Experimentally determined deposition of ambient urban ultrafine particles in the respiratory tract of children

Health risks for children exercising in an air-polluted environment can be reduced by monitoring air quality with low-cost particle sensors

A child's body is highly sensitive to air quality, especially regarding the concentration of particulate matter (PM). Nevertheless, due to the high cost of precision instruments, measurements of PM concentrations are rarely carried out in school areas where children spend most of their daily time. This paper presents the results of PM measurements made by a validated, low-cost university air pollution measurement system operating in a rural area near schools. An assessment of children's exposure to PM during school hours (8 a.m.-6 p.m.) at different times of the year was carried out. We show that PM10 concentrations in the air, particularly in winter, often exceeded the alert values of 50 µg m-3, posing a health risk to children, especially when children exercise outside the school building. We also calculated the rate and total PM10 deposition in the respiratory tract during various physical activities performed in clean and polluted air. Monitoring actual PM10 concentrations as presented in this paper, using a low cost sensors, offer school authorities and teachers an opportunity to reduce health risks for children. This can be achieved by adjusting the duration and exercise intensity of children's outdoor physical activities according to the measured air quality.

A novel in-situ method to determine the respiratory tract deposition of carbonaceous particles reveals dangers of public commuting in highly polluted megacity

Background

Exposure to air pollutants is one of the major environmental health risks faced by populations globally. Information about inhaled particle deposition dose is crucial in establishing the dose–response function for assessing health-related effects due to exposure to air pollution.

Objective

This study aims to quantify the respiratory tract deposition (RTD) of equivalent black carbon (BC) particles in healthy young adults during a real-world commuting scenario, analyze factors affecting RTD of BC, and provide key parameters for the assessment of RTD.

Methods

A novel in situ method was applied to experimentally determine the RTD of BC particles among subjects in the highly polluted megacity of Metro Manila, Philippines. Exposure measurements were made for 40 volunteers during public transport and walking.

Results

The observed BC exposure concentration was up to 17-times higher than in developed regions. The deposition dose rate (DDR) of BC was up to 3 times higher during commute inside a public transport compared to walking (11.6 versus 4.4 μg hr⁻¹, respectively). This is twice higher than reported in similar studies. The average BC mass deposition fraction (DF) was found to be 43 ± 16%, which can in large be described by individual factors and does not depend on gender.

Conclusions

Commuting by open-sided public transport, commonly used in developing regions, poses a significant health risk due to acquiring extremely high doses of carcinogenic traffic-related pollutants. There is an urgent need to drastically update air pollution mitigation strategies for reduction of dangerously high emissions of BC in urban setting in developing regions. The presented mobile measurement set-up to determine respiratory tract deposition dose is a practical and cost-effective tool that can be used to investigate respiratory deposition in challenging environments.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00501-x.

Particulate matter exposure at urban traffic intersection during haze episodes: A case study in Changsha

Urban intersection has been identified as a major contributor to the total personal exposure and short-term high exposure of particulate matter (PM) in modern cities. The main aim of this study was to get a better understanding of the determinants of traffic-related PM temporal variations and personal exposure to PMs at a viaduct-covered intersection controlled by traffic signals during the winter haze episodes. A two-day field sampling campaign was conducted with a portable device during evening rush hour and measured the PMs in the 0.3-10 μm size range both on the surface crosswalk and underground passage. PM variations and related cumulative respiratory deposition dose (RDD) along two routes with six road crossing scenarios were estimated on a severe pollution day and a typical day for both adults and children, respectively. The PM concentration on the severe pollution day ranged 59.2-67.9 μg/m³ for PM₁, 163.8-257.0 μg/m³ for PM₂, and 258.2-469.1 μg/m³ for PM₁₀, respectively, as compared to 47.9-57.9 μg/m³for PM₁, 112.7-199.8 μg/m³ for PM₂, and 151.0-301.0 μg/m³ for PM₁₀ on the typical day, respectively. The variability could be explained largely by the built-up environment, traffic component, signal setting, and ventilation condition. Our data suggest that an appropriate setting of the traffic signal would help reduce the personal exposure dose on the surface crosswalk at urban intersections and the ventilation condition had a significant influence on local PM distributions inside the underground passage. Results here provide possible suggestions for the future design of a walkable city.

The physics of respiratory particle generation, fate in the air, and inhalation

Given that breathing is one of the most fundamental physiological functions, there is an urgent need to broaden our understanding of the fluid dynamics that governs it. There would be many benefits from doing so, including a better assessment of respiratory health, a basis for more precise delivery of pharmaceutical drugs for treatment, and the understanding and potential minimization of respiratory infection transmission. We review the physics of particle generation in the respiratory tract, the fate of these particles in the air on exhalation and the physics of particle inhalation. The main focus is on evidence from experimental studies. We conclude that although there is qualitative understanding of the generation of particles in the respiratory tract, a basic quantitative knowledge of the characteristics of the particles emitted during respiratory activities and their fate after emission, and a theoretical understanding of particle deposition during inhalation, nevertheless the general understanding of the entire process is rudimentary, and many open questions remain.

Characteristics of inhalable bioaerosols on foggy and hazy days and their deposition in the human respiratory tract

Atmospheric bioaerosols contain live and dead biological components that can enter the human respiratory tract (HRT) and affect human health. Here, the total microorganisms in a coastal megacity, Qingdao, were characterized on the basis of long-term observations from October 2013 to January 2021. Particular attention was given to the size dependence of inhalable bioaerosols in concentration and respiratory deposition in different populations on foggy and hazy days. Bioaerosol samples stained with 4,6-diamidino-2-phenylindole (DAPI) were selected to measure the total airborne microbe (TAM) concentrations with an epifluorescence microscope, while a multiple-path particle dosimetry model was employed to calculate respiratory deposition. The mean TAM concentrations in the particle size range of 0.65-1.1 μm (TAM_0.65-1.1) were 1.23, 2.02, 1.60 and 2.33 times those on sunny reference days relative to the corresponding values on days with slight, mild, moderate and severe levels of haze, respectively. The mean concentration of TAMs in the particle size range of 0.65-2.1 μm (TAM_0.65-2.1) on severely hazy days was (2.02 ± 3.28) × 10⁵ cells/m³, with a reduction of 4.16% relative to that on the reference days. The mean TAM_0.65-2.1 concentration changed from (1.50 ± 1.37) × 10⁵ cells/m³ to (1.76 ± 1.36) × 10⁵ cells/m³, with TAM_0.65-1.1 increasing from (7.91 ± 7.97) × 10⁴ cells/m³ to (1.76 ± 1.33) × 10⁵ cells/m³ on days with light fog days and medium fog, respectively. The modeling results showed that the majority of TAM_0.65-2.1 deposition occurred in the extrathoracic (ET) region, followed by the alveolar (AL) region. When different populations were examined separately, the deposition doses (DDs) in adult females and in children ranked at the minimum value (6.19 × 10³ cells/h) and maximum value (1.08 × 10⁴ cells/h), respectively. However, the inhalation risks on polluted days, such as hazy, foggy and mixed hazy-foggy (HF) days, were still below the threshold for adverse impacts on human health.

Characteristics of PM10 Levels Monitored in Bangkok and Its Vicinity Areas, Thailand

The ambient air concentrations of PM10 were observed in Bangkok and its vicinity areas including Nonthaburi and Nakhon Pathom, Thailand. The selected study areas are located near heavy-traffic roads with a high concentration of traffic-related air pollution. The ambient air samples were collected in the winter season (October 2019 to February 2020). The highest average level of PM10 was found in Nonthaburi (66.63 µg/m3), followed by Bangkok (56.79 µg/m3) and Nakhon Pathom (40.18 µg/m3), respectively. The morphology of these particles is typically spherical and irregular shape particles. At the sampling site in Bangkok, these particles are primarily composed of C, O, and Si, and a certain amount of metals such as Fe, Cu, and Cr. Some trace amount of other elements such as Ca, Na, and S are present in minor concentration. The particles collected from Nakhon Pathom and Nonthaburi sampling sites contain the main abundant elements C, O, and Si, followed by Cu, Cr, S, Fe, Ca, and Na, respectively. These particles are an agglomeration of carbon particles resulting from the incomplete combustion of organic matter. Their origin may be associated with road dust, vehicle emission, and the erosion of building products. It can be noted that the levels and characteristics of PM10 are key factors in understanding the behavior of the particles in not only atmospheric visibility but also human health risks.

Novel measurement system for respiratory aerosols and droplets in indoor environments

The SARS-CoV-2 pandemic has created a great demand for a better understanding of the spread of viruses in indoor environments. A novel measurement system consisting of one portable aerosol-emitting mannequin (emitter) and a number of portable aerosol-absorbing mannequins (recipients) was developed that can measure the spread of aerosols and droplets that potentially contain infectious viruses. The emission of the virus from a human is simulated by using tracer particles solved in water. The recipients inhale the aerosols and droplets and quantify the level of solved tracer particles in their artificial lungs simultaneously over time. The mobile system can be arranged in a large variety of spreading scenarios in indoor environments and allows for quantification of the infection probability due to airborne virus spreading. This study shows the accuracy of the new measurement system and its ability to compare aerosol reduction measures such as regular ventilation or the use of a room air purifier.

Marathon race performance increases the amount of particulate matter deposited in the respiratory system of runners: an incentive for "clean air marathon runs"

Background

In the last decades, marathon running has become a popular form of physical activity among people around the world. It should be noticed that the main marathon races are performed in large cities, where air quality varies considerably. It is well established that breathing polluted air results in a number of harmful effects to the human body. However, there have been no studies to show the impact of marathon run performance on the amount of the deposition of varied fractions of airborne particulate matter (PM) in the respiratory tract of runners. This is why the present study sought to determine the impact of marathon run performance in the air of varying quality on the deposition of the PM₁, PM_2.5, PM₁₀ in the respiratory tract in humans.

Methods

The PM₁, PM_2.5 and PM₁₀ deposition was determined in an “average runner” (with marathon performance time 4 h: 30 min) and in an “elite marathon runner” (with marathon performance time 2 h: 00 min) at rest, and during a marathon race, based on own measurements of the PM content in the air and the size-resolved DF(d) profile concept.

Results

We have shown that breathing air containing 50 µg m⁻³ PM₁₀ (a borderline value according to the 2006 WHO standard - still valid) at minute ventilation (V_E) equal to 8 L min⁻¹ when at rest, resulted in PM₁₀deposition rate of approximately 9 µg h⁻¹, but a marathon run of an average marathon runner with the V_E = 62 L min⁻¹ increased the deposition rate up to 45 µg h⁻¹. In the elite runner, marathon run with the V_E= 115 L min⁻¹ increased PM₁₀ deposition rate to 83 µg h⁻¹. Interestingly, breathing the air containing 50 µg m⁻³of PM₁₀ at the V_E = 115 L min⁻¹by the elite marathon runner during the race resulted in the same PM₁₀deposition rate as the breathing highly polluted air containing as much as 466 µg m⁻³ of PM₁₀ when at rest. Furthermore, the total PM₁₀ deposition in the respiratory tract during a marathon race in average runners is about 22% greater (203 / 166 = 1.22) than in elite runners. According to our calculations, the concentration of PM₁₀in the air during a marathon race that would allow one not to exceed the PM₁₀ deposition rate of 9 µg h⁻¹should be lower than 10 µg m⁻³ in the case of an average runner, and it should be lower than 5.5 µg m⁻³ in the case of an elite runner.

Conclusions

We conclude that a marathon run drastically increases the rate of deposition of the airborne PM in the respiratory tract of the runners, as a consequence of the huge V_E generated during the race. A decrease of the PM content in the air attenuates this rate. Based on our calculations, we postulate that the PM₁₀ content in the air during a “clean air marathon run”, involving elite marathon runners, should be below 5.5 µg m⁻³.

Particulate matter exposure at a densely populated urban traffic intersection and crosswalk

Exposure to elevated particulate matter (PM) pollution is of great concern to both the general public and air quality management agencies. At urban traffic intersections, for example, pedestrians are often at a higher risk of exposure to near-source PM pollution from traffic while waiting on the roadside or while walking in the crosswalk. This study offers an in-depth investigation of pedestrian exposure to PM pollution at an urban traffic intersection. Fixed-site measurements near an urban intersection were conducted to examine the variations in particles of various sizes through traffic signal cycles. This process aids in the identification of major PM dispersion patterns on the roadside. In addition, mobile measurements of pedestrian exposure to PM were conducted across six time intervals that correspond to different segments of a pedestrian's journey when passing through the intersection. Measurement results are used to estimate and compare the cumulative deposited doses of PM by size categories and journey segments for pedestrians at an intersection. Furthermore, comparisons of pedestrian exposure to PM on a sunny day and a cloudy day were analyzed. The results indicate the importance of reducing PM pollution at intersections and provide policymakers with a foundation for possible measures to reduce pedestrian PM exposure at urban traffic intersections.

Experimentally determined deposition of ambient urban ultrafine particles in the respiratory tract of children

A critical element of the risk assessment of exposure to airborne ambient ultrafine particles (UFP) is the quantification of respiratory tract deposition (RTD) of the particles, which is intrinsically challenging, particularly at the population scale. In this study, we used a recently proposed method to experimentally determine the RTD of urban UFP in a large group of children exposed to these particles in a school setting in Brisbane, Australia. Children are one of the most susceptible population groups; However, little is known about the deposition of UFP from urban traffic in their airways. In order to advance the knowledge in this field, the objectives of this study were: to determine the deposition of ambient urbane UFP in large number children, to catergorize the source of inhaled UFPs and hence to assess the contribution of air pollution sources to the deposition. RTD was measured in children aged 8-11 at primary schools using a flow-through chamber bag system. First, the inhaled and exhaled air was separated; then the particle number size distribution and particle number concentration were measured. The sources of inhaled UFP were categorized according to their particle number size distribution by a K means cluster technique. A total of 128 children from five schools performed the RTD measurement. The mean total deposition fraction of urban UFP in all children was 0.59 ± 0.10. Inhaled UFP were categorized into two groups: traffic and urban background, with the GMD of corresponding particle number size distribution of 20 nm and 40 nm, respectively. The total deposition fraction (mean ± SD) of UFP from these two groups was 0.68 ± 0.09 for traffic and 0.55 ± 0.08 for urban background respectively. This is the first study in which RTD was measured in a large group of children inhaling real urban UFP. First, we proved that this novel method can indeed be applied easily and quickly to a large group of people. Second, we quantified the RTD of children, thus providing an important input to the risk assessment for exposure to UFP.

Transmission risk of infectious droplets in physical spreading process at different times: A review

Droplets provide a well-known transmission media in the COVID-19 epidemic, and the particle size is closely related to the classification of the transmission route. However, the term "aerosol" covers most particle sizes of suspended particulates because of information asymmetry in different disciplines, which may lead to misunderstandings in the selection of epidemic prevention and control strategies for the public. In this review, the time when these droplets are exhaled by a patient was taken as the initial time. Then, all available viral loads and numerical distribution of the exhaled droplets was analyzed, and the evaporation model of droplets in the air was combined with the deposition model of droplet nuclei in the respiratory tract. Lastly, the perspective that physical spread affects the transmission risk of different size droplets at different times was summarized for the first time. The results showed that although the distribution of exhaled droplets was dominated by small droplets, droplet volume was proportional to the third power of particle diameter, meaning that the viral load of a 100 μm droplet was approximately 10⁶ times that of a 1 μm droplet at the initial time. Furthermore, the exhaled droplets are affected by heat and mass transfer of evaporation, water fraction, salt concentration, and acid-base balance (the water fraction > 98%), which lead them to change rapidly, and the viral survival condition also deteriorates dramatically. The time required for the initial diameter (d_o) of a droplet to shrink to the equilibrium diameter (d_e, about 30% of d_o) is approximately proportional to the second power of the particle diameter, taking only a few milliseconds for a 1 μm droplet but hundreds of milliseconds for a 10 μm droplet; in other words, the viruses carried by the large droplets can be preserved as much as possible. Finally, the infectious droplet nuclei maybe inhaled by the susceptible population through different and random contact routes, and the droplet nuclei with larger d_e decompose more easily into tiny particles on account of the accelerated collision in a complex airway, which can be deposited in the higher risk alveolar region. During disease transmission, the infectious droplet particle size varies widely, and the transmission risk varies significantly at different time nodes; therefore, the fuzzy term "aerosol" is not conducive to analyzing disease exposure risk. Recommendations for epidemic prevention and control strategies are: 1) Large droplets are the main conflict in disease transmission; thus, even if they are blocked by a homemade mask initially, it significantly contains the epidemic. 2) The early phase of contact, such as close-contact and short-range transmission, has the highest infection risk; therefore, social distancing can effectively keep the susceptible population from inhaling active viruses. 3) The risk of the fomite route depends on the time in contact with infectious viruses; thus, it is important to promote good health habits (including frequent hand washing, no-eye rubbing, coughing etiquette, normalization of surface cleaning), although blind and excessive disinfection measures are not advisable. 4) Compared with the large droplets, the small droplets have larger numbers but carry fewer viruses and are more prone to die through evaporation.

Assessment of indoor air exposure at residential homes: Inhalation dose and lung deposition of PM10, PM2.5 and ultrafine particles among newborn children and their mothers

Accurate assessment of particulate matter (PM) dose and respiratory deposition is essential to better understand the risks of exposure to PM and, consequently, to develop the respective risk-control strategies. In homes, this is especially relevant in regards to ultrafine particles (UFP; <0.1 μm) which origin in these environments is mostly due to indoor sources. Thus, this study aimed to estimate inhalation doses for different PM mass/number size fractions (i.e., PM₁₀, PM_2.5 and UFP) in indoor air of residential homes and to quantify the deposition (total, regional and lobar) in human respiratory tract for both newborn children and mothers. Indoor real-time measurements of PM₁₀, PM_2.5 and UFP were conducted in 65 residential homes situated in Oporto metropolitan area (Portugal). Inhalation doses were estimated based on the physical characteristics of individual subjects and their activity patterns. The multi-path particle dosimetry model was used to quantify age-specific depositions in human respiratory tract. The results showed that 3-month old infants exhibited 4-fold higher inhalation doses than their mothers. PM₁₀ were primarily deposited in the head region (87%), while PM_2.5 and UFP depositions mainly occurred in the pulmonary area (39% and 43%, respectively). Subject age affected the pulmonary region and the total lung deposition; higher deposition being observed among the newborns. Similarly, lower lobes (left lobe: 37% and right lobe: 30%) received higher PM deposition than upper and middle lobes; right lobes lung are prone to be more susceptible to respiratory problems, since asymmetric deposition was observed. Considering that PM-related diseases occur at specific sites of respiratory system, quantification of site-specific particle deposition should be predicted in order to better evidence the respective health outcomes resulting from inhaled PM.