Higher Particle Number Concentrations Research Articles

Beyond the Runway: Respiratory health effects of ultrafine particles from aviation in children

Aviation has been shown to cause high particle number concentrations (PNC) in areas surrounding major airports. Particle size distribution and composition differ from motorized traffic. The objective was to study short-term effects of aviation-related UFP on respiratory health in children.In 2017–2018 a study was conducted in a school panel of 7–11 year old children (n = 161) living North and South of Schiphol Airport. Weekly supervised spirometry and exhaled nitric oxide (eNO) measurements were executed. The school panel, and an additional group of asthmatic children (n = 19), performed daily spirometry tests at home and recorded respiratory symptoms. Hourly concentrations of various size fractions of PNC and black carbon (BC) were measured at three school yards. Concentrations of aviation-related particles were estimated at the residential addresses using a dispersion model. Linear and logistic mixed models were used to investigate associations between daily air pollutant concentrations and respiratory health.PNC20, a proxy for aviation-related UFP, was virtually uncorrelated with BC and PNC50-100 (reflecting primarily motorized traffic), supporting the feasibility of separating PNC from aviation and other combustion sources. No consistent associations were found between various pollutants and supervised spirometry and eNO. Major air pollutants were significantly associated with an increase in various respiratory symptoms. Odds Ratios for previous day PNC20 per 3,598pt/cm3 were 1.13 (95%CI 1.02; 1.24) for bronchodilator use and 1.14 (95%CI 1.03; 1.26) for wheeze. Modelled aviation-related UFP at the residential addresses was also positively associated with these symptoms, corroborating the PNC20 findings. PNC20 was not associated with daily lung function, but PNC50-100 and BC were negatively associated with FEV1.PNC of different sizes indicative of aviation and other combustion sources were independently associated with an increase of respiratory symptoms and bronchodilator use in children living near a major airport. No consistent associations between aviation-related UFP with lung function was observed.

Influence of a large commercial airport on the ultrafine particle number concentration in a distant residential area under different wind conditions and the impact of the COVID-19 pandemic

Exposure to ultrafine particles has a significant influence on human health. In regions with large commercial airports, air traffic and ground operations can represent a potential particle source. The particle number concentration was measured in a low-traffic residential area about 7 km from Frankfurt Airport with a Condensation Particle Counter in a long-term study. In addition, the particle number size distribution was determined using a Fast Mobility Particle Sizer.The particle number concentrations showed high variations over the entire measuring period and even within a single day. A maximum 24 h-mean of 24,120 cm−3 was detected. Very high particle number concentrations were in particular measured when the wind came from the direction of the airport. In this case, the particle number size distribution showed a maximum in the particle size range between 5 and 15 nm. Particles produced by combustion in jet engines typically have this size range and a high potential to be deposited in the alveoli. During a period with high air traffic volume, significantly higher particle number concentrations could be measured than during a period with low air traffic volume, as in the COVID-19 pandemic.A large commercial airport thus has the potential to lead to a high particle number concentration even in a distant residential area. Due to the high particle number concentrations, the critical particle size, and strong concentration fluctuations, long-term measurements are essential for a realistic exposure analysis.

Land Use Regression Models for Particle Number Concentration and Black Carbon in Lanzhou, Northwest of China

It is necessary to predict the spatial variation in particle number concentration (PNC) and black carbon (BC) because they are considered air pollutants associated with traffic and many diseases. In this study, land use regression (LUR) models for PNC and BC were developed based on a mobile monitoring campaign in January 2020 in Lanzhou, and the performance of models was evaluated with hold-out validation (HV) and leave-one-out cross-validation (LOOCV). The results show that the adjusted R2 of the LUR models for PNC and BC are 0.51 and 0.53, respectively. The R2 of HV and LOOCV are 0.43 and 0.44, respectively, for the PNC model and 0.42 and 0.50, respectively, for the BC model. The performances of the LUR models are of a moderate level. The spatial distribution of the predicted PNC is related to the distance from water bodies. The high PNC is related to industrial pollution. The BC concentration decreases from south to north. High BC concentrations are associated with freight distribution centres and coal-fired power plants. The range of PNC particle sizes in this study is larger than in most studies. As one of few studies in Lanzhou to develop LUR models of air pollutants, it is important to accurately estimate pollutant concentrations to improve air quality and provide health benefits for residents.

Estimation of Particle Emission Rates and Calculation of Human Dose from Arc Welding and Cutting of Stainless Steel in a Simulated Confined Workspace

The objective of this study was to estimate the particle emission rates, human dose and retention from two arc welding processes and cutting of stainless steel. The two arc welding processes were Shielded Metal Arc Welding (SMAW) and Tungsten Inert Gas (TIG). In a simulated confined workspace of experimental chamber under controlled conditions, four different scenarios were considered, including the use of filtering face piece respirator (FFR), leaving or staying in the workspace after the emission. Deposited and retained dose in the respiratory tract was assessed for the different regions of the human respiratory tract using a dosimetry model (ExDoM2). The three investigated processes generated high particle number concentrations ranging from 2.4 to 3.6 × 106 particles/cm3 and were the highest during TIG. Among all three processes, PM10 concentrations from cutting reached the highest levels [11 and 22 (× 103) μg/m3], while SMAW had the highest contribution of fine particles [~ 4.1 (× 103) μg/m3], consisting mostly of PM1–2.5. The examination of different scenarios revealed that there is only a slight difference in respect to deposited dose while staying in the workspace for the entire investigated time period (4 h) with or without use of Filtering Facepiece Respirator (FFR). It would be more beneficial in respect to deposited dose if the exposed subject was not wearing a FFR during the emission process and would leave the polluted workspace immediately after the emission period. In the first two scenarios (staying 4 h in the polluted workspace with and without FFR), both welding processes had higher cumulative deposited (~ 23%) and retained dose (~ 20%) in thoracic region compared to cutting (~ 9% and ~ 7%). These results demonstrate that even a short emission period can cause a considerable increase in concentrations of harmful respirable particles, thus increasing the human dose. The approach applied in this study could be used for the determination of personal exposure and dose to particles of known composition particularly in confined workspaces.

6 Characterization of Aerosolized Particles Generated During Cutting of Carbon Nanotubes-Embedded Concrete

Abstract Engineered nanomaterials are revolutionizing many industries, but little is known about potential exposures during the life cycle of nano-enabled composites. This study was conducted to characterize aerosolized particles using direct-reading instruments and integrated air samplers during cutting multi-walled carbon nanotubes (MWCNT)-embedded concrete cylinder blocks. Three types of blocks, 0% (reference), low%, and high% MWCNT, were tested in a specially designed enclosure housing an apparatus for the cutting of a block with an automated computer-controlled process. The highest particle number concentration (163,821 particles/cm3) was measured for the reference cylinder, while others showed similar concentrations (131,689 particles/cm3 and 140,954 particles/cm3 for the low% and high% blocks, respectively). Regardless of the cylinder type, the size-selected particle number concentrations revealed one main mode with a peak at 0.72 µm indicating no shift in the size distribution from addition(s) of MWCNT. Respirable mass concentrations were 342 mg/m3, 405 mg/m3, and 432 mg/m3 for the reference, low%, and high% blocks, respectively. The mass median aerodynamic diameters were similar, 5.23 µm for the reference and 5.05 µm for both low% and high% blocks, indicating a predominant respirable fraction. Respirable particles (quartz, feldspar, paste, etc.) often appeared to be agglomerated materials that included both paste and aggregate minerals. No free MWCNT were observed by electron microscopy from low% and high% samples. These initial studies found no evidence of free MWCNT by cutting concrete test blocks and only minor differences in the particulate aerosol generated, which included a general increase in respirable mass with increasing % CNT.

Emission Characteristics of Tyre Wear Particles from Light-Duty Vehicles

Tyre wear particle emissions have gained significant attention due to their harmful effects on the environment and human health. However, studies on tyre wear particles generated under chassis dynamometer conditions are still scarce. This study measures the instantaneous number concentrations and elemental species of tyre wear particles in different light-duty vehicle test cycles. The results show that the particle number (PN) concentrations of the US06 test cycle are much higher than those of the WLTC test cycle due to the larger and more frequent accelerations and decelerations in the former. High PN concentrations are observed during high driving speeds with rapid accelerations, while PN concentrations are much lower during low driving speed with rapid acceleration. Furthermore, tyre tread temperature is found to be related to the formation of tyre wear particles. The PN concentration in the second and third US06 test cycles are similar, indicating that once the tyre temperature exceeds the critical value, the tyres become heated to a steady state, and the PN concentrations will not be affected by the average temperature of the tyre. A low initial tyre temperature can produce high PN concentrations during the cold start phase of test cycles and prolong the time required for tyres to warm up. In addition, the particles contained a high mass fraction of Zn, which can serve as a tracer of tyre wear particles in non-exhaust particle tests of vehicles.

Concentration, chemical composition and toxicological responses of the ultrafine fraction of urban air particles in PM1

Epidemiological and toxicological evidence show that PM1 is a key driver of PM2.5. However, the particle sizes that play the major damaging role in PM1 is unclear. Our aims were to (1) explore the concentration and chemical composition of ultrafine particles in PM1; (2) evaluate and compare the differences in toxicity of PM1-0.2 and PM0.2 to different airway cell models. We collected PM1-0.2 and PM0.2 in Guangzhou in December 2017, monitored and detected their concentrations, size, and components. A549, THP-1 mono-cultures and A549/THP-1 co-cultured cells were exposed to PM1-0.2 and PM0.2, and evaluated for toxicological responses. PM0.2 contributed to15% PM1 mass and 87.67% to particle number (PN). Most of PM0.2 was PM0.1 (exceed 75%). Structure of particles in PM0.2 were mostly spherical, whereas in PM1-0.2 they were more diverse. Within the same mass unit, PM0.2 contained more chemical components than PM1-0.2; within the same volume, a higher mass of components was found in PM1-0.2. IL-6 and IL-8 were secreted by co-cultured cells in higher manner compared to mono cell cultures. PM0.2-induced higher toxicological responses compared to PM1-0.2. Our findings suggest that high PN concentration and toxicity of ultrafine or PM1 cannot be ignored. Mono-cell culture may underestimate the true PM toxicity.

Time-Resolved Small-Angle X-ray Scattering Studies during the Aqueous Emulsion Polymerization of Methyl Methacrylate.

Recently, we reported time-resolved synchrotron small-angle X-ray scattering (TR-SAXS) studies during aqueous emulsion polymerization using a bespoke stirrable reaction cell (J. Am. Chem. Soc. 2021, 143, 1474-1484). This proof-of-concept study utilized a semifluorinated specialty monomer (2,2,2-trifluoroethyl methacrylate) to ensure high X-ray contrast relative to water. Herein, we extend this approach to emulsion polymerization of methyl methacrylate (MMA) in the presence or absence of sodium dodecyl sulfate (SDS) at 70 °C. Solution conductivity measurements for this anionic surfactant indicated a critical micelle concentration (CMC) of 10.9 mM at this temperature. Thus, SDS was employed at either 1.0 or 20.0 mM, which corresponds to well below or well above its CMC. Postmortem analysis by 1H NMR spectroscopy indicated MMA conversions of 93-95% for these three formulations. We demonstrate that the X-ray contrast between water and PMMA is sufficiently large to produce high-quality scattering patterns during TR-SAXS experiments. Such patterns were fitted using a hard-sphere scattering model to monitor the evolution in particle diameter. This enabled (i) determination of the time point for the onset of nucleation and (ii) the evolution in particle size to be monitored during the MMA polymerization. The final particle diameters obtained from such TR-SAXS studies were consistent with postmortem DLS analyses, while TEM studies confirmed that near-monodisperse latex particles were formed. Micellar nucleation occurs within just 2 min when the SDS concentration is well above its CMC, resulting in a high particle number concentration and relatively small latex particles. In contrast, when SDS is either absent or present below its CMC, particle nuclei are formed by homogeneous nucleation over significantly longer time scales (14-15 min). In the latter case, adsorption of SDS onto nascent particles reduces their coagulation, giving rise to a larger number of smaller particles compared to the surfactant-free polymerization. However, the characteristic time required for the onset of nucleation is barely affected because this is mainly controlled by the kinetics of homogeneous polymerization of the relatively water-soluble MMA monomer within the aqueous phase. These results suggest that the aqueous emulsion polymerization of several other (meth)acrylic monomers, and perhaps also vinyl acetate, may be amenable to TR-SAXS studies.

Investigation of local process in granular segregation based on discrete element method

The phenomenon of granular size segregation under vibration has plagued researchers due to the unsteady and high particle number concentration. Discrete element method (DEM) is employed to simulate the process of intruder rising through small background particles from the bottom to the top in a cylindrical container. To describe the segregation level during this process, a segregation evaluation parameter, α, is introduced. It is found that the granular process can be divided into two stages according to the evaluation of α, an initial stage (IS) and a stable intermediate stage (SIS). For a better understanding of the segregation process in these different stages, a new viewpoint focused on the local processes is presented in this article. The segregation mechanism is clarified through numerical simulation of local processes and reference to previous research results.

Influence of emission size distribution and nucleation on number concentrations over Greater Paris

Abstract. With the growing evidence that high particle number concentrations may impact health, modelling their emissions and understanding formation processes is necessary, especially in cities where many people are exposed. As emission inventories of particle numbers and size distribution over cities are usually not available, a methodology is defined to estimate them from PM2.5 emissions and ratios of PM1 / PM2.5 and PM0.1 / PM2.5 by activity sector. In this methodology, a fitting parameter αem is used to redistribute the number concentrations in the lowest emission diameter range. This parameter is chosen by comparing measured and simulated number concentrations during non-nucleation days. The emission size distribution is then finely discretised by conserving both mass and number in each of the size ranges where emissions are specified. The methodology is applied over Greater Paris during the MEGAPOLI campaign (July 2009). Three-dimensional simulations are performed using the chemistry transport model Polair3D/Polyphemus coupled to the aerosol module SSH-aerosol to represent the evolution of particles by condensation, evaporation, coagulation, and nucleation, with a sectional approach for the size distribution. The model is first compared to measurements during non-nucleation days, and the influence over the month of July 2009 of three different nucleation parameterisations is assessed, i.e. binary (sulfuric acid, water), ternary (sulfuric acid, ammonia, water), and heteromolecular (extremely low-volatility organic compounds (ELVOCs) from monoterpenes and sulfuric acid). The modelled number concentrations compare very well to measurements, with an average normalised mean error of 42 % for the daily number concentrations of particles larger than 10 nm and 37 % for the number concentrations of particles larger than 100 nm. The influence of the binary nucleation is low, and the ternary nucleation scheme leads to better simulated number concentrations (in terms of bias and error) at only one site out of three, but it systematically reduces the model to measurement correlation, suggesting that ternary nucleation may not be the dominant process in new particle formation. However, the relative bias and error, as well as the correlation at suburban sites, are systematically improved using the heteromolecular nucleation scheme involving sulfuric acid and ELVOCs from monoterpenes. This suggests that heteromolecular nucleation may be important in cities, especially at suburban sites in summer, and that a better characterisation of the emissions of ELVOC precursors from traffic is needed.

Presence of nano-sized mercury-containing particles in seafoods, and an estimate of dietary exposure

The toxicity of nano-sized particles of mercury (NP–Hg), which are thought to be generated during the detoxification of methyl mercury (MeHg), may differ from that of MeHg, elemental Hg (Hg0), and inorganic Hg (I–Hg). From a human health perspective, it is important to evaluate the presence of NP-Hg in seafoods. We investigated the in vivo formation of NP-Hg in fish and shellfish, which are the main sources of Hg exposure in humans. NP-Hg was measured in 90 fish samples with single-particle inductively coupled plasma mass spectrometry (spICP-MS) after enzyme degradation with pancreatin and lipase. In addition to NP-Hg, total Hg (T-Hg), MeHg, and selenium (Se) concentrations were evaluated. Transient Hg signals were detected as nanoparticles from almost all samples by using spICP-MS. Higher particle number concentrations (CPN) were observed in the tuna–swordfish group than in the shellfish group (17.7 × 107 vs. 1.2 × 106 particles/g, respectively). Although the CPN and maximum particle mass increased significantly with increasing T-Hg concentration, the increase in CPN was greater than those in maximum particle mass. Assuming that the NP-Hg detected was HgSe (tiemannite) and spherical based on previous reports, the maximum particle diameter was estimated to be 89 nm. The mean dietary exposures to NP-Hg, T-Hg, and MeHg were estimated to be 0.067, 5.75, and 5.32 μg/person per day, respectively. Generation of NP-Hg was inferred to be widespread in marine animals, with a preferential increase in the number of particles rather than an increase in particle size. The mean dietary exposure to NP-Hg in Japanese people was estimated to be 1.2 ng/kg body weight (BW) per day. Compared to PTWI of 4 μg/kg BW per week (0.57 μg/kg BW per day) derived by JECFA (2011), the health risk from redissolved I–Hg from NP-Hg is small.

Analysis of aerosol particle number size distribution and source attribution at three megacities in China

Air pollution has been a major concern in China, especially in densely populated megacities. Particulate pollutants, generally known as aerosols, have sizes that range widely and complex physical and chemical compositions with high spatiotemporal variabilities. We have conducted a series of experiments using the same comprehensive observation system, measuring various aerosol properties in the three megacities of Beijing, Shanghai, and Guangzhou. Although there are differences in the total particle number concentration and particle number size distribution among the three sites due to differences in emission sources and sampling seasons, a high proportion of ultrafine particles was observed in all cities, i.e., 86.33%, 88.34%, and 81.1%, respectively. The high particle number concentration at the Beijing and Guangzhou sites was caused by an increase in nucleation-mode particles at nighttime. The concentration of nucleation-mode particles at nighttime was significantly higher than during the daytime. We call this phenomenon a nocturnal nucleation event, and combined with analyses of factors involved, attribute this event to traffic emissions. To investigate the pollution sources at each location, we identified and quantified the pollution contributions from different sources by applying the k-means clustering analysis to observational datasets of environmental quantities. Clustering results showed that traffic emissions were the main contributor in Beijing and Guangzhou, with direct and significant impacts ranging from 37% to 45%, respectively.

Characterization of brake particles emitted from non-asbestos organic and low-metallic brake pads under normal and harsh braking conditions

The physicochemical characteristics of micro- and nano-sized brake particles emitted from non-asbestos organic (NAO) and low-metallic (LM) brake pads were investigated under normal and harsh braking conditions using a brake dynamometer. Under normal braking conditions, 28% and 12% of the total wear mass of brake pad and disc was emitted as PM10 and PM2.5, respectively. Overall, the LM pad emitted 4 times higher brake wear PM than the NAO pad. There was no difference in the morphology of brake wear particles (BWPs) according to pad type from the two pad types. BWPs emitted from the NAO pad were mainly composed of Fe oxide and potassium hexatitanate particles, whereas BWPs from the LM pad were almost entirely of Fe oxide particles. Even when the critical pad temperature was not reached, nanoparticles 80–200 nm in size were emitted from both pad types, and the emission concentration of the LM pad was 3–4 times higher than that of the NAO pad. When the pad temperature exceeded the critical temperature by repeated harsh braking, high particle number (PN) concentrations of volatile nanoparticles were measured. Brake nanoparticles 10–50 nm in size formed out of 10 nm sized particles through volatilization and nucleation. Notably, the PN concentration of volatile NAO pad nanoparticles was 3–4 times higher than that of LM pad nanoparticles due to a higher organic fraction in NAO pads. Volatile nanoparticles smaller than 50 nm could be efficiently removed using volatile particle removers such as an evaporation tube and a catalytic stripper, and the evaporation tube had a higher removal efficiency of volatile nanoparticle than the catalytic stripper. Scanning transmission electron microscopy and energy dispersive spectroscopy analysis showed that nanoparticles of size around 50 nm were round and adhered to larger particles.

Toward Cleaner Transport Alternatives: Reduction in Exposure to Air Pollutants in a Mass Public Transport.

Commuters are often exposed to higher concentrations of air pollutants due to its proximity to mobile sources. Despite recent trends in urban transport toward zero- and low-tailpipe emission alternatives, the assessments of the impact of these transformations on commuter exposure are limited by the low frequency of such studies. In this work, we use a unique data set of personal exposure concentration measurements collected over the span of 5 years to analyze changes due to the introduction of a new fleet for Bogotá's Bus Rapid Transit System. In that system, over a thousand Euro-II and -III diesel-powered buses were replaced with Euro-VI compressed natural gas and filter-equipped Euro-V diesel buses. We measured personal exposure concentrations of equivalent black carbon (eBC), fine particulate (PM2.5), and ultra fine particles (UFP) during and after the retirement of old buses and the introduction of new ones. Observations collected prior to the fleet renewal were used as baseline and later compared to data collected over two follow-up campaigns in 2019 and 2020. Significant reductions in the concentration of PM2.5 and eBC were observed during the 2019 campaign, with a 48% decrease for mean in-bus eBC (89.9 to 46.4 μg m-3) and PM2.5 (180.7 to 95.4 μg m-3) concentrations. Further reductions were observed during the 2020 follow-up, when the fleet renovation was completed, with mean in-bus eBC decreasing to 17.7 μg m-3 and PM2.5 to 42.3 μg m-3. These observations imply nearly a 5-fold reduction in eBC exposure and a 4-fold decrease in PM2.5. There was a much smaller reduction of in-bus UFP concentration between 2019 and 2020, indicating a persistent presence of high particle number concentrations in the near-road environment despite the fleet renovation process. In-bus UFP concentrations ranged between 65 000 and 104 500 cm-3 during the follow-up campaigns. The results in this work illustrate the immediate benefits of reducing personal exposure through the adoption of vehicles with more stringent emission standards.

Retrieval of refractive index of ultrafine single particle using hygroscopic growth factor obtained by high sensitive surface plasmon resonance microscopy

When exposed to different relative humidities (RHs), the optical properties of atmospheric aerosols will change because of changes in the aerosol particle size and complex refractive index (RI), which will affect haze formation and global climate change. The potential contributions of ultrafine particles to the atmospheric optical characteristics and to haze spreading cannot be ignored because of their high particle number concentrations and strong diffusibility; measurement of the optical properties of wet ultrafine particles is thus highly important for environmental assessment. Therefore, a surface plasmon resonance microscopy with azimuthal rotation illumination (SPRM-ARI) system is designed to determine the RIs of single particle aerosols with diameters of less than 100 nm in the hygroscopic growth process. Measurements are taken using mixed single particles with different mass ratios. The RIs of mixed single aerosols at different RHs are retrieved by measuring the scattering light intensity using the SPRM-ARI system and almost all the RIs of the bicomponent particles with different mass ratios decrease with increasing water content under high RH conditions. Finally, for each of the bicomponent particles, the maximum standard deviations for the retrieved RI values are only 2.06×10−3, 3.08×10−3 and 3.83×10−3, corresponding to the NaCl and NaNO3 bicomponent particles with a 3:1 mass ratio at 76.0% RH, the NaCl and glucose particles with a 1:3 mass ratio at 89.0% RH, and the NaCl and OA particles with a 1:1 mass ratio at 78.0% RH, respectively; these results indicate that the high-sensitivity SPRM-ARI system can measure the RI effectively and accurately.

Influence of Regional Pollution Outflow on Particle Number Concentration and Particle Size in Airshed of Guangzhou, South China

A measurement campaign of particle number concentration and size distribution was conducted at urban (SYSU) and suburban (Panyu) areas of Guangzhou, South China, during 16 January to 3 February 2020 before and during the Chinese New Year (CNY) holiday. Average particle number concentration (PNC) was 6.3 × 103 cm-3 and 9.7 × 103 cm-3, respectively, at urban and suburban sites, indicating the severe particulate matter (PM) pollution. The PNC in the region was influenced by monsoon and the land–sea breeze systems. During monsoon seasons, PM pollution occurred at a regional scale affecting the urban and suburban areas as indicated by the high PNC correlation (r value = 0.70), but the PNCs were lower than that during land-sea breeze period (with lower PNCM1/PNCLSB1 and PNCM2/PNCLSB2 ratios) due to the higher atmospheric dispersion. There is a strong local emission (mainly vehicular emissions) in both urban and suburban areas which was significantly lowered during the CNY period due to reduced human activities. The PM pollution was found to be significantly influenced by local emissions (dominated by Aitken mode particles) and new particle formation (NPF) process (dominated by nucleation mode particles). NPF event was found to be associated with a higher N10-25/H2SO4 proxy ratio during the low wind speed condition.

Aerosol generation from graphite at high temperature: Role of heating rate and air flow rate

Behavior of graphite at high temperature in terms of emission characteristics of aerosols has received notable importance in the recent past. Information on the physico-chemical characteristics of generated particles during air ingress conditions for high temperature reactors (HTRs) is crucial for design and safety considerations. The present study focuses on studying the effects of varying heating rate and air flow rate on the number concentration characteristics of particles and gases (CO and CO2) generated from heated graphite. Overall, the peak of evolution profile of number concentration of particles and volume concentration of CO gas was observed in between 600 and 800 °C. With an increase in heating rate, higher particle number concentration and shifting of peak towards high temperatures was noted. Although this trend remained more or less similar, number concentration reduced with the increase in air flow rate. Experimental observations have also been supplemented with plausible mechanism in this work.

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.

Seasonal variations of particle number concentration and its relationship with PM2.5 mass concentration in industrial-residential airshed

The smaller particles that dominate the particle number concentration (PNC) in the ambient air only contribute to a small percentage of particulate matter (PM) mass concentration although present in high particle number concentration. These small particles may be neglected upon assessing the health impacts of the PM. Hence, the knowledge on the particle number concentration size distribution deserves greater attention than the particulate mass concentration. This study investigates the measurement of the particle mass concentrations (PM2.5) and PNC of 0.27μm < Dp < 4.50μm during the southwest (SW), inter-monsoon (IM) and northeast (NE) monsoons in the industrial-residential airshed of Skudai, Johor Bahru, Malaysia. The PM2.5 mass concentrations and PNC were measured using a multi-channel GRIMM Environmental Dust Monitor (GRIMM EDM-SVC 365) equipped with a global positioning system. Diurnal variations, statistical analysis and regression plots were utilised from a six-month hourly data set to examine the patterns of the PNC size distributions and its relationships with the PM2.5 mass concentration. The overall mean PM2.5 mass concentration was 21.85μgm-3, with the 24h mean values of 26.80μgm-3, 26.08μgm-3 and 13.76μgm-3 for the SW, IM and NE monsoons, respectively. It was found that the hourly mean of PNC was recorded at the highest concentration during the SW monsoon (373.20 # cm-3). The particles in the accumulation mode (Dp < 1.0μm) were the prevalent form of the particle number concentration (94-98%). The scatter plots between the PM2.5 mass concentration and particle number size distribution showed that the PNC mode of 0.27 < Dp < 1.0μm has the highest correlation value of r2 = 0.87 due to the emission from the anthropogenic activities. The results of this study highlight the importance of the PNC measurement in the seasonal variations of the PM2.5 pollution, indicating the significance of the regional-scale emission control actions in the local air quality management.

Numerical and experimental investigations on brake particle dispersion in the flow generated by a train in an underground station

Rolling stock operation generates several metallic particles related to wheel-rail and pantograph-catenary contacts and to the wear of braking components. Despite a composition different from outdoors, particulate matter pollution in underground stations must not be ignored as no consensus exists about its health impact on commuters and workers. Assessment of commuters and workers exposure has then become of major interest. Indeed, depending on the time spent underground, their daily exposure to particles can significantly differ. As spatiotemporal distribution of particulate pollutants can influence personal exposure, in the present work, numerical simulations and wind-tunnel experiments were conducted to assess particle concentrations. The dispersion of brake particles in the wake of a typical double-deck French train within an underground station with a central platform is assessed. Results obtained at a constant train speed show a strong correlation between the wake topology and particle dispersion in relation with the dynamics of vortical structures. Higher particle number concentrations (PNC) are found between the train and the station wall compared to those depicted at the platform side.