter (deff) from 2.3 to 19.4 μm and coarse mode volume median diameter (dvc) from 5.8 to 45.3 μm. The mean size distribution had a larger relative proportion of coarse mode particles than previous aircraft measurements. The largest particles (with deff > 12 μm, or dvc > 25 μm) were only encountered within 1 km of the ground. Number concentration, mass loading and extinction coefficient showed inverse relationships to dust age since uplift. Dust particle size showed a weak exponential relationship to dust age. Two cases of freshly uplifted dust showed quite different characteristics of size distribution and number concentration. Single Scattering Albed (SSA) values at 550 nm calculated from the measured size distributions revealed high absorption ranging from 0.70 to 0.97 depending on the refractive index. SSA was found to be strongly related to deff. New instrumentation revealed that direct measurements, behind Rosemount inlets, overestimate SSA by up to 0.11 when deff is greater than 2 μm. This is caused by aircraft inlet inefficiencies and sampling losses. Previous measurements of SSA from aircraft measurements may also have been overestimates for this reason. Radiative transfer calculations indicate that the range of SSAs during Fennec 2011 can lead to underestimates in shortwave atmospheric heating rates by 2.0 to 3.0 times if the coarse mode is neglected. This will have an impact on Saharan atmospheric dynamics and circulation, which should be taken into account by numerical weather prediction and climate models. © 2013 Author(s).

Williams D.E.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Henshaw G.S.,Aeroqual Ltd | Bart M.,Aeroqual Ltd | Laing G.,Aeroqual Ltd | And 3 more authors.
Measurement Science and Technology | Year: 2013

This paper presents a novel low-cost instrument that uses a sensor based on conductivity changes of heated tungstic oxide, which is capable of accurately measuring ambient concentrations of ozone. A combination of temperature steps and air flow-rate steps is used to continually reset and re-zero the sensor. A two-stage calibration procedure is presented, in which a nonlinear transformation converts sensor resistance to a signal linear in ozone concentration, then a linear correlation is used to align the calibration with a reference instrument. The required calibration functions specific for the sensor, and control system for air flow rate and sensor temperature, are housed with the sensor in a compact, simple-to-exchange assembly. The instrument can be operated on solar power and uses cell phone technology to enable monitoring in remote locations. Data from field trials are presented here to demonstrate that both the accuracy and the stability of the instrument over periods of months are within a few parts-per-billion by volume. We show that common failure modes can be detected through measurement of signals available from the instrument. The combination of long-term stability, self-diagnosis, and simple, inexpensive repair means that the cost of operation and calibration of the instruments is significantly reduced in comparison with traditional reference instrumentation. These instruments enable the economical construction and operation of ozone monitoring networks of accuracy, time resolution and spatial density sufficient to resolve the local gradients that are characteristic of urban air pollution. © 2013 IOP Publishing Ltd.

Henshaw G.S.,Aeroqual Ltd | Smith H.A.,Aeroqual Ltd | Bart M.,Aeroqual Ltd
Air and Waste Management Association - Air Quality Measurement Methods and Technology Conference 2013 | Year: 2013

Two light scattering nephelometer PM10 instruments have been field tested according to the MCERTS Performance Standard for indicative particle mass monitors and have been found to comply despite some discrepancies in comparison with FRM and FEM co-location data. The light scattering instruments exhibited low daily means on seven days out of 55 days which were shown to coincide with hotter, and more humid meteorological conditions. It was speculated that this could be due to losses of semi-volatile species in the hot inlet of the Dust Sentries. Further work is underway to identify this. The fast speed of response of the light scattering instruments could be utilised in applications where real-time information is important.

Aeroqual Ltd. | Date: 2015-03-26

One or more inexpensive electrochemical gas sensors are paired with a selective ozone sensor. Ozone in ambient air influences the output signals of the electrochemical gas sensors. The unwanted ozone effects are removed from the output signals of the electrochemical gas sensors by comparing them with the selective ozone sensor output signals. The selective ozone sensor signals are removed from and/or added to output signals from the electrochemical gas sensors. True indications of concentrations of the sensed gases in the ambient air result from the compensation for ozone interference.

AEROQUAL Ltd | Date: 2015-12-15

Air analysis apparatus, namely, air quality sensors, equipment, instruments, monitors, meters and stations; pollutant sensors, namely, airborne pollutant and contaminant sensors, equipment, instruments, monitors, meters and stations; airborne pollutant and contaminant sensors, equipment, instruments, monitors, meters and stations all in the nature of scientific instruments, namely, electronic analyzers for measuring, testing and detecting contaminants and environmental pollutants; particulate and dust monitoring sensors, equipment, instruments, meters and stations all in the nature of scientific instruments, namely, electronic analyzers for measuring, testing and detecting contaminants and environmental pollutants; air analysis apparatus, namely, ambient air monitoring sensors, equipment, instruments, meters and stations; gas sensors for measuring gas concentration, gas testing instruments, and gas detector for detecting the presence of gas and ozone gases, namely, sensors and instruments for monitoring gas and the ozone; computer software for obtaining, interpreting and reporting measurements and readings from sensors, equipment, instruments, monitors, meters and stations in relation to air quality, airborne pollutants and contaminants, ambient air, particulate and dust levels and gas levels including ozone gases.

PubMed | University of Auckland and Aeroqual Ltd.
Type: | Journal: The Science of the total environment | Year: 2016

Ozone (O

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