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Pathways of transmission of coronavirus (COVID-19) disease in the human population are still emerging. However, empirical observations suggest that dense human settlements are the most adversely impacted, corroborating a broad consensus that human-to-human transmission is a key mechanism for the rapid spread of this disease. Here, using logistic regression techniques, estimates of threshold levels of population density were computed corresponding to the incidence in the human population. Regions with population densities greater than 3000 person per square mile in the United States have about 95% likelihood to get infected with COVID-19. Since case numbers of COVID-19 dynamically changed each day until November 30, 2020, ca. 4% of US counties were at 50% or higher risk of COVID-19 transmission. While threshold on population density is not the sole indicator for predictability of coronavirus in human population, yet it is one of the key variables on understanding and rethinking human settlement in urban landscapes.Plane language SummaryPopulation density is certainly one of the key factors influencing the transmission of infectious diseases like COVID-19. It is approximated that in continental United States, population density of 1192 per square mile and higher presents 50% probability of getting infected with COVID-19.Key PointsBased on data from the USA, the population density of 1192 persons per square mile represented a 50% or higher probability of risk of transmission of COVID-19.About 35 counties in the USA are at very high risk of transmission potential (95% or higher) for COVID-19.Analysis shows the vulnerability of urban towns to respiratory infectious disease

The B.1.617.2 (Delta) variant of SARS-CoV-2 emerged in India in October of 2020 and spread widely to over 145 countries, comprising over 99% of genome sequence-confirmed virus in COVID-19 cases of the United States (US) by September 2021. The rise in COVID-19 cases due to the Delta variant coincided with a return to in-person school attendance, straining COVID-19 mitigation plans implemented by educational institutions. Some plans required sick students to self-isolate off-campus, resulting in an unintended consequence: exposure of co-inhabitants of dwellings used by the sick person during isolation. We assessed air and surface samples collected from the bedroom of a self-isolating university student with mild COVID-19 for the presence of SARS-CoV-2. That virus' RNA was detected by real-time reverse-transcription quantitative polymerase chain reaction (rRT-qPCR) in air samples from both an isolation bedroom and a distal, non-isolation room of the same dwelling. SARS-CoV-2 was detected and viable virus was isolated in cell cultures from aerosol samples as well as from the surface of a mobile phone. Genomic sequencing revealed that the virus was a Delta variant SARS-CoV-2 strain. Taken together, the results of this work confirm the presence of viable SARS-CoV-2 within a residential living space of a person with COVID-19 and show potential for transportation of virus-laden aerosols beyond a designated isolation suite to other areas of a single-family home.

Fitness centers are considered high risk for SARS-CoV-2 transmission due to their high human occupancy and the type of activity taking place in them, especially when individuals pre-symptomatic or asymptomatic for COVID-19 exercise in the facilities. In this study, air (N = 21) and surface (N = 8) samples were collected at a fitness center through five sampling events from August to November 2020 after the reopening restrictions were lifted in Florida. The total attendance was ~2500 patrons during our environmental sampling work. Air samples were collected using stationary and personal bioaerosol samplers. Moistened flocked nylon swabs were used to collect samples from high-touch surfaces. We did not detect SARS-CoV-2 by rRT-PCR analyses in any air or surface sample. A simplified infection risk model based on the Wells-Riley equation predicts that the probability of infection in this fitness center was 1.77% following its ventilation system upgrades based on CDC guidelines, and that risk was further reduced to 0.89% when patrons used face masks. Our model also predicts that a combination of high ventilation, minimal air recirculation, air filtration, and UV sterilization of recirculated air reduced the infection risk up to 94% compared to poorly ventilated facilities. Amongst these measures, high ventilation with outdoor air is most critical in reducing the airborne transmission of SARS-CoV-2. For buildings that cannot avoid air recirculation due to energy costs, the use of high filtration and/or air disinfection devices are alternatives to reducing the probability of acquiring SARS-CoV-2 through inhalation exposure. In contrast to the perceived ranking of high risk, the infection risk in fitness centers that follow CDC reopening guidance, including implementation of engineering and administrative controls, and use of personal protective equipment, can be low, and these facilities can offer a relatively safe venue for patrons to exercise.

Since mask use and physical distancing are difficult to maintain when people dine indoors, restaurants are perceived as high risk for acquiring COVID-19. The air and selected environmental surfaces in two restaurants in a mid-scale city located in north central Florida that followed the Centers for Disease Control and Prevention (CDC) reopening guidance were sampled three times from July 2020 to February 2021. Sixteen air samples were collected for 2 hours using air samplers, and 20 surface samples by using moistened swabs. The samples were analyzed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) for the presence of SARS-CoV-2 genomic RNA. A total of ~550 patrons dined in the restaurants during our samplings. SARS-CoV-2 genomic RNA was not detected in any of the air samples. One of the 20 surface samples (5%) was positive. That sample had been collected from a plastic tablecloth immediately after guests left the restaurant. Virus was not isolated in cell cultures inoculated with aliquots of the RT-PCR-positive sample. The likelihood that patrons and staff acquire SARS-CoV-2 infections may be low in restaurants in a mid-scale city that adopt CDC restaurant reopening guidelines, such as operation at 50% capacity so that tables can be spaced at least 6 feet apart, establishment of adequate mechanical ventilation, use of a face covering except while eating or drinking, and implementation of disinfection measures.

To overcome limitations of existing air-cleaning filters in capturing and deactivating aerosolized microorganisms, this study was embarked to evaluate novel Ag, Zn, and Fe nanoparticle-doped cotton filters (AgCt, ZnCt, FeCt), as biocidal filters for bioaerosol attenuation. To evaluate the biocidal activity of the nanocomposite filters, the survival of lab-generated E. coli after collection on each filter material was compared to collection on an undoped cotton control filter and in a BioSampler. Relative humidity (RH) affected the survival of bacteria on the filters, and the optimal RH was found to be 50 ± 5%. The physical removal efficiency (PRE) determined by an optical particle counter was 99.9 ± 0.7% for ZnCt, 97.4 ± 1.2% for AgCt, and 97.3 ± 0.6% for FeCt, where the control showed only 77.4 ± 6.3% for particles > 500 nm. The doped filters showed 100% viable removal efficiency (VRE). Importantly, the VRE of the nanocomposite filters after four cycles remained nearly 99% and was greater than the cotton control filter at 76.6 ± 3.2%. Adding to its benefits, the AgCt filters had a lower pressure drop than the FeCt and ZnCt filters and the cotton control. The permeability for the cotton control filter was 3.38 × 10−11 m2 while that for the AgCt filter was slightly higher (3.64 × 10−11 m2) than the other filters as well. Overall, these results suggest that nanocomposite-doped filter media, particularly AgCt, can provide effective protection against airborne pathogens with a lower pressure drop, elevated collection efficiency, and better disinfection capability as compared to untreated cotton filters, which are all important features for practical biocidal applications. Graphical 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 (< 100 nm). 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 BASIC's 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 103.5 kPa and water temperature of 25 °C was sufficient to increase the particle diameter from < 100 nm to > 1 µm; 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 BASIC's capability as a simple, quick and inexpensive tool for rapid sampling of viable airborne viruses., Highlights • A novel device for virus aerosol sampling based on adiabatic expansion is developed. • The performance of the device is evaluated considering both physical and biological aspects. • Key parameters (e.g., compression pressure, NO. of cycles, temperature) were tested to achieve the optimal design.

Individuals with COVID-19 are advised to self-isolate at their residences unless they require hospitalization. Persons sharing a dwelling with someone who has COVID-19 have a substantial risk of being exposed to the virus. However, environmental monitoring for the detection of virus in such settings is limited. We present a pilot study on environmental sampling for SARS-CoV-2 virions in the residential rooms of two volunteers with COVID-19 who self-quarantined. Apart from standard surface swab sampling, based on availability, four air samplers positioned 0.3–2.2 m from the volunteers were used: a VIable Virus Aerosol Sampler (VIVAS), an inline air sampler that traps particles on polytetrafluoroethylene (PTFE) filters, a NIOSH 2-stage cyclone sampler (BC-251), and a Sioutas personal cascade impactor sampler (PCIS). The latter two selectively collect particles of specific size ranges. SARS-CoV-2 RNA was detected by real-time Reverse-Transcription quantitative Polymerase Chain Reaction (rRT-qPCR) analyses of particles in one air sample from the room of volunteer A and in various air and surface samples from that of volunteer B. The one positive sample collected by the NIOSH sampler from volunteer A's room had a quantitation cycle (Cq) of 38.21 for the N-gene, indicating a low amount of airborne virus [5.69E-02 SARS-CoV-2 genome equivalents (GE)/cm3 of air]. In contrast, air samples and surface samples collected off the mobile phone in volunteer B's room yielded Cq values ranging from 14.58 to 24.73 and 21.01 to 24.74, respectively, on the first day of sampling, indicating that this volunteer was actively shedding relatively high amounts of SARS-CoV-2 at that time. The SARS-CoV-2 GE/cm3 of air for the air samples collected by the PCIS was in the range 6.84E+04 to 3.04E+05 using the LED-N primer system, the highest being from the stage 4 filter, and similarly, ranged from 2.54E+03 to 1.68E+05 GE/cm3 in air collected by the NIOSH sampler. Attempts to isolate the virus in cell culture from the samples from volunteer B's room with the aforementioned Cq values were unsuccessful due to out-competition by a co-infecting Human adenovirus B3 (HAdVB3) that killed the Vero E6 cell cultures within 4 days of their inoculation, although Cq values of 34.56–37.32 were measured upon rRT-qPCR analyses of vRNA purified from the cell culture medium. The size distribution of SARS-CoV-2-laden aerosol particles collected from the air of volunteer B's room was >0.25 μm and >0.1 μm as recorded by the PCIS and the NIOSH sampler, respectively, suggesting a risk of aerosol transmission since these particles can remain suspended in air for an extended time and travel over long distances. The detection of virus in surface samples also underscores the potential for fomite transmission of SARS-CoV-2 in indoor settings., Graphical abstract Image 1

Airborne transmission of pathogenic aerosols via human breath plays a major role in infectious disease outbreaks in indoor environments. Yet, their bioaerosol emission profiles are still not well quantified. Here, we first studied bioaerosol emission rates of human exhaled breath from 12 healthy subjects, and then evaluated the bioaerosol emissions when wearing two different respirators “Doctor masks” and N95 in a controlled environment (27 m3) using a bioaerosol sensor-ultraviolet aerodynamic particle spectrometer (UV-APS). The human bioaerosol contribution was further confirmed through classroom observation. The results showed that there was a peak around 1.5 µm for the fluorescent particles emitted from humans’ breath. For the controlled environment, the presence of 5 people without wearing masks increased bioaerosol concentration by 107% within 30 min at an average emission rate of 8.4 × 105 fluorescent particles person–1 hour–1 resulting from the occupancy. When wearing N95 masks or “Doctor masks”, bioaerosol increases were observed to be 81% or 31% for the controlled environment, respectively, lower compared to those without masks. In-classroom observation also showed a fluorescent particle concentration increase of about 50%. In all experiments, we observed a decline in PM number concentration. Bioaerosol emission from exhaled breath was calculated to account for about 17% of the increase in the controlled environment. The results here suggest the need for re-evaluating microbial aerosol exposure risks for medical sites that demand high levels of hygiene even while wearing a respirator.

Converting optical diameter measured by an optical particle counter (OPC) to aerodynamic diameter measured by an aerodynamic particle sizer (APS) is of interest because the OPC is more affordable and portable. In this study, optical diameter was compared with volume equivalent diameter derived from aerodynamic diameter using monodisperse oleic acid and sodium chloride test aerosols generated by a Vibrating Orifice Aerosol Generator (VOAG). While prior studies assumed optical diameter to be equal to volume equivalent diameter, experimental results showed the assumption to be valid only if the aerosol has the same optical properties as standard polystyrene (PSL) particles. For oleic acid aerosol, the optical diameter was less than the derived volume equivalent diameter because its refractive index ( m =1.46) is less than of PSL ( m =1.60). While the refractive index of sodium chloride ( m =1.54) is close to that of PSL, a much larger optical diameter of sodium chloride than its volume equivalent diameter was observed due to its irregular crystallography. Regression equations derived from the calibration were verified by testing with a validated respirable sampler. With known refractive index and shape factor, these equations can convert optical diameter directly to aerodynamic diameter with a residual bias less than 1 µm.

In assessing the biological impact of airborne particles in vitro, air-liquid interface (ALI) exposure chambers are increasingly preferred over classical submerged exposure techniques, albeit historically limited by their inability to deliver sufficient aerosolized dose. A novel ALI system, the Dosimetric Aerosol in Vitro Inhalation Device (DAVID), bioinspired by the human respiratory system, uses water-based condensation for highly efficient aerosol deposition to ALI cell culture. Here, welding fumes (well-studied and inherently toxic ultrafine particles) were used to assess the ability of DAVID to generate toxicological responses between differing welding conditions. After fume exposure, ALI-cultured cells showed reductions in viability that were both distinct between welding conditions and linearly dose-dependent with respect to exposure time; comparatively, submerged cell cultures ran in parallel did not show these trends across exposure levels. DAVID delivers a substantial dose in minutes (> 100 μg/cm2), making it preferable over previous ALI systems, which require hours of exposure to deliver sufficient dose, and over submerged techniques, which lack comparable physiological relevance. DAVID has the potential to provide the most accurate assessment of in vitro toxicity yet from the perspectives of physiological relevance to the human respiratory system and efficiency in collecting ultrafine aerosol common to hazardous exposure conditions.

The concentrations and distribution of hazardous air pollutants (HAPs) metals emitted from four phosphate fertilizer plants in Central Florida, as well as their environmental and health impacts, were investigated. It was hypothesized that the modern control devices employed in the plants would lower the exposure, if any, to an acceptable level. The dominant HAP metals emitted from the stacks of these plants were identified to be Mn, Cr, Ni, and Se. The ambient concentrations at six receptors (Zephyrhills, Plant City, Tampa, Lakeland, Tower Dairy, and Sydney) downwind the plants estimated by AERMOD revealed the maximum ground level concentrations were lower than the European Communities and USEPA standards. Source apportionment estimated by the chemical mass balance (CMB) model indicated that marine (45.5 ± 17.1 %) and geological (17.3 ± 10.6 %) were the top two contributors for 26 elements, while the phosphate fertilizer plants contributed only 1.14 ± 0.55 %. Unexpectedly, the maximum ground-level risks for Cr from plant A (1.3 × 10−6 ± 8.4 × 10−8) and plant D (1.1 × 10−6 ± 6.7 × 10−8) were slightly higher than the general guideline of 1 × 10−6, but they occurred within the facility limit. No other metals approached levels of concern for non-cancer risks. One possible source for Cr emissions from these plants may be stainless steel milling balls used in the production process. Sensitivity analysis of the meteorological data in 2001–2005 showed only 7.7 % variation in the corresponding risk. Overall, phosphate fertilizer plants make minor contribution to the ambient levels of HAP metals compared to other sources for the general population in the Tampa Bay area, although more in-depth investigation into the Cr emissions is recommended.

For a constant aerosol concentration, it is traditionally assumed that a Poisson process describes the behavior of particle detections during sampling and consequently fluctuations in the measured concentration. Recent studies, however, have shown that sampling of micrometer-sized aerosols has non-Poissonian behavior with positive correlations. The validity of the Poisson assumption for nanometer-sized aerosols has not been established and thus was tested in this study. Its validity was tested for four particle sizes—10 nm, 25 nm, 50 nm, and 100 nm—by sampling from indoor air with a differential mobility analyzer-condensation particle counter (DMA-CPC) setup to obtain a time series of particle counts. Five metrics were calculated from the data: pair-correlation function (PCF), scaled clustering index (SCI), coefficient of variation, probability of measuring a concentration at least 25% greater than average, and posterior distributions from Bayesian inference. To identify departures from Poissonian behavio...

To characterize the release of ammonia (NH3) from ammoniated fly ash in concrete, laboratory experiments were carried out with concrete added with fly ash containing ammonium loading ranging from 65 to 3,200 mg NH4 +/kg fly ash. A physical description of the NH3 release from concrete was given, and a quantitative diffusion model was developed. In the experiments, NH3 gas release lasted 5 days to 3 weeks. After the ammonia gas release rate gradually decreased to a non-detectable level, there was still 20 to 70 % of ammonium retained in the concrete. Of all the NH3 gas released, over 80 % was emitted in the first 8 h after the concrete was mixed. According to the physical and chemical condition of the concrete, NH3 release from concrete was divided into three periods: mixing, initial settling, and curing. Mechanics of NH3 release in the three periods were quantitatively analyzed for the first time. Convective mass transfer caused by air movement dominated NH3 release in the first two periods. In the curing period, due to decreased moisture content and filled capillaries in the concrete, diffusion of NH3 from inside of concrete to its surface became the rate-limiting factor. Diffusivity of the mixing period and the initial settling period was 9.1 × 10−8 (±1.25 × 10−7) and 3.93 × 10−9 (±2.78 × 10−9) m2/s, respectively. In the curing period, NH3 diffusivity in the concrete continuously decreased, ranging from 5.36 × 10−9 m2/s to below detection limit in 3 weeks. The difference in diffusivity among different periods reflected the physical and chemical change of the concrete.

The dusty environment of the moon and the deposition of charged particles were troublesome in previous NASA explorations. In this study, an electrostatic lunar dust repeller (ELDR) was developed to mitigate the dust deposition problem. The ELDR consists of an arrangement of thin, needle-shaped electrodes in front of the protected surface to repel approaching, like-charged lunar dust. A discrete element method (DEM) was applied to track particle trajectories for determining the removal efficiency. Simulation results for single electrodes ( L =5 cm, D =1 mm and L =10 cm, D =1 mm) both protecting a 5-cm×5-cm surface indicated that 4 kV and 1.5 kV were the respective-applied voltages required to achieve 100% protection from falling 20-µm lunar dust particles. The electrical particle–particle interaction was identified to be a beneficial factor. Finite element analysis concluded that an x -shaped pattern was the most effective arrangement of the ensemble electrodes to protect a 30-cm×30-cm surface. Modeling results showed that 2.2 kV and 1.4 kV were the minimum voltages applied to electrodes of length L =5 and 10 cm, respectively, on each electrode of the ensemble model to achieve complete removal of 20-µm-sized particles. The ensemble-electrode ELDR required lower applied voltage than the single-electrode ELDR, and in the most conservative scenario, it consumed only 9 times more electric power to protect an area 36 times larger.

Fuel blends that contain biodiesel are known to produce greater NOx (nitrogen oxide) emissions in diesel engine exhaust than regular diesel, and this is one of the key barriers to the wider adoption of biodiesel as an alternative fuel. In this study, a water-containing ABE (acetone–butanol–ethanol) solution, which simulates products that are produced from biomass fermentation without dehydration processing, was tested as a biodiesel-diesel blend additive to lower NOx emissions from diesel engines. The energy efficiency and the PM (particulate matter) and PAHs (polycyclic aromatic hydrocarbons) emissions were investigated and compared under various operating conditions. Although biodiesel had greater NOx emissions, the blends that contained 25% of the water-containing ABE solution had significantly lower NOx (4.30–30.7%), PM (10.9–63.1%), and PAH (polycyclic aromatic hydrocarbon) emissions (26.7–67.6%) than the biodiesel–diesel blends and regular diesel, respectively. In addition, the energy efficiency of this new blend was 0.372–7.88% higher with respect to both the biodiesel–diesel blends and regular diesel. Because dehydration and surfactant addition are not necessary, the application of ABE–biodiesel–diesel blends can simplify fuel production processes, reduce energy consumption, and lower pollutant emissions, meaning that the ABE–biodiesel–diesel blend is a promising green fuel.

Protecting sensitive surfaces from dust deposition in the limiting condition of the lunar atmosphere is imperative for space exploration. In this study, how back electrostatic field due to charge build-up on collection plates may affect the performance of an electrostatic lunar dust collector (ELDC) was investigated. The relationships between ELDC dimensions, collection efficiency and electrical properties of lunar dust particles were derived to develop a model, appropriate for any size of the ELDC. A Lagrangian-based discrete element method (DEM) was applied to track particle trajectories, and sensitivity analyses were conducted for the concentration of the incoming particles, the number of pre-collected particles and the applied voltages. The results revealed that the collection efficiency reduced over time due to the back electrostatic field of the collected particles, which ultimately led to a suspended regime, rather than just collected and penetrated fractions considered in conventional models. The generated back electrostatic field and the cloud of suspended particles were strong enough to disrupt the performances of both the ELDC and the protected device. The maximum time ELDC can run without significant loss in collection efficiency was estimated to be 10 terrestrial days for the studied ELDC size and applied voltage. Because the electrical power was negligible compared to the provided power by the solar panels, increasing the applied voltage was found to be the best option to counteract back electrostatic growth.

Previous studies have shown that bioaerosols can be inactivated in less than a second when exposed to temperatures of hundreds of degrees Celsius in an ultra-high temperature (UHT) process. Here, a new UHT system was developed to make UHT safer and more predictable, in which a heated porous cloth was oriented perpendicularly to the flow direction to produce more uniform flow temperatures. Infrared radiation, which can provide uniform heating for flat surfaces, was used to heat the cloth. Temperature measurements indicated that high temperatures were obtained at the cloth surface and that the downstream flow temperature was more axially uniform than radially/azimuthally uniform. For both Escherichia coli and MS2 virus test bioaerosols, the inactivations were found to be greater than 4.7 log for a cloth temperature of about 450 °C and residence time of 0.41 s. Results from gel electrophoresis showed that infrared–UHT treatment resulted in DNA damages to E. coli. Besides lab testing, the UHT system was found to reduce the concentration of outdoor culturable bacteria by 1–2 orders of magnitude at 210 °C and residence time of 0.1 s, but was less effective against fungi. On the other hand, SEM imaging and sampling downstream of the cloth revealed that the cloth emitted unidentified particles. The results of the work proved that this IR system – with its perpendicular orientation – can achieve high temperatures and high bioaerosol disinfection, and can be used to better relate temperature to inactivation. Furthermore, the ambient inactivation data, which are not available in literature, allow insights into the real-world applications of an UHT system.

The emission factors and compositions of volatile organic compounds (VOC) in exhaust gas from in-use gasoline passenger cars were characterized using a chassis dynamometer. Three passenger cars were tested at the ECE and the EUDC drive cycles to represent both urban and suburban driving scenarios. Exhaust gas was collected in Summa canisters and analyzed by gas chromatography-mass spectrometry (GC-MS). Common gaseous emissions (CH(4), NOx, CO, and CO(2)) were measured by an on-board monitoring system. The VOC emission factors of different cars ranged from 0.10 to 0.25 g km(-1) at the ECE cycle, and 0.01-0.02 g km(-1) at the EUDC cycle. A total of 57 individual VOC were detected in the exhaust gas, and the weight percentages were very consistent among the three cars. Ethylene (11.80 wt.%), toluene (11.27 wt.%), and benzene (8.83 wt.%) were the most abundant VOC in exhaust gas. Aromatics (38.32%) dominated the low speed conditions (ECE), while alkanes (37.34%) were the major compounds at the high speed condition (EUDC). The total amount of alkenes did not change much between those two cycles, while ethylene is abundant in the ECE and EUDC cycles. Ozone formation potential (OFP) was calculated to estimate the ozone yield from VOC emissions by gasoline cars and the results showed that OFP of VOC emission at the ECE cycle was about ten times higher than that at the EUDC cycle.

MnO x -CeO 2 mixed-oxide supported on TiO 2 (Mn-Ce/Ti) was synthesized by an ultrasound-assisted impregnation method and employed to oxidize elemental mercury (Hg 0 ) at 200 °C in simulated coal combustion flue gas. Over 90% of Hg 0 oxidation was achieved on the Mn-Ce/Ti catalyst at 200 °C under simulated flue gas representing those from burning low-rank coals with a high gas hourly space velocity of 60,000 h −1 . Gas-phase O 2 regenerated the lattice oxygen and replenished the chemisorbed oxygen, which facilitated Hg 0 oxidation. HCl was the most effective flue gas component responsible for Hg 0 oxidation. 10 ppm HCl plus 4% O 2 resulted in 100% Hg 0 oxidation under the experimental conditions. SO 2 competed with Hg 0 for active sites, thus deactivating the catalyst's capability in oxidizing Hg 0 . NO covered the active sites and consumed surface oxygen active for Hg 0 oxidation, hence limiting Hg 0 oxidation. Water vapor showed prohibitive effect on Hg 0 oxidation due to its competition with HCl and Hg 0 for active adsorption sites. This study provides information about the promotional or inhibitory effects of individual flue gas components on Hg 0 oxidation over a highly effective Mn-Ce/Ti catalyst. Such knowledge is of fundamental importance for industrial applications of the Mn-Ce/Ti catalyst in coal-fired power plants.

Highly efficient collection of infectious pandemic Influenza H1N1 virus (2009) through laminar-flow water based condensation

Inactivation of collected viral aerosols is important for preventing a filter medium’s serving as a fomite. The focus of this study was to evaluate the inactivation efficiency (IE) achieved through filtration coupled with microwave irradiation. MS2 aerosolized through a Collison nebulizer was fed into the system and collected onto the filter. For in-flight microwave decontamination, microwave irradiation was applied to an HVAC (heating, ventilation and air conditioning) filter supported on a SiC disk for three cycles of selected irradiation times per 10 min (i.e., 1, 2.5, 5, and 10 min/10 min) at power levels ranging from 125 W to 375 W. The survival fraction (SF) on the substrate and the IE through the entire system were investigated to determine the efficacy of this approach. SF decreased and IE increased as microwave power level was increased (p = 0.02 and p < 0.01, respectively) or the application time was extended (p = 0.03 and p < 0.01, respectively). Both measures changed sharply above a threshold temperature of around 90°C and reached 2 logs at 116 and 109°C, respectively. The log SF and IE of –2.59 and 3.62, respectively, were observed when the operating condition of 375 W for 10 min/cycle was used and the SiC disk facilitated microwave absorption. When a quartz frit was used as a support instead of the SiC disk, log inactivation efficiencies of 0.8, 1.0, and 1.3 were measured at relative humidities of 30%, 60% and 90%, respectively, under the same irradiation conditions. Relative humidity is a significant parameter from 50–80°C (p = 0.01). The results demonstrate that microwave-assisted filtration systems can be used as an effective means for inactivating viruses.

Conventional denuders made of glass or metal are too heavy and bulky to be used in personal sampling systems. In this study, a portable Porous Membrane Denuder (PMD) was developed for personal sampling. The PMD utilizes the porosity of the membrane material and a configuration of multiple parallel flow channels to reduce the size and weight of the device, while increasing the gas collection efficiency. Four types of PMDs (PMD I, II, III and IV) with increasing numbers of channels and smaller channel openings were constructed and tested. Using 10% sodium carbonate coating and a feed concentration of 1 ppm, PMD Ia's collection efficiency for sulfur dioxide over 8 hours was higher than 99.9%. For a feed concentration of 10 ppm, the 5-hr time-weighted-average collection efficiency for sulfur dioxide was 73.1%, 82.8%, 90.9%, 97.2% for PMD Ib, II, III and IV, respectively, compared with 96.6% of the Glass Honeycomb Denuder (GHD), which has similar structure to PMD IV. However, the weight of PMD IV is only one-tenth of that of the GHD. It is clear that with a similar physical structure, PMDs have similar capacities to traditional Glass Honeycomb Denuders, yet are much lighter and less expensive. This study demonstrates the great potential of this new type of denuder for many applications in the field of environmental and industrial hygiene monitoring. Particle loss fractions of the four types of PMDs in the size range of 1 to 10 μm were also measured and were 2.9%, 5.2%, 5.7% and 7.3%, respectively.

The chemical characteristics of airborne particulate matter (PM) have been extensively studied; however, little information exists for its biological components (bioaerosol) especially during a haze event in mega cities. Herein, we studied the bioaerosol (fluorescent particle) dynamics on both haze and sunny days in Beijing from Dec. 2013 to March 2014 by employing a widely used real-time bioaerosol sensor-ultraviolet aerodynamic particle spectrometer (UV-APS). Firstly, we studied the fluorescent particle (BioPM) concentration and size distributions during three independent haze and three independent sunny days. Secondly, we investigated BioPM dynamics over a two-week long monitoring period which included consecutive haze days and alternated sunny days. In addition, we analyzed bacterial community structures and endotoxin levels in the air samples using pyrosequencing and Limulus amebocyte lysate (LAL) method, respectively. More than 6-fold higher fluorescent particle concentrations up to 5×10(5)/m(3) with peaks at night or early dawn were detected at the time of haze occurrences than those observed on sunny days. When the haze episode progressed for 3-5days, the BioPM concentrations were observed to decrease to the levels that were typically observed on sunny days. In general, ozone levels were found to be elevated at noon, while BioPM, NOx and relative humidity were reduced. Gene sequence analysis revealed no significant difference in abundances and community structures for top 13 bacterial genera between haze and sunny days, yet about twice higher endotoxin levels (12.4EU/m(3)) were detected on haze days than on sunny days. The results here facilitate a better understanding of atmospheric fluorescent particle dynamics including those under haze events.

Welding fumes contain heavy metals, such as chromium, manganese, and nickel, which cause respiratory diseases and cancer. In this study, a SiO(2) precursor was evaluated as an additive to the shielding gas in an arc welding process to reduce the biotoxicity caused by welding fume particles. Transmission electron micrographic images show that SiO(2) coats on the surface of welding fume particles and promotes particle agglomeration. Energy dispersive X-ray spectroscopy further shows that the relative amount of silicon in these SiO(2)-coated agglomerates is higher than in baseline agglomerates. In addition, Escherichia coli (E. coli) exposed to different concentrations of pure SiO(2) particles generated from the arc welding process exhibits similar responses, suggesting that SiO(2) does not contribute to welding fume particle toxicity. The trend of E. coli growth in different concentrations of baseline welding fume particle shows the most significant inhibition occurs in higher exposure concentrations. The 50% lethal logarithmic concentrations for E. coli in arc welding particles of baseline, 2%, and 4.2% SiO(2) precursor additives were 823, 1605, and 1800 mg/L, respectively. Taken together, these results suggest that using SiO(2) precursors as an additive to arc welding shielding gas can effectively reduce the biotoxicity of welding fume.

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 3–4 μm, respectively, around the loading location when 35% relative humidity was applied. The average loading density was ∼2×10 3 plaque-forming units/cm 2 for 5-min loading time with a virus titer of 10 7 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.

Airborne biological agents, albeit intentionally released or naturally occurring, pose one of the biggest threats to public health and security. In this study, a microwave assisted nanofibrous air filtration system was developed to disinfect air containing airborne pathogens. Aerosolized E. coli vegetative cells and B. subtilis endospores, as benign surrogates of pathogens, were collected on nanofibrous filters and treated by microwave irradiation. Both static on-filter and dynamic in-flight tests were carried out. Results showed that E. coli cells were efficiently disinfected in both static and in-flight tests, whereas B. subtilis endospores were more resistant to this treatment. Microwave power level was found to be the major factor determining the effectiveness of disinfection. Both thermal and non-thermal effects of microwave irradiation contributed to the disinfection. Reducing flow velocity to decrease heat loss yielded higher disinfection efficiency.

Hexavalent chromium (Cr 6+ ) emission from stainless steel welding operations poses a serious threat to worker safety and ambient air quality. In this study, tetraethyloxysilane (TEOS) was used as a silica precursor additive to welding shield gas during gas tungsten arc welding (GTAW) operations to determine the feasibility of using these chemicals for Cr 6+ exposure reduction. Fume aerosol samples were analyzed for Cr 6+ concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES). At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO 2 ) which can condense on the existing metal aerosols. The inert silica layer surrounding the aerosols can prevent further chromium oxidation by insulating chromium aerosols. Experimental results showed approximately 45% Cr 6+ reductions when 3.0% TEOS was added to the shield gas. Nitrate concentration also decreased by 53%, indicating that reactive oxygen species were also reduced. Transmission electron microscopy (TEM) images of collected fume aerosols showed SiO 2 coating on metal particles, verifying the proposed mechanism.

Nanofiber filtration is drawing great interest nowadays because of its large surface collection area as well as low air resistance. In this study, electrospun nanofiber mats of different thicknesses were evaluated for their filter quality factors. Shorter-term electrospun fiber mats exhibited a better quality factor than those longer-term electrospun ones. Multiple thin layers of nanofiber mats to improve the filter quality of the nanofiber filters were then evaluated. Filtration test results showed that the filter made up of multiple thin layers of nanofiber mats had a filter quality factor much higher than the single thick layer nanofiber mat. Better thickness uniformity in the multi-layer structure due to stacking compensation and smaller fiber diameters in nanofibers of short-term deposition time are two possible reasons for the improvement of the filter quality.

Nanomaterial, due to its unique physical, chemical and biological properties compared to its bulk counterparts, has the potential to provide a product superior to its bulk predecessor. In this study, a novel alumina nanofiber filter was assessed for its removal and retention capability for MS2 aerosol. Its physical removal efficiency in the 10–400 nm range was 94.35%, while its viable removal efficiency was 98.87%, which was slightly lower than three conventional HEPA filters tested. However, its pressure drop was much lower than HEPA filters, yielding a higher filter quality than HEPA filters. The average extracted fraction from the nanofiber filter was 8.64×10 −2 ±7.00×10 −2 , which is three orders lower than other HEPA filters, demonstrating that the viruses were effectively retained in the nanofiber filter. Furthermore, the performance of the nanofiber filter showed no dependence on relative humidity. In conclusion, this novel alumina nanofiber filter presents advantageous potential for removal and retention of viral aerosol agents.

Strong inorganic acid mists containing sulfuric acid (H2SO4) have been reported to correlate well with lung and laryngeal cancers in humans. Phosphate fertilizer manufacturing facilities are listed as one of the many occupational exposures to strong acid. To better protect workers from potential exposure, a field campaign was carried out to investigate aerosol characteristics at eight phosphate fertilizer facilities using a UW-cascade impactor for size information and ion chromatography for water soluble species. The results show that acid mists were dominantly in the coarse mode when high concentrations were identified. An aerosol thermodynamic model was established to estimate the aerosol acidity. In the high-relative-humidity environment, the aerosol can reach its equilibrium size within 0.014 s, which is shorter than the traveling time of an aerosol in the upper respiratory system. The results indicate that aerosols sampled in this study may deposit in the upper respiratory tract, which is consistent with epidemiological evidence of a correlation between inhalation of strong inorganic acid mists and laryngeal cancer. However, extensive epidemiological studies of phosphate industry workers have not shown an increased incidence of any type of cancer.

Poly(styrene-divinylbenzene)-4-(methyltrimethylammonium) triiodide (PMT) has recently been applied onto nonwoven air filter media to purportedly combine filtration and iodine disinfection to achieve enhanced attenuation of viable airborne pathogens without aggravating the pressure drop of the medium. This paper reports and compares the physical capture efficiency and biological removal efficiency of the novel biocidal filter medium. During challenges with inert fluorescent particles, bothiodine-treated and untreated media displayed statistically equivalent physical capture efficiencies ＞ 97%, and typically ＞ 99%. The pressure drag (3.2 kPa•s/m) was less than 10% that of a glass fiber HEPA (38 kPa•s/m) medium. Biological disinfection by the media was evaluated using aerosols containing M. luteus and E. coli vegetative bacterial cells. Biological removal efficiency (99.997%) was observed to be two logs greater than inert particle capture. Viable penetration through the biocidal filters was observed in only two of 10 experiments. The results suggest that an antimicrobial-coated filter medium can provide effective protection against airborne pathogens with a significantly lower pressure drop than that imposed by conventional high-efficiency filtration systems. A near-contact mechanism is proposed in which the distances of nearest approach to treated fiber surfaces as a microbe penetrates through the filter define the probability that charge sites on the microbe’s surface will capture enough iodine molecules from triiodide complexes at the surfaces to terminate viability.

A mechanistic study of vanadium-sorbent interaction at high temperature was conducted to investigate the underlying mechanisms of sorbent injection for controlling vanadium emissions from combustion systems. Both calcium- and silica-based sorbents successfully reduced the formation of vanadium submicron particles. The capture of vanadium was found to correlate well with sorbent surface area, demonstrating that the dominant mechanism was condensation. Bimodal lognormal modeling based on the experimental conditions verified that condensation on injected sorbents was a very effective means of scavenging vanadium vapor. However, if vanadium vapor quickly nucleated (e.g., through gas phase hydrolysis in the studied system) to form a large number of ultrafine particles, their much larger specific surface area overshadowed that of the sorbent particles and scavenged the rest of the vanadium vapor. Using the residence times employed in this study, intra-coagulation of and condensation onto these ultrafine vanadiu...

The kinetics of photocatalytic oxidation of elemental mercury (Hg0) on a SiO2–TiO2 nanocomposite with UV irradiation was studied in a fix-bed reactor under both dry and humid conditions. The experimental data were analyzed using a Langmuir-Hinshelwood (L-H) model. The reaction rate was successfully expressed using the model, indicating the L-H nature of Hg0 photocatalytic oxidation on the SiO2–TiO2 nanocomposite. The L-H model prediction suggests a great potential of the SiO2–TiO2 nanocomposite for Hg0 removal from high concentration emission sources. On the other hand, the rate of photocatalytic Hg0 oxidation was found to be significantly inhibited by the presence of water vapor. This may be explained by the competitive adsorption of water vapor on the TiO2 surface, which results in the reduction of available adsorption sites for Hg0.

Nitrogen oxides (NOx) are the key air pollutants emitted by mobile and stationary sources, and are a major cause of adverse health and environmental effects. One promising alternative material to conventional noble metal-based catalysts for NOx emission control is the group of transition metal oxides, in particular, CuO. In this study, well-dispersed CuO and CuO/Al2O3 nanocatalysts coated onto durable Al2O3 fiber substrates were assessed for NO conversion efficiency. The resultant composite materials had high surface area with good dispersion for enhanced NO conversion. Operating parameters, including nanocatalysts loading and temperature, were investigated for their effects on the catalytic performance for NO conversion. The experimental results showed that the activity of the catalysts is strongly related to the loading amount and the degree of dispersion of CuO nanoparticles. The binary CuO/Al2O3 system yielded a higher NO conversion efficiency than the system consisting of CuO alone. Small amounts of ...

An interactive web-based program consisting of three integrated modules has been developed to enhance the understanding of the multidisciplinary nature and the complex principles of aerosol science and technology at the introductory level. Formative evaluation resulted in many suggestions from potential users on the improvement of the format and message. Feedback from students showed that the majority thought this mode of learning was effective, and they liked the dynamic animation and interactive features. Many also indicated that they prefer the modules be used to enhance rather than to replace in-class instruction. Summative evaluation based upon pre- and post-tests demonstrated that the website was effective for teaching the content. The results of the t-tests showed a statistically significant difference in the pre- and post-test scores. In summary, the evaluation data clearly indicate both the usefulness of the modules as teaching tools and a high degree of acceptance by students and faculty.

The health risks to workers in the Florida phosphate industry resulting from chronic inhalation of radionuclide-containing aerosols have not been adequately addressed. The present study establishes a database of information on the particle size distribution, density, shape, chemical composition, and radioactivity concentration for six phosphate facilities in the northern and central regions of the state. A seven-stage cascade impactor was employed to sample aerosols at various processing areas in these plants. Aerosol mass loadings are lowest mainly at shipping areas where they are approximately one order of magnitude less than at granulator areas within equivalent particle size intervals. Aerosol mass concentrations increase as the aerosol size increases for the majority of the plants and operational areas. The aerosol loading at each area varies widely depending on plant, and the variance is largest at the storage areas due to the variability of mechanical operations and patterns of building ventilation...

Five major sources for the ambient aerosol in Gainesville, FL were sampled by using a MicroOrifice Uniform Deposit Impactor (MOUDI) and a University of Washington Mark III Cascade Impactor. The samples were analyzed for carbons and ions. Soil dust, unpaved road dust, cement dust particles and marine aerosols were mainly in the coarse mode, while particles from transportation showed a bi-modal or tri-modal distribution. Carbon in soil dust was mainly organic, while carbon in unpaved road dust was mainly elemental. In transportation aerosols, carbons were mostly found in the ultra-fine range (< 0.18 μm) and were likely from gasoline vehicles. For ionic species, soil dust was rich in Na + , Cl - , K + , NH4 + , and Ca 2+ . In unpaved road dust, Ca 2+ was the dominant species followed by NO3 - and K + . Marine aerosols were predominantly Na + and Cl - , and they were found primarily in the coarse mode. The major ionic species in the fine mode of the transportation aerosols were NH4 + and SO4 2- , while Na + , Ca 2+ , and Cl - were the key components in the coarse mode. In the cement dust, Ca 2+ was the dominant species.

Continuous mercury monitors (CMMs) have the advantage of performing real-time or near real-time measurement, although they are often vulnerable to measurement interferences. For example, CMMs based on atomic absorption spectrometry (AAS) are subject to interferences by components of the sample gas, such as ozone, if they happen to have strong absorption bands or lines overlapping the Hg absorption line. Studies on a selected commercially available CMM showed that 120 ppb of ozone could exert an interference of approximately 63 ng/m 3 on Hg measurement. This interference may consequently affect the risk assessment of human exposure to Hg. On a similar basis, it was found that Hg can also result in significant interferences on an ozone analyzer based on UV absorption. Results showed that Hg at a concentration of 300 ng/m 3 can potentially cause a bias in ozone measurement of approximately 35 ppb, comparable to the average ambient ozone concentration. It should be noted that interferences discussed in this paper are applicable only to UV-absorption-based Hg and ozone analyzers. It is also possible that certain models of such analyzers are not compromised by the reported interferences, and thus, the findings in this work should be considered as analyzer-specific.

Controlling the emission of submicron particles of toxic metals in a combustion system poses a challenge. One possible mechanism for removing these fine particles is through intercoagulation with coarse particles. A bimodal lognormal model was applied to investigate the impact of intercoagulation rate on the size distributions of fine-mode aerosols. Fine-mode particle removal time was found to depend strongly on the number concentration of coarse-mode particles, but it was independent on the number concentration of fine-mode particles. An increase of geometric standard deviation of fine-mode particles from 1 to 1.6 significantly increased the dimensionless removal time 27 times. On the contrary, an increase of the deviation of coarse-mode particles in the same range only decreased 3% of the dimensionless removal time. The variation of geometric mean size ratio, meanwhile, had only insignificant effects on dimensionless removal time. For a constant mass concentration, removal time decreased as geo...

The U.S. Environmental Protection Agency (EPA) has proposed initial regulations to control mercury (Hg) emissions from coal-burning utilities, the primary source of airborne Hg emissions in the United States. Promising new techniques in capturing Hg involve transformation of elemental Hg into a product that is much more easily collected using conventional air pollution collection devices. In this study, the removal ability of high surface area iron oxide (Fe2O3) nanoparticles prepared on solid glass beads by a dry mechanical coating process was examined. The experimental results showed different mechanisms responsible for the removal depending on the air composition. In pure air, the Fe2O3 nanoparticles adsorbed and desorbed, while in the presence of nitrogen dioxide (NO2) they took on a catalytic role. The maximum specific capacity observed in this study was 1528 μg Hg/g Fe2O3. This study also identified the effective temperature range (180-320℃) for Hg removal, with the optimal temperature being ~260℃. The study reveals the important role of metal oxides in Hg chemistry in combustion systems through heterogeneous oxidation, and demonstrates the potential of Fe2O3 nanoparticles as an alternative material to traditional control techniques, such as activated carbon for reducing Hg emissions from incinerators.

Equilibrium analyses are carried out to determine the potential sorbent materials for effective chemisorption of arsenic in combustion systems. Al-, Fe-, Li-, Na-, K-, Be-, Mg-, Ca-based sorbents are found to be effective. Excellent removal of arsenic is achieved in a wide range of temperatures. However, the effectiveness of these sorbents may be reduced when chlorine or sulfur is present in the system. The presence of chlorine in the system greatly reduces the performance of alkali metal and Fe-based sorbents due to the formation of chlorides. The impact of chlorine on alkaline earth metal and Al-based sorbents is found to be less significant. The presence of sulfur reduces the effectiveness of most sorbents due to the formation of sulfates. The only exception is Al-based sorbent. The affinity to adsorb arsenic generally follows the order: Li > K > Na > Al > Ca > Mg > Fe > Be, if there is no chlorine or sulfur in the system. However, the order of effectiveness will be altered if chlorine or sulfur is pre...

Condensational growth of monodisperse aerosols in a system with limited vapor is studied. The equations for particle size and vapor concentration variation due to condensation are derived for the free molecular and continuum regimes, respectively. The corresponding condensation characteristic times for both size regimes are also developed. The particle size increase and vapor concentration decrease in a system with a limited vapor source are examined for varying surface vapor concentration and particle loading. The differences in the characteristic time expression derived in this work and those developed previously for constant particle size and unlimited vapor source are discussed. The expression of the condensation characteristic time developed is used to study the effect of sample aerosol concentration on the operation of the condensation particle counter, and compared to the characteristic times of other mechanisms such as nucleation, coagulation, and chemical reaction. The characteristic tim...

In situ–generated sorbent titania particles with ultraviolet (UV) irradiation have been shown to be effective in capture of mercury in combustor exhausts. Results of experiments conducted with the (1) sorbent precursor only, (2) mercury only, (3) mercury and UV irradiation, and (4) mercury, titania, and UV irradiation are presented to elucidate the mechanisms of the capture process. Capture efficiencies (percentage of Hg captured on the filter) as high as 96% were measured for mercury by titania with UV irradiation. A very high surface area titania sorbent was first formed, with mercury vapors condensing onto this surface, followed by photocatalytic oxidation and binding with the sorbent particles. The process has significant potential as a low-cost methodology for mercury control in practical combustion systems. Minimal retrofitting may be necessary as conventional particulate control devices such as electrostatic precipitators have coronas with UV radiation present. Key words: Mercury; sorbents...

The discrete-sectional model is an important tool used to study aerosol dynamics, although it suffers inherent numerical diffusion errors that are dependent on the model parameters including section spacing, numerically conserved aerosol property, and number of discrete sizes. An analytical evaluation of the errors due to the deviations of the derived aerosol properties in the sectional formulation and the interchange between discrete-size and sectional aerosols is carried out. The errors are larger if the difference in the aerosol property function index (ξ) between the derived and conserved properties is larger. Results of parametric studies are reported for condensation and coagulation systems. The results for condensation systems show that the υ-model is better than the n-model and the υ2-model in predicting the integral properties of the size distribution. However, the deviation in the results between the n-model, υ-model, and υ2-model reduces as the section spacing is decreased. A finite va...

Incineration is an effective way of treating municipal solid wastes; however, the emission of toxic metal compounds is an issue of concern. An algorithm has been developed to relate waste feed and incineration operating parameters to the ultimate exposure to metallic emissions. The different aspects considered are waste characteristics, operating conditions of the incinerator, operating conditions of the pollution control devices, atmospheric dispersion and exposure to these metallic emissions. The model predictions are validated by comparison to data reported in the literature. The model is also applied to mass burn and RDF incinerators to compare relative exposures of metallic emissions. Sensitivity analyses are performed to determine the effect of various parameters.

In the event of a pandemic, the general public would use filters as protective devices. However, most commercial filters only remove airborne viruses physically without inactivating them, allowing reproduction on the surface and yielding the mask as a fomite. The objective of this study was to investigate the inactivation performance of dialdehyde starch (DAS) treated filters against airborne viruses. The viable removal efficiency by and relative survivability on the biocidal filters prepared with dialdehyde starch compared to untreated filters were investigated using MS2 bacteriophage at high relative humidity (80-90%) and room temperature. Experimental results showed no significant difference in viable removal efficiency and pressure drop between the treated and untreated filters for polypropylene filtering facepiece respirators. The pressure drop of DAS treated cellulose filters significantly decreased although there was no significant change in viable removal efficiency; the combination of these two factors resulted in an increase of filter quality. All biocidal filters showed a significantly lower relative survivability than untreated filters, and the relative survivability decreased as the concentration of DAS increased. The biocidal filter treated with 4% DAS presented an average of 30% survivability compared to the baseline of untreated filters. The results demonstrate that dialdehyde starch can be incorporated onto filters to provide an effective means for inactivating MS2 viruses through surface contact.

Reduction of viable airborne Staphylococcus epidermidis and Aspergillus niger spore concentrations using two types of photocatalytic fluorescent lamps under controlled environmental conditions (25 vs. 35°C and 55 vs. 75% relative humidity) were investigated. Visible white-light and UVA black light were in-house spray-coated with TiO(2) and then compared with a commercially coated visible white-light for microbial concentration reduction. The white-light photocatalytic lamps reduced the concentration of culturable S. epidermidis up to 92% independent of temperature or humidity change, while the black light photocatalytic lamps completely inactivated the culturable bacteria at 25°C, 55% relative humidity. Humidity seemed to alleviate UVA damage since better bacteria survival was found. For A. niger spores, rising humidity or temperature could lower their concentration or drop their culturabilities so that a difference between the natural decay and photocatalytic disinfection could not be distinguished. Reductions of total bacteria and total fungi concentrations using these lamps were also examined under uncontrolled environmental conditions in an office and a waste-storage room. It was found that photocatalytic lamps could reduce total culturable bacteria concentration from 9 to 97% and total culturable fungi concentration from 3 to 95% within irradiation time of 30-480 min, respectively. Insignificant difference in concentration reduction among these photocatalytic lamps was pronounced.

An analysis of the formation and growth of metallic particles during incineration is studied. The first step is the entrainment of the metallic species from the waste stream into the gas phase. An equilibrium analysis is carried out to determine the partitioning of the metals amongst the various species. A lognormal, multicomponent model incorporating chemical reactions and aerosol growth dynamics was used to predict the evolution of the aerosol size distribution. The model was used to predict the aerosol size distributions in a lead-oxygen-chlorine system in a typical rotary kiln incinerator.

Ambient aerosols were collected during 2000-2001 in Gainesville, Florida, using a micro-orifice uniform deposit impactor (MOUDI) to study mass size distribution and carbon composition. A bimodal mass distribution was found in every sample with major peaks for aerosols ranging from 0.32 to 0.56 microm, and 3.2 to 5.6 microm in diameter. The two distributions represent the fine mode (2.5 microm) and the coarse mode (2.5 microm) of particle size. Averaged over all sites and seasons, coarse particles consisted of 15% carbon while fine particles consisted of 22% carbon. Considerable variation was noted between winter and summer seasons. Smoke from fireplaces in winter appeared to be an important factor for the carbon, especially the elemental carbon contribution. In summer, organic carbon was more abundant. The maximum secondary organic carbon was also found in this season (7.0 microg m(-3)), and the concentration is between those observed in urban areas (15-20 microg m(-3)) and in rural areas (4-5 microg m(-3)). However, unlike in large cities where photochemical activity of anthropogenic emissions are determinants of carbon composition, biogenic sources were likely the key factor in Gainesville. Other critical factors that affect the distribution, shape and concentration were precipitation, brushfire and wind.