Yu-Mei Hsu

Method for contamination of filtering facepiece respirators by deposition of MS2 viral aerosols

Abstract A droplet/aerosol loading chamber was designed to deliver uniform droplets/aerosols onto substrates. An ultrasonic nebulizer was used to produce virus-containing droplets from artificial saliva to emulate those from coughing and sneezing. The operating conditions were determined by adjusting various parameters to achieve loading density and uniformity requirements. The count median diameter and mass median diameter were 0.5–2 and 3–4μm, respectively, around the loading location when 35% relative humidity was applied. The average loading density was ∼2×103 plaque-forming units/cm2 for 5-min loading time with a virus titer of 107 plaque-forming units/mL. Six different filtering facepiece respirators from commercial sources were loaded to evaluate uniform distribution. For each of the six FFRs, the virus loading uniformity within a sample and across numerous samples was 19.21% and 12.20%, respectively. This system supports a standard method for loading viable bioaerosols onto specimen surfaces when different decontamination techniques are to be compared.

Chemical Characteristics of Aerosol Mists in Phosphate Fertilizer Manufacturing Facilities

Of the carcinogens listed by the National Toxicology Program (NTP), strong inorganic mists containing sulfuric acid were identified as a known human carcinogen. In this study, aerosol sampling was conducted at 24 locations in eight Florida phosphoric acid and concentrated fertilizer manufacturing plants and two locations as background in Winter Haven and Gainesville, Florida, using dichotomous samplers. The locations were selected where sulfuric acid mist may potentially exist, including sulfuric acid pump tank areas, belt or rotating table phosphoric acid filter floors, sulfuric acid truck loading/unloading stations, phosphoric acid production reactors (attack tanks), and a concentrated fertilizer granulator during scrubbing with a weak sulfuric acid mixture. An ion chromatography system was used to analyze sulfate and other water soluble ion species. In general, sulfate, fluoride, ammonium, and phosphate were the major species in the fertilizer facilities. For the rotating table/belt phosphoric acid filter floor, phosphate and fluoride were the dominant species for PM10, and the maximum concentrations were 170 and 106 μ g/m3, respectively. For the attack tank, fluoride was the dominant species for PM10, and the maximum concentration was 462 μ g/m3. At the sulfuric acid pump tank, sulfate was the dominant species, and the maximum PM10 sulfate concentration was 181 μ g/m3. The concentration of PM10 sulfate including ammonium sulfate, calcium sulfate, and sulfuric acid were lower than 0.2 mg/m3 at all locations. The aerosols at the filter floor and the attack tank were acidic. The coarse mode aerosol at the sulfuric acid pump tank (an outdoor location) was acidic, whereas the fine mode aerosol was neutral to basic.

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.