3.1. Emission Inventory and Spatial Distribution of PM from soil dust
1259 piece of bare grounds were identified in Zhengzhou in 2016 with a total area of 68.97 km2, which were mainly distributed in Zhongmou and Xinzheng. Zhongmou has the largest exposed area, which accouts for 52.50% of the total area of bare ground in Zhengzhou, followed by Xinzheng, Dengfeng and Xinmi. (Fig. 2(a)). Figure 2(b), 2(c) and 2(d) display the spatial distribution of PM emission from soil dust source with a grid of 3km × 3 km resolution. Results show that the emission of TSP, PM10 and PM2.5 from soil dust source were 507.40 t·a-1, 45.53 t·a-1 and 1.30 t·a-1, respectively in Zhengzhou. The maximum PM emission from soil dust source concentrated in Zhongmou and Xinzheng, which is consistent with the distribution characteristic of bare grounds. The Airport Economy Zone also has high PM emission, the main reason is that the soil type is mainly silt soil, which can be easily raised into air by wind and human activities, therefore lead to high emission coefficient. Dengfeng has a complex terrain that decreases from north to south, Xinmi is surrounded with mountains, although the area of bare ground are not small in the two regions, the limitation of topography reduced the effects of wind and human farming activities and lead to low PM emission. Xingyang, Gongyi and the urban area of Zhengzhou have the minimum PM emission, and it is mainly due to the small area of bare grounds.
3.2. Emission Inventory and Spatial Distribution of PM from construction dust
The number of construction sites was 1,793 in Zhengzhou with a total area of 145.25 km2 in 2016, which was mainly distributed in the urban area (Fig. 3(a)). The emission of TSP, PM10 and PM2.5 from construction dust source was calculated to be 181.5 kt·a-1, 93.0 kt·a-1and 19.8 kt·a-1, respectively. Figure 3 showed the spatial distribution of PM emission from construction dust sources in Zhengzhou City in 2016. The result suggests that PM emission from construction dust is closely related to regional development degree. The emission of TSP, PM10 and PM2.5 from construction dust sources are centered in 4 districts with high developed culture and economics, including Zhongyuan, Huiji, Jinshui and Zhengdong New District, the four regions formed a urban area-centered high emission circle. Zhongmou, Xingyang and Xinzheng, bordering the main urban area, also have high PM emission under the influence of regional conditions and urban economic radiation. Low PM emission area located in Gongyi and Dengfeng, which is far away from the main urban zone of Zhengzhou and lack of leading industries for economic development.
Compared with other cities in China, TSP emission from construction dust sources in Zhengzhou is 1.26 times of Beijing and 1.89 times of Wuhan, PM10 emission is 1.32 times of Beijing and 0.98 times of Wuhan, and PM2.5 emisson is 0.35 times of Beijing and 1.06 times of Wuhan[24–25]. It is assumed that the reason resulting in high PM emisson in Zhengzhou was the reconstruction of the urban village. The Government of Zhengzhou demand that all the urban villages within the fourth ring road of Zhengzhou should be demolished by the end of 2016. To complete the target on schedule, large number of construction work has been conducted in the main urban area in the year of 2016, which result in a substantial increase of PM emission from construction sources.
3.3. Emission Inventory and Spatial Distribution of PM from Road dust
The total length of paved roads in Zhengzhou in 2016 was 10,601.50 km, and the length of national road, provincial road, county road and township road were 396.30 km, 901.40 km, 2,439.88 km and 6,863.92 km, respectively. It has been calculated that the total emission of TSP, PM10 and PM2.5 from paved roads were 55.5 kt·a-1, 10.7 kt·a-1 and 2.6 kt·a-1, respectively (Table 2). Among different levels of roads, township road has the largest PM emission, followed by provincial road, county road and national road. This is because the length of township road is far more than other types of roads, and the road dust load of township road is relatively large. Although the dust load of provincial road is small, the heavy traffic volume lead to high PM emissions. It can be seen that the TSP, PM10 and PM2.5 emission from road dust is large in Zhengzhou, but compared with other cities of similar size in China, PM emission from road dust in Zhengzhou are still at low level[26–27].
The spatial characteristics of TSP, PM10 and PM2.5 emission from road dust source in Zhengzhou was shown in Fig. 4b, c, d. For different levels of roads, high PM emission mainly concentrated in the main urban areas such as Zhongyuan, Huiji, Jinshui and Zhengdong New District, it is because the main urban region is the intersection of the Longhai Railway and the Beijing-Guangzhou Railway, besides, the 107 National Highway, the 310 National Highway, the Beijing-Hongkong-Macao Expressway and the Lianhuo Expressway all pass through the area. PM emission from roads is also higher in the junction of Zhongmou, Xingyang, Xinzheng and the main city in the area, and the emission of the area which are far from the urban area such as Shangjie and Dengfeng is small.
Table 2
Emission of TSP, PM10 and PM2.5 from paved roads
Type | Length(km) | TSP(t/a) | PM10(t/a) | PM2.5(t/a) |
State road | 396.30 | 7958.07 | 1527.56 | 369.57 |
Provincial road | 901.40 | 14387.84 | 2761.75 | 668.17 |
County road | 2439.88 | 9285.82 | 1782.42 | 431.23 |
Township road | 6863.92 | 23857.19 | 4579.40 | 1107.92 |
Total | 10601.50 | 55488.93 | 10651.13 | 2576.89 |
3.4. Total PM emissions from dust source
The calculation results showed that the emission of TSP, PM10 and PM2.5 of Zhengzhou in 2016 were 237.5kt·a-1, 103.7kt·a-1 and 22.4 kt·a-1, respectively. By analyzing the source of PM, it can be found that the construction dust was the main dust sources of PM emission in Zhengzhou, TSP, PM10 and PM2.5 emission from construction dust accounted for 76.43%, 89.69% and 88.50%, respectively of total dust sources (Table 3).
The spatial distribution of total PM emission was shown in Fig. 5b, 5c and 5d, it can be seen that the emission of TSP, PM10 and PM2.5 were mainly concentrated in the Zhongyuan, Huiji, Jinshui, Zhengdong New District and other main urban areas. Zhongmou, Xingyang and Xinzheng, which bordering with the main urban area, were also the high PM emission area. While the areas that far away from the main urban area had low emission intensity such as Shangjie and Dengfeng. Three aspects of reasons of the emission characteristics was concluded. Firstly, the majority of construction sites are distributed in the main urban area, secondly, the dense road network and heavy traffic flow of the main urban area increases the PM emission, moreover, although soil dust is more prevalent in the suburbs than in the urban area, but due to the small PM emission from soil dust, it doesn't make much difference to the general characteristic of total emissions.
Results from the analysis revealed that the key zones for PM emission control from dust sources are mainly distributed in the main urban area of zhengzhou, which is consist of Zhongyuan, Huiji, Jinshui, Zhengdong New District. Furthermore, areas such as Zhongmou, Airport Economy Zone and Xinzheng are more likely to face increasing serious PM emission problems due to the acceleration of urbanization under policy orientation, so it is necessary to conduct early prevention of PM emission in these potential PM emission areas.
Table 3
Emission of TSP, PM10 and PM2.5 from dust sources
Dust type | Soil dust | Construction dust | Road dust | Total |
TSP | Total annual emission t·a-1 | 507.40 | 181547.25 | 55488.93 | 237543.58 |
| percentage % | 0.21 | 76.43 | 23.36 | 100 |
PM10 | Total annual emission t·a-1 | 45.53 | 93047.65 | 10651.13 | 103744.31 |
| percentage % | 0.044 | 89.69 | 10.27 | 100 |
PM2.5 | Total annual emission t·a-1 | 1.30 | 19842.70 | 2576.89 | 22420.89 |
| percentage % | 0.006 | 88.50 | 11.49 | 100 |