A Natural Approach to Improving Winter Indoor Air Quality for Clinics in China

  • Hao Mu

    Student thesis: Doctoral ThesisDoctor of Philosophy


    The threat of air pollution to health has become the focus of attention, especially in cities in developing countries (Cao et al. 2018). In China, “Haze days” often occur in winter, especially in Shandong Province (Yang et al. 2021). Exposure to this toxic outdoor air has led to an exponential increase in the number of clinic visits (Chiang et al. 2021). However, it is worth noting that hospitals’ indoor air quality (IAQ) faces many problems (Leung and Chan 2006), including formaldehyde (HCHO) and carbon dioxide (CO2) pollution, and poor perception of IAQ. Plants may be a natural and sustainable solution to improve hospital IAQ. Some experiments have demonstrated the ability of plants to remove indoor gas pollutants (Brilli et al. 2018). Furthermore, exposure to a natural environment has a positive impact on human health and well-being (Yin et al. 2018). Consequently, this research aims to determine if placing indoor green plants can act as a natural method improve the clinical IAQ in China. This research was divided into four main phases. Initially, comprehensive literature reviews of hospitals’ IAQ, and the impact of plants on IAQ and occupants were undertaken. This identified the potential research gaps. A semi-structured interview A collected and analysed initial data, including determining the sample hospital, evaluating influencing factors on IAQ, and selecting indoor plants along with their placement. In the second phase of this research, subjective and objective assessments of four clinics investigated both the perceived IAQ of occupants and the IAQ index (indoor temperature, relative humidity, CO2 and HCHO concentration). Thirdly, two experiments were carried out based on clinic and laboratory environments to evaluate the actual impact of plants on IAQ, their impact on the occupants of the clinics, and the plants’ ability to absorb HCHO. Finally, the results of semi-structured interview B provided subjective supplementary information on the influence of plants on both IAQ and occupants. After interview B, the results of each research step were combined to conduct a conclusive assessment. The subjective surveysfound that hospital staff were more satisfied with IAQ than visitors. Medical staff consider clinics to be their workplaces, whereas the hospital environment is often associated with feelings of fear, uncertainty, and anxiety for visitors (Dijkstra, Pieterse, and Pruyn 2008). It was determined that plants can provide a relatively relaxing and pleasant indoor environment and relieve the stress of visitors to clinics. Plants also have a positive impact on the work efficiency of staff in the clinics and can alleviate their physical symptoms whilst working. Placing plants in more conspicuous places (such as on a windowsill) will help increase their positive impact on the occupants. Objective assessments found that overheating problems occurred in the clinics in winter. It is therefore recommended to use electric heaters reasonably and to control the room temperature at an appropriate range (18 - 24 °C) to avoid low relative humidity (RH) caused by overheating. Plants cannot effectively improve indoor RH. It is further recommended to use a humidifier in the clinics to increase RH and relieve the staff members’ dryness symptoms (Hashiguchi et al. 2008). Through the laboratory-based experiments, this study determined the efficiency of certain plants to remove HCHO, namely C. comosum and E. aureum. Under the conditions of constant temperature and RH and a background concentration of HCHO (0.015 - 0.05 mg/m3 ), the removal rate ranges of C. comosum were 0.003 - 0.004 mg/m3 per hour during the daytime and 0.0008 - 0.001 mg/m3 per hour at night. The removal rate ranges of E. aureum were 0.001 - 0.003 mg/m3 per hour during the daytime and between 0.0007 to 0.001 mg/m3 per hour at night. Plants therefore can reduce indoor CO2 and HCHO concentrations in clinics. It is also worth noting that the removal efficiency of plants is slow and continuous. The difference is not statistically significant due to the complex influencing factors in the actual clinic environment, especially human activities. Due to outdoor pollution in winter and the need to conserve indoor heating, the doors and windows were closed for most of the time. A high CO2 concentration was also recorded in the clinics. Hence, this study suggests installing mechanical supply and exhaust ventilation systems (Simanic et al. 2019). It should also be noted that in winter, haze weather frequently occurs, and the main pollutant is particulate matter (PM). Filters are therefore suggested to be used at outdoor air intakes to remove PM (Zhang et al. 2011). Although the ability of plants to remove HCHO was determined in a laboratory environment, the method of simply placing green plants in clinics cannot effectively and directly improve IAQ. Hence, combining indoor plants with other air purification technologies (such as ultraviolet germicidal irradiation, sorption, and filtration) and making comprehensive use of their respective advantages will be a major trend in future research.
    Date of AwardDec 2021
    Original languageEnglish
    Awarding Institution
    • Coventry University
    SupervisorAbdullahi Ahmed (Supervisor), Araz Agha (Supervisor), Shuli Liu (Supervisor) & Ashish Shukla (Supervisor)

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