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PERSONAL EXPOSURE ASSESSMENT OF FINE PARTICULATE MATTER FOR COMMUTERS IN HANOI

Received: 25/12/2020 Epidemiological studies showed that commuters exposed fine particles (PM2.5) have adverse health effects and cause diseases. Comprehensive personal exposure studies have been limited in Vietnam. This study aimed to assess the exposure of PM2.5 to motorcyclists and cyclists on some roads in Hanoi. Personal exposure samples were taken by the Airbeam sensor. Preliminary results showed that the exposure concentration of PM2.5 for cyclists (105 μg/m) was higher than for motorcyclists (95 μg/m) and level of PM2.5 in ambient air (34 μg/m). Influencing factors were also assessed in this study. PM2.5 exposure concentration was the highest in the morning and decreased at noon and in the afternoon for both types of vehicles. Exposure concentrations of PM2.5 highly fluctuated during peak hours. The bicyclists were at higher risk than the motorcyclists due to higher inhalation dose. The findings provide initial warnings about the health impacts to commuters to the managers to give timely interventions. Revised: 13/5/2021


Introduction
Air pollution is a global-scale problem while fine particulate matter (PM2.5) is considered as a major cause of illnesses such as respiratory, heart disease, and stroke [1]. The global air quality report stated that seven million people were estimated to die each year due to the ambient air, in which 2.5 million deaths were from cardiovascular diseases and 1.4 million deaths due to lung-related diseases and lung cancer. WHO report stated that the mortality ratio for the patients associated with heart and lung diseases raised by 6-13% when PM2.5 levels increased by 10 µg/m 3 [2].
Many studies of particulate matter personal exposure to the commuters with various vehicles have been carried out worldwide [3]- [6]. A study in California showed that exposure to PM2.5 during commuting accounted for 28-55% of the total exposure level and bicyclists exposed the most [3]. The exposure level depends on the type of vehicles as well as the characteristics of the roads. Another research was also conducted in Arnhem, Netherlands to evaluate PM2.5 exposure to bicycle riders on two roads with different traffic density. The results showed that the higher the traffic density of the road, the higher the exposure level and the more harmful it was to the health of commuters [5]. Other PM2.5 exposure studies in high traffic density countries in Asia, such as India and Thailand, were also publised. These studies assessed the level of exposureamong buses, cars, and motorcycles at different periods of the day. The morning exposure level was higher than the evening for all vehicles in India [6]. Exposure to PM2.5 during traveling by subway was the lowest, compared with buses, taxis, and motorcycles in Bangkok [7].
Currently, many big cities in Vietnam are facing high levels of PM2.5. Monitoring data in recent years have shown that PM2.5 concentrations in urban areas exceed national standards many days in a year [8]. Air pollutant emissions from traffic predominate in Vietnam due to increasing the number of vehicles, in which the motorcycles account for over 90% of total vehicles [9]. More than 60,000 people died in 2016 due to air pollution caused by heart disease, stroke, lung cancer, and chronic obstructive pulmonary disease were reported in 2016 [2]. However, studies on personal exposure by PM2.5 have been limited. Most studies were evaluating the impact of air pollution on public health using concentration of PM2.5 in ambient air, rather than personal exposure concentration. One of the most recent exposure studies conducted in Ho Chi Minh City in 2017 provided preliminary information on PM2.5 exposure to the community. The personal exposure concentration of PM2.5 was higher than the level of PM2.5 in the ambient air at the stationary monitoring stations and it is noticeable that those values exceeded the threshold of the ambient air quality standard value in the QCVN 05:2013/BTNMT [8], [10]. Therefore, the impact on PM2.5 exposure on commuters should be in attention. Studying personal exposure to PM2.5 from traffic activities is practical and necessary to take any intervention to protect public health. The objectives of this study are i) to determine personal exposure concentration by PM2.5 to bicycle and motorbike riders on some routes in Hanoi at rush hours; ii) to compare the concentrations of personal exposure with those of ambient air concentrations; and (3) to estimate PM2.5 exposure level for each transportation mode.

Site description
Five routes in Hanoi were selected, including major arteries (Giai Phong and Nguyen Trai), residential roads (Lines around Hoan Kiem Lake, and Ho Chi Minh Mausoleum), and internal lanes (Vinhome riverside urban area). Major arteries are the representative for a multi-lane, twoway route with a large number of vehicles. The residential road is mainly intersection roads, densely populated areas, and have many political, cultural, and commercial centers surrounded. Internal lanes in Vinhomes Riverside urban area are characterized as the background due to low impact from traffic activities and economic-industrial activities. The characteristics and locations of the routes are shown in Table 1 and Figure 1.

Sampling strategy
The personal exposure measurement by PM2.5 was conducted by Airbeam sensors within the breathing zone during commuting, following the USEPA guideline [12]. The exposure measurement study was performed 3 times per day at rush hours (7:00 -8:00, 13:00 -14:00, and 17:00 -18:00) continuously for three days on different routes from March to April 2018. The devices were worn on the chest (in the breathing zone) for the motorcyclists and bicyclists during sampling periods. The data was recorded minutely and the aircasting application was used to display the data and saved daily as MS excel format. GPS data acquired through the Longer GPX application has recorded the route as well as to determine the moving speed. The meteorological data (temperature, humidity, wind direction, wind speed) and PM2.5in the ambient air were collected from the website [13], [14].

Data processing
This research used R software version 3.5.2 to conduct corelation analysis among research subjects by "paired sample t-test".

Traffic density surveillance on routes
Traffic volume was determined simultaneously during personal exposure measurement by counting vehicles in the recorded video. High traffic density mainly occurred during rush hours in the morning (7h-8h) and afternoon (17h-18h). The traffic volume decreased at noon (13h-14h). The results presented that the traffic volumes of major arteries (Nguyen Trai and Giai Phong) were higher than residential roads (Lines around Hoan Kiem Lake and Ho Chi Minh Mausoleum) and internal lanes of Vinhome urban area. h). The large variation in traffic density was due to the difference in the structure, size, and type of the roads. The average speed was maintained at 12 km/h and 20 km/h for bicycles and motorbikes respectively. GPX software was installed on mobile phones for easy tracking and speed control.

Variation of exposure concentration of PM2.5
The statistical values of the exposure concentration to PM2.5 during traveling by bicycles and motorbikes show that the personal exposure levels to PM2.5 of the motorcyclists varied from 32-190 µg/m 3 (mean value of 95 µg/m 3 ), whereas, those of PM2.5 for the cyclists varied from 30-195 µg/m 3 (mean value of 105 µg/m 3 ). The concentration of PM2.5 in the ambient air from the US embassy station varied from 15-83 µg/m 3 (mean value of 34 µg/m 3 ). Personal exposure levels by PM2.5 for the cyclists in this study were higher than those in Ho Chi Minh City (64 µg/m 3 ) [11] and the Netherlands (72 µg/m 3 ) [5], wherease, the personal exposure concentrations of PM2.5 to the motorcyclists were lower than those in Bangkok (136 µg/m 3 ) [8] and India (222 µg/m 3 ) [7]. In case in Ho Chi Minh City, the lower PM2.5 concentrations in ambient air than those in Hanoi can lead less personal exposure concetrations to PM2.5 despite more traffic modes. It is ascribed to prefered meterological and topographic conditions which may faciliate the air disperion. The exposure concentrations to PM2.5 varied in different sampling locations due to disimalities on ambient air quality and characteristics of sampling, traffic, meterological and topographic conditions. In addition, personal exposure by PM2.5 of cyclists and motorbikers were three times higher than PM2.5 in the ambient environment, which were consistent with previous studies [11], [16].
Personal exposure concentration to PM2.5 during riding by bicycle and motorbike at different times is shown in Figure 2. PM2.5 exposure concentrations for motorcycles were 112 µg/m 3 , 90 µg/m 3 , 84 µg/m 3 while those for bicycles were 119 µg/m 3 , 105 µg/m 3 and 94 µg/m 3 in the morning, noon and afternoon, respectively. Exposure levels were the highest in the morning and lower in the afternoon and noon for both vehicle types. The difference in personal exposure concentrations may be due to meteorological factors, traffic volume and ambient air condition. The highest exposure concentration and ambient air in the morning may be due to a high volume of traffic in the morning (8162 vehicles/h), in the conditions of low temperature and wind speed (vtb<1 m/s), high humidity, resulting in PM2.5 elevation. The low temperature in the morning may cause the heat inversion, preventing the air mass below the ground to move up. Besides, high humidity also can make PM2.5 adhere to create the coarse particles, facilitate the settling in the low atmosphere, consequently, concentration of particles tends to be higher [17]. Although the afternoon (rush-hour) also has a comparable traffic volume (8118 vehicles/h), the high wind speed (vtb = 5m/s) facilitates the dispersion, leading to a lower exposure concentration than in the morning. The variation of personal exposure concentrations to PM2.5 in this study are consistent with the trend in India and China [6], [16]. Personal exposure to PM2.5 during commuting depends on several factors such as number of vehicles (density), and microclimate conditions such as temperature (T), humidity (RH), wind speed (V). These influencing factors were all correlated and shown in Figure 3. PM2.5 exposure concentrations of motorcyclists (PM2.5 XM) were strongly correlated with those of bicyclists (PM2.5 XD) (r = 0.76) and ambient air (DSQ) (r = 0.69), in which the correlation between motorcyclists and ambient air was medium (r = 0.43). It is attributable that PM2.5 can be generated from the same source [15]. The correlation between vehicle volume and exposure concentration for motorcyclist (r = 0.51) and bicycle (r = 0.6) was moderate, but then a weak correlation was observed for vehicle volume and ambient air (r = 0.25). The correlation between http://jst.tnu.edu.vn 52 Email: jst@tnu.edu.vn temperature and PM2.5 exposure as well as ambient PM2.5 in the study was negative, meaning that the rising of temperature made PM2.5 concentration decrease. There was not consistent correlation between humidity (RH) and exposure PM2.5 concentration. These correlation results are consistent with personal exposure to the commuters in Turkey [18].

Variation of exposure among different route
The exposure concentrations of PM2.5 and PM2.5 in ambient air are shown in Figure 4. The exposure concentrations of PM2.5 for bicycle and motorcycle riders varied in different routes as following: Nguyen Trai > Giai Phong > Hoan Kiem > Ho Chi Minh Mausoleum > Vinhomes. The two routes (Nguyen Trai and Giai Phong) had the highest fleets at peak hours, while those at the background as Vinhome lanes were the lowest.
The variation coefficients were determined to assess the variation of the PM2.5 exposure concentration for bicyclists and motorcyclists by time. The variation coefficients were in the range of 4-16%; 12-18%; 4-15% in the morning, afternoon and noon for the motorcyclists, respectively; whereas, those varied from 3-25%; 9-24%; 5-25% in the morning, afternoon and noon for the bicyclists, respectively. More significant variations were seen in peak hours, which agrees with the study in India [6]. Meanwhile, PM2.5 concentration in the ambient air fluctuated slightly (1-3%). There is insignificant difference of PM2.5 exposure between the two major arteries (Nguyen Trai and Giai Phong) and the residential roads (Hoan Kiem Lake and Ho Chi Minh Mausoleum lines). In contrast, a significant difference in the concentration of PM2.5 was observed among major arteries, residential roads, and internal lanes (Vinhomes). Internal lanes (Vinhomes) could be regarded as an urban ground road. This area is far from residential areas, less impacts on outside traffic and industrial activities, and a new infrastructure system. It is worth noting that the exposure concentration of PM2.5 for bicyclists and motorcyclists were higher than the ambient PM2.5 at morning, noon, afternoon during sampling campaign. PM2.5 exposure concentrations for bicyclists were greater than those of motorcyclists in major arteries and residential roads.

Exposure levels of PM2.5
The inhalation doses of PM2.5 during commuting by motorcycle and bicycle depended on physical activities. According to the USEPA's physical activity classification (2011), riding a motorbike is considered a light activity, and riding bicycle is medium activity. The parameters were referenced from the USEPA exposure handbook [15] and field measurements. The exposure doses during riding bicycle and motorbike were estimated by the formulas (1,2). The exposure doses by PM2.5 during riding motorcycle and bicycle were presented in Figure 5. The temporal variation of the exposure doses of PM2.5 were due to different exposure concentrations of PM2.5 at different moments during riding motorbike and bicycle. The personal doses of PM2.5 in the morning, noon, afternoon were 63 µg/h, 47 µg/h and 44 µg/h for the motorcyclists and 116 µg/h, 78 µg/h and 88 µg/h for the bicyclists, respectively. The higher dose of PM2.5 for a bicyclist was due to a higher inhalation rate for heavier physical activity.