Influence of natural ventilation design on the dispersion of pathogen-laden droplets in a coach bus.

Natural ventilation is an energy-efficient design approach to reduce infection risk (IR), but its optimized design in a coach bus environment is less studied. Based on a COVID-19 outbreak in a bus in Hunan, China, the indoor-outdoor coupled CFD modeling approach is adopted to comprehensively explore how optimized bus natural ventilation (e.g., opening/closing status of front/middle/rear windows (FW/MW/RW)) and ceiling wind catcher (WCH) affect the dispersion of pathogen-laden droplets (tracer gas, 5 µm, 50 µm) and IR. Other key influential factors including bus speed, infector's location, and ambient temperature (Tref) are also considered. Buses have unique natural ventilation airflow patterns: from bus rear to front, and air change rate per hour (ACH) increases linearly with bus speed. When driving at 60 km/h, ACH is only 6.14 h-1 and intake fractions of tracer gas (IFg) and 5 µm droplets (IFd) are up to 3372 ppm and 1394 ppm with ventilation through leakages on skylights and no windows open. When FW and RW are both open, ACH increases by 43.5 times to 267.50 h-1, and IFg and IFd drop rapidly by 1-2 orders of magnitude compared to when no windows are open. Utilizing a wind catcher and opening front windows significantly increases ACH (up to 8.8 times) and reduces IF (5-30 times) compared to only opening front windows. When the infector locates at the bus front with FW open, IFg and IFd of all passengers are <10 ppm. More droplets suspend and further spread in a higher Tref environment. It is recommended to open two pairs of windows or open front windows and utilize the wind catcher to reduce IR in coach buses.

Particle Deposition in Large-Scale Human Tracheobronchial Airways Predicted by Single-Path Modelling.

The health effects of particles are directly related to their deposition patterns (deposition site and amount) in human airways. However, estimating the particle trajectory in a large-scale human lung airway model is still a challenge. In this work, a truncated single-path, large-scale human airway model (G3-G10) with a stochastically coupled boundary method were employed to investigate the particle trajectory and the roles of their deposition mechanisms. The deposition patterns of particles with diameters (dp) of 1-10 µm are investigated under various inlet Reynolds numbers (Re = 100-2000). Inertial impaction, gravitational sedimentation, and combined mechanism were considered. With the increasing airway generations, the deposition of smaller particles (dp < 4 µm) increased due to gravitational sedimentation, while that of larger particles decreased due to inertial impaction. The obtained formulas of Stokes number and Re can predict the deposition efficiency due to the combined mechanism in the present model, and the prediction can be used to assess the dose-effect of atmospheric aerosols on the human body. Diseases in deeper generations are mainly attributed to the deposition of smaller particles under lower inhalation rates, while diseases at the proximal generations mainly result from the deposition of larger particles under higher inhalation rates.

Airborne transmission of the Delta variant of SARS-CoV-2 in an auditorium.

The Delta variant of SARS-CoV-2 has inflicted heavy burdens on healthcare systems globally, although direct evidence on the quantity of exhaled viral shedding from Delta cases is lacking. The literature remains inconclusive on whether existing public health guidance, based on earlier evidence of COVID-19, should respond differently to more infectious viral strains. This paper describes a study on an outbreak of the Delta variant of COVID-19 in an auditorium, where one person contracted the virus from three asymptomatic index cases sitting in a different row. Field inspections were conducted on the configuration of seating, building and ventilation systems. Numerical simulation was conducted to retrospectively assess the exhaled viral emission, decay, airborne dispersion, with a modified Wells-Riley equation used to calculate the inhalation exposure and disease infection risks at the seat level. Results support the airborne disease transmission. The viral emission rate for Delta cases was estimated at 31 quanta per hour, 30 times higher than those of the original variant. The high quantity of viral plume exhaled by delta cases can create a high risk zone nearby, which, for a mixing ventilation system, cannot be easily mitigated by raising mixing rates or introducing fresh air supply. Such risks can be reduced by wearing an N95 respirator, less so for social distancing. A displacement ventilation system, through which the air is supplied at the floor and returned from the ceiling, can reduce risks compared with a mixing system. The study has implications for ventilation guidelines and hygiene practices in light of more infectious viral strains of COVID-19.

Role of pathogen-laden expiratory droplet dispersion and natural ventilation explaining a COVID-19 outbreak in a coach bus.

The influencing mechanism of droplet transmissions inside crowded and poorly ventilated buses on infection risks of respiratory diseases is still unclear. Based on experiments of one-infecting-seven COVID-19 outbreak with an index patient at bus rear, we conducted CFD simulations to investigate integrated effects of initial droplet diameters(tracer gas, 5 µm, 50 µm and 100 µm), natural air change rates per hour(ACH = 0.62, 2.27 and 5.66 h-1 related to bus speeds) and relative humidity(RH = 35% and 95%) on pathogen-laden droplet dispersion and infection risks. Outdoor pressure difference around bus surfaces introduces natural ventilation airflow entering from bus-rear skylight and leaving from the front one. When ACH = 0.62 h-1(idling state), the 30-min-exposure infection risk(TIR) of tracer gas is 15.3%(bus rear) - 11.1%(bus front), and decreases to 3.1%(bus rear)-1.3%(bus front) under ACH = 5.66 h-1(high bus speed).The TIR of large droplets(i.e., 100 µm/50 µm) is almost independent of ACH, with a peak value(∼3.1%) near the index patient, because over 99.5%/97.0% of droplets deposit locally due to gravity. Moreover, 5 µm droplets can disperse further with the increasing ventilation. However, TIR for 5 µm droplets at ACH = 5.66 h-1 stays relatively small for rear passengers(maximum 0.4%), and is even smaller in the bus middle and front(<0.1%). This study verifies that differing from general rooms, most 5 µm droplets deposit on the route through the long-and-narrow bus space with large-area surfaces(L∼11.4 m). Therefore, tracer gas can only simulate fine droplet with little deposition but cannot replace 5-100 µm droplet dispersion in coach buses.

Insufficient ventilation led to a probable long-range airborne transmission of SARS-CoV-2 on two buses.

Uncertainty remains on the threshold of ventilation rate in airborne transmission of SARS-CoV-2. We analyzed a COVID-19 outbreak in January 2020 in Hunan Province, China, involving an infected 24-year-old man, Mr. X, taking two subsequent buses, B1 and B2, in the same afternoon. We investigated the possibility of airborne transmission and the ventilation conditions for its occurrence. The ventilation rates on the buses were measured using a tracer-concentration decay method with the original driver on the original route. We measured and calculated the spread of the exhaled virus-laden droplet tracer from the suspected index case. Ten additional passengers were found to be infected, with seven of them (including one asymptomatic) on B1 and two on B2 when Mr. X was present, and one passenger infected on the subsequent B1 trip. B1 and B2 had time-averaged ventilation rates of approximately 1.7 and 3.2 L/s per person, respectively. The difference in ventilation rates and exposure time could explain why B1 had a higher attack rate than B2. Airborne transmission due to poor ventilation below 3.2 L/s played a role in this two-bus outbreak of COVID-19.

Predominant airborne transmission and insignificant fomite transmission of SARS-CoV-2 in a two-bus COVID-19 outbreak originating from the same pre-symptomatic index case.

The number of people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to increase worldwide, but despite extensive research, there remains significant uncertainty about the predominant routes of SARS-CoV-2 transmission. We conducted a mechanistic modeling and calculated the exposure dose and infection risk of each passenger in a two-bus COVID-19 outbreak in Hunan province, China. This outbreak originated from a single pre-symptomatic index case. Some human behavioral data related to exposure including boarding and alighting time of some passengers and seating position and mask wearing of all passengers were obtained from the available closed-circuit television images/clips and/or questionnaire survey. Least-squares fitting was performed to explore the effect of effective viral load on transmission risk, and the most likely quanta generation rate was also estimated. This study reveals the leading role of airborne SARS-CoV-2 transmission and negligible role of fomite transmission in a poorly ventilated indoor environment, highlighting the need for more targeted interventions in such environments. The quanta generation rate of the index case differed by a factor of 1.8 on the two buses and transmission occurred in the afternoon of the same day, indicating a time-varying effective viral load within a short period of five hours.

Evidence for lack of transmission by close contact and surface touch in a restaurant outbreak of COVID-19.

BACKGROUND: Coronavirus disease 2019 (COVID-19) is primarily a respiratory disease that has become a global pandemic. Close contact plays an important role in infection spread, while fomite may also be a possible transmission route. Research during the COVID-19 pandemic has identified long-range airborne transmission as one of the important transmission routes although lack solid evidence. METHODS: We examined video data related to a restaurant associated COVID-19 outbreak in Guangzhou. We observed more than 40,000 surface touches and 13,000 episodes of close contacts in the restaurant during the entire lunch duration. These data allowed us to analyse infection risk via both the fomite and close contact routes. RESULTS: There is no significant correlation between the infection risk via both fomite and close contact routes among those who were not family members of the index case. We can thus rule out virus transmission via fomite contact and interpersonal close contact routes in the Guangzhou restaurant outbreak. The absence of a fomite route agrees with the COVID-19 literature. CONCLUSIONS: These results provide indirect evidence for the long-range airborne route dominating SARS-CoV-2 transmission in the restaurant. We note that the restaurant was poorly ventilated, allowing for increasing airborne SARS-CoV-2 concentration.

Airborne transmission of pathogen-laden expiratory droplets in open outdoor space.

Virus-laden droplets dispersion may induce transmissions of respiratory infectious diseases. Existing research mainly focuses on indoor droplet dispersion, but the mechanism of its dispersion and exposure in outdoor environment is unclear. By conducting CFD simulations, this paper investigates the evaporation and transport of solid-liquid droplets in an open outdoor environment. Droplet initial sizes (dp = 10 µm, 50 µm, 100 µm), background relative humidity (RH = 35%, 95%), background wind speed (Uref = 3 m/s, 0.2 m/s) and social distances between two people (D = 0.5 m, 1 m, 1.5 m, 3 m, 5 m) are investigated. Results show that thermal body plume is destroyed when the background wind speed is 3 m/s (Froude number Fr ~ 10). The inhalation fraction (IF) of susceptible person decreases exponentially when the social distance (D) increases from 0.5 m to 5 m. The exponential decay rate of inhalation fraction (b) ranges between 0.93 and 1.06 (IF=IF0e-b(D-0.5)) determined by the droplet initial diameter and relative humidity. Under weak background wind (Uref = 0.2 m/s, Fr ~ 0.01), the upward thermal body plume significantly influences droplet dispersion, which is similar with that in indoor space. Droplets in the initial sizes of 10 µm and 50 µm disperse upwards while most of 100 µm droplets fall down to the ground due to larger gravity force. Interestingly, the deposition fraction on susceptible person is ten times higher at Uref = 3 m/s than that at Uref = 0.2 m/s. Thus, a high outdoor wind speed does not necessarily lead to a smaller exposure risk if the susceptible person locating at the downwind region of the infected person, and people in outdoors are suggested to not only keep distance of greater than 1.5 m from each other but also stand with considerable angles from the prevailing wind direction.

Interactive effect between long-term and short-term thermal history on outdoor thermal comfort: Comparison between Guangzhou, Zhuhai and Melbourne.

Thermal history can influence human thermal comfort through physiological (short-term) and psychological (long-term) aspects. However, the nature of the interaction between long-term and short-term thermal history is unclear. To investigate the interactive effects of long-term and short-term thermal history on outdoor thermal comfort, we conducted summer thermal comfort surveys in Melbourne (n = 3293, January-February 2014), Guangzhou, and Zhuhai (n = 4304, September 2018). The mean thermal sensation of residents of Guangzhou was higher than that of Melbourne and Zhuhai residents under a similar Universal Thermal Climate Index (UTCI) range. The preferred UTCI was the highest for Melbourne residents (19.62 °C). When UTCI was 25.6-38.4 °C, respondents' mean thermal sensation from Köppen climate zones A, B, and C was significantly higher in Guangzhou than those of Zhuhai and Melbourne. A three-way ANOVA test revealed that peoples' thermal sensations depended on a significant interaction among UTCI thermal stress levels, climate zones, and prior exposure environment. The prior exposure environment could affect the difference in thermal perception between climate zones. However, there was no significant interaction between climate zones and activity engaged in before taking the survey on thermal sensation. The difference in the thermal perception of various climate zones diminished under universally uncomfortable conditions for specific prior exposure environments and activities. The socio-ecological system model, environmental perception theory, climatocultural adaptation, and alliesthesia are useful for understanding the interactive effect of long- and short-term thermal history on outdoor thermal comfort. By revealing how people adapt to different climatic environments, our results can help ensure that people with diverse climatic backgrounds can experience thermal comfort outdoors.

Transmission of pathogen-laden expiratory droplets in a coach bus.

Droplet dispersion carrying viruses/bacteria in enclosed/crowded buses may induce transmissions of respiratory infectious diseases, but the influencing mechanisms have been rarely investigated. By conducting high-resolution CFD simulations, this paper investigates the evaporation and transport of solid-liquid mixed droplets (initial diameter 10 µm and 50 µm, solid to liquid ratio is 1:9) exhaled in a coach bus with 14 thermal manikins. Five air-conditioning supply directions and ambient relative humidity (RH = 35 % and 95 %) are considered. Results show that ventilation effectiveness, RH and initial droplet size significantly influence droplet transmissions in coach bus. 50 µm droplets tend to evaporate completely within 1.8 s and 7 s as RH = 35 % and 95 % respectively, while 0.2 s or less for 10 µm droplets. Thus 10 µm droplets diffuse farther with wider range than 50 µm droplets which tend to deposit more on surfaces. Droplet dispersion pattern differs due to various interactions of gravity, ventilation flows and the upward thermal body plume. The fractions of droplets suspended in air, deposited on wall surfaces are quantified. This study implies high RH, backward supply direction and passengers sitting at nonadjacent seats can effectively reduce infection risk of droplet transmission in buses. Besides taking masks, regular cleaning is also recommended since 85 %-100 % of droplets deposit on object surfaces.

Scaled outdoor experimental studies of urban thermal environment in street canyon models with various aspect ratios and thermal storage.

Street aspect ratios and urban thermal storage largely determine the thermal environment in cities. By performing scaled outdoor measurements in summer of 2017 in Guangzhou, China, we investigate these impacts on spatial/temporal characteristics of urban thermal environment which are still unclear so far. Two types of street canyon models are investigated, i.e. the 'hollow' model resembling hollow concrete buildings and the 'sand' model consisting of buildings filled with sand attaining much greater thermal storage. For each model, three street aspect ratios (building height/street width, H/W = 1, 2, 3; H = 1.2 m) are considered. The diurnal variations of air-wall surface temperatures are observed and their characteristics are quantified for various cases. The daily average temperature and daily temperature range (DTR) of wall temperature vary significantly with different aspect ratios and thermal storage. During the daytime, wider street canyon (H/W = 1) with less shading area experiences higher temperature than narrower ones (H/W = 2, 3) as more solar radiation received by wall surfaces. At night, wider street canyon cools down quicker due to stronger upward longwave radiation and night ventilation. For hollow models, H/W = 1 attains DTR of 12.1 °C, which is 1.2 and 2.1 °C larger than that of H/W = 2, 3. Moreover, the sand models experience smaller DTR and a less changing rate of wall temperature than hollow models because larger thermal storage absorbs more heat in the daytime and releases more at night. DTR of hollow models with H/W = 1, 2, 3 is 4.5, 4.6 and 3.8 °C greater than sand models respectively. For both hollow and sand models, wider streets experience a little higher daily average temperature (0.3-0.6 °C) than narrower ones. Our study provides direct evidence in how man-made urban structures influence urban climate and also suggests the possibility to control outdoor thermal environment by optimize urban morphology and thermal storage.

Production of activated carbons from four wastes via one-step activation and their applications in Pb2+ adsorption: Insight of ash content.

Natural biomass is a renewable source for precursors of porous carbon. Four agriculture wastes of corn cob (CC), wheat bran (WB), rice husk (RH), and soybean shell (SS) were applied to produce activated carbons (ACs) via one-step activation by sodium hydroxide. The effects of ash contents and NaOH dosage ratio (1-5) on surface area for ACs were investigated. Owing to ash etching, the high ash precursor (like RH) exhibited less alkali consumption and larger surface area than low ash one (like CC). All four ACs expressed developed pore structure and outstanding surface area of ∼2500 m2g-1. During adsorption of lead ions in simulated wastewater, RH-based AC revealed superior capture capacity of 492 ± 15 mgg-1. One-step activation had the potential to deliver savings around 1/3 of energy consumption, enabling the cost performance of high ash RH-based AC reaching 194 ± 12 g Pb2+$-1, 76% larger than low ash CC-based AC. High ash biomass is a promising candidate to obtain eco-friendly carbon products.

Numerical modeling of particle deposition in the conducting airways of asthmatic children.

Mounting evidence has linked long- and short-term exposure to particulate air pollution with the incidence and exacerbation of asthma in children, but the biological pathogenesis is unclear. We examined the deposition of particles in the airways of asthmatic children. A planar and symmetric model of airways for 4-year-old asthmatic children was considered. Airflow and particle deposition in the upper (G3-G6) and lower (G9-G12) conducting airways were numerically investigated using computation fluid dynamics (CFD) method. We considered the manifestation of moderate (30% reduction in airway diameter) and severe (60% reduction) asthma. Micron particles (1-10 µm) were considered. We found that particle deposition in the asthmatic children was significantly higher than that in healthy children. The deposition efficiency increased slowly with particle size for healthy children, but increased rapidly for asthmatic children, such that smaller particles could be deposited in the conducting airways of asthmatics. For healthy children, particles were deposited by inertial impaction and gravitational sedimentation respectively in the upper and lower airways, but deposited by inertial impaction in asthmatic children. The severity of the asthma increased the particle deposition in the airways. Our study indicated that asthmatic children were more susceptible to the effect of particulate air pollution. The constricted airways increased the particle deposition by inertial impaction, which may be the biological pathogenesis that causes the hospitalization of asthma in children. Avoiding exposure during air pollution events will be an effective measure to reduce the asthma attack.

Inhalation bioaccessibility of polycyclic aromatic hydrocarbons in heavy PM2.5 pollution days: Implications for public health risk assessment in northern China.

Airborne (PM2.5) with aerodynamic diameter ≤ 2.5 µm was collected from 4 types of cities in northeast China during the heating period. The objectives of this study were to assess the concentrations variation of PM2.5-bound 12 carcinogenic polycyclic aromatic hydrocarbons (PAH12), to study the influence of simulated lung fluids on bioaccessibility of PAH12 and to estimate the variation of lifetime excess cancer risk to the residents, artificial lysosomal fluid (ALF) and Gamble's solution were used. The number of lifetime excess cancer cases (determined by California Environmental Protection Agency method) as a result of PAH12 exposure (total concentration) was 4.00-430 (provincial central cities), 24.0-261 (energy-mining cities), 17.0-109 (forested city), and 20.0-69.0 (agricultural city) per million people, which relatively corresponded to a 92.2% and 96.2%, 92.6% and 97.3%, 92.2% and 94.2%, and 86.5% and 92.6% decrease after considering bioaccessibility following 24-h of Gamble's solution and ALF extraction, respectively. Phenanthrene (Phe), dibenz[a,h]anthracene (DahA) and benzo[a]pyrene (BaP) were found to be the most bioaccessible types of PAH12 after the Gamble's solution and ALF extraction in the PM2.5 samples from all the studied cities. Based on the point-estimate approach, short-term predictions of pulmonary toxicity caused by potential inhalation of airborne PM into the pulmonary system might be overestimated if bioaccessibility of PM2.5-bound PAH12 is not fully evaluated.

Health effects of physical activity as predicted by particle deposition in the human respiratory tract.

Although health benefits of physical activity are well known, the risk of physical activity in polluted air is unclear. Our objective is to investigate health effects resulting from physical activity in polluted air by looking at particle deposition in human tracheobronchial (TB) airways. Airflow and particle deposition in TB airways were investigated using a computational fluid dynamics (CFD) method. We chose three regional airways: upper (G3-G5), central (G9-G11) and lower (G14-G16). Physical activity was described by breathing rate at the mouth, for three levels of activity: sedentary (15 l/min), moderate (30 l/min) and intense (60 l/min). We found that particle deposition was strongly affected by physical activity. Particles are deposited in greater number in the lower airways (G14-G16) during sedentary activity, more in the upper airways (G3-G5) during intense activity, and uniformly in the airways during moderate activity. The difference in the deposition pattern was due to the reason that physical activity increased the airflow which increased inertial impaction. Our modeling of particle deposition in the human respiratory airways shows that there are different health effects for different activity levels: sedentary activity leads to chronic health effects, intense activity results in acute effects, and moderate activity minimizes the adverse health effects of physical activity in polluted air.

Bioaccessibility and exposure assessment of trace metals from urban airborne particulate matter (PM10 and PM2.5) in simulated digestive fluid.

We describe a batch-extraction with simulated digestive fluid (salivary fluid, gastric fluid and intestinal fluid) to estimate the bioaccessibility of inhaled trace metals (TMs) in particulate matter less than 10 and 2.5 µm in aerodynamic diameter (PM10 and PM2.5). Concentrations of the assayed TMs (As, Cd, Cr, Ni, Mn, Cu, Zn, Sb, Hg and Pb) were determined in PM10 and PM2.5 samples by inductively coupled plasma-mass spectrometry. The TMs with the largest soluble fractions for airborne PM collected from winter and summer in saliva were Mn and Sb, respectively; in seasons this became Co in gastric fluid and Cu in intestinal fluid. Clearly, bioaccessibility is strongly dependent on particle size, the component of simulated digestive fluids (e.g., pH, digestive enzymes pepsin and trypsin), and the chemical properties of metal ions. The particle size and seasonal variation affected the inhaled bioaccessible fraction of PM-bound TMs during mucociliary clearance, which transported PM from the tracheal and the bronchial region to the digestive system. This study provides direct evidence for TMs in airborne PM being bioaccessible TMs are likely to possess an enhanced digestive toxic potential due to airborne PM pollution.

Particle deposition in tracheobronchial airways of an infant, child and adult.

BACKGROUND: Particle deposition in human airways is important for assessing both health effects of inhaled particles and therapeutic efficacy of inhaled drug aerosols, but is not well understood for infants and children. OBJECTIVE: We investigate particle deposition in infants and children by using computational fluid dynamics (CFD), and compare this with particle deposition in adults. METHODS: We chose three population age groups: 7-month infant, 4-year old child, and 20-year old adult. Both airway structures and breathing conditions are considered to vary as a human grows from infancy to adulthood. We investigated deposition of micron-size particles (1-10µm) in both the upper (G3-G6) and lower (G9-G12) tracheobronchial (TB) airways under sedentary conditions. RESULTS: We found that particle deposition in both upper and lower airways is the highest in an infant, next in a child, and lowest in an adult. As age increases, particle deposition decreases in the upper airways but increases in the lower. For infants, inertial impaction is the dominant deposition mechanism, thus particles are deposited more in the upper airways than in the lower. However, particles are deposited more in the lower airways than in the upper in adults, as gravitational sedimentation is the dominant deposition mechanism. CONCLUSION: Given the differences in the airway structure and particle deposition mechanisms, particle deposition in infants and children differs from that in adults, not only in the efficiency of deposition but also in the site. Our findings provide evidence that "children are not small adults".

Preconceptional and perinatal exposure to traffic-related air pollution and eczema in preschool children.

BACKGROUND: Evidence linking prenatal exposure to outdoor air pollution with eczema in early childhood is scare, and the role of components of air pollution and exposure timing remains unclear. OBJECTIVES: We investigated the association between exposure to air pollution during preconceptional and perinatal period and the risk of eczema in preschool children. METHODS: We conducted a prospective cohort study of 2598 children aged 3-6 years in Changsha, China. The prevalence of eczema was assessed by a standardized health questionnaire administered by the parents. Individual exposures to nitrogen dioxide (NO2), sulfur dioxide (SO2) and particulate matter with an aerodynamic diameter≤10µm (PM10) during the 4th-6th and 1st-3rd month before pregnancy, entire pregnancy, and three trimesters were estimated by an inverse distance weighted (IDW) method based on concentrations measured at monitoring stations. Association between childhood eczema and exposure to air pollution was examined by logistic regression models in terms of odds ratio (OR) and 95% confidence interval (CI) for an interquartile range (IQR) increase in exposure. RESULTS: Life-time prevalence of eczema in preschool children in Changsha was 28.6%. Childhood eczema was associated with traffic-related air pollutant NO2 during 3 months before pregnancy and entire pregnancy with adjusted ORs=1.19 (95% CI: 1.04-1.37) and 1.21 (95% CI: 1.03-1.42) respectively. The highest risk of eczema was observed for the 1st trimester exposure to NO2 [OR=1.26 (95% CI: 1.09-1.46)]. However, no association was detected for SO2 and PM10 exposure during any window. High-level exposure to NO2 during the whole time period significantly increased the effect of NO2 in all windows on eczema risk as compared with low-level exposure. Sensitivity analysis indicated that the association between both preconceptional and perinatal exposure to NO2 and childhood eczema was consistent and robust, and this association was modified by some personal, parental hereditary and indoor environmental factors. CONCLUSION: Our findings support the hypothesis that early childhood eczema is associated with exposure to traffic-related air pollutant during both preconceptional and perinatal period, especially at a high level of exposure.

Preconceptional, prenatal and postnatal exposure to outdoor and indoor environmental factors on allergic diseases/symptoms in preschool children.

BACKGROUND: Environmental factors have been found to be associated with allergic diseases, but it is unclear which environmental factor during which exposure window causes what kind of allergic diseases. OBJECTIVES: We investigated association between exposure to some predominant outdoor and indoor environmental factors during preconceptional, prenatal, and postnatal periods and allergic diseases/symptoms in 2598 children in China. METHODS: Children's lifetime incidence of allergic diseases and current prevalence of allergic symptoms and exposure to indoor new furniture/redecoration and mold/dampness was surveyed by a questionnaire. Exposure to outdoor air pollutants was estimated by the concentrations measured at air quality monitoring stations. Multiple logistic regression model was used to evaluate the associations between outdoor air pollutants and indoor environmental factors and allergic diseases (asthma, allergic rhinitis, and eczema) and symptoms (wheezing, night cough, and rhinitis-like). RESULTS: We found that preconceptional, prenatal, and postnatal exposure to outdoor industrial and traffic air pollutants were significantly associated with increase in the risk of childhood asthma, and also positively associated with allergic rhinitis and eczema. However, we cannot distinguish the effect of outdoor air pollutants and exposure windows because of their high correlations. New furniture was associated with eczema and allergic rhinitis during postnatal exposure, but redecoration associated with asthma and eczema during prenatal exposure. Indoor visible mold/damp stains was significant for eczema during prenatal exposure and asthma during postnatal exposure respectively, but window condensation was significant for all childhood allergic diseases during both prenatal and postnatal exposures. Allergic symptoms in children were found to be associated with exposure to indoor factors only. CONCLUSIONS: Associations between outdoor air pollutants and indoor environmental factors and childhood allergic diseases/symptoms were divergent and related to the timing of exposure.