Weiwei Liu

Early life exposure to ambient air pollution and childhood asthma in China

BACKGROUND Early life is suggested to be a critical time in determining subsequent asthma development, but the extent to which the effect of early-life exposure to ambient air pollution on childhood asthma is unclear. OBJECTIVES We investigated doctor-diagnosed asthma in preschool children due to exposure to ambient air pollution in utero and during the first year of life. METHODS In total 2490 children aged 3-6 years participated in a questionnaire study regarding doctor-diagnosed asthma between September 2011 and January 2012 in China. Childrens exposure to critical air pollutants, sulfur dioxide (SO2) as proxy of industrial air pollution, nitrogen dioxide (NO2) as proxy of traffic pollution, and particulate matter≤10µm in diameter (PM10) as a mixture, was estimated from the concentrations measured at the ambient air quality monitoring stations by using an inverse distance weighted (IDW) method. Logistic regression analysis was employed to determine the relationship between early-life exposure and childhood asthma in terms of odds ratio (OR) and 95% confidence interval (CI). RESULTS Association between early-life exposure to air pollutants and childhood asthma was observed. SO2 and NO2 had significant associations with adjusted OR (95% CI) of 1.45 (1.02-2.07) and 1.74 (1.15-2.62) in utero and 1.62 (1.01-2.60) and 1.90 (1.20-3.00) during the first year for per 50 µg/m(3) and 15 µg/m(3) increase respectively. Exposure to the combined high level of SO2 and NO2 in China significantly elevated the asthmatic risk with adjusted OR (95% CI) of 1.76 (1.18-2.64) in utero and 1.85 (1.22-2.79) during the first year compared to the low level exposure. The associations were higher for males and the younger children aged 3-4 than females and the older children aged 5-6. CONCLUSIONS Early-life exposure to ambient air pollution is associated with childhood asthma during which the level and source of air pollution play important roles. The high level and nature of combined industrial and traffic air pollution in China may contribute to the recent rapid increase of childhood asthma.

Use of mean skin temperature in evaluation of individual thermal comfort for a person in a sleeping posture under steady thermal environment

A new model to evaluate individual thermal comfort using mean skin temperature was proposed. Twenty-two subjects’ local skin temperatures were measured in a sleeping posture at air temperatures of 21℃, 24℃, 26℃ and 29℃. Mean skin temperatures were calculated using a formula with 10 measuring locations on the skin. The thermal comfort levels and thermal sensation of the subjects were also investigated by questionnaire. Based on the experimental data, an evaluation model of an individual’s thermal comfort using mean skin temperature was developed using the Mahalanobis distance discrimination method. Seventy two per cent of the total subjects’ thermal comfort levels was correctly evaluated using this evaluation model. The evaluation models were further improved by a consideration of the gender difference in mean skin temperature. The study revealed that the human mean skin temperature could be used as an effective physiological indicator to reflect an individual’s thermal comfort under steady thermal environment. The proposed evaluation model based on mean skin temperature provides an effective and simple method to evaluate an individual’s thermal comfort in a sleeping posture under steady thermal environment.

Urban Ventilation - A New Concept and Lumped Model

Abstract With the rapid development of urbanization, the economy and number of vehicles, the urban climate has worsened in recent years, causing serious urban problems including urban heat islands, air pollution and infectious disease transmission. Ventilation is indicated as one of the most effective approaches to solve these problems. Based on the traditional concept of room ventilation, the present work developed a new physical model and lumped mathematical model for urban ventilation, which is the product of both horizontal wind speed and vertical mixing layer height. This urban ventilation model was validated by a case study implemented in the city of Changsha. Both Pearson correlation analysis and principal component analysis (PCA) indicated that the urban heat island intensity and PM10 concentration are significantly negatively correlated with the urban ventilation rate, i.e. urban mixing layer height and wind speed.

The influence of air-conditioning managerial scheme in hybrid-ventilated classrooms on students’ thermal perception

Hybrid ventilation employing both natural ventilation and air-conditioning (AC) is used in Taiwanese schools as a mechanism to maintain indoor environmental quality. A field survey was conducted in two high schools in central Taiwan, one adopting a centralized management for control of AC use and the other employing a user-controlled approach, to investigate the influence of AC management scheme on thermal perception as well as the behaviours of AC usage. As shown in the results, the AC usage was significantly affected by the managerial scheme selected for AC control. When the AC was in use, the mean operative temperature (top) in the classroom regulated under central management was 2.9℃ less than the value observed in user management. The cumulative hours of AC operation in central management was three folds of the level recorded in user management. Linear regression of thermal sensation vote against top indicated a greater thermal sensitivity in the user management group to the shift of top. These findings provide insights on the attributes of adaptive thermal comfort, which may facilitate design in hybrid ventilation that balances between energy-saving and thermal comfort, particularly in areas of similar weather to that of Taiwan.