Levels of selected indoor air pollutants in three Ha Noi offices - Bich Thuy Ly

Vietnam Journal of Science and Technology 56 (2C) (2018) 148-156 LEVELS OF SELECTED INDOOR AIR POLLUTANTS IN THREE HA NOI OFFICES Bich-Thuy Ly1, Hien Thi Thu Nguyen1, Minh-Thang Nguyen1, Mitsuru Matsui2, Trang Thi Phuong Ly3, Trung-Dung Nghiem1, * 1School of Environmental Science and Technology, Hanoi University of Science and Technology, 1 Dai Co Viet, Ha Noi, Viet Nam 2Daikin Industries, Ltd., Umeda Center Building, 2- 4- 12, Nakazaki-Nishi, Kita-ku, Osaka, 530-8323, Japan 3Daikin Vietnam, 201-203 Cach Mang Thang Tam street, Ward 4, District 3, Ho Chi Minh City, Viet Nam *Email: dung.nghiemtrung@hust.edu.vn Received: 10 May 2018; Accepted for publication: 22 August 2018 ABSTRACT A study on the levels of indoor air pollutants in Ha Noi was conducted. Three offices in Ha Noi were selected for this purpose. Selected indoor air pollutants including SO2, NO2 and respirable particulate matter (PM10) were monitored in the wet and dry seasons of 2015. Air conditioners were turned on for the whole time, while air purifiers were turned on for haft of the time in each sampling site. An hourly measurement of outdoor levels was also conducted before indoor measurement. Levels of outdoor PM10 varied in the range of 13.4-106.0 µg/m3. The level of indoor PM10 varied in the range of 3.5-25.1 µg/m3. The average levels of indoor PM10 were lower than that of outdoor one in all cases. High time resolution data showed that indoor PM10 levels temporarily increased sharply by activities (walking and room sweeping) and high frequency of opening the doors. Concentrations of outdoor/indoor SO2 varied in the range of < 0.4-34.5 /< 0.4-47.1 ppb. Concentrations of outdoor/indoor NO2 varied in the range of 4.3-33.4/3.3-27.8 ppb. Keywords: indoor air pollution, PM10, SO2, NO2, air purifier, offices. 1. INTRODUCTION Nowadays, people tend to spend more time of their daily life in closed spaces thus resulting in an increasing rate of healthy problems due to the indoor air pollution. WHO (2018) has released a news saying that indoor air pollution leads to earlier death of 4 million people each year worldwide [1]. Skolnick [2] reported that a population living in the tight energy efficient buildings contracted upper respiratory diseases at rates 46 to 50 % higher than a compared group living in better ventilated houses. Indoor PM10, SO2, NO2 levels in offices in Ha Noi, Viet Nam 149 Researches on indoor air quality in Ha Noi as well as in Viet Nam are scarce. Recently, Quang et al. conducted a study on the number concentration of ultrafine particles in indoor and outdoor air in Ha Noi [3]. Occurrence of phthalate diesters in indoor air in northern Viet Nam was investigated by Tran et al. [4]. Tran et al. studied about cyclic and linear siloxanes in indoor air in northern cities in Viet Nam [5]. The levels of indoor airborne black carbon in Ha Noi was assessed by Tran et al. [6]. Indoor PM10, SO2 and NO2 have not yet been investigated in Viet Nam as far as we know. This study is designed to determine the levels of those pollutants in Ha Noi offices. 2. MATERIALS AND METHODS 2.1. Monitoring design Monitoring sites were selected to represent for three levels of air quality: good, average and bad. Map of the sites is presented in Figure 1. The sites were chosen provided that no specific pollutant source such as cooking, incense burning, etc. can directly affect indoor air quality. Both indoor and outdoor air quality were monitored in each site. Details of indoor sites and sampling positions are presented in Figure 2. Outdoor sampling positions were selected in a manner representing for ambient air quality meaning that they were not directly affected by local sources and not so close to any obstructed objects such as wall. The inlets of indoor and outdoor samplers were at 1.5-meter height. Schedule for the monitoring of indoor and outdoor air quality is presented in Table 1. The monitoring was conducted in two periods, the dry and wet seasons. For the wet season, the monitoring campaign was conducted from 15th July to the beginning of August 2015. In the dry season, the monitoring campaign was conducted from 10th Nov. 2015 to 25th Nov. 2015. All sampling days were in the weekdays without raining. Air conditioners were turned on at least 30 minutes before measurement in all sites. Air purifiers were turned on in 2/4 invested days in each site. All activities in the room during the sampling period were also recorded. Table 1. Schedule for monitoring of indoor and outdoor air at the office sites. 1st day 2nd day 3rd day 4th day Ind o o r PM10 measurement NO2, SO2 sampling O utd o o r PM10 measurement NO2, SO2 sampling Figure 1. Map of monitoring sites. 18 10 11 17 18 10 10 9 10 9 18 10 11 17 18 10 18 10 11 17 18 10 18 10 11 17 18 10 10 9 10 9 10 9 10 9 10 9 10 9 Bich Thuy Ly et al. 150 2.2. The methodology of measurement PM10 concentrations were directly measured onsite by AEROCET 531S (Met One) based on the principle of light scattering method with measuring range from 0 to 1,000 µg/m3. The collection of SO2 and NO2 samples were done using absorption method with Kimoto pump at a flow rate of 0.5 L/min in 60 minutes. SO2 from air was absorbed by the solution of potassium tetrachloromercurate (TCM) and NO2 was absorbed by the solution of sodium hydroxide and sodium arsenite. The amount of SO2 collected during sampling was determined colorimetrically accordance with MASA 704A method and the amount of NO2 was determined by reacting the nitrite ion with phosphoric acid, sulfanilamide, and N-(1-naphthyl)-ethylenediamine dihydrochloride (NEDA) and measuring the absorbance of the highly colored azodye at 540 nm (MASA 406 method). 2.3. Data analysis Statistical analysis (t-test) was carried by R software version 3.4.1. Figure 2. Description of sites: a) A site, air conditioner is a Cassette type; the indoor site is a meeting room located at the 13nd floor, the outdoor site is located at the 19th floor, b) B site, a working room located at 3rd floor in a university building adjacent with 2 main roads and a small road but more than 100 m away from each road. People coming in and out at high frequency; c) C site is at 1st floor, near a mechanical pilot laboratory. 3. RESULTS AND DISCUSSION 3.1. PM10 concentrations The levels of PM10 during the sampling time are presented in Table 2. As shown in Table 2, the PM10 levels varied with the monitoring sites and the seasons. The outdoor PM10 concentrations of the 3 sites were from 10.8 to 67.8 (mean = 38.2) µg/m3 in the wet season and from 13.4 to 106.0 (mean = 42.5) µg/m3 in the dry season. The PM10 concentration in this study is lower but comparable with previous research of Thuy et al. in which PM10 concentration was of 106.47 ± 63.95 µg m-3 [7]. Outdoor PM10 concentrations on some monitoring days were higher than WHO guideline of 50 µg/m3 for daily average [8]. On the contrary, the indoor PM10 a b c Indoor PM10, SO2, NO2 levels in offices in Ha Noi, Viet Nam 151 concentrations of these sites in the wet season and dry season were lower than the level of WHO guideline: the range were 3.5-25.1 (mean = 13.3) µg/m3 and 3.7-24.7 (mean = 11.2) µg/m3, respectively. Research of Oh et al. showed that the levels of indoor PM10 reached the range of 66.7 µg/m3-101.0 µg/m3 for 10 different childcare centers in Korea, which were much higher than those in this study although air conditioners and air purifiers were installed and fully operated in almost all of those centers (7 of 10 sites having air purifiers turned on during sampling time and the remaining sites having only air conditioners turned on) [9]. It is documented that indoor to outdoor (I/O) ratios of PM10 are close to 1 when no smokers are presented [10]. The I/O ratios are normally calculated based on simulated data. In this research, outdoor levels were measured in the period of 1 hour and earlier than indoor measurement (Figure 3). Those I/O ratios of PM10 concentrations in this study were significantly lower than 1 in all tests (data were not shown). Those low I/O ratios implied the good effect of air conditioners on the reduction of PM10 level. I/O ratio is the lowest in site A. The reason is that site A is a meeting room at elevated height and air was mainly exchanged though central air conditioner, and there was almost no activity in the room. Whereas, site C is located near a mechanical pilot experiment room and site B had a high frequency of opening the doors. To determine the effect of air purifier on PM10 removal, we conducted t-test analysis between groups of indoor PM10 concentrations when air purifiers were turned on and off. The t-test analysis showed that the difference of indoor PM10 between the two conditions were not statistical significant with p value > 0.05. Table 2. Average level of PM10 (µg/m3). Site Air purifier Wet season Dry season Date Outdoor (µg/m3) Indoor (µg/m3) Date Outdoor (µg/m3) Indoor (µg/m3) A OFF 23-Jul 57.9 ± 7.3 3.5 ± 2.4 10-Nov 31.6 ± 12.3 5.7 ± 4.0 24-Jul 61.7 ± 10.8 10.8 ± 11.4 11-Nov 25.2 ± 6.0 5.8 ± 3.0 ON 27-Jul 47.2 ± 7.6 7.7 ± 5.9 12-Nov 30.4 ± 1.6 4.3 ± 3.3 06-Aug 10.8 ± 2.0 4.0 ± 2.6 16-Nov 42.8 ± 7.7 3.7 ± 3.5 B OFF 29-Jul 12.9 ± 3.4 11.5 ± 5.9 10-Nov 13.4 ± 3.5 8.5 ± 5.6 31-Jul 38.8 ± 10.0 24.1 ± 10.0 11-Nov 26.8 ± 6.9 15.2 ± 6.7 ON 04-Aug 23.5 ± 2.7 16.0 ± 32.6 12-Nov 14.5 ± 1.8 5.0 ± 2.6 05-Aug 43.1 ± 5.8 10.9 ± 6.7 13-Nov 27.7 ± 3.7 6.1 ± 4.5 C OFF 21-Jul 27.4 ± 8.6 25.1 ± 15.2 17-Nov 55.5 ± 22.9 17.2 ± 8.4 23-Jul 67.8 ± 41.3 13.8 ± 6.5 18-Nov 106.0 ± 26.9 24.7 ± 13.7 ON 24-Jul 44.5 ± 8.7 15.1 ± 13.0 19-Nov 64.0 ± 14.3 16.9 ± 15.0 25-Jul 22.5 ± 13.3 17.3 ± 7.4 20-Nov 71.6 ± 19.0 21.6 ± 15.1 3.2. Dynamic nature of indoor PM10 Bich Thuy Ly et al. 152 The dynamic nature of indoor PM10 was clearly observed in this study. Different factors including number of people and their activities in the room clearly affected the levels of PM10. Examples of the variation in the concentration of PM10 in different cases are presented in Figure 3. When there was no activity in the room, PM10 was stably low as in Figure 3a. PM10 increased about three times comparing with normal conditions when there were activities such as performance as presented in Figure 3b. Similarly, room sweeping activity could make the level of PM10 increasing abruptly from a level lower than 20 µg/m3 to 10 folds higher (as shown in Figure 3c). The peak existed in a very short time. This phenomenon happened because such activities made the settled PM10 to resuspend. Figure 3d presents the large variations of PM10 in a room in which door was opened at frequency of about 1 time every 3 minute. The reasons for high levels of indoor PM10 can be explained as following. When the door was opened more frequently, more PM10 from outside entering the room. Besides that, the actions of opening the doors and moving of the people doing that can also make settled particles to resuspend. Figure 3. Variations in PM10 levels a) when there was no activity in a new, clean room; b) performance practice of dozen people in the room from 14 to 16 h; c) the room was swept from 12:36; d) when the door was opened at high frequency (about 1 time every 3 minute). 3.3. SO2 and NO2 concentrations Table 3 and Table 4 show the concentrations of SO2 and NO2 at the 3 sites in the wet and dry season, respectively. In the wet season, the outdoor and indoor NO2 concentrations ranged from 7.8 to 33.4 (mean = 13.3) ppb and from 3.3 to 27.8 (mean = 9.3) ppb, respectively. In the dry season, outdoor and indoor NO2 concentrations were in the range of 4.3-27.7 (mean = 12.3) ppb and 4.7-19.4 (mean = 10.2) ppb, respectively. The level of outdoor NO2 was comparable with monthly average of NO2 from February to December 2016 of 14.5-34.8 ppb in the research of Sakamoto et al. [10]. The range of outdoor NO2 in dry season were slightly lower than that in the wet season. Indoor and outdoor levels of NO2 cannot be compared because they were taken at different time. All of the measured NO2 concentrations are below the recommended value of WHO for hourly average of 106.5 ppb (200 µg/m3) [8]. Baek et. al. [11] reported that the level of indoor NO2 in Korean urban offices ranged from 9 to 58 ppb, while the outdoor level ranged from 10 to 73 ppb. The levels of NO2 in this research were lower than those in Baek’s research. a b d c Indoor PM10, SO2, NO2 levels in offices in Ha Noi, Viet Nam 153 Table 3. SO2 and NO2 concentrations in offices in the wet season (ppb). Site Air purifier Date Outdoor Indoor Start sampling time (hour) SO2 (ppb) NO2 (ppb) Start sampling time (hour) SO2 (ppb) NO2 (ppb) A OFF 27-Jul 9 9.2 8.9 10 7.3 4.5 17 11.9 5 06-Aug 9 10.7 8.4 10 8.8 3.3 17 10.3 6.7 ON 23-Jul 9 20.7 25.6 10 19.1 22.8 17 47.1 23.9 24-Jul 9 12.3 11.1 10 20.3 5 17 13.4 5 B OFF 29-Jul 9 34.5 10 10 3.8 6.7 17 5 7.8 31-Jul 9 16.8 7.8 10 14.2 5.6 17 10.7 6.1 ON 04-Aug 9 14.9 10.6 10 13.8 8.9 17 7.7 8.4 05-Aug 9 11.1 12.8 10 11.1 7.8 17 8.4 7.2 C OFF 21-Jul 9 33.7 33.4 10 47.1 27.8 17 5 7.8 25-Jul 9 12.6 7.8 10 9.6 12.3 17 8.4 5.6 ON 23-Jul 9 34.5 11.7 10 44 10.6 17 34.5 7.2 24-Jul 9 8.8 11.7 10 17.2 10.6 17 11.9 7.2 In the wet season, the ranges of outdoor and indoor SO2 concentrations were 8.8-34.5 (mean = 18.3) ppb and 3.8-47.1 (mean = 16.3), respectively. In the dry season, the ranges of outdoor and indoor SO2 concentrations were < 0.4-15.7 (mean = 9.3) ppb and < 0.4-20.7 (mean = 9.5) ppb, respectively. The outdoor SO2 concentrations in this study were higher but comparable with the annual average SO2 concentration of 4-18 ppb in inner districts of Ha Noi [12]. The range of outdoor SO2 in dry season were lower than in the wet season. Indoor and outdoor levels of SO2 cannot be compared because they were taken at different time. WHO does not recommend hourly average level of SO2. Therefore, directly comparing of hourly SO2 level with WHO guideline is impossible. However, it is still meaningful to mention that some SO2 concentrations were about some fold higher than the limit recommended by WHO guidelines for Bich Thuy Ly et al. 154 daily average of 10.6 ppb (20 µg/m3) [8]. Klinmalee et al. measured SO2 concentration in Thailand’s public buildings and revealed the results being between 1.3 and 5 ppb [13]. The sites were two universities classrooms and a shopping mall, which had some resemblances to the sites in this study. Those results indicated that indoor SO2 levels in Thailand were much lower than those in Viet Nam. Table 4. SO2 and NO2 concentrations in offices in dry season (ppb). Site Air purifier Date Outdoor Indoor Start sampling time (hour) SO2 (ppb) NO2 (ppb) Start sampling time (hour) SO2 (ppb) NO2 (ppb) A OFF 10-Nov 9 15.3 7.2 9 8.8 4.7 10 14.2 5.9 16 15.7 7.8 16 10.3 6.3 17 10.7 10.7 11-Nov 9 12.3 10.2 10 7.7 6.7 16 9.2 18.3 17 20.7 5.7 ON 12-Nov 9 <0.4 8.1 10 20.3 8.7 16 6.1 8.1 17 7.3 10.2 16-Nov 9 11.5 4.3 10 10.3 8.2 16 6.1 11.8 17 6.5 14.1 B OFF 10-Nov 9 14.6 10.4 10 5.7 8.3 16 6.5 8.4 17 7.3 9.1 11-Nov 9 7.7 27.7 10 6.9 12.3 16 8.8 9.3 17 6.5 9 ON 12-Nov 9 8.8 22.6 10 6.5 9 16 6.1 20.1 17 6.5 8.1 13-Nov 9 13.8 10.3 10 16.1 12.3 16 6.1 9.1 17 20 19.4 C OFF 17-Nov 9 10.4 20.6 10 8.4 6.8 16 <0.4 6.5 17 5.4 11 18-Nov 9 5.4 19.9 10 3.5 17.1 16 7.7 9.3 17 3.8 11 ON 19-Nov 9 12.3 11.1 10 8.4 14.2 16 14.1 6.1 17 11.1 14.3 20-Nov 9 12.3 15.9 10 13.8 13.1 16 11.5 10.9 17 <0.4 9.8 Indoor PM10, SO2, NO2 levels in offices in Ha Noi, Viet Nam 155 4. 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