Search

In this dissertation, new, compact, hand-held, portable aerosol collectors were developed and evaluated for sample collection and analysis by optical spectroscopies or microscopy with high sensitivity and low detection limits. Firstly, the design and evaluation of a multi-stage focusing nozzle was performed for collection of spot samples for subsequent chemical analysis via optical spectroscopies. The new, multi-stage focusing nozzle consisted of a succession of smooth converging stages for the concentration of a broad range of particle sizes into a narrow particle beam to obtain minute particulate deposits. A numerical computation method was employed along with the experiments, for comparison. Aerosol collection through the multi-stage focusing nozzle was the only method that could ensure high analytical measurement sensitivity at high Reynolds numbers, when compared with other conventional techniques. Moreover, a new, compact, high-flowrate, water-based, Mixing-flow type, Condensation Aerosol Concentrator (MCAC) prototype was presented and evaluated for concentration of submicrometric particles that are challenging to collect. The droplet growth characteristics promoted in the MCAC were calculated theoretically and were compared with the experimental results. The MCAC allows direct collection of particles either as a minute spot sample for onsite direct-reading spectroscopic analysis or as a liquid suspension for offline chemical analysis. Nanoparticles with an initial aerodynamic diameter down to 25 nm are enlarged into easily collectable droplets with an activation efficiency greater than 90%. Finally, the performance evaluation of a prototype, triple-tube, laminar-flow type, condensation aerosol collector, the NanoSpotTM Collector was described. The NanoSpotTM Collector was developed for direct aerosol sample collection on a miniscule sample deposition area, onto an electron microscopy stub or grid for direct electron or optical microscopy and laser spectroscopic analysis. Particles as small as 7 nm could be activated and collected. The NanoSpotTM Collector exhibited the highest measurement sensitivity among other conventional aerosol collection techniques. A simulation software was also used for the study of the droplet growth characteristics, the trajectories and the losses of particles/droplets conveyed across the NanoSpotTM Collector.The aerosol collection techniques developed and evaluated here possess the following key features: (i) Effective collection of nano and micro-size ranged particles; (ii) Implementation of high aerosol sample flow rate, with low pressure drop that can be supported using personal sampling pumps; (iii) Aerosol sample micro-concentration as a small “spot sample”; (iv) Aerosol concentration as a liquid suspension for off-line, filter-less chemical analysis; and (v) Compact size and portability. These new collection techniques are expected to advance various aspects of on-site direct-reading methods for aerosol chemical analysis, as well as to improve the sensitivity and reliability of laboratory optical spectroscopy and microscopy methods for environmental and occupational aerosol measurements.

Continuous monitoring of dust concentration is vital to understanding the impact of air pollution on human exposure and health. Miniature, low-cost sensors are being increasingly used for air quality measurements. Several studies have shown the usefulness of the semi-quantitative measurements provided by these sensors. However, the response of these sensors suffers from large uncertainties as function of temperature, humidity, and particle physical and chemical properties. The objective of this Thesis was to study the response of a variety of low-cost dust sensors from various manufacturers which use scattered light (Model PPD42NS from Shinyei, model PPD60PV-T2 from Shinyei, model GP2Y1010AU0F from Sharp, and model SDS011 from Nova Fitness), or units that their operation is based on light scattering (Dylos DC1700), or they include an inexpensive optical sensor (Speck monitor).The sensors were calibrated and then evaluated using DUSTTRAK™ Aerosol Monitor Model 8520, a laser-photometer that measures and records airborne dust mass concentrations, and Hand Held Portable Counter (HHPC-6), a portable instrument for detecting, counting and storing number concentrations. Calibration curves were obtained by correlating the sensor response with the reference instruments’ measurements. Pairwise correlations between the sensors’ output and the aerosol concentrations were high: The coefficient of determination was greater than 0.9 for some sensors, for durations less than 15 seconds. The results show that (a) each sensor unit from the same manufacturer/model provides varying responses, indicating the need for calibrating each unit prior to its use, and (b) different aerosol composition can significantly affect the sensors’ response in some cases. Our correlation results offer information and a procedure to calibrate the individual sensors for some case specific situations when the source of the aerosols is known.Dylos DC1700 and Speck monitor were evaluated during a series of experiments at the laboratory, as well as at an occupational area and a residency. Linear regression analysis demonstrated that Speck monitor could successfully detect abrupt changes in PM concentrations and it was proposed for qualitative indications of the lever of air contamination (i.e. low, moderate and high level of air pollution). The Dylos DC1700 performed with high linearity and accuracy with a recommended upper detection limit of 2 million pcs cf-1. Additionally, at relatively `clean’ atmospheres, the monitor’s response over the time interval of ten minutes was preferable, but when higher concentrations are monitored, with abrupt concentration changes, minute-by minute monitoring is recommended. The significantly inexpensive cost and compact size, along with a variety of features provided with some of these monitors, in contrast to unaffordable and bulky instruments conventionally used, can reassure promising applications with their proper preparation. The results obtained by our research constitute a contribution to the existing ever-growing concern regarding the low-cost sensors’ feasibility.