Equipment Selection and Testing for the Study

The instrument choice was primarily based on precision and durability. Although the available financial resources were a key determining factor in relation to this, the study did secure a precision instrument, on which a series of tests were conducted before implementation see section ‎4.1. The description of the equipment and the process used to detect the particles are addressed in this section along with the limitations of the equipment.

The instrument primarily used in this study for PM₁₀ monitoring was the DustTrak 8534, chosen because of its level of precision, durability and given the budget constraints. The DustTrak 8534 is a portable and easy-to-use device, and can detect the mass concentration of particles with a diameter of less than 10 µm. DustTrak monitors PM₁₀ to a resolution of 1 µg m^-3 and a range from 1-150,000 µg m^-3 (TSI Incorporated, 2011). DustTrak’s monitoring is based on light scattering techniques (TSI Incorporated, 2013), where the amount of scattered light is proportional to the volume concentration of the aerosol.

DustTrak 8533 and 8534 are an advanced version of the DRX models. All models have the ability to measure size fractions of the aerosol sample and estimate the size mass fraction concentrations based on photometric measurement. The manufacture stated that “This method combines a photometric measurement to cover the mass concentration range and a single particle detection measurement to be able to size

discriminate the sampled aerosol”. The Figure ‎3-4 shows a schematic illustrating the process of detection of DustTrak. A diaphragm pump provides a continuous aerosol flow stream which is drawn through the sensing chamber. The aerosol stream is split in two, one part is passed through a HEPA filter then injected back to the main stream as sheath flow and combine back with the aerosol flow before passing through the sensing chamber. A light laser sheet is created from a laser diode which passes through a collimating lens and through a cylindrical lens before illuminating the aerosol stream in the chamber. The fraction of laser light scattered by particles is captured by a spherical mirror coated with gold and focused onto the photo detector. The signal from the photo detector is divided onto two components, the first is the photometric signal pulses to find the volume and thus to estimate the mass based on the Arizona Test Dust (ISO 12103-1, A1 test Dust) and the second is single particle pulses which were converted to aerodynamic size by proprietary factory algorithms based on the Arizona Test Dust or custom calibrations. The calibration factor can be modified by introducing correction factor. DustTrak 8533 can be fitted with filter cassette sampler which can be used to conduct a gravimetric analysis. This instrument was not used in this research.

Figure ‎3-4 A schematic illustrating the process of detection using DustTrak (Source: TSI)

There are a number of studies that state that the measurements of PM by using the photometric method are overestimated by a factor of 2 to 3 (Lehocky and Williams, 1996; Ramachandran et al., 2000; Chang et al., 2001; Chung et al., 2001; R. A. Jenkins et al., 2004; Zhu et al., 2011). Braniš and Kolomazníková (2010) concluded that the

ratio between the DustTrak SidePak and the portable nephelometer measurements was approximately 3.5. As the two monitoring devices were not collocated therefore, it is not reasonable to compare the data from the two devices as they monitor different microenvironment and activity. However, there were a number of studies that have compared the data from similar DustTrak devices (or other equipment based on the photometric method) to that from gravimetric sampler measurements which found a different result to Braniš and Kolomazníková (2010). Instead, they concluded that DustTrak measurements were lower than gravimetric sampler measurement (Park et al., 2009; Watson et al., 2011; Goossens and Buck, 2012). Park et al. (2009) stated that DustTrak underestimated by an average factor of 0.48 compared to the gravimetric sampler. The DustTrak 8534 mass measurements based on photometric measurement were estimated based on the Arizona Test Dust calibration factor, which was the reason the PM10 levels were underestimated relative to the gravimetric sampler. The author was mindful of this limitation of the DustTrak throughout this thesis however, the data will not be rescaled. In this research at the beginning of each measurement conducted with DustTrak 8534, the zero calibration procedure was carried out according to the manufacture instruction. Given that two similar systems were used for simultaneous measurements there was consistency in the data collected and could be compared directly.

A Langan T15n was used to measure the level of CO in the range of 0-200 ppm with a resolution of 0.05 ppm (Langan Products Inc, 2006). The Langan T15n has been used in several studies (De Bruin et al., 2004; Kaur et al., 2005a; Kaur et al., 2005b;

McCreanor et al., 2005). A number of tests were conducted to examine the CO monitors available for this study for their accuracy and reliability. Therefore, two scenarios were established with nine co-located Langan monitors with a view to evaluating the comparability of results. The monitors were seven Langan T15v monitors (10 years old) and two Langan T15n monitors (purchased new for this study).

The first scenario was to place all the monitors in three microenvironments namely office, garden and living room for a specific period. Further details of these evaluation tests will be presented is section ‎4.1.1.

A GPS tracker was used to track the location of the back pack carrier second by second during dynamic monitoring. Four trackers were available namely the QStarz BT-Q1000XT, i-gotU GT-600 and three Garmin GPS devices and these were tested, with

the aim of find the most suitable and accurate GPS device for the study. Details of these tests along with the results are presented in section ‎4.1.2.