Alexandros Theodore

Development and evaluation of a novel bioaerosol amplification unit (BAU) for improved viral aerosol collection

Abstract A novel bioaerosol amplification unit (BAU) that increases the size of viral particles by condensational growth has been designed and evaluated for improved viral aerosol collection. In the BAU, water was used as the condensing vapor to preserve viability of virus, and supersaturation conditions for condensational growth of particles were achieved by either conductive cooling or mixing with hot, water-saturated air. MS2 bacteriophage (28nm) was used as the test agent, and changes in collection efficiency of an SKC Biosampler with and without the BAU were determined by assaying plaque-forming units (PFUs) in the collection medium. Results showed that the mixing-type BAU (mBAU) was a promising device for improved viral aerosol sampling. The number of viruses (PFU) collected in the Biosampler increased 2–3 fold after passing through the mBAU. However, PFU increases in the cooling-type BAU (cBAU) were insignificant. APS results likewise showed that the mBAU was better in growing particles than the cBAU. After growth, number concentrations of particles larger than 327nm in the cBAU and mBAU increased 1.3 and 15.0 fold, respectively. The relatively high molecular diffusivity of water vapor compared to the thermal diffusivity of air and the temperature gradient in the cBAU tube limited particle growth by causing condensation to occur predominantly at the colder wall.

Double Shroud Delivery of Silica Precursor for Reducing Hexavalent Chromium in Welding Fume

The welding process yields a high concentration of nanoparticles loaded with hexavalent chromium (Cr6+), a known human carcinogen. Previous studies have demonstrated that using tetramethylsilane (TMS) as a shielding gas additive can significantly reduce the Cr6+ concentration in welding fume particles. In this study, a novel insulated double shroud torch (IDST) was developed to further improve the reduction of airborne Cr6+ concentration by separating the flows of the primary shielding gas and the TMS carrier gas. Welding fumes were collected from a welding chamber in the laboratory and from a fixed location near the welding arc in a welding facility. The Cr6+ content was analyzed with ion chromatography and X-ray photoelectron spectroscopy (XPS). Results from the chamber sampling demonstrated that the addition of 3.2∼5.1% of TMS carrier gas to the primary shielding gas resulted in more than a 90% reduction of airborne Cr6+ under all shielding gas flow rates. The XPS result confirmed complete elimination of Cr6+ inside the amorphous silica shell. Adding 100∼1000 ppm of nitric oxide or carbon monoxide to the shielding gas could also reduce Cr6+ concentrations up to 57% and 35%, respectively; however, these reducing agents created potential hazards from the release of unreacted agents. Results of the field test showed that the addition of 1.6% of TMS carrier gas to the primary shielding gas reduced Cr6+ concentration to the limitation of detection (1.1 μg/m3). In a worst-case scenario, if TMS vapor leaked into the environment without decomposition and ventilation, the estimated TMS concentration in the condition of field sampling would be a maximum 5.7 ppm, still well below its flammability limit (1%). Based on a previously developed cost model, the use of TMS increases the general cost by 3.8%. No visual deterioration of weld quality caused by TMS was found, although further mechanical testing is necessary.

Development of a thoracic personal sampler system for co-sampling of sulfuric acid mist and sulfur dioxide gas

ABSTRACT A novel personal sampler was designed to measure inorganic acid mists and gases for determining human exposure levels to these acids in workplaces. This sampler consists of (1) a parallel impactor for classifying aerosol by size following the ISO/CEN/ACGIH defined human thoracic fraction, (2) a cellulose filter to collect the residual acid mist but allowing penetration of sulfur dioxide gas, and (3) an accordion-shaped porous membrane denuder (aPMD) for adsorbing the penetrating sulfur dioxide gas. Acid-resistant PTFE was chosen as the housing material to minimize sampling interference. To test the performance of the parallel impactor, monodisperse aerosol was created by a vibrating orifice aerosol generator. The results showed that the penetration curve of the impactor run at 2 LPM flow rate agreed well with the defined thoracic fraction. Almost all sampling biases were within 10% for particle size distributions with MMAD between 1–25 µm and GSD between 1.75–4, which meets the criteria of the EN 13205 standard. To evaluate the performance of the aPMDs, sulfur dioxide gas was sourced directly from a cylinder. The aPMDs maintained a gas collection efficiency greater than 95% for 4 hr when sampling 8.6 ppm of sulfur dioxide gas. While the aPMD had similar performance to the commonly adopted annular or honeycomb denuders made of glass, this shatterproof aPMD is only half of the volume and 1/25th the weight of the honeycomb denuder. Testing of the entire sampler with a mixture of sulfuric acid mist and sulfur dioxide gas showed the system could sample both with negligible interference. All the test results illustrate that the new sampler, which is flat, lightweight, and portable, is suitable for personal use and is capable of a more accurate assessment of human exposure to inorganic acid mist and SO2 gas.

An efficient virus aerosol sampler enabled by adiabatic expansion

Abstract Protection of public health against pathogenic viruses transmitted through the airborne route requires effective sampling of airborne viruses for determination of their concentration and distribution. However, sampling viable airborne viruses is challenging as conventional bioaerosol sampling devices operate on inertia-based mechanisms that inherently have low sampling efficiency for virus aerosols in the ultrafine size range (< 100nm). Herein, a Batch Adiabatic-expansion for Size Intensification by Condensation (BASIC) approach was developed for efficient sampling of virus aerosols. The BASIC utilizes adiabatic expansion in a supersaturated container to activate condensation of water vapor onto virus aerosol particles, thus amplifying the size of the particles by orders of magnitude. Using aerosolized MS2 bacteriophage, the BASICs performance was evaluated and optimized both from the perspectives of physical size amplification as well as preservation of the viability of the MS2 bacteriophage. Experimental results show that one compression/expansion (C/E) cycle under a compression pressure of 103.5kPa and water temperature of 25°C was sufficient to increase the particle diameter from < 100nm to > 1µm; further increases in the number of C/E cycles neither increased particle number concentration nor diameter. An increase in compression pressure was associated with physical size amplification and a higher concentration of collected viable MS2. Water temperature of 40°C was found to be the optimal for size amplification as well as viability preservation. No significant effect on particle size enlargement was observed by changing the dwell time after expansion. The results illustrate the BASICs capability as a simple, quick and inexpensive tool for rapid sampling of viable airborne viruses.