Estimation of NOx Emission from Fossil Fuel Consumption in China for the Period 1980-2012

As the largest consumer of fossil fuel, China NOx emission from energy consumption has become a hotspot for studies. In this study, emission inventory was used to analysis the historical variation of NOx emission in china for the period 1980 to 2012. Results indicate that NOx mission of China has increased from 446.45 104t to 2499.72 104t during 1980-2012, electricity, industry and transportation was the main contributor and NOx emission has increased from 145.04 104t, 206.75 104t, 39.44 104t to 1311.6 104t, 479.46 104t, 576.31 104t respectively; from the spatial pattern, high total NOx emission with mainly concentrated in the north of China and the high emission intensity mainly concentrate in eastern China.


Introduction
It is now well known that NO x emissions play an important role in acidification, haze, summer photochemical smog and the increase of tropospheric ozone level [1].Fossil fuel combustion is identified as one of the main contributors to the escalation of air pollution such as NO x [2].China is the largest energy consumer in the world and have contributed amount of various emission during past three decades because of its rapid industrializations and urbanizations.Although China has implement strict environment policy in recent years, NO x emission still keeps an increase trend all the way.Data from satellite measurements indicated that NO x vertical column density have increased significantly in East Asia [3].
A systematic emission inventory is helpful for environmental policy maker to understand the essential information of emission source and control air pollution effectively.Several national and provincial level NO x emission inventories have been presented by several researchers.For instance, D.G. Streets(2000) used emission factor estimate China provincial NO x emissions of 1995 and forecasted emissions for the year 2020 [4]; Tian Hezhong(2001) build up 1980-1998 NO x emissions inventory of China on the basis of historical energy consumption data and NO x emission factors [5]; Qing Lu(2013) took use of emission inventory estimate the NO x emission of Pearl River Delta region and found NO x emissions went up consistently during 2000-2009 except for a break point in 2008 [6] Yun Shi et al. (2014) established a NOx emissions inventory of China from for the period 2000-2010 [7].These study focus more on short period or annual emission and pay no more attention to spatial distribution variation of NO x emission.As a country with the fast developing speed in the world, China NO x emission changed greatly over the past years, in this paper we established a bottom-up NO x emission inventory of China from 1980 to 2012 for different economic sectors and different fuel styles, then, based on the provincial fossil fuel consumption of 2012, we analyses spatial distribution characteristic of NO x emission in provincial level.

Data and methods
Following the approach of Tian Hezhong(2001) [5] and Qing Lu(2013) [6] NOx emission source were classified into seven categories: power plants and heating, industry, construction, transportation, commercial, residential consumption and other resources.Ten fuel types such as coal, coke, crude oil etc, are considered and their emission factors are different for different period.NO x emission was estimated by an emission factor approach which was implemented by the Equation below: , , , , , , , ( ) where Q N is the emission of NO x , K N is the emission factors of NO x weighted by N 2 O, F is the fuel consumption, P is the average removal efficiency of NO x , i, j, f, t represent different province (municipality or Autonomous Region, except Hong Kang, Macau and Taiwan due to the lack of available data), economic sectors, fuel styles and years respectively.Emission factor is the basis for inventory, in order to improve the precise and systematic of estimation, we performed an extensive literature reviews on NO x emission factors and adopted the emission of Tian Hezhong [5] and Zhang Chuying [8].Considering the technology development of electricity and industry in fact, new factors was used in the two sectors from the year of 2005 and new emission factors of 2005 was marked with * .The unit for all emission factors was expressed by kg/t except for natural gas and coal gas expressed by kg/10 3 Results

Temporal and sector variation of China NO x emission
Fig. 1 and Fig. 2  hezhong(2005) [5], data of 1990 from Wang wenxing(1996) [9], data of 2000 and 2005 was from Shi Yun (2014) [7].Although data source and method was different, NO x emission had same increase trend and had a little difference both in this paper and other researchers, which was less than 10% except data of 2000 and 2005.
So we thought the estimation result of this paper was reliable.

Spatial distribution of China NO x emission
There are great disparities in total NO x emission from different provinces and mainly lie in north of China for the year 2012 (Fig. 5).Shandong, Inner Mongolia, Jiangsu, Guangdong and Hebei province had a high NO x emission and their NO x emission was 279.66×10Due to difference in land area, the spatial distribution of NO x intensity took a distinct feature of zonality in eastern, middle and western China (Fig. 6).Shanghai, Tianjin and Beijing, Jiangsu, Shandong and Zhejiang, had the highest emission density of NOx due to their concentration of population and industry polluted area, their NOx intensity reached to 131.8t/km 2 , 40.72 t/km 2 , 21.28 t/km 2 , 19.62 t/km 2 , 18.01 t/km 2 and 12.05 t/km 2 respectively, which were similar to data via satellite monitoring [1].NOx intensity of western China such as Qinghai, Xinjiang, Gansu, Sichuan, Yunnan, Inner Mongolia, Heilongjiang provinces was low owing to their broader land area, whose NOx intensity only 0.15 t/km 2 , 0.43 t/km 2 , 0.97 t/km 2 , 1.65 t/km 2 , 1.66 t/km 2 , 1.74 t/km 2 , 1.78 t/km 2 respectively.

NO x speciation by provinces
Fig. 7 showed the NO x speciation by provinces for the year of 2012.The profile for provinces were somewhat similar, mainly electricity and industry.However, some differences can be seen, for example, transportation was predominant in Shanghai, Beijing and Hainan, industry was predominant in Sichuan, Chongqing, Hubei and Hunan province.The contribution of economic sector indicated that NOx emission control policy should be suited to local condition.

Discussion and conclusions
Using the inventory method on based emission factor, we estimated the NO x emission of China from 1980 to 2012 and provincial distribution for the year 2012 for the first time.Results indicated that NO x had increased 4.6 times during the past 32 years and had an apparent upward trend in recent years, because of rapid fossil fuel consumption.Electricity has exceeded industry and become the main contributor of NO x emission.Because of its rising ratio in NO x emission, electricity is the key sector for NO x emission control in the future.Industry was the important contributor for its gigantic total NO x emission although its emission ratio has declined, improving industrial energy consumption efficiency and enforcing pollution control was the only way for NO x emission.Transportation was the fast growing contributor for NO x emission and the public transport system should be as a priority measures to reducing the growth of NOx emission.From the perspective of energy structure, coal as the main energy source for NO x emission and the promotion of green energy would be significant to decrease the NO x emission.The spatial patterns of NOx emission in China energy consumption were primary concentrated in eastern of China because of their dense population and industrialization.A long time series NO x emission inventory was developed for the first time.Although different in data source and the method, the estimation of this had little difference to official data and other researchers, so the estimation results was reliable.To further improve the emission inventory, local emission factors and technology change should be considered in the future.

Figure 5 .
Figure 5. Spatial distribution of NOx emission from fossil fuel combustion for the year 2012.

Figure 6 .
Figure 6.Spatial distribution of NOx intensity from fossil fuel combustion for the year 2012.

Table 1 .
4•m3.All emission factors used in this paper were listed in tab.1.Fuel consumption data of different sectors came from national and provincial energy balance table (physical quantity) of National Statistic Yearbook(1985- 2013).NOx emission factors for seven sectors and different fossil fuels of China (kg/t).

500 1000 1500 2000 2500 NOx Emission : 10 4 t 1980 1985 1990 1995 2000 2005 2012 Figure 1. NO
Transportation was the fast growing source, NO x emission has increased from 39.44×10 4 t to 576.31×104t and increased about 13.61 times than that of 1980.NO x emission from other sectors, including construction, residential, others, was little and takes up less than 5% of emission only.Although NO x emission proportion of coal consumption have declined in recent years, coal still was the main contributor of NO x and NO x emission of coal combustion has increased from 328.63×10 4 t to 1610.45×10 4 t from 1980 to 2012(Fig.3).NO x emission of diesel and gasoline combustion has increased from 20.94×10 4 t, 18.50×10 4 t to 430.70×104t 152.53×10 4 t because of rapid increased motor vehicle.Coke was the important component of steelmaking; NO x emission from coke has increased from 38.54×10 4 t to 181.11×10 4 t and had a stable status in NO x emission.Other fuel style contributed little NO x and took no more than 3% of NO x emission.x emission of main sectors from 1980-2012.
NOx speciation by provinces for the year 2012.