Study on the air pollution in typical transportation microenvironment: Characteristics and health risks

Abstract

The concentration of formaldehyde in micro-traffic atmospheric environment (including buses, cars, bus stations, and traffic artery) of Lin’an City was carefully investigated. The results showed that the formaldehyde average concentration was 0.0162 mg/m³ in the buses, 0.0225 mg/m³ in the cars, 0.0047 mg/m³ in the West Bus Stations, and 0.0133 mg/m³ in the East Bus Stations. The concentration of formaldehyde along the traffic artery decreased with the height increased. From 0 to 140 cm, the formaldehyde concentration decreased from 0.031 to 0.018 mg/m³. The formaldehyde concentration decreased when far away from the traffic artery. When the distance reached 200 m, the formaldehyde concentration decreased from 0.018 to 0.005 mg/m³. Based on the health risk assessment model, using 1 hr as the average retention time, the average health risk in buses, cars, and West/East Bus Stations was 2.106 × 10⁻⁴, 2.925 × 10⁻⁴, and 1.157 × 10⁻⁴, respectively.

Implications: The data of carbonyl concentrations in transportation microenvironment in China are limited. In this paper, the authors investigated carbonyl levels in selected transportation microenvironment, discussed the possible sources of indoor carbonyls, and assessed health risks for carbonyls inside transportation microenvironment.

Introduction

Air pollution has been one of the key points of environmental workers both at home and abroad with the development of “person is the core” (Hauptmann, 2004). From the view of human breath exposure, the human living environment can be divided into these three important parts: indoor environment, outdoor atmosphere, and transportation microenvironment. Based on the investigation of human activities by the U.S. Environmental Protection Agency (EPA), the time of human activities spent on these three environmental parts were at rates of 85%, 7%, and 8%, respectively (EPA, 1989). Nowadays, the pollution of indoor air has received high attention (Baez et al., 2003; Khoder et al., 2006; Golden et al., 2011; Abdel-Salam et al., 2013); in China, the pollution of indoor air has received some attention (Xu et al., 2012; Cheng et al., 2014), but the air pollution of transportation microenvironment has not received enough attention to match with the popularization of cars, whereas the pollution of air by transportation microenvironment in foreign countries has been received high attention (Johnson et al., 2014).

Nowadays, cars have gradually become part of people’s life, but together with the convenience to people’s life, the car also brings the problem of environmental pollution, especially the pollution of formaldehyde. The formaldehyde pollution in cars and other traffic microenvironment comes from different sources. Firstly, the potential sources are the contamination of plastic accessories installed in the vehicle, such as the carpet and sofa release. This kind of pollution mainly involves volatile organic compounds, with the car containing plastic, rubber, fabric, leather, paint, and adhesive materials. Secondly, during the car in use, pollutants discharged from the exhaust pipe, fuel evaporation emission, can come from the ventilation system of the car into the compartment. The pollutants of vehicle emission will cause environmental pollution along the traffic artery, producing photochemical smog. When the vehicles are close, one car’s exhaust pipe just in front of the next vehicle’s air inlet, large amount of pollutants will come into the car from the ventilation system of the car, this becomes one of the main sources of the vehicle air pollution.

Therefore, this paper investigated the formaldehyde concentration of the Hangzhou Ling’an City typical traffic microenvironment (including buses, taxis, and bus stations, etc.) and traffic artery. Based on the quantitative health risk analysis, this paper provided basic data for formaldehyde pollution in transportation microenvironment analysis and health risk assessment.

Experimental

Sampling

Constant-flow-rate samplers were used for determination of formaldehyde concentration of various kinds of traffic microenvironment with the ventilation conditions on, such as in the buses, taxis, bus stations, and traffic trunk. The sampling methods were as following: sampling 10 L air at a gas flow rate of 0.5 L/min with a large bubble absorption tube with 5 mL absorption liquid inside. The bus station air samples were taken in the middle of the sampling area at approximately 1.50 m above the floor inside the waiting room, and the sampling point temperature and atmospheric pressure were measured. The samples should be analyzed within 24 hr at room temperature after sampling. Each point was sampled three times, with the average value as the result for analysis. The typical sample points were as follows: 5 typical the running buses, 3–5 taxis, 6 bus station selecting points. The main road alongside air was also sampled based on different distances (five points, each point at a distance of 50 m) and different heights, with the height between 0.5 and 1.5 m.

Analysis

The concentration of formaldehyde was determined with phenol reagent spectrophotometry, which is the National Standard Methods of China (GB/T 18204.26-2000), and the concentration of formaldehyde in air was calculated by eq 1.

(1)

where C is formaldehyde concentration (mg/m³), A is absorptance of the solution, A₀ is absorptance of blank solution, B_g is computation factor (μg/absorptance), and V₀ is sampling volume at standard condition (L).

Results and Discussion

Formaldehyde inside bus and taxi microenvironment

Bus and taxi are major public transportation. Based on the analysis of the age of the car and car decoration conditions, five buses, no. 2, no. 3, no. 6, no. 7, and no. 11, and four taxi cars were selected and the air inside was sampled, with the weather being sunny. The formaldehyde concentrations measured are shown in Table 1.

Table 1. Concentrations of formaldehyde in buses

Bus	Concentration (mg/m^3)
No. 2	0.010
No. 3	0.022
No. 6	0.017
No. 7	0.014
No. 11	0.018

The sampled buses were built and used above 5 yr and without any new furniture. The no. 0 diesel oil was used as fuel, and the buses were driven with good air refreshing. The temperature of inside of the buses would influence the concentration of formaldehyde. As shown in Table 1, no. 2 had relative low concentration of formaldehyde, whereas no. 3 had a higher concentration. This was because there were few people (less than 5) in no. 2 bus, whereas the no. 3 bus was crowded with students after school. As was reported (Mentese and Gullu, 2006; Seaman et al., 2007), human activities, such as smoking, would enhance the formaldehyde pollution. Therefore, we could draw the conclusion that the people inside the bus would contribute to the formation of formaldehyde, and the concentration would be higher with increase in passengers.

As shown in Figure 1, the concentrations of formaldehyde in the taxis were 0.019, 0.028, 0.022, and 0.021 mg/m³, which were slightly higher than the concentrations of formaldehyde in the buses. The differences were mainly due to the actual sampling conditions, because the air sampled in the taxis was in a relative closed condition when driving. The four taxis all used no. 93 gasoline as the fuel, and taxis A, C, and D was more than 4 years after the beginning of use, whereas taxi B was less than half a year after use. As was reported, the formaldehyde and other air pollutants would emit from the car decoration materials and the results showed that temperature would influence the organic concentration more obviously than other factors (Jo and Lee, 2002; Mapou et al., 2013; Smith et al., 2013). According to Figure 1, we could find that the formaldehyde concentration in taxi B was far higher than other three cars, so it can be speculated that the formaldehyde concentration inside was influenced by the car-using conditions and car decoration materials. The newer the parts of the car, the higher the concentration of formaldehyde would be.

Figure 1. Concentrations of formaldehyde in taxis.

Formaldehyde inside bus stations

There are two long-distance bus stations in Ling’an City, including West Bus Station and East Bus Station. Both of the air samples were collected, and each was sampled at three points with the sampling weather being sunny. The analysis results of the samples obtained are listed Table 2.

Table 2. Concentrations of formaldehyde in West and East Bus Stations

	Formaldehyde Concentration	Average Concentration
Bus Station	(mg/m^3)	(mg/m^3)
West Bus Station 1	0.005	0.0047
West Bus Station 2	0.004
West Bus Station 3	0.005
East Bus Station 1	0.009	0.0133
East Bus Station 2	0.019
East Bus Station 3	0.012

Since the East Bus Station expansion in December 2010, after the operation most vehicles have moved to the East Bus Station. From Table 2 it could be seen that the average concentration of formaldehyde of the East Bus Station in first half-year of 2011 was 0.0133 mg/m³, which was significantly higher than the average concentration of West Bus Station at 0.0047 mg/m³. Thus, the formaldehyde concentration increased with the passenger flow and vehicle increasing, so the exhaust emissions of vehicles were the main source of the formaldehyde in the air of bus stations.

Formaldehyde in air of main traffic artery

The air alongside the main traffic artery of Ling’an City was sampled. The road east around the city was selected as the sampling road, and air samples were collected from five different heights, which were heights from the ground level: 0, 40, 70, 100, and 140 cm, respectively. Then, the distance away from the starting point was measured at five points. The height from the ground of 140 cm was set as a uniform height, the total five points were from the starting point of 0 cm, then the distances of other points from the starting point were 50, 100, 150, and 200 cm, respectively. The results were shown in Figure 2 and Figure 3.

Figure 2. Concentrations of formaldehyde at different heights.

Figure 3. Concentrations of formaldehyde at different distances.

As shown in Figure 2, the concentration of formaldehyde at a height of 0 cm was 0.031 mg/m³, and when the height increased to 140 cm, the concentration of formaldehyde decreased to 0.018 mg/m³, which showed that the concentration of formaldehyde decreased along with the increase of height. This was because the car exhaust tube was close to the ground, so the formaldehyde concentration of low position was higher. On the other hand, an appropriate height was suitable for the spread of formaldehyde, and the formaldehyde concentration would also decrease slightly.

Figure 3 showed the formaldehyde concentrations in different distances from main traffic artery. The traffic flow was one of the highest in Lin’an City. The results showed that an increase of the distance would obviously lead to the decrease of formaldehyde. The formaldehyde concentration in the edge of main traffic artery was measured with the result of 0.018 mg/m³. Also, the formaldehyde concentration did not change within 50 m. When the distance from the main road reached 100 m, the formaldehyde concentration decreased to 0.014 mg/m³, and when the distance reached 150 and 200 m, the concentration of formaldehyde was 0.008 and 0.005 mg/m³, respectively. The results also showed that when the distance from the main road reached 150 m, the formaldehyde concentration would decay quickly, and the value was almost all below 50%.

Health risk assessment

Health risk assessment was based on the human exposure risk calculation. Human exposure amount (E_i) was in accordance with the EPA standard 1992 version by a series of single factor (i) obtained by calculation (EPA, 1992), the calculation formula is as follows:

(2)

where C is the concentration of formaldehyde (μg/m³), IR is the inhalation rate (m³/hr), t is the exposure time (hr/day), and j is the type of microenvironment.

Among them, the average indoor respiratory rate (IR = 0.63 m³/hr) was according to EPA exposure factor (EPA, 1990), and the calculation of exposure amount (E) was according to different locations. Exposure time (t) was based on the average residence time. The waiting time was in accordance with the calculation of passengers for 1 hr on the bus, taxi, and car.

The health risk of formaldehyde was calculated by the average concentration of the respiratory health risk value per unit, and formaldehyde unit respiratory risk value was 1.3 × 10⁻⁵ (μg/m³)⁻¹ (EPA, 1991). As shown in Table 3, the risk of exposure of formaldehyde for 1 h was the highest in a taxi, with the value of 2.925 × 10⁻⁴, and in the two car stations the formaldehyde concentration was 8.9 μg/m³, with the minimum corresponding exposure risk of 1.157 × 10⁻⁴.

Table 3. Concentrations (C) and estimated exposure values (E) and health risks of formaldehyde in air

Microenvironment	C (μg/m^3)	E (μg/day)	Risk
Bus	16.2	10.206	2.106 × 10^−4
Taxi	22.5	14.175	2.925 × 10^−4
Bus station	8.9	5.607	1.157 × 10^−4

Compared with other studies, the formaldehyde risks of different places in this study were lower than those of the corresponding formaldehyde exposure risk in Mexico (Serrano-Trespalacios et al., 2004) and in Guangzhou (Feng et al., 2004). The higher level of health risks could lead to the increase of cancer.

Conclusion

The concentration of formaldehyde in typical traffic microenvironment of Hangzhou Ling’an (including buses, taxis, bus stations, and so on) and the air alongside traffic artery was systematically studied, and the quantitative health risk assessment was investigated. The main conclusions are as follows: (1) The average concentration of formaldehyde in the buses was 0.0162 mg/m³, whereas the average concentration in the taxis, West Bus Station, and East Bus Station were 0.0225, 0.0047, and 0.0133 mg/m³, respectively. (2) The concentration of formaldehyde in air alongside the traffic artery decreased with the height increasing, and when the height increased from 0 to 140 cm, the formaldehyde concentration decreased from 0.031 to 0.018 mg/m³. The concentration of formaldehyde decreased significantly with the distance from traffic artery increasing, and when the distance reached 200 m, the formaldehyde concentration decreased from 0.018 to 0.005 mg/m³. (3) Based on health risk assessment model, the average health risk with the average for 1 hr in buses, taxi, and West/East Bus Stations was 2.106 × 10⁻⁴, 2.925 × 10⁻⁴, and 1.157 × 10⁻⁴, respectively.

Funding

The authors are grateful for the financial support provided by the National Natural Science Foundation of China (21207116) and the Scientific Research Foundation of Zhejiang Agriculture and Forestry University (2010FR090).

Additional information

Funding

The authors are grateful for the financial support provided by the National Natural Science Foundation of China (21207116) and the Scientific Research Foundation of Zhejiang Agriculture and Forestry University (2010FR090).

Notes on contributors

Mili Weng

Mili Weng is an assistant professor and Xin Jin is an undergraduate of the School of Environmental and Resource Sciences, Zhejiang Agriculture and Forestry University.

Xin Jin

Mili Weng is an assistant professor and Xin Jin is an undergraduate of the School of Environmental and Resource Sciences, Zhejiang Agriculture and Forestry University.