The Determinants of Mass Concentration of Indoor Particulate Matter in a Nursing Home

The study was conducted to evaluate the determinants of mass concentration of indoor particulate matter in a nursing home located in Taichung, Taiwan. PM2.5, PM10, temperature, relative humidity, CO, CO2, O3 and colony counts were collected in 2 bedrooms and their adjacent outdoor environments from November 2009 to January 2010. The results of multiple regression analysis suggested that the explanatory variables which included outdoor particle concentrations, indoor occupancy, different types of activities and ventilation accounted for 40.9% and 63.4% of the variance in the indoor PM2.5 concentration in Room A which is close to neighboring buildings and Room B which is close to main traffic, respectively. The explanatory variables accounted for 49.1% and 85.5% of the variance in the indoor PM10 concentration in Room A and B, respectively. Moreover, the result of correlation analysis showed that both indoor PM2.5 and PM10 concentrations were correlated to temperature, relative humidity and CO.


Introduction
To maintain people's health and quality of indoor living environment, "Recommended Indoor Air Quality Value" was publicly announced by EPA, Taiwan in 2005. The announced parameters include CO 2 , CO, HCHO, TVOC, bacteria, fungi, PM 2.5 , PM 10 , O 3 and temperature. Particulate matter (PM), as one of the indicators to quantify the air quality of Taiwan [1], has been reported to have harmful effects on human health. Higher blood pressure and increased heart rate have been proved to be associated with indoor particles [2]. PM 10 , referred to particles of 10 µm or less in aerodynamic diameter, can deposit in the bronchi and lungs and have been demonstrated to cause lung disorders, respiratory and cardiovascular diseases [3]. PM 2.5 , referred to particles of 2.5 µm or less in aerodynamic diameter, tends to penetrate the alveoli in the lungs and has been shown to significantly correlated with cardiopulmonary disease and lung cancer [3].
Indoor particles can be generated from both indoor and outdoor sources. Indoor sources include use of combustion devices and indoor activities such as walking, children playing, cleaning, cooking, smoking, religious practice of incense burning and mosquito coil incense burning etc. [3, 4,  1. to evaluate the determinants of mass concentration of indoor particulate matter; 2. to explore the relationships between indoor particulate matter and the measured parameters.

Experimental methods
Site description. Residents in nursing homes are mostly elderly who suffer from chronic diseases with weaker immune system. More than half of them are physically restrained on bed when they are awake. Therefore, the investigation of the determinants of indoor particulate concentration is beneficial in maintaining residents and caregiver's health. The study was conducted in a nursing home located in Taichung County, Taiwan. In order to investigate the relationships between indoor and outdoor particulate levels, Room A which is close to neighboring buildings and Room B which is close to main traffic ( Fig. 1)  Measuring Parameters. The selection of the measuring parameters was based on the parameters of "Recommended Indoor Air Quality Value." Since the interior decoration capacity of the nursing home is low, HCHO and TVOC were excluded in the study. Bacteria and fungi were replaced by colony counts. Relative humidity was included due to the indoor climate conditions is one of the contribution of indoor air quality. Therefore, the measuring parameters of the study included PM 2.5 , PM 10 , temperature, relative humidity, CO, CO 2 , O 3 and colony counts. Other parameters taken into account were the weather conditions, indoor occupancy, indoor activities and room ventilation.
Sampling methods. Two portable aerosol particulate monitors (Aerocet 531/Met One) were used to monitor PM 2.5 and PM 10 . Both of these aerosol samplers were factory calibrated before the sampling test. The samplers were operating at a flow rate of 0.1cfm with 2 minutes sample interval. Indoor and outdoor PM 2.5 /PM 10 samples were concurrently collected between 9:00am to 11:30am,

Applied Mechanics and Materials Vols. 44-47 3027
once every two weeks from November 2009 to January 2010. The inlet of indoor particulate sampler was set at 90cm above floor (as the level of the breathing zone of a lying nursing home resident) and 90cm from the wall (to avoid disturbing residents) between each bed in both rooms. The numbers of sampling points in Room A were 6 and in Room B were 5 (Fig. 2&3). Due to the site accessibility, the inlet of the outdoor particulate sampler for Room A was set at 110cm above floor and 60cm from window A (Fig. 2), while the inlet of the outdoor sampler for Room B was set at 110cm above floor and 30cm from window B (Fig. 3). The parameters of temperature, relative humidity, CO, CO 2 and O 3 were monitored by AirBoxx/KD Engineering with 1 minute sample interval. Colony counts were sampled by MAS-100NT in 5 minutes sampling time in each sampling point. Agar used was BAP which contained 5% sheep blood. Petri-dishes were cultured in a 37 ° C incubator for 24 hours. Colony calculations were done afterward.

Results and discussion
Activities observed in the bedrooms of the nursing home could be divided into two categories.
Activity 1 referred to activities with torso and hand movements only, such as standing, talking and nursing activities. Activity 2 referred to activities involved whole body movements, such as walking, nursing cart moving and wheelchair moving. The mean indoor PM 2.5 and PM 10 concentrations in Room A were 4.9 and 23.0 µg m -3 , respectively. The corresponding mean outdoor levels were 9.8 and 27.8µg m -3 , respectively. By contrast, the mean indoor PM 2.5 and PM 10 concentrations in Room  and temperature (r=.721, p<0.01), medium correlation between indoor PM 10 and colony counts (r=.609, p<0.01), low correlations between indoor PM 10 and RH, CO concentrations. The results suggested that higher temperature and relative humidity were along with higher PM concentrations. concentrations were correlated to temperature, relative humidity and CO. A detailed study of why lower CO concentrations was along with higher PM concentrations should be carried out to have better understandings of indoor air quality.