Estimation of interannual trends of ammonia emissions from agriculture in Jiangsu Province from 2000 to 2017

ABSTRACT

As the only alkaline gas in the atmosphere, ammonia could react with sulfur dioxide and nitrogen oxides to form the secondary particles. A large amount of NH₃ in the atmosphere accelerates the rate of formation of fine particles; it therefore plays an important role in haze pollution. Livestock and poultry farming and nitrogen fertilizer application are the two main NH₃ emission sources. Jiangsu Province contributes the largest proportion of NH₃ emissions from agriculture in key areas of national air pollution control in China. The aims of this study are to investigate NH₃ emissions from agriculture in Jiangsu Province using the emissions factor method, and analyze and summarize the characteristics and trends of NH₃ emissions from 2000 to 2017. Results show that the NH₃ emissions from agriculture in Jiangsu Province from 2000 to 2017 were mainly contributed by livestock and poultry farming (78.08%) and nitrogen fertilizer application (21.92%). Furthermore, a general fluctuation trend of an initial decrease and then an increase, of NH₃ emissions from agriculture, could be found from 2000 to 2012, with minimum NH₃ emissions in 2007 (708.76 kt yr⁻¹) and maximum emissions in 2012 (837.64 kt yr⁻¹); and then a decreasing trend was apparent from 2012 (837.64 kt yr⁻¹) to 2017 (690.64 kt yr⁻¹). A detailed estimation of the interannual trends and potential measures are also proposed. This study provides a solid theoretical foundation for the development of NH₃ emissions control in Jiangsu Province.

Graphical abstract

摘要

氨气是大气中的微量碱性气体, 可以与酸性气体二氧化硫和氮氧化物的氧化产物发生化学反应, 生成硫酸铵和硝酸铵等二次颗粒物。大量氨存在会加速细颗粒物的生成速率, 在霾污染的形成过程中具有重要作用。畜禽养殖和氮肥施用是氨排放清单中最主要的两个排放源。江苏省农业源氨排放量居于国家大气污染防治重点区域各省市第一。本文利用排放因子法对2000–2017年江苏省农业源氨排放进行了估算, 研究江苏省18年来氨排放的特征及变化趋势。结果表明, 2000–2017年江苏省农业源氨排放平均78.08%来源于畜禽养殖, 21.92%来源于氮肥施用, 并且排放趋势呈现波动式变化。2000–2012年氨排放呈现先降低后增加的趋势, 2007年出现最小氨排放为708.76 kt yr⁻¹, 2012年出现最大氨排放为837.64 kt yr⁻¹。2012–2017年呈现下降趋势, 2017年农业源氨排放为690.64 kt yr⁻¹。本文对年际变化趋势进行了详细的估计, 并提出了可能的应对措施, 将为江苏省开展氨气排放控制提供科学基础。

KEYWORDS:

• Agricultural source
• ammonia emissions
• livestock and poultry farming
• nitrogen fertilizer application

关键词:

• 农业源
• 氨气排放
• 畜禽养殖
• 氮肥施用

1. Introduction

Ammonia (NH₃) is the only alkaline trace gas with appreciable concentration in the atmosphere (Zeng, Tian, and Pan 2018; Li et al. 2019a; Huang et al. 2014). It has been confirmed that the sulfur dioxide and nitrogen oxides released by fuel burning and automobile exhausts could convert to sulfuric acid and nitric acid in the atmosphere, which would further react with NH₃ to form ammonium sulfate and ammonium nitrate. These products become condensation nuclei that can absorb water and combine with other pollutants to form fine particles (Cui et al. 2015; Huang et al. 2019; Torpo et al. 2007; Xu et al. 2019; Yu et al. 2019; Zheng et al. 2015). Therefore, NH₃ is an important precursor for secondary particles, and is therefore considered as an important component of haze, bringing potential risks to public health (Kim et al. 2019; Pan et al. 2018; Zhang et al. 2019; Huang et al. 2014). In addition to the haze pollution caused by NH₃ emissions, after atmospheric deposition, NH₃ can dissolve in water to cause water eutrophication, destroying aquatic ecosystems (Posch et al. 2015; Duan et al. 2016; Li et al. 2019b). Yet, little is known about the sources and change trends of atmospheric NH₃.

Ammonia emissions derive mainly from anthropogenic sources, including agricultural emissions, industrial processes, traffic emissions, waste treatment, and other human activities (Huang et al. 2012; Clarisse et al. 2009; Zeng, Tian, and Pan 2018), among which the largest contributor is agricultural emissions, including two main pathways: nitrogen fertilizer application, and livestock and poultry farming. Of these, nitrogen fertilizer application accounts for approximately 40%, and livestock and poultry farming approximately 50%, of total anthropogenic NH₃ emissions worldwide (Zhang et al. 2018). Therefore, estimating the characteristics of NH₃ emissions from agricultural sources, especially from livestock and poultry farming and nitrogen fertilizer application, is imperative for developing NH₃ reduction strategies for specific regions.

Jiangsu Province is the largest contributor to China’s agricultural NH₃ emissions in key areas of national air pollution control (Shen, Yu, and Xiang 2018; http://meicmodel.org/about.html). In addition, Jiangsu Province applies the second largest amount of nitrogen fertilizer in China. Therefore, the aims of this study are to investigate the NH₃ emissions from agriculture in Jiangsu Province from 2000 to 2017, using the emissions factor method, and analyze and summarize the characteristics and trends of NH₃ emissions during this period.

2. Materials and methods

2.1. Study area

The study area is Jiangsu Province, located in eastern China, in the lower Yangtze River Delta region. It is a plain area with many lakes and an abundance of water systems. It belongs to the transitional climate from temperate to subtropical. It has moderate rainfall, and the average temperature is between 13°C and 16°C.

2.2. Estimation method

According to the ‘Technical Guide for the Preparation of Atmospheric Ammonia Source Emission Inventory’ (Song 2014), the most commonly used NH₃ emissions calculation method at home and abroad —the emissions factor method— was selected in this study. The quantity of NH₃ emissions is presented by the activity level multiplied by the emissions factor. The calculation can be summarized as:

${E_i}_{,j}=A_{i,j}\times {\mathrm{E}\mathrm{F}}_{i,j},$

where i is the source type, j is the year, and E_i,j is the NH₃ emissions of year j for source i. A is the activity level and EF is the emissions factor.

Activity level refers to the amount of NH₃ activity in a certain area within a certain period of time. In this study, activity level means the amount of livestock and poultry and the amount of nitrogen fertilizer applied. The emissions factor refers to the amount of NH₃ emitted per unit of activity level.

2.3. Determination of emissions factor

There are three main methods for determining the emissions factor: actual measurement, model calculation, and literature research. However, the emissions factor is considerably uncertain, due to the complex sources and factors of influence involved in NH₃ emissions.

For nitrogen fertilizer application sources, the main influencing factors include soil acidity and alkalinity, temperature, nitrogen fertilizer type, and application rate. The types of nitrogen fertilizer commonly used in China are urea, ammonium nitrate, ammonium bicarbonate, thiamine, and other nitrogen fertilizers. According to the ‘Chinese Soil Acid-base Distribution Map’, soil in most parts of Jiangsu is weakly alkaline and alkaline. Based on the ‘Technical Guide for the Preparation of Atmospheric Ammonia Source Emission Inventory’ (Song 2014), the NH₃ emission factors of nitrogen fertilizer application in alkaline soil at 10°C–20°C are summarized as follows: urea (14.66), ammonium bicarbonate (6.93), ammonium nitrate (0.4), thiamine (1.4), other nitrogen fertilizers (0.23).

For livestock and poultry farming sources, NH₃ emission factors are mainly affected by temperature, housing, and manure management. As pig, cattle, sheep, and poultry are the top four livestock in Jiangsu Province, the NH₃ emission factors of these four livestock types were investigated in this study. According to the ‘Technical Guide for the Preparation of Atmospheric Ammonia Source Emission Inventory’ (Song 2014), the NH₃ emission factors of intensive culture and free-range culture at 10–20°C are calculated as follows: pig > 1a (4.21), pig <1a (0.48), cattle > 1a (39.24), cattle < 1a (11.84), sheep > 1a (5.48), sheep < 1a (3.34), poultry > 1a (0.36), poultry < 1a (0.04). ‘1a’ indicates the farming cycle is one year. As there is little difference between these two culture methods, the average values of these two methods were used for calculating the NH₃ emissions of various livestock and poultry in this study.

2.4. Sources of activity level data

The activity level data in this study mainly include the amount of nitrogen fertilizer applied and the amount of livestock and poultry (pig, cattle, sheep, poultry) in Jiangsu Province. The data for nitrogen fertilizer application come from ‘The China Statistical Yearbook’ (National Bureau of Statistics 2001–18). The proportions of urea, ammonium bicarbonate, ammonium nitrate, thiamine, and other nitrogen fertilizers in total nitrogen fertilizer application in Jiangsu Province are 70%, 12%, 1.5%, 1.3%, and 15.2%, respectively (Deng and Luo 2018).

The data for livestock and poultry farming come from ‘The China Animal Husbandry and Veterinary Yearbook’ (Editorial Board of China Animal Husbandry and Veterinary Yearbook 2014–18) and ‘The China Animal Husbandry Yearbook’ (Editorial Board of China Animal Husbandry and Veterinary Yearbook, 2001–13).

3. Results

3.1. Estimation of NH₃ emissions from nitrogen fertilizer application

A relatively stable nitrogen fertilizer application rate was found from 2000 to 2009 (Figure 1), with an average of 170–180 kt yr⁻¹, followed by a clear decrease for 2010–17, and the least NH₃ emissions were found in 2017, at 151.36 kt yr⁻¹, which was a decrease of 16.7% compared to 2009. The maximum rate of NH₃ emissions over the study period was 189.27 kt yr⁻¹ in 2000, the minimum was 151.36 kt yr⁻¹ in 2017, and the average was 175.82 kt yr⁻¹. The reason for this trend was that the agriculture commission of Jiangsu Province formulated ‘The Action Plan of Zero Growth of Fertilizer Use in Jiangsu Province by 2020’ (http://nynct.jiangsu.gov.cn/art/2015/4/15/art_51418_6178564.html).

Figure 1. Ammonia emissions from nitrogen fertilizer application in Jiangsu Province, China, from 2000 to 2017.

In addition, both urea and ammonium bicarbonate were the main sources of NH₃ emissions, accounting for more than 80% of total NH₃ emissions from nitrogen fertilizer applications. Stable NH₃ emissions from both of them (~128.58 kt yr⁻¹ for urea and ~22.04 kt yr⁻¹ for bicarbonate) were found before 2010. From 2010, a continuous decline can be seen for both of them, and the NH₃ emissions reached a minimum in 2017, which was mainly because of the decrease in the total nitrogen application rate for the last seven years (Song et al. 2018). The results further indicated that, with the development of techniques and improvement in agricultural production structure, agricultural production gradually requires less fertilizer (Song et al. 2018). By contrast, ammonium nitrate, thiamine, and other nitrogen fertilizers released less NH₃, accounting for less than 20% in total.

3.2. Estimation of NH₃ emissions from livestock and poultry farming

Moderate fluctuations of NH₃ emissions from livestock and poultry farming were found in the study period (Figure 2). Specifically, there was a fluctuating decline before 2007 and a continuous increase between 2007 and 2012. The lowest value was reached in 2007 (525.92 kt yr⁻¹) and a peak of 668.45 kt yr⁻¹ was reached in 2012. After 2012, the NH₃ emissions from livestock and poultry farming from 2000 to 2017 kept falling to 539.28 kt yr⁻¹ in 2017, which was a decrease of 19.3% compared to that of 2012. The lowest rate of NH₃ emissions from livestock and poultry farming from 2000 to 2017 was 525.92 kt yr⁻¹ in 2007, the highest was 668.45 kt yr⁻¹ in 2012, and the average was 596.12 kt yr⁻¹. The decrease verifies the effect of the government’s policy of developing high-quality, efficient, ecological animal husbandry (http://nynct.jiangsu.gov.cn/art/2012/3/22/art_13251_2573444.html).

Figure 2. Ammonia emissions from livestock and poultry farming in Jiangsu Province, China, from 2000 to 2017. '1a' indicates the farming cycle is one year.

Additionally, poultry and pigs contributed the largest fraction of NH₃ emissions from livestock and poultry, accounting for more than 80%. In comparison, less than 20% of NH₃ emissions could be found from cattle and sheep, mainly because of their lower feeding rate in Jiangsu Province.

3.3. Estimation of NH₃ emissions from agriculture

The estimation results of NH₃ emissions from agriculture in Jiangsu Province from 2000 to 2017 are summarized in Figure 3. Similar fluctuation trends to the results for livestock and poultry farming can be seen; that is, a decline to a minimum of 708.76 kt yr⁻¹ in 2007, then an increase to a maximum of 837.64 kt yr⁻¹ in 2012, and finally a fall to 690.64 kt yr⁻¹ in 2017. Generally, the NH₃ emissions fluctuated within 708.76 kt yr⁻¹ to 837.64 kt yr⁻¹, with an average of 771.94 kt yr⁻¹.

Figure 3. Annual agricultural ammonia emissions in Jiangsu Province, China, from 2000 to 2017.

4. Discussion

During the study period, NH₃ emissions from the application of nitrogen fertilizers presented a trend of remaining stable (average of 183 kt yr⁻¹ before 2010) followed by a gradual decline (from 179.53 kt yr⁻¹ in 2010 to 151.36 kt yr⁻¹ in 2017). Among them, urea and ammonium nitrate were the main emission sources, accounting for more than 80% of the NH₃ emissions from all nitrogen fertilizers.

With regards to the NH₃ emissions from livestock and poultry farming, moderate fluctuation could be found during this period, with a peak of 668.45 kt yr⁻¹ occurring in 2012 and a minimum of 525.92 kt yr⁻¹ in 2007. Poultry and pigs were the main sources of NH₃ emissions from livestock and poultry farming, accounting for 80%–90% in total. In general, agricultural NH₃ emissions in Jiangsu Province from 2000 to 2017 were mainly composed of those from livestock and poultry farming (78.08%) and nitrogen fertilizer application (21.92%).

As the NH₃ emissions from livestock and poultry farming and from nitrogen fertilizer application are the two primary pathways of agricultural NH₃ emissions, it is reasonable to assume that these two contribute all agricultural NH₃ emissions. The relative contribution of livestock and poultry farming and nitrogen fertilizer application from different regions of China were also compared and discussed in this study. As shown in Table S1, the NH₃ emissions from livestock and poultry farming contributed 47.21% to 84.89% of the total agricultural NH₃ emissions, while nitrogen fertilizer application contributed 15.11% to 52.79%, for six different study areas (Dong et al. 2009; Dong, Xing, and Wang 2010; Fang et al. 2015; Feng et al. 2017; Li and Li 2012; Li et al. 2019; Zhang et al. 2018; Zhou et al. 2016). The estimation of NH₃ emissions has shown variability in different studies, meaning it highly depends on the selected emission factors and the different activity level data from region to region. Therefore, estimation work should be carried out on the basis of carefully selecting emission factors and activity level data.

Currently, haze pollution is getting worse in China. Due to the important role of NH₃ in haze formation, reducing NH₃ emissions is of great significance for air pollution control. In addition, the NH₃ emissions profile is greatly different from region to region, so it is necessary to take measurements based on an understanding of the specific characteristics of NH₃ emissions in the target region. Taking Jiangsu Province for example, on the one hand, due to the large amount of feeding of poultry and pigs, controlling NH₃ emissions should be paid more attention. On the other hand, because the NH₃ emissions from urea and ammonium bicarbonate account for about 80% of the nitrogen fertilizer application, the main focus for reducing NH₃ emissions should be developing alternative fertilizers to urea and bicarbonate. Furthermore, as some factors of influence, such as soil acidity and alkalinity, temperature, nitrogen fertilizer type, application rate, and the kind of crop (i.e. wet or dry crops), could affect NH₃ emissions from nitrogen fertilizer sources (Xu, Peng, and Yang 2009; Xia et al. 2010), the implementation of an NH₃ control strategy should also give full consideration to the above factors.

Disclosure statement

No potential conflicts of interest were reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This study was funded by the National Natural Science Foundation of China [grant numbers 41771291 and 21806080], the Jiangsu Specially-Appointed Professor Program, the Six Talent Peaks Project in Jiangsu Province [grant number NY-083], the Startup Foundation for Introducing Talent of NUIST, and the Innovation and Entrepreneurship Training Program for College Students in Jiangsu Province.