Aerosols II

Aerosols II

Wednesday, June 3, 2015, 10:00 AM - 12:00 PM

SR-120-01 Characterization of Aerosol Emission from the Burst of a Single Bubble

W. Ke, J. Lai, S. Huang, C. Chen, National Taiwan University, Taipei, Taiwan;Y. Kuo, Chung Hwa University of Medical Technology, Tainan, Taiwan

Objective: Aeroso​​l emission due to bubble bursting has been studied extensively in the past decades. These studies were largely based on multiple bubbles. The main objective of this work was to experimentally characterize the aerosol emission from the burst of only one bubble.

Methods: The single bubble could be generated by supplying a fixed volume of air through a small diameter tube, from above the liquid, or releasing the air volume from the bottom of the liquid. The generated droplets were then carried by a dried and aerosol-free air flow upward to the test chamber. The distilled, deionized water was used as the solvent, and sodium chloride as the solute. The surface tension was adjusted, ranging from 33 to 50 dyne/cm, by adding different amount of surfactant, i.e. sodium dodecyl sulfate. The size of bubble was controlled by using a syringe pump. The generated droplets after dried were monitored by two aerosol instruments. An Aerodynamic Particle Sizer (APS) was used to measure the aerosol number concentration and size distribution from 0.7 to 20 μm. A Condensation Particle Counter (CPC) was used to monitor the total number concentration, which supplemented the size information for aerosols smaller than 0.7 μm. For each combination of bubble size and surface tension, 100 bubbles were generated and measured.

Results: The results showed that the generated droplet number, from the burst of a 3-cm bubble, increased from 24,000 to 37,000 #/bubble, as the air flow increased from 8 to 30 L/min. For air flow higher than 30 L/min, this increase in number count was marginal. The droplet size and number count generated from a burst bubble increased with increasing bubble size. For example, the CPC count increased from 5600 to 34000 #/bubble, as the bubble increased from 2 to 4 cm. The count median diameter based on APS measurements also increased from 2.12 to 2.68 μm. The surface tension appeared to be crucial in droplet generation. As the surface tension decreased, the generated droplets became smaller, but more in number count. For most of the measurements, the ratio of CPC count to APS count was about 1.5, indicating that about 33% of the aerosol particles were smaller than 0.7 μm.

Conclusions: Bubble size and surface tension were the major factors affecting the size and number of generated droplets. For the bubble size studied in this work, only film droplets were observed.

SR-120-02 Particulate Matter Exposure in a Police Station Located Near a Highway

C. Hsu, P. Tsai, M. Lin, National Cheng Kung University, Tainan, Taiwan; Y. Chen, National Health Research Institutes, Miaoli County, Taiwan; C. Wang, National Sun Yat-Sen University, Kaohsiung, Taiwan

Objective: Exposure to particulate matter (PM) in the workplace can result in adverse health effects such as cardiovascular and respiratory diseases. Workers working near highways are exposed to high concentration of nanoparticles especially during traffic rush hours. Vehicle engine exhaust during driving, acceleration and deceleration is a major source of nanoparticles. In this study, we aim to characterize the PM exposure of a highway police station that is located right next to the Sinying highway toll station located in Tainan, Taiwan.

Methods: We measured PM at two locations, the first location was inside the police station. The second location was located approximately 50 meters upwind of the highway, serving as a background station to help us understand the contribution of PM from the highway. The instruments used for the two locations includes the Scanning Mobility Particle Sizers (SMPS, model 3936, TSI, Inc.), Dusttrak (model 8520, TSI, Inc.), CO/CO2 analyzer (model 7572, TSI, Inc.), and Polycyclic Aromatic Hydrocarbons’ monitor (PAH, EcoChem PAS). We also have a weather station (Watch Dog 2550) that monitors temperature, relative wind speed, and wind direction at the upwind location. During the one week measurement period, the wind direction was mostly from the highway.

Results: Preliminary results indicate that highway is a major source of nanoparticle emission. During periods of downwind conditions, the nanoparticle number concentration inside the police station can be 5 times higher than the background concentration. Moreover, nanoparticle number concentration correlates with highway traffic density.

Conclusions: The study results can enhance our understanding of PM exposure in workplaces near busy roadway. Improving the ventilation system and/or using face masks can help reduce the risk of workers working in vicinity of a busy roadway.

SR-120-03 Assessing Respirator Use and Particulate Matter Exposure in Aluminum Manufacturing Facilities

S. Liu, UC Berkeley, Berkeley, CA

Objective: Industrial hygiene samples for particulate matter (PM) in aluminum production facilities 1977–2011 were analyze to evaluate respirator use and its impact on PM exposure.

Methods: Descriptive analyses were performed to evaluate where and how often respirators were used, as well as how many jobs from which PM exposure would be affected by respirator adjustment. According to the respirator type recorded in the data base, assigned protection factor (APF) was identified. Respirator APFs were then applied to the PM measurements when respirator use was recorded. PM exposures before and after respirator adjustment were compared to evaluate the potential impact of respirator use on PM exposure.

Results: There were 59,683 PM measurements in the company IH database. Respirator use was recorded for 36% of measurements. Use of mechanical filter and chemical cartridge respirators were documented, with occasionally use of supplied air respirators and self-contained breathing apparatus (SCBA). The respirator style included full-face, half-face, quart-face and Helmet/Hood. PM concentration ranged from less than detectable to 11,833 mg/m3, with arithmetic mean of 14.8 mg/m3, median of 0.84 mg/m3 and standard deviation of 720 mg/m3. Among 12 facilities that were intensively examined, respirators were used at a significantly higher rate in smelting facilities (37%) than in fabrication units (16%) or refinery facilities (24%) (p = 0.01). Job titles with high respirator use rates (>95%) include bag house repair, preheat furnace operator, process potline operator, carpenter/painter and pot hood repair, etc. Application of APFs to the PM measurements in these 12 plants resulted in a reduction of overall mean from 12.4 mg/m3 to 5.83 mg/m3 in these plants.

Conclusions: Respirators were widely used in the aluminum manufacturing facilities. Prevalence of use and types of respirator used varied by facility type, process and task. Respirator use adjustment substantially reduced estimated PM exposure, which needs to be considered in occupational health studies of PM exposure in these facilities.

SR-120-04 Estimation of Airborne Subtilisins Concentrations Using Real-Time Portable Aerosol Monitoring Instruments

L. Pahler, R. Larson, D. Sleeth, University of Utah, Salt Lake City, UT

Objective: Currently, there is no real-time method for measuring occupational exposure to subtilisins. This study investigated whether a Grimm 1.109 Aerosol Spectrometer and a DustTrak DRX 8533 could be used to estimate airborne concentrations of subtilisins in real-time as compared to an SKC Personal Button sampler.

Methods: A study was conducted relating the concentration of subtilisins in detergent as measured by SKC Button Inhalable Aerosol Samplers when compared to Grimm and DustTrak Aerosol Spectrometer particulate concentrations. Button Sampler Subtilisin concentrations were determined using a Thermo Scientific Konelab Arena 20 photometric analyzer. Linear regression and Pearson’s correlation comparing the concentration of subtilisins collected from the Button Sampler filter to total particulate concentrations measured by the Grimm and DustTrak were performed for sampling events conducted in an enclosure. A 2% subtilisin and detergent mixture of <25 µm particle diameter was routinely introduced into an enclosure for sampling. Additionally, linear regression and Pearson’s correlation comparing the concentration of total aerosol, as determined by gravimetric analysis, collected by the Button Samplers to total particulate concentrations measured by the Grimm and DustTrak were performed for all sampling events.

Results: Results of the linear regression analysis of the Grimm and aerosol data and Button Sampler data and DustTrack data with Button Sampler data for subtilisins obtained during sampling events show a strong relationship between the these methods (R2=0.922 [p<0.001], r=0.96 [p<0.001]) and (R2=0.72 [p<0.002], r=0.85 [p<0.002]), respectively. Relating the gravimetric analysis of total aerosol collected on the filters also shows a strong relationship (R2=0.98, [p<0.001], r=0.99 [p< 0.001] when compared to the Grimm data and (R2=0.77, [p<0.001], r=0.88 [p< 0.001] when compared to the DustTrak data.

Conclusions: Results of this study demonstrate that a strong association exists between Grimm, DustTrak and Button Sampler for subtilisins, when sampling was carried out in an enclosure with particles of known size and concentration. Additionally, the Grimm and DustTrak data show a strong association with the Button Samplers for inhalable sized particles based on gravimetric analysis.

SR-120-05 Occupational Exposures to Diesel and Alternative Fuel Emissions in Underground Mining: A Simulated Pilot Study

E. Lutz, R. Reed, V. Lee, University of Arizona, Tucson, AZ

Objective: Diesel fuel is commonly used for underground mining equipment, yet diesel engine exhaust is a known human carcinogen. Alternative fuels, including biodiesel, and a natural gas/diesel blend, offer the potential to reduce engine emissions and associated health effects. This study aimed to compare personal exposures to diesel and alternative fuel emissions at an underground mine.

Methods: For this pilot study, personal exposure monitoring was performed in a hard rock underground mining laboratory during operation of a load-haul-dump (LHD) vehicle. Use of low-sulfur diesel, 75% biodiesel/25% diesel blend (B75), and natural gas/diesel blend (GD) fuels were compared. Personal samples were collected for total and respirable diesel particulate matter (tDPM and rDPM, respectively), total and respirable elemental and organic carbon (tEC, rEC, tOC, rOC, respectively), as well as carbon monoxide (CO), formaldehyde, acetaldehyde, naphthalene, nitric oxide (NO), and nitrogen dioxide (NO2). NIOSH methods 5040, 6014, 2016, and 5506 were utilized. Study subjects operated the LHD for 200-minute exposure periods for diesel and B75 emission exposures, consisting of specific mucking activities. Research scientists conducted the same procedures for GD, albeit for 100-minute exposure rotations. Mine ventilation was controlled as much as possible during exposure assessments, and the area was allowed to ventilate for one week between sessions.

Results: Compared to diesel, B75 use was associated with a 33% reduction in rDPM, reductions in rEC, tEC and naphthalene, increased tDPM, tOC and NO, and no change in rOC, CO and NO2. Compared to diesel, GD was associated with a 66% reduction in rDPM and a reduction in all other exposures except CO. 

Conclusions: The alternative fuels tested both resulted in reduced rDPM, which is the basis for the current Mine Safety and Health Administration (MSHA) occupational exposure standard. Although additional study is needed with a wider variety of equipment, use of alternative fuels have the promise of reducing exposures from vehicular exhaust in underground mining settings. 

SR-120-06 Characterization of Metal Fume Emitted from Stainless Steel Plasma Cutting

J. Wang, T. Hoang, E. Floyd, University of Oklahoma Health Sciences Center, Oklahoma City, OK

Objective: Plasma cutting is a metal fabrication technique commonly seen in industries. The process creates a high-temperature arc zone to melt metals and hence produces clean cuts at high speed. Workers are exposed to metal fumes emitted during the cutting process. Metal fume from plasma cutting performed on stainless steel may consist of hexavalent chromium (Cr6+), nickel, and manganese. These toxic metals are either carcinogen or neurological toxin, all can cause serious health effects upon inhalation. The size of the particles is critical for the respiratory deposition and pulmonary toxicity. The study aimed to evaluate the effects of operation parameters on the fume formation rates, metal compositions, fume particle size distributions (PSD) and morphology.

Methods: A conical American Welding Society (AWS) fume chamber and high-volume air sampling pump were used to collect plasma cutting fume, respectively. 308L stainless steel metal plates were cut using a plasma cutter with operating arc currents between 20 to 50 amperes (A). The total fume collected on glass fiber filters were determined gravimetrically and normalized to arc time. Cr6+ in the fume was analyzed using an ion chromatograph following NIOSH 7604 method. Nitrate in the fume was also measured as an indicator of oxidation levels. The fume PSD was examined using a scanning mobility particle sizer and aerodynamic particle sizer for sub-micron and super-micron particles, respectively. The particle morphology was imaged through a transmission electron microscope.

Results: Total fume generation rates under different arc currents ranged from 17.54 mg/min arc time at low current (20 A), to 110.41 mg/min arc time at high current (50 A). The fume generation rates increased with higher current, but decreased with longer arc time. Estimated Cr6+ concentration in the sampled air was above OSHA PEL of 5 µg/m3. Both TEM images and PSD measurement confirmed the primary particles in metal fume were in the ultrafine to sub-micron range, with a median diameter around 150 nm.

Conclusions: The experiment results indicated the plasma cutting fume contained high concentration of nanoparticles loaded with toxic metals such as Cr6+. The operating parameters (arc time and current) affected the fume generation rate and Cr6+ concentration. Proper respiratory protection and adequate ventilation should be utilized to reduce the worker’s exposure.​