3.1. Characteristics of black carbon concentration and inversely calculated spatial variation characteristics of BC concentration
3.1.1. Annual variation characteristics of BC concentration
The annual average BC concentration data of 23 stations with continuous BC observation data in China from 2006 to 2017 were calculated, and the inter-annual variation characteristics of BC were analyzed as well (Fig. 3). As can be seen, the annual average concentration of BC in China has been fluctuating and declining year by year since 2006. It dropped from 5.64 ug/m3 in 2006 to 2.64 ug/m3 in 2017, a drop of more than 50%.
3.1.2. The spatial variation of BC concentration based on ratio method
The BC concentration of more stations in the whole country was estimated by the Ratio Method, and the spatial distribution of BC concentration from 2015 to 2017 was calculated based on GIS platform. Figure 4 is an average BC concentration interpolated graph of 2015–2017 calculated by the Ratio Method .
As can be seen from Fig. 4, in 2015–2017, the annual average BC concentration in China is higher than 7 ug/m3 in eastern Sichuan, southern Shaanxi, southern Shanxi, northwest and southeastern Henan, southern Beijing, Tianjin and Hebei, and the south of Northeast China. The low BC concentration is mainly distributed in Northwest China, Southwest China, Inner Mongolia, Northern Jiangxi, and the average exposure concentration is below 2 ug/m3.Multi-resolution Emission Inventory for China (MEIC, Source: http://www.meicmodel.org/index.html.) is a set of anthropogenic emission inventory models of atmospheric pollutants and greenhouse gases in China based on cloud computing platform. The products cover 10 major atmospheric pollutants, greenhouse gases and more than 700 anthropogenic emission sources. Drawing the MEIC2016 BC emission classification distribution map (Fig. 5), we can see that the BC high-emission areas in China are in the south-central part of Northeast China, the south of North China, the west of Huanghuai, the east of Southwest China, the Yangtze River Delta, and the Pearl River Delta. The graded distribution of the average BC concentration in China from 2015 to 2017 calculated by the ratio method shows that the high value areas are in the eastern part of Southwest China, the western part of Huanghuai River, the central and south part of Hebei Province and the central and southern part of northeast China. The BC concentration distribution is basically consistent with distribution of MEIC black carbon emission.
3.2 Assessment of BC exposure level in China
3.2.1. The general situation of exposure level of BC in China
The spatial distribution characteristics of population and BC concentration in China are different, so only BC concentration in China is not enough to reflect the exposure level of population. According to the method of population-weighted atmospheric pollutant calculation (formula 5), the BC population-weighted exposure concentration in each region was obtained.
PWEL = Σ(Pi × Ci)/Σ(Pi) (5)
In formula (5), i is the number of analysis areas; Pi is the number of populations in the analysis area; Ci is the concentration of BC in the analysis area.
Using GIS software, this paper analyzes the national BC concentration and population density from 2015 to 2017, and calculates the exposure area of BC in different concentration ranges (Table 1) and population status (Table 2).As can be seen from Table 1, from 2015 to 2017, the area of China exposed to areas that below 2 ug/m3 increased year by year, while the area exposed between 2–5 ug/m3 decreased year by year, indicating that more areas of China exposed to lower concentration of BC in recent years. In addition, from 2015 to 2017, 3.02%, 1.15% and 1.22% of the areas exposed to BC above 7 ug/m3 in China respectively, while the areas exposed to BC between 5–7 ug/m3 did not change much, all of which were about 4%.It can be seen from the three-year average that the land area exposed to 1–2 ug/m3 concentration range is the largest, about 43.21%, followed by 32.01% of the land area exposed to 2–3 ug/m3 concentration range, while the land area exposed to more than 9 ug/m3 is only 0.32%.
Table 1. Area Ratio of Exposure to Different BC Concentrations in China from 2015 to 2017
BC concentration range
|
2015
|
2016
|
2017
|
3 years average
|
BC<1
|
2.26%
|
6.00%
|
14.41%
|
6.45%
|
1<BC<2
|
33.15%
|
34.59%
|
43.73%
|
43.21%
|
2<BC<3
|
35.79%
|
35.26%
|
24.64%
|
32.01%
|
3<BC<4
|
16.64%
|
13.64%
|
8.40%
|
9.87%
|
4<BC<5
|
5.32%
|
4.87%
|
2.97%
|
2.78%
|
5<BC<6
|
1.99%
|
2.93%
|
2.86%
|
2.61%
|
6<BC<7
|
1.84%
|
1.56%
|
1.77%
|
1.66%
|
7<BC<8
|
0.99%
|
0.55%
|
0.86%
|
0.80%
|
8<BC<9
|
0.81%
|
0.34%
|
0.26%
|
0.29%
|
9<BC
|
1.22%
|
0.26%
|
0.11%
|
0.32%
|
As can be seen from the exposure of the population, from 2015 to 2017 the ratio of population exposed to BC concentration above 9 ug/m3 in China decreased year by year from 4.78% in 2015 to 0.74% in 2017. Indicating that the proportion of population exposed to BC concentration in high-value areas decreased year by year. The ratio of population exposed to concentrations below 3 ug/m3 increased year by year, from 43.45% in 2015 to 61.84% in 2017. Indicating that more and more people in China are exposed to relatively low BC concentration. It can be seen from three years average that the population exposed to 2–3 ug/m3 concentration range is the largest, accounting for 30.10% of the national population, followed by the population exposed to 1–2 ug/m3 concentration range, accounting for 19.36% of the national population, 8.35% of the population less than 1 ug/m3, while the population exposed to 9 ug/m3 or more accounts for 1.16% of the total population.
Table 2. Population ratios of exposed to different BC concentrations in China from 2015 to 2017
BC concentration range
|
2015
|
2016
|
2017
|
3 years average
|
BC<1
|
4.87%
|
9.30%
|
8.44%
|
8.35%
|
1<BC<2
|
17.26%
|
18.53%
|
26.31%
|
19.36%
|
2<BC<3
|
21.32%
|
29.60%
|
27.09%
|
30.10%
|
3<BC<4
|
23.25%
|
13.11%
|
12.91%
|
16.45%
|
4<BC<5
|
12.24%
|
9.74%
|
6.31%
|
5.95%
|
5<BC<6
|
5.49%
|
11.24%
|
7.52%
|
8.67%
|
6<BC<7
|
4.65%
|
5.14%
|
5.30%
|
6.81%
|
7<BC<8
|
3.32%
|
1.40%
|
4.05%
|
2.32%
|
8<BC<9
|
2.82%
|
0.90%
|
1.32%
|
0.83%
|
9<BC
|
4.78%
|
1.04%
|
0.74%
|
1.16%
|
3.2.2. Assessment of BC Population Exposure Level in 11 Climate Regions of China
China has a vast territory, special geographical location. The complex topography and various elements of the atmosphere circulation affect climate together. It makes climate types and natural landscape extremely diverse. According to meteorological and geographical zoning map, China is divided into 11 climatic regions (Fig. 6). We can get conclusion that the high value area of BC population weighted concentration in China is in the southwest and North China, by calculating the BC population weighted concentration of each region from 2015 to 2017 (Table 3),. The average concentration of BC population weighted concentration in these two regions is about 4 ug/m3, followed by the northwest, Northeast and Huanghuai regions, the average concentration of BC population weighted concentration in these three regions is about 3 ug/m3. The lowest concentration of BC population weighted concentration in Tibet is about 2 ug/m3. In terms of annual change, BC population weighted concentration in Northeast, South China, Huanghuai, Jianghuai, Northwest and Southwest China decreased year by year. In Inner Mongolia, it increased slightly year by year, but remained a relatively low level.
Table 3. Weighted BC Population Concentrations in 11 Climate Regions of China from 2015 to 2017
11Climate region
|
2015
|
2016
|
2017
|
3 years average
|
1Northeast China
|
3.37
|
3.11
|
2.66
|
3.05
|
2North China
|
5.95
|
4.77
|
5.46
|
5.39
|
3South China
|
3.00
|
2.63
|
2.12
|
2.58
|
4HuangHuai area
|
4.09
|
3.08
|
2.76
|
3.31
|
5Jianghan area
|
2.74
|
2.38
|
2.47
|
2.53
|
6Jianghuai Region
|
3.38
|
2.81
|
2.51
|
2.90
|
7Jiangnan area
|
2.68
|
2.08
|
2.25
|
2.34
|
8Inner Mongolia
|
2.05
|
2.04
|
2.10
|
2.06
|
9Northwest China
|
3.61
|
3.24
|
2.91
|
3.25
|
10Tibet area
|
1.93
|
2.48
|
1.25
|
1.88
|
11Southwest China
|
4.38
|
4.10
|
3.51
|
4.00
|
The difference between the weighted concentration of BC population in each climatic region and the regional spatial average BC concentration, and the ratio of BC concentration to the regional spatial average BC concentration, can reflect the population exposure of BC in this region. Table 4 shows that the ratio of northwest, southwest and south of the Yangtze River is the highest, indicating that more people are exposed to the high concentration of BC in this region, while the ratio of Huanghuai area is the lowest, indicating that more people are exposed to the low concentration of BC in this region. On the basis of the annual change, the ratios of South China, Jianghan and Inner Mongolia are decreasing year by year, which indicates that more and more people in these areas are exposed to low BC concentration. Meanwhile, the ratios of North, Northwest and Southwest are increasing year by year, which indicates that more and more people are exposed to high BC concentration.
Table 4. Comparative analysis of BC population weighted concentration and spatial average concentration in 11 climatic regions of China from 2015 to 2017
11Climate region
|
2015
|
2016
|
2017
|
3-year average
|
1Northeast China
|
-3.49%
|
-6.08%
|
-5.82%
|
-5.07%
|
2North China
|
1.66%
|
4.19%
|
7.57%
|
4.34%
|
3South China
|
0.93%
|
-0.03%
|
-4.64%
|
-0.98%
|
4Huang Huai area
|
-11.19%
|
-10.18%
|
-11.41%
|
-10.94%
|
5Jianghan area
|
2.47%
|
2.04%
|
0.58%
|
1.71%
|
6Jianghuai Region
|
0.06%
|
-1.86%
|
-0.35%
|
-0.68%
|
7Jiangnan area
|
13.36%
|
13.68%
|
11.90%
|
12.98%
|
8Inner Mongolia
|
2.27%
|
2.11%
|
-3.30%
|
0.26%
|
9Northwest China
|
11.77%
|
10.97%
|
17.59%
|
13.17%
|
10Tibet area
|
4.40%
|
4.84%
|
0.75%
|
3.76%
|
11Southwest China
|
11.11%
|
13.21%
|
15.43%
|
13.06%
|
3.3 Black carbon health economic loss assessment in China
3.3.1. Black carbon exposure response relationship
The exposure-response relationship coefficient of the representative city of Beijing is calculated by GAM model and is used to calculate the economic loss due to black carbon exposure. The percentage excess risk (ER (%)) is a percentage of the change in death at 1 ug/m3 change in BC concentration. The mortality risks were strongest on the exposure day (lag1) (Table 5).
Table 5. Exposure-response coefficient and estimated excess risk of excess death in representative city of Beijing (95%CI)
city
|
lag day
|
β(95%CI)
|
ER (%) (95% CI)
|
Beijing
|
lag1
|
0.003 (0.002~0.004)
|
0.26*** (0.17,0.36)
|
Footnote 1: *** p < 0.001
3.3.2. Economic loss of human exposure to BC in China from 2015 to 2017
One can calculate the number of excess deaths associated with BC in 2,372 districts and counties from 2015 to 2017 (formula 2). One can also calculate the unit economic value of each district and county (formula 3). And finally, the health-related economic loss from BC in 2,372 districts and counties in China can be obtained (Fig. 7A).This figure shows that 77.3% of the targeted districts or counties claimed a loss per square kilometer of 50 million RMB or less, and the regions with higher annual losses are mainly located in Wuhan, Chengdu, Shenyang, Changchun, Xi’an, Hangzhou, and Shanghai, with an annual loss value of more than 200 million RMB.
One can obtain the distribution of China’s BC-related health economic loss as a proportion of GDP (BC ratio) by dividing the BC-related health economic losses registered in 2,372 districts and counties by their annual GDPs (Fig. 7B). From 2015 to 2017, the BC ratio of most districts and counties in China was lower than 1‰, mainly located in northwest, southwest and northeast China. Districts and counties with BC ratio greater than 3‰ mainly located in the eastern part of northeast China, the eastern part of Sichuan and parts of Henan and North China. The number of districts and counties with BC ratio lower than 1‰ increases year by year, and the BC ratio of Yunnan, Guangdong, Guangxi, Fujian, Anhui and Zhejiang decreases year by year, while the BC ratio of Beijing-Tianjin-Hebei and Hunan increases year by year (table 6).
As an estimate, from 2015 to 2017, China's BC ratio showed a decreasing trend year by year. The China's BC-related health economic loss in 2017 was the lowest, about 95.956(63.970, 127.941) billion RMB, accounting for 1.16‰ (0.77‰, 1.55‰) of the GDP. The loss cost in 2015 was the highest, 116.795(77.863, 155.726) billion RMB, accounting for 1.70‰ (1.13‰, 2.26‰) of the GDP. In 2016, the loss cost was 98.887(65.925, 131.850) billion RMB, accounting for 1.33‰ (0.89‰, 1.77‰) of the GDP.
Table 6. Distribution of economic losses associated with BC at different levels in China from 2015 to 2017
|
2015
|
2016
|
2017
|
<1‰
|
44.35%
|
52.87%
|
57.93%
|
1‰-2‰
|
35.62%
|
30.61%
|
25.42%
|
2‰-3‰
|
11.64%
|
13.45%
|
13.95%
|
3‰-4‰
|
5.23%
|
2.53%
|
2.49%
|
4‰-5‰
|
2.19%
|
0.46%
|
0.21%
|
>5‰
|
0.97%
|
0.08%
|
0.00%
|
3.3.3. Economic loss of human health in 11 major climatic regions of China from 2015 to 2017
By calculating the human health economic loss value and BC ratio of 11 climatic regions in China from 2015 to 2017 (table 7), it can be seen that North China, Jiangnan and Southwest China have the highest annual loss, while Inner Mongolia and Tibet have the lowest annual loss. The BC ratio in North China, Huanghuai, and Southwest China is relatively high, fluctuating between 1‰ and 2‰, while the BC ratio in Inner Mongolia and Tibet area is relatively low, around 0.6‰. The annual loss values of Northeast, South China, Huanghuai, Jianghuai, Northwest and Southwest China decreased year by year, while those of North China, Jianghan and Southwest China increased year by year. The BC ratio decreased year by year in Northeast China, South China, Huanghuai, Jianghuai, Northwest China, Tibet and Southwest China.
Table 7. The changes of human health economic loss value and BC ratio in 11 climatic regions in China from 2015 to 2017
|
Total loss (billion RMB)
|
BC ratio (‰)
|
|
2015
|
2016
|
2017
|
2015
|
2016
|
2017
|
1Northeast China
|
91.84
|
85.15
|
69.88
|
1.53
|
1.46
|
1.24
|
2North China
|
243.11
|
201.84
|
238.22
|
2.12
|
1.63
|
1.81
|
3South China
|
137.70
|
128.62
|
102.10
|
0.93
|
0.82
|
0.69
|
4Huang Huai area
|
138.42
|
100.13
|
94.02
|
1.86
|
1.38
|
1.26
|
5Jianghan area
|
18.70
|
16.05
|
16.79
|
1.13
|
0.98
|
1.03
|
6Jianghuai Region
|
52.77
|
42.44
|
39.19
|
1.41
|
1.19
|
1.04
|
7Jiangnan area
|
230.76
|
178.63
|
192.65
|
0.94
|
0.74
|
0.84
|
8Inner Mongolia
|
8.51
|
8.21
|
8.41
|
0.61
|
0.61
|
0.66
|
9Northwest China
|
69.05
|
61.17
|
57.13
|
1.18
|
1.08
|
0.91
|
10Tibet area
|
0.65
|
0.85
|
0.45
|
0.57
|
0.73
|
0.38
|
11Southwest China
|
176.43
|
165.78
|
140.72
|
1.62
|
1.49
|
1.27
|