In the last decade, numbes of bus and bike commuters increased due to the public concern in environmental and health issues. Because of being close to roadways, bus and bike commuters could be exposed to considerable amount of air pollutants. Therefore, their personal exposure to air pollution could increase even though these transportation modes might improve the overall air quality.
This study was conducted through a series of field campaigns to investigate the distribution of air pollutants near the bus and bike lanes in Taipei City. The Bus campaigns were conducted in Feburary to March and August to early September while the Bike campaign was conducted in July to early August. Selected volatile organic compounds (VOCs) and fine particulate matter (PM2.5) mass concentrations were measured at 6 sites on Xinyi Road (H1-H6) and 6 sites on Songjiang Road/Xinsheng South Road (V1-V6). In addition, vehicle detector (VD) and land use data were collected to examine their associations with VOCs and PM2.5 measurements using a mixed effect model.
Each site was monitored for one week. The average PM2.5 mass concentration was 20.51 μg/m3 (Range of mean: 12.14－33.77 μg/m3) at bus stops and 16.29 μg/m3 (9.43 －20.99 μg/m3) at bike lanes during the monitoring periods. The differences of average concentrations were less than 5 and 7 μg/m3 among sites monitored in the same week for the bus and bike campaigns. For the bus stops, two studies showed that the PM2.5 measurements ranged from 120 to 248 and 37 to 40 μg/m3 in Delhi and Hong Kong, respectively. There was also a mean result of 25 μg/m3 measured on the bus in Spain. For the measurements on the bike or in bike way, there are several study results: 285 μg/m3 in Deli, 71.61－88.14 μg/m3 in Ireland, 49.10 μg/m3 in China, 39－46 μg/m3 in Hong Kong, 29 μg/m3 in Spain, 23.1 μg/m3 in Italy, 5.24－10.9 μg/m3 in USA, and 3.5－3.8 μg/m3 in Belgium. Among the selected VOCs at all sites, toluene had the highest concentrations. In general, the measurements at bus stops and bike lanes were higher than those measured at the surrounding air quality monitoring stations of Taiwan EPA, indicating that the exposures are different between in atmospheric environment and in microenvironment.
In addition, peak exposurs also should not be ignored.
We used the mixed models to exame the assocaitons between air pollutants, vehicle fleets and land-use variables after controlling the meteorogical factors. During the bus monitoring periods, number of large vehicle (NL), number of small vehicle (NS), and number of motorcycle (NT) were significantly associated with most of the pollutants while lengh or area of rodas were the main significant land-use variables. Further analysis identified significant effects of emission standards of buses (i.e., number of phase 4 buses > number of phase 5 buses) for Benzene and BTEX. During the bike monitoring period, the single-vehicle type model showed that the number of total vehicle (NTV), NL, NS and NT were siginificantly associated with all the pollutants other than the association between NL and PM2.5, Toluene, Ethylbenzene and o-xylene. In the multi- vehicle type models, the NS and NT were signigcantly and positively associated with most pollutants.
This study indicates that the levels of pollutants at the bus stops and along the bike lanes are mainly affected by the number of nearby vehicle fleets, especially by the fleets of motorcycle and small vehicles. The relatively low proportion of NL to NTV may explain its non-significant effects in this study. On the other hand, it was difficault to differentiate the effects between phase 4 and phase 5 buses on PM2.5 levels at bus stops. In order to reduce the exposures and improve the air quality for the comuters, the clean zone plocy might be needed. In addition, by assessing the traffic flows along the bus lanes or bike ways, the proper communication or biking periods could be suggested to the public.
