Paul Quincey

Characterisation of the de-agglomeration effects of bovine serum albumin on nanoparticles in aqueous suspension

This paper describes the use of nanoparticle characterisation tools to evaluate the interaction between bovine serum albumin (BSA) and dispersed nanoparticles in aqueous media. Dynamic light scattering, zeta-potential measurements and scanning electron microscopy were used to probe the state of zinc oxide (ZnO) and titanium dioxide (TiO(2)) nanoparticles in the presence of various concentrations of BSA, throughout a three-day period. BSA was shown to adhere to ZnO but not to TiO(2). The adsorption of BSA led to subsequent de-agglomeration of the sub-micron ZnO clusters into smaller fragments, even breaking them up into individual isolated nanoparticles. We propose that certain factors, such as adsorption kinetics of BSA on to the surface of ZnO, as well as the initial agglomerated state of the ZnO, prior to BSA addition, are responsible for promoting the de-agglomeration process. Hence, in the case of TiO(2) we see no de-agglomeration because: (a) the nanoparticles are more highly agglomerated to begin with and (b) BSA does not adsorb effectively on the surface of the nanoparticles. The zeta-potential results show that, for either ZnO or TiO(2), the presence of BSA resulted in enhanced stability. In the case of ZnO, the enhanced stability is limited to BSA concentrations below 0.5 wt.%. Steric and electrostatic repulsion are thought to be responsible for improved stability of the dispersion.

Studies using the sorbent Carbopack X for measuring environmental benzene with Perkin–Elmer-type pumped and diffusive samplers

Studies with the sorbent Carbopack X in pumped and diffusive samplers, of the Perkin–Elmer-type, have been carried out in a controlled atmosphere test facility (CATFAC) employed to generate volatile organic compound (VOC) atmospheres. The benzene safe sampling volume for Carbopack X has been measured, using an indirect method, and found to be (5400 ± 740) 1 g−1, suggesting that this sorbent is suitable for long-term pumped sampling. Good agreement in concentration has been obtained between calibrated benzene test atmospheres and values derived from pumped samplers, well within the expected uncertainty for this technique. The 2-week benzene diffusive uptake rate for Carbopack X has been determined to be (1.99 ± 0.18) ng ppm−1 min−1 for environmental applications, and was found to be constant over a wide range of VOC concentrations. The 2-week toluene and o-xylene diffusive uptake rates for this sorbent are also reported, over a more limited range, together with the 2-week benzene, toluene and o-xylene diffusive uptake rates for Chromosorb 106.

Mobility particle size spectrometers: Calibration procedures and measurement uncertainties

ABSTRACT Mobility particle size spectrometers (MPSS) belong to the essential instruments in aerosol science that determine the particle number size distribution (PNSD) in the submicrometer size range. Following calibration procedures and target uncertainties against standards and reference instruments are suggested for a complete MPSS quality assurance program: (a) calibration of the CPC counting efficiency curve (within 5% for the plateau counting efficiency; within 1 nm for the 50% detection efficiency diameter), (b) sizing calibration of the MPSS, using a certified polystyrene latex (PSL) particle size standard at 203 nm (within 3%), (c) intercomparison of the PNSD of the MPSS (within 10% and 20% of the dN/dlogDP concentration for the particle size range 20–200 and 200–800 nm, respectively), and (d) intercomparison of the integral PNC of the MPSS (within 10%). Furthermore, following measurement uncertainties have been investigated: (a) PSL particle size standards in the range from 100 to 500 nm match within 1% after sizing calibration at 203 nm. (b) Bipolar diffusion chargers based on the radioactive nuclides Kr85, Am241, and Ni63 and a new ionizer based on corona discharge follow the recommended bipolar charge distribution, while soft X-ray-based charges may alter faster than expected. (c) The use of a positive high voltage supply show a 10% better performance than a negative one. (d) The intercomparison of the integral PNC of an MPSS against the total number concentration is still within the target uncertainty at an ambient pressure of approximately 500 hPa. Copyright

Implications of adopting plane angle as a base quantity in the SI

The treatment of angles within the SI is anomalous compared with other quantities, and there is a case for removing this anomaly by declaring plane angle to be an additional base quantity within the system. It is shown that this could bring several benefits in terms of treating angle on an equal basis with other metrics, removing potentially harmful ambiguities, and bringing SI units more in line with concepts in basic physics, but at the expense of significant upheaval to familiar equations within mathematics and physics. This paper sets out the most important of these changes so that an alternative unit system containing angle as a base quantity can be seen in the round, irrespective of whether it is ever widely adopted. The alternative formulas and units can be treated as the underlying, more general equations of mathematical physics, independent of the units used for angle, which are conventionally simplified by implicitly assuming that the unit used for angle is the radian.

Air Pollution Monitoring Strategies and Technologies for Urban Areas

Current ambient air quality monitoring is solely based on fixed monitoring sites, not always reflecting the exposure and effects on humans. This article reviews the current situation in Europe, the USA and Asia and discusses the main differences and similarities. Based on the analysis of the relation between monitoring techniques and strategies as well as the analysis of current trends and developments in monitoring strategies, new concepts and directions of future urban monitoring networks and strategies are presented and discussed.

Dependence of CPC cut-off diameter on particle morphology and other factors

ABSTRACT In this investigation, we summarize performance parameters of 24 TSI CPCs model 3772 and 9 TSI CPCs model 3790 determined at the World Calibration Aerosol Centre Physics hosted by the Leibniz Institute for Tropospheric Research. Model 3790 CPCs are basically identical to model 3772 laminar continuous flow type butanol-based CPCs with a modified temperature difference between saturator and condenser. The average 50% detection efficiency for silver particles for 3772 and 3790 instruments was found to be 7.52 ± 0.04 nm and 24.34 ± 0.29 nm (average mobility diameter ± standard deviation), respectively. Small changes of the temperature difference between saturator and condenser cause larger shifts of the 50% detection efficiencies of 3790 CPCs compared to 3772 CPCs. In addition to the known calibration material dependence of the 50% detection efficiencies of 3790 CPCs, we found a dependence on the morphology of the particles used for calibration. In our experiments more spherical particles shifted the 50% detection efficiencies towards larger mobility diameters. Copyright

Ambient air particulate matter PM10 and PM2.5: developments in European measurement methods and legislation.

The measure of airborne particulate matter PM10 is effectively defined for European regulatory purposes by the European Committee for Standardisation (CEN) standard EN 12341:1998 – a gravimetric filter-based method. However, compared with the reference methods written for other pollutants, specifically to address the needs of the Air Quality Directives, EN 12341 falls short in areas such as ongoing Quality Assurance and Quality Control. Also, scientific knowledge about PM has moved on considerably since 1998, so that we now realize that implementations of variations allowed within EN 12341:1998 can lead to substantial differences in results obtained. These issues were partially addressed within the CEN standard for PM2.5, EN 14907:2005, which, for example, included tighter control of the handling of sampled filters to reduce losses of semi-volatile material. CEN Technical Committee 264 Working Group 15 is currently revising EN 12341, and has the opportunity to improve the reference method further, for example by tighter specification of the filter material, or by changing the specification for the humidity at which the filters are brought to equilibrium. Any changes must, however, be considered in the context of the regulatory implications of the standard, so that improvements in scientific quality must be balanced with the effect of a step change in reference method, and with associated costs. The paper outlines the present position of the EN 12341 revision and recent changes to EU Air Quality legislation.

The development of gas standards and calibration techniques for measurements of vehicle, aircraft and industrial emissions, natural gas, occupational exposure and air quality

The National Physical Laboratory (NPL) is involved in the dissemination of nationally traceable standards to which measurements of air quality, occupational exposure and air pollution source emissions, and natural gas analyses, can be referenced. This has required the development of national primary gas standards using absolute gravimetric and other techniques, and the development of dynamic calibration techniques for gaseous species which would be unstable in high-pressure cylinders. The methodology used for preparing gas standards gravimetrically is described, together with the rigorous quality assurance measurements and consistency checks which are used to demonstrate their accuracy and stability. The uncertainty budget assigned to these standards will also be summarised. NPL primary standards are used to certify traceable ‘secondary’ gas standards which are disseminated so as to ensure the accuracy of gas analysis measurements. Examples of the applications of these secondary standards are presented. The gas standards are employed in proficiency testing of industrial stack-testing organisations, and results of the initial rounds are presented. NPL gas standards are also now being used as the basis of the United Kingdom Environment Agencys new type-approval and certification scheme for continuous industrial stack-emission analysers. A recent important international initiative, in the field of gas analyses, is the agreement by national standards laboratories across the world to demonstrate the equivalence of their calibrations, by means of key comparisons between them. These worldwide key comparisons are complemented in Europe through the EUROMET initiative which seeks to establish the equivalence and comparability of calibration standards held at national standards laboratories across Europe. Examples of these intercomparisons are presented.

The changing role of base units within the revised SI: an opportunity to take dimensional analysis back to its roots

The role of base units, base quantities and dimensions in the proposed revision of the SI is discussed. Although the primary role of the seven current base units would be lost when the SI is fixed by seven defining constants, we suggest that there would still be seven base units, but with some flexibility in how they are selected. We agree with the proposal that the current set of seven SI base quantities and associated units should retain special status, but point out that this would become a convention and would not be a direct consequence of the set of defined constants. Although dimensional analysis is currently described within the SI brochure as directly linked to the SI base units, we suggest that this is not necessary and that the flexibility introduced by the revised SI should be seen as an opportunity to allow different sets of dimensions to be chosen in different circumstances. This would bring dimensional analysis closer to its original form.

A rapid scan interferometer for near millimetre wavelength radiometry

A near millimetre wavelength radiometer has been constructed, based on a rapid scan polarising interferometer. The design and procedure are described, and some results are presented.