Breathing Zone Concentrations Research Articles

Performance of local supply-exhaust ventilation around stove with numerical simulation in a residential kitchen

A large number of fine particulate matters (PM2.5) are generated during cooking, which have negative impacts on kitchen environment. This study proposed a novel ventilation strategy of local supply-exhaust ventilation around stove (LSEVAS) for improving air quality in a residential kitchen during cooking. Five factors affecting the performance of LSEVAS were explored with orthogonal design and computational fluid dynamics (CFD). Evaluation indexes including PM2.5 mass concentration in breathing zone (CB), capture efficiency (CE) of fume exhaust device and intake fraction (IF) of occupant were also analyzed. The performance of LSEVAS was also identified without air supply condition in kitchen in terms of these above evaluation indexes. Results show that the emission rate and exhaust air volume were the most significant factors, followed by the upside air supply angle, upside air supply speed and downside air supply speed. The CB in LSEVAS was reduced by 83%, 60% and 66% than without air supply condition under low, medium and high emission rates, respectively. The CE was improved by 1.8%, 13.9% and 14.5%, respectively. The IF value was decreased by one order of magnitude. Furthermore, with increasing of upside and downside air supply speed, the ability of air supply airflow in preventing the escape of PM2.5 became stronger, while the core concentration distribution of PM2.5 was gradually closer to breathing zone of occupant. It means that the novel local ventilation strategy proposed in this study is effective in improving cooking environment in the residential kitchen.

Micro-environmental factors impact breathing zone exposures: A simulated petrochemical manufacturing facility task

This study investigates the impact of micro-environmental factors on worker breathing zone exposure levels in petrochemical facilities. A laboratory simulation study evaluated near-field exposure to methane for a typical maintenance task. Individual and combinations of micro-environmental factors significantly affected methane exposure. Airflow direction and speed were significant determinants of exposure concentration reduction. A side airflow direction at medium to high speed produced the lowest gas concentration in the breathing zone. Worker body orientation relative to the methane emission point was also a critical factor affecting gas concentration in the worker's breathing zone. The study provides insights into how variations in airflow and small changes in position impact near-field exposures for petrochemical tasks, guiding industrial hygiene professionals' training on qualitative exposure estimation and providing input for near-field exposure modeling to guide quantitative exposure and risk assessment.

Concurrent reduction of the fume and Cr (VI) concentrations of inhalable and respirable particle using a new covered stainless-steel SMAW electrode

In this work, a new covered electrode was developed for a SMAW process by the concurrent use of two fume reduction techniques viz; nano-arc stabilizer coating on welding core wire and nano-particle substitution on the welding flux. The experimental core electrode wires were coated with nano-zirconium to improve the electrode’s arc stability and reduce the effective oxygen concentration in the arc atmosphere. To further improve the arc stability, size-reduced synthetic rutile was mixed with the electrode flux. Total fume formation from experimental and conventional electrodes was evaluated and compared. Compared to the conventional electrode, the experimental electrode showed an 82 % reduction in fume production and an 85 % reduction in breathing zone concentration. The combined effect of nano zirconia and size-reduced synthetic rutile increased the reactivity of the arc atmosphere and favoured the reduction of inhalable and respirable fume mass concentration by improving arc stability and reducing spatter formation. The experimental electrodes showed a significant reduction in Cr(VI) concentration in fume up to 68 %. The Cr (VI) concentration in the inhalable and respirable fumes was also reduced by 36 % and 52 % in that order.

Effect of activated fluxes on the BZC and Cr (VI) concentration in stellite hardfacing operation

Hardfacing is a surface coating method commonly used to deposit materials having high corrosion and wear resistance on a base metal. In this work, the effect of single and multicomponent fluxes on the breathing zone concentration (BZC) and Cr (VI) concentration, during a stellite hardfacing operation were studied. Flux components used were TiO2, Al2O3 and SiO2. The mixture design of the design of experiments (DoE) was used to identify the influence of each flux component on the reduction of breathing zone concentration (BZC) and Cr (VI) concentration. The findings of the study indicated that binary flux composition comprising 50% Al2O3 and 50% TiO2 offered a significant reduction in breathing zone concentration of fumes by more than 90%. This was attributed to the lower ionization potential of these flux materials and the consequent improvement in the arc stabilization reactions in the weld atmosphere SiO2 in the flux composition was found to befit the reduction of Cr (VI) concentration in fumes through the encapsulation and agglomeration of chromium fumes. The mixture design of design of experiments (DoE) was used to identify the influence of each flux component in the reduction of BZC and Cr (VI) concentration.

The effect of noise barriers on viaducts on pollutant dispersion in complex street canyons

• The viaduct-noise barrier can remarkably influence the flow structure. • Using field synergy theory to analyze noise barrier-viaduct system. • Noise barrier-viaduct reduced the CO concentration in pedestrian breathing area. The noise reduction effect of noise barriers has been extensively studied, but the effect on pollutant dispersion remains unclear. A computational fluid dynamics (CFD) simulation is conducted to investigate the effects of different heights, lengths, and types of noise barriers and different wind speeds on pollutant dispersion in street canyons with viaducts. The field synergy theory of the convective mass transfer process is used for quantitative analysis of pollutant dispersion in street canyons. The results show that as the height and length of the noise barrier increase, the pollutant dispersion capacity decreases. As the wind speed increases, the rate of decrease in the average CO concentration declines. The effect of the wind speed on the synergistic improvement of the speed and concentration gradient vectors differs for different types of noise barriers. The performance follows the order: fully-closed noise barrier > left noise barrier > right noise barrier > semi-closed noise barrier. The different noise barrier types significantly impact the flow field and pollutant dispersion and reduce the CO concentration to varying degrees, except for the fully-closed type. The average CO concentration in the pedestrian breathing zone is reduced by a maximum of 55.85% on the leeward side and by 53% on the windward side, indicating that an appropriate noise barrier on the viaduct reduces noise pollution and improves the air quality in street canyons, especially in the pedestrian breathing zone.

Personal breathing zone concentrations of PM2.5 among workers in different occupational groups at a brick kiln in Nepal

Personal breathing zone concentrations of PM2.5 among workers in different occupational groups at a brick kiln in Nepal

Bone Cement Fumes Generated in Laminar Airflow Versus Conventionally Ventilated Operating Rooms: Does the Mixing System Matter?

Bone cement is commonly utilized in a variety of orthopaedic procedures and contains methylmethacrylate (MMA) monomer. MMA is a colorless, clear, flammable liquid of intense odor. Its vapor concentration in the immediate breathing zone can vary considerably in the operative setting and, in higher concentrations, can become an occupational health hazard. Therefore, reducing MMA vapor is desirable. The aim of this study was to compare the MMA vapor levels emitted during mixing among 5 commercially available cement-mixing systems across 2 operative settings: an operating room (OR) with conventional ventilation (CV) and an OR with laminar airflow (LAF). A prospective, in vitro study was conducted at a single hospital in an OR with LAF and in an OR with CV. MMA vapor release during the cement preparation of a SAWBONES femoral canal was measured with use of a calibrated MiniRAE 3000. A total of 5 different vacuum cement-mixing systems were utilized to mix the same cement type according to the manufacturer instructions of each system. MMA vapor concentrations were measured during 5 phases of mixing, and each mixing system was randomly utilized 10 times in each OR. When comparing the MMA concentration levels of each system between the 2 settings, emissions remained generally higher in the CV setting for every system and in nearly every phase. Among the 5 systems analyzed, System #5, the only entirely closed system, had the lowest overall emissions for each of the 5 phases in the CV setting. This study demonstrated that an operative environment with LAF is conducive to clearing the fumes of MMA during mixing as well as limiting the amount of time that residual fumes linger after mixing. Additionally, the entirely closed cement-mixing system was the most effective in minimizing fume levels within the CV setting. Utilizing this closed system, especially in an OR with CV, may reduce exposure to MMA fumes from bone cement, potentially creating a more favorable working environment. This study provides evidence that a closed cement-mixing system utilized under vacuum in both an OR with CV and an OR with LAF is effective in keeping MMA fume levels below those considered harmful by the U.S. Occupational Safety and Health Administration.

Study on the soluble and insoluble fume and hexavalent chromium emitted from a new covered electrode with micro and nano sized-sodium and potassium titanate-based flux.

The present study discusses the effect of the addition of nano-sized arc stabilizing materials on fume emissions and its solubility characteristics. Micro and nano-sized sodium/potassium titanates were added to the SMAW electrode flux as a substitute for the conventional sodium and potassium silicate compounds. The total and soluble metal concentration of fumes from the newly developed electrodes were estimated and compared with that of commercially available electrodes. The estimation of fume formation rate and breathing zone concentration of fumes followed the ISO 15011-1 and ISO 10882-1 standard. An average 50% reduction in the soluble fraction of fumes was observed from the electrodes containing micro-sized potassium-titanate compounds, and the reduction was further improved by 60% when nano-sodium titanate was added to the flux. Whereas, the reduction in soluble metal concentration for potassium titanate coated electrodes were 45% and 55%, in that order, for their micro and nano-structured forms. The soluble fraction of hexavalent chromium from the electrodes containing 100% nano sodium/potassium titanates was reduced up to 50% in each impactor stage. The inclusion of nano-sized sodium titanate in the flux resulted in a reduction in fume formation rate up to 55% and breathing zone concentration of fumes by 58% compared to the conventional sodium silicate coated electrodes. The electrode assaying 100% nano-potassium titanate showed a reduction of 59% in fume formation rate and 61% in breathing zone concentration compared to that of conventional potassium silicate-coated electrodes.

Urinary Amino-PAHs in relation to diesel engine emissions and urinary mutagenicity

Diesel exhaust has long been of health concern due to established toxicity including carcinogenicity in humans. However, the precise components of diesel engine emissions that drive carcinogenesis are still unclear. Limited work has suggested that nitrated polycyclic aromatic hydrocarbons (NPAHs) such as 1-nitropyrene and 2-nitrofluorene may be more abundant in diesel exhaust. The present study aimed to examine whether urinary amino metabolites of these NPAHs were associated with high levels of diesel engine emissions and urinary mutagenicity in a group of highly exposed workers including both smokers and nonsmokers. Spot urine samples were collected immediately following a standard work shift from each of the 54 diesel engine testers and 55 non-tester controls for the analysis of five amino metabolites of NPAHs, and cotinine (a biomarker of tobacco smoke exposure) using liquid chromatography–mass spectrometry. An overnight urine sample was collected in a subgroup of non-smoking participants for mutagenicity analysis using strain YG1041 in the Salmonella (Ames) mutagenicity assay. Personal exposure to fine particles (PM2.5) and more-diesel-specific constituents (elemental carbon and soot) was assessed for the engine testers by measuring breathing-zone concentrations repeatedly over several full work shifts. Results showed that it was 12.8 times more likely to detect 1-aminopyrene and 2.9 times more likely to detect 2-aminofluorene in the engine testers than in unexposed controls. Urinary concentrations of 1-aminopyrene were significantly higher in engine testers (p < 0.001), and strongly correlated with soot and elemental carbon exposure as well as mutagenicity tested in strain YG1041 with metabolic activation (p < 0.001). Smoking did not affect 1-aminopyrene concentrations and 1-aminopyrene relationships with diesel exposure. In contrast, both engine emissions and smoking affected 2-aminofluorene concentrations. The results confirm that urinary 1-aminopyrene may serve as an exposure biomarker for diesel engine emissions and associated mutagenicity.

Optimal sensor placement for personal inhalation exposure detection in static and dynamic office environments

Modern health and productivity concerns related to air pollutant exposure in buildings have sparked the need for occupant-centric monitoring and ventilation control. The existing personal exposure monitoring is often restricted to stationary air quality sensors and static occupancy. This study aims to identify optimal stationary sensor placement that best represents exposure to CO2, PM2.5, and PM10 under static and dynamic office occupancies. A total of 48 controlled chamber experiments were executed in four office layouts with variation of occupant numbers (2, 4, 6 or 8), activities (sitting/standing and static/dynamic), ventilation strategies (mixing/displacement) and air change rates (0.5–0.7 h−1, 2.4–2.6 h−1, and 3.8–4.2 h−1). The breathing zone concentration of a reference occupant was monitored with concurrent measurements at seven stationary locations: front edge of the desk, sides of two desks, two sidewalls, and two exhaust vents. The proximity of sensors to the reference occupant and ventilation rate/strategy were important determinants of personal exposure detection. Regression analyses showed that the wall- and desk-mounted CO2 sensors near the occupant (<1 m) best captured CO2 exposure under dynamic–standing activities (R2∼0.4). The wall immediately behind the seated occupant and the ceiling-mounted exhaust near the standing occupant (<1–1.5 m) were the best sensor placements for capturing exposure to particles (R2=0.8–0.9). Separating static from dynamic occupancy activities resulted in improved exposure prediction by 1.4-6.1× . This study is a step towards provision of practical guidelines on stationary air quality sensor placement indoors with the consideration of dynamic occupancy profiles.

Influence of air inlet distance on coal dust pollution characteristics in working environment during tunneling based on CFD method

Coal dust is one of the pollutants generated during the coal tunneling process. However, the air inlet distance will increase with the advancement of the working face, resulting in the redistribution of the air flow field, further affecting the pollution characteristics of coal dust. This effect weakens the effectiveness of dust removal equipment. Therefore, transient CFD modeling was used to study the influence of air inlet distance on air flow, dust migration distance, and dust concentration distribution in the breathing zone and achieve the highest dust reduction efficiency. Results showed that the air flow formed two reflows in the tunnel under forced ventilation. When the air inlet distance increased from 6.0 m to 8.4 m, wind flow diffusion distance (along the return side coal wall) Lp and air inlet distance d can be described as Lp = 34.272–7.108d + 0.570d2 . Furthermore, the dust diffusion time to the outlet increased from 35 s to 40 s, and the dust migration distance increased as a power function of air inlet distance. Meanwhile, the dust migration distance in the first 10 s accounted for 45–50% of that for the entire time period. In addition, the dust migration distance decreased only after 25 s, and the dust concentration in the return side breathing zone gradually increased. Finally, air curtains and dust removal fans were recommended for dust control, and the dust in the daily tunneling process can be effectively controlled when da = 15.0 m and de = 8.0 m. The dust reduction efficiency was 85.29–99.90%. The research results provide technical support for the dust outlet installation of dust extraction fans during tunneling and guidance for dust control in the similar working environment.

Environmental chamber studies of eye and respiratory irritation from use of a peracetic acid-based hospital surface disinfectant.

To characterize personal exposures and measures of eye and respiratory tract irritation in controlled environmental chamber studies of 44 healthy adult volunteers simulating upper-bound use of peracetic acid (PAA)-based surface disinfectant for terminal cleaning of hospital patient rooms. Experimental, within-subject, double-blinded cross-over design. Objective and subjective exposure effects were assessed for PAA and its components: acetic acid (AA) and hydrogen peroxide (HP). Deionized water was included as a control. Breathing-zone concentrations of PAA, AA, and HP were assessed for 8 female multiday volunteers (5 consecutive days) and 36 single-day volunteers (32 females and 4 males). Wetted cloths were used to wipe high-touch surfaces for 20 minutes per trial. Also, 15 objective measures of tissue injury or inflammation and 4 subjective odor or irritation scores were assessed. Disinfectant trials showed 95th percentile breathing zone concentrations of 101 ppb PAA, 500 ppb AA, and 667 ppb HP. None of the volunteers observed over 75 test days exhibited significant increases in IgE or objective measures of eye and respiratory tract inflammation. Subjective ratings for disinfectant and AA-only trials showed similar increases for odor intensity and nose irritation, with lower ratings for eye and throat irritation. Females were 2.5-fold more likely than males to assign moderate + irritation ratings. Simulated upper-bound hospital use of PAA-based disinfectant led to no significant increases in objective markers of tissue injury, inflammation, or allergic sensitization, and no frank signs of eye or respiratory tract irritation.

Study on mass concentration and morphology of SMAW fume particles with a new covered electrode using nano-CaTiO3 as an arc stabilizer

Advances in manufacturing emphasize on the development of sustainable and green manufacturing processes. Welding is a popular manufacturing process practiced worldwide. The paper presented here describes a new covered electrode for a shielded metal arc welding (SMAW) process wherein nano-sized calcium titanate (CaTiO3) powder was used as an arc stabilizer, replacing the conventional micro sized CaTiO3 in the flux. The effect of this flux modification on the mass concentration and morphology of welding fume particulates was systematically investigated. The mass concentration of coarse, fine and sub-micron sized fume particulates was measured by segregating the fumes in a four-stage personal cascade impactor. The particle mass distribution was estimated from the mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) of the fume particulates. The morphology of fumes at each impactor stage was analysed using scanning electron microscopy and its count median diameter (CMD) was determined. The results indicated as much as 48 % reduction in total fumes and 54 % reduction in the breathing zone concentration of fumes when the entire CaTiO3 in the electrode flux was substituted with nano-CaTiO3. Morphological analysis indicated that a large fraction of the fumes from the conventional electrode were polydispersed particles, while the new electrodes predominantly contained monodispersed particles which have a relatively faster rate of removal from the lungs. Overall, the present work indicated that introducing nano sized CaTiO3 as an arc stabilizer to the flux covering of SMAW electrode could not only reduce the hazardous fume emissions but also reduce its biological activity and toxicity, thus making the process more sustainable and environment friendly.

Effect of simultaneous exposure to inhalational anesthetics and radiation on the adaptive response in operating room personnel.

Some operating room personnel, such as orthopedic surgeons, are exposed simultaneously to inhalational anesthetics (IAs) and radiation that both can cause DNA damage. Some studies have shown that low doses of radiation reduce DNA damage when the cells are followed by a higher dose of the same or related agent. This study, therefore, set out to compare DNA damage in the anesthesiologists, radiologists, orthopedic surgeons, and healthcare staff (non-exposed group). In this cross-sectional study, breathing zone concentrations of anesthetic gas nitrous oxide (N2O) were measured in the studied groups using standard method. Additionally, DNA damage was measured by micronucleus (MN) assay. The mean concentrations of N2O in the anesthesiologists and orthopedic surgeons were 450.27 ± 327.44ppm and 313.64 ± 216.14ppm, respectively. The mean annual exposure to X-rays radiation in radiologists and orthopedic surgeons was 15.65 ± 8.46 mSy/year and 3.56 ± 1.32 mSy/year, respectively. MN frequencies were significantly higher in anesthesiologists and radiologists exposed to IAs and X-rays radiation respectively than in the non-exposed healthcare staff. While, there were no statistically significant differences between MN frequencies of orthopedic surgeons exposed to both IAs and radiation and healthcare staff.These findings suggest that an earlier exposure of orthopedic surgeons to a small dose of ionizing radiation can increase their resistance to genotoxicity caused by high doses of N2O, a phenomenon that is called adaptive response.

Combined impacts of the ceiling radiant cooling and ventilation on dispersion and deposition of indoor airborne particles

• Integrated ventilation-cooling effects on indoor particle dispersion are evaluated. • The CRCP surface temperature is a dominant parameter in particle deposition rate. • Particle decay rate in the up-supply ventilation is faster than down-supply one. • Particle decay is associated to temperature difference between CRCP and walls. • Concentration in breathing zone diminishes by decreasing temperature of CRCP. The present study investigates the integrated effects of the ceiling radiant cooling and ventilation on dispersion and deposition of indoor airborne particles. Five groups of particles with different sizes, ranging from 0.1 to 10 µm, are selected to be injected inside a ventilated space equipped with the ceiling radiant cooling panel (CRCP). Two ventilation strategies under different air change rates are considered, namely up-supply and down-supply ventilations. The conjugate heat transfer between the CRCP and indoor air is examined for different inlet temperatures of the chilled water. An Eulerian-Lagrangian CFD model is developed and validated by experimental data in order to predict the turbulent airflow characteristics and thermal performance of the CRCP system as well as the transient particle trajectories. The results indicate that the particle decay rate is associated with the temperature difference between the CRCP surface and surrounding walls. A sensitivity analysis on the results shows that the surface temperature of CRCP in both ventilation methods is a more effective parameter in particle deposition rate, compared to the inlet air velocity; a 40% augmentation of the ventilation rate leads to 2.6% increase in particle decay rate, whereas the same alteration in inlet water temperature of the CRCP results in 7.3% enhancement of the decay rate. It is shown that while the particle decay rate in up-supply ventilation is faster than down-supply one, the down-supply mode removes higher number of particles, for a given ventilation rate. Furthermore, it is shown that the particle concentration in breathing zone diminishes by decreasing the temperature of radiant cooling panel. Findings of the present study are expected to provide insights into future design of the ventilation and ceiling radiant cooling system for a better indoor air quality.

Experimental study on the effect of the split-type air-conditioner on the transmission of smoking pollutants in a room

ABSTRACT Environmental tobacco smoke (ETS) has become one of the most important sources of indoor air pollution. The study aimed to obtain the variation characteristics of typical air pollutant concentrations when people smoke in a closed room and explore the effect of the air-conditioner. A closed and air-conditioned room of 21 m2 was taken as the research object. Fine particulate matter (PM2.5) and total volatile organic compound (TVOC) were measured while 10 cigarettes were burnt in smoldering or smoking mode, with the air-conditioner on or off. The contents of nicotine in condensate samples were obtained by liquid chromatography. The impact of ETS on indoor air quality lasted for hours, causing typical pollutant concentrations to far exceed the Chinese standard. The PM2.5 produced by smoking was 11 times higher than by smoldering, but the TVOC produced by smoldering was more than by smoking. After one hour of the cigarette burning off, the PM2.5 concentration would be decreased by 96.1% with the air-conditioner on, in contrast to 67.9% with the air-conditioner off. Nicotine was detected in all samples of condensate from the air-conditioner. It is concluded that smoking cigarettes cannot be replaced by smoldering to evaluate the pollution of ETS. The air-conditioner has a positive effect on reducing the concentration of air pollutants produced by cigarette burning. More than 10% of the indoor nicotine may be taken away by condensate discharge, and its possible pollution should be paid attention to. Implications: This study provides new evidence of the effect of the split-type air-conditioner on ETS. The TVOC concentrations, which were less considered previously, were measured. PM2.5 concentration in human breathing zone can be reduced more quickly with the air-conditioner on. This study shows that there is a big difference in the concentrations of typical pollutants between smoking and smoldering. And it could be a guide for the formulation of relevant research methods. This study also demonstrates that the air conditioning condensate from the smoking room may contain nicotine. Attention should be paid to the recovery and utilization of such condensate.

Personal exposure to concentrations and inhalation of black carbon according to transport mode use: The MobiliSense sensor-based study.

Epidemiological evidence suggests that motorized vehicle users have a higher air pollutant exposure (especially from vehicle exhaust) than active (walking or cycling) transport users. However, studies often relied on insufficiently diverse sample and ignored that minute ventilation has an effect on individuals' inhaled dose. This study examined commuters' breathing zone concentration and inhaled doses of black carbon (BC) when travelling by different transport modes in the Grand Paris region. Personal exposure to BC was continuously measured with MicroAethalometer (MicroAeth AE51) portable monitors strapped on participants' shoulder with tube inlet at the level of the neck (breathing zone), and inhaled doses were derived from several methods estimating ventilation [based on metabolic equivalents from accelerometry [METs], heart rate, and breathing rate]. Trip stages and transport modes were assessed from GPS and mobility survey data. Breathing zone concentrations and inhaled doses of BC were compared across transport modes at the trip stage level (n=7495 for 283 participants) using linear mixed effect models with a random intercept at individual level. Trip stages involving public transport and private motorized transport were associated with a 2.20µg/m3 (95% CI: 1.99, 2.41) and 2.29µg/m3 (95% CI: 2.10, 2.48) higher breathing zone concentration to BC than walking, respectively. Trip stages with other active modes had a 0.41µg (95% CI: 0.25, 0.57) higher inhaled dose, while those involving public transport and private motorized transport had a 0.25µg (95% CI: -0.35, -0.15) and 0.19µg (95%CI: -0.28, -0.10) lower inhaled dose of BC per 30min than walking. The ranking of transport modes in terms of personal exposure was markedly different when breathing zone concentrations and inhaled doses were considered. Future studies should take both into account to explore the relationship of air pollutants in transport microenvironments with physiological response.

Application of the Bayesian spline method to analyze real-time measurements of ultrafine particle concentration in the Parisian subway.

Air pollution in subway environments is a growing concern as it often exceeds WHO recommendations for indoor air quality. Ultrafine particles (UFP), for which there is still no regulation nor a standardized exposure monitoring method, are the strongest contributor to this pollution when the number concentration is used as exposure metric. We aimed to assess the real-time UFP number concentration in the personal breathing zone (PBZ) of three types of underground Parisian subway professionals and analyze it using a novel Bayesian spline approach. Consecutively, we investigated the effect of job, week day, subway station, worker location, and some further events on UFP number concentrations. The data collection procedure originated from a longitudinal study and lasted for a total duration of 6 weeks (from October 7 to November 15, 2019, i.e. two weeks per type of subway professionals). Time-series were built from the real-time particle number concentration (PNC) measured in the PBZ of professionals during their work-shifts. Complementarily, contextual information expressed as Station, Environment, and Event variables were extracted from activity logbooks completed for every work-shift. A Bayesian spline approach was applied to model the PNC within a Bayesian framework as a function of the mentioned contextual information. Overall, the Bayesian spline method suited a real-time personal PNC data modeling approach. The model enabled estimating the differences in UFP exposure between subway professionals, stations, and various locations. Our results suggest a higher PNC closer to the subway tracks, with the highest PNC on subway station platforms. Studied event and week day variables had a lesser influence. It was shown that the Bayesian spline method is suitable to investigate individual exposure to UFP in underground subway settings. This method is informative for better documenting the magnitude and variability of UFP exposure, and for understanding the determinants in view of further regulation and control of this exposure.

Aerosol Analysis Using Handheld Raman Spectrometer: On-site Quantification of Trace Crystalline Silica in Workplace Atmospheres.

A method for aerosol chemical analysis using handheld Raman spectrometer has been developed and its application to measurement of crystalline silica concentration in workplace atmosphere is described. The approach involves collecting aerosol as a spot sample using a wearable optical aerosol monitor, followed by direct-on-filter quantitative analysis of the spot sample for crystalline silica using handheld Raman spectrometer. The filter cassette of a commercially available optical aerosol monitor (designed to collect aerosol for post-shift analysis) was modified to collect 1.5-mm-diameter spot sample, which provided adequate detection limits for short-term measurements over a few tens of minutes or hours. The method was calibrated using aerosolized α-quartz standard reference material in the laboratory. Two Raman spectrometers were evaluated, one a handheld unit (weighing less than 410 g) and the other a larger probe-based field-portable unit (weighing about 5 kg). The lowest limit of quantification for α-quartz of 16.6 μg m-3 was obtained using the handheld Raman unit at a sample collection time of 1 h at 0.4 l min-1. Short-term measurement capability and sensitivity of the Raman method were demonstrated using a transient simulated workplace aerosol. Workplace air and personal breathing zone concentrations of crystalline silica of workers at a hydraulic fracturing worksite were measured using the Raman method. The measurements showed good agreement with the co-located samples analyzed using the standard X-ray powder diffraction (XRD) method, agreeing within 0.15-23.2% of each other. This magnitude of difference was comparable to the inter- and intra-laboratory analytical precision of established XRD and infrared methods. The pilot study shows that for silica-containing materials studied in this work it is possible to obtain quantitative measurements with good analytical figures of merit using handheld or portable Raman spectrometers. Further studies will be needed to assess matrix interferences and measurement uncertainty for several other types of particle matrices to assess the broader applicability of the method.

Transient and continuous effects of indoor human movement on nanoparticle concentrations in a sitting person's breathing zone

Particle concentration in a sitting person's breathing zone can be influenced by human movement around the person, and the transient and continuous effects may differ. In this study, a set of full-scale experiments was conducted to sample the nanoparticle concentration in the breathing zone of a sitting thermal breathing manikin (STBM). The transient fluctuation of the nanoparticle concentration was recorded continuously and analyzed. The results showed that when a manikin moved (at 1 m/s) past the STBM, the nanoparticle concentration in the STBM's breathing zone decreased and reached its lowest after the standing manikin had passed, decreasing 37.6 (±5.7) % compared with the peak value. The average concentration in the STBM's breathing zone during influence periods was 5.18 (±0.99) % less than that during non-influence Periods (NP). This finding reflected the fact that the transient inhalation (over several seconds) of the STBM may be reduced by manikin movement. On the other hand, the exposure of the STBM increased 2.88 (±1.24) % when there was a continuously moving manikin compared with the stable state in a 10-min observation. This finding may be explained by the fuller mix of indoor air and nanoparticles caused by manikin movement, as well as the increase of nanoparticle suspension time. The difference in the transient and continuous effects of the manikin movement on the STBM's exposure shows the importance of considering these effects separately in different scenarios.