Identifying Patterns and Sources of Fine and Ultrafine Particulate Matter in London Using Mobile Measurements of Lung-Deposited Surface Area.

We performed more than a year of mobile, 1 Hz measurements of lung-deposited surface area (LDSA, the surface area of 20-400 nm diameter particles, deposited in alveolar regions of lungs) and optically assessed fine particulate matter (PM2.5), black carbon (BC), and nitrogen dioxide (NO2) in central London. We spatially correlated these pollutants to two urban emission sources: major roadways and restaurants. We show that optical PM2.5 is an ineffective indicator of tailpipe emissions on major roadways, where we do observe statistically higher LDSA, BC, and NO2. Additionally, we find pollutant hot spots in commercial neighborhoods with more restaurants. A low LDSA (15 µm2 cm-3) occurs in areas with fewer major roadways and restaurants, while the highest LDSA (25 µm2 cm-3) occurs in areas with more of both sources. By isolating areas that are higher in one source than the other, we demonstrate the comparable impacts of traffic and restaurants on LDSA. Ratios of hyperlocal enhancements (ΔLDSA:ΔBC and ΔLDSA:ΔNO2) are higher in commercial neighborhoods than on major roadways, further demonstrating the influence of restaurant emissions on LDSA. We demonstrate the added value of using particle surface in identifying hyperlocal patterns of health-relevant PM components, especially in areas with strong vehicular emissions where the high LDSA does not translate to high PM2.5.

Laser ablation direct writing of metal nanoparticles for hydrogen and humidity sensors.

A UV pulsed laser writing technique to fabricate metal nanoparticle patterns on low-cost substrates is demonstrated. We use this process to directly write nanoparticle gas sensors, which operate via quantum tunnelling of electrons at room temperature across the device. The advantages of this method are no lithography requirements, high precision nanoparticle placement, and room temperature processing in atmospheric conditions. Palladium-based nanoparticle sensors are tested for the detection of water vapor and hydrogen within controlled environmental chambers. The electrical conduction mechanism responsible for the very high sensitivity of the devices is discussed with regard to the interparticle capacitance and the tunnelling resistance.

Revision of the whitefly genus, Asterochiton Maskell (Hemiptera: Aleyrodidae) from New Zealand, a study of intraspecific variation.

All the specimens of Asterochiton species (Hemiptera: Aleyrodidae) on slides in the New Zealand Arthropod Collection, Auckland, were examined. The study reveals that the genus is currently restricted to New Zealand and is redescribed here. Obvious generic characters are the sub-elliptical to sub-circular puparium with distinct invaginations at the thoracic and caudal pores. Seven species are described: Asterochiton asteliae sp. n. from Astelia trinervia (Asteliaceae), and A. arboreae sp. n., A. areolatae sp. n., A. foetidissimae sp. n., A. propinqua sp. n., A. rhamnoidis sp. n., and A. rotundifoliae sp. n. from small-leaved Coprosma spp. (Rubiaceae). There are now 12 named species of Asterochiton, but the Brazilian species, Asterochiton auricolor (Bondar, 1923), does not belong in the genus. Details of minute setae, previously overlooked in described species, are provided. The setae length was found to vary at specific positions. Two species infesting three species of Pittosporum (Pittosporaceae) were observed having long and short setae on the abdomen, sometimes varying within a population from a single tree/host. Asterochiton pittospori Dumbleton is therefore synonymized with A. simplex. Additionally, the location of some setae varied on the subdorsal/submarginal area within a puparium. Chaetotaxy for Asterochiton species is proposed. A key to the puparia of Asterochiton species is provided.

Facile synthesis of titania nanowires via a hot filament method and conductometric measurement of their response to hydrogen sulfide gas.

Titania nanostructures are of increasing interest for a variety of applications, including photovoltaics, water splitting, and chemical sensing. Because of the photocatalytical properties of TiO2, chemical processes that occur at its surface can be exploited for highly efficient nanodevices. A facile and fast synthesis route has been explored that is free of catalysts or templates. An environmental scanning electron microscopy (ESEM) system was employed to grow titania nanowires (NWs) in a water vapor atmosphere (∼1 mbar) and to monitor the growth in situ. In addition, the growth process was also demonstrated using a simple vacuum chamber. In both processes, a titanium filament was heated via the Joule effect and NWs were found to grow on its surface, as a result of thermal oxidation processes. A variety of nanostructures were observed across the filament, with morphologies changing with the wire temperature from the center to the end points. The longest NWs were obtained for temperatures between ∼730 °C and 810 °C. Typically, they have an approximate thickness of ∼300 nm and lengths of up to a few micrometers. Cross sections prepared by focused-ion-beam milling revealed the presence of a porous layer beneath the NW clusters. This indicates that the growth of NWs is driven by oxidation-induced stresses in the subsurface region of the Ti filament and by enhanced diffusion along grain boundaries. To demonstrate the potential of titania NWs grown via the hot filament method, single NW devices were fabricated and used for conductometric sensing of hydrogen sulfide (H2S) gas. The NW electric resistance was found to decrease in the presence of H2S. Its variation can be explained in terms of the surface depletion model.