Microsoft Word - EES-V2N1-p15.doc Energy and Earth Science Vol. 2, No. 1, 2019 www.scholink.org/ojs/index.php/ees ISSN 2578-1359 (Print) ISSN 2578-1367 (Online) 15 Original Paper Ammonia Nitrogen Pollution Characteristics of Natural Rainfall in Urban Business District in Southern China: A Case Study of Chengdu City Xintuo Chen1, 2, Yiyao Wang1, Chengyue Lai1, 2, Jia She1, 3, Ke Zhong1, 4, Jiayang Chen5, Zhaoli Wang1* 1 Institute of Water Environment Research, Chengdu Research Academy of Environmental Protection Science, Chengdu, China 2 Environmental Monitoring and Analysis Laboratory, Chengdu Research Academy of Environmental Protection Science, Chengdu, China 3 Institute of Drinking Water Safety, Chengdu Research Academy of Environmental Protection Science, Chengdu, China 4 Institute of Watershed Research, Chengdu Research Academy of Environmental Protection Science, Chengdu, China 5 Chengdu Experimental Primary School, Chengdu, China *Zhaoli Wang, E-mail: 9755014@qq.com Received: March 28, 2019 Accepted: April 12, 2019 Online Published: April 23, 2019 doi:10.22158/ees.v2n1p15 URL: http://dx.doi.org/10.22158/ees.v2n1p15 Abstract Chengdu city was chosen as the representative of southern cities in China in this work, characteristics of ammonia nitrogen (NH3-N) pollution in natural rainfall were analyzed by measuring the concentration in 15 natural rainfalls from April to September in 2017. The influence of ammonia emission from toilet vent of building on NH3-N pollution in rainfall was investigated, and the variation of total NH3-N pollutants and its influencing factors were expounded. The results showed that the average concentration of NH3-N in first rainfall was the highest, reaching 18.2mg/L, the average concentration of NH3-N in the subsequent 14 rainfalls was between 2.0 and 5.0mg/L, which is higher than Grade V (≤2mg/L) of Environmental Quality Standards of Surface Water (GB 3838-2002), and was an important source of NH3-N pollution in water. The concentration of NH3-N in natural rainfalls decreased with the increase of the distance between the sampling point and the toilet vent, indicating that the ammonia discharged from toilet exhaust is a major source of NH3-N pollution in urban atmosphere. The main factors affecting total NH3-N pollutants in natural precipitation include rainfall www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 16 Published by SCHOLINK INC. intensity, rainfall duration and drought days. The total amount of NH3-N pollutants in surface runoff is less than that in natural rainfall. Keywords southern city in China, natural rainfall, ammonia nitrogen pollution, total pollutant amount, pollution characteristics 1. Introduction Rainfall is a natural way to clean the atmosphere (Wang & Xu, 2009), so the air pollutants are an important source of pollution in rainwater. At present, the air pollution in cities of China has turned to the complex air pollution formed by fine particulate matter (PM2.5) and polluted gases (O3, SOx, NOx, NH3) (Cao, 2014; Samen J M et al., 2000; Gao, 2012). Some researches (Ge et al., 2015)pointed out that water-soluble inorganic ions (WSII) like SOx, NOx and NH3 are important chemical components of PM2.5, secondary water-soluble inorganic ions like SO4 2-, NO3 -, NH4 + are the most important chemical species in the process of regional particulate matter pollution. Among them, (NH4)2SO4 and NH4NO3 formed by reaction of the secondary pollutants such as sulfuric acid or nitric acid with NH3 have become the main water-soluble secondary pollutants in the atmosphere; Yang (Yang et al., 2007) observed atmospheric aerosols in Jinan city and found that secondary ions in PM2.5 mainly exist in the form of (NH4)2SO4 and NH4NO3, nitrogen deposition has been taken into account as an important nitrogen source in the study of nitrogen cycle in river basins; Huang (Huang et al., 2016) studied nitrogen deposition in Huanghuai Plain from May 2008 to April 2012. It was found that NH3-N was the main type of nitrogen deposition and the proportion of NH3-N in nitrogen deposition was 6%-79%, with an average of 53%; Zhu (Zhu et al., 2015) considered 41 ecological research sites in China, and found that particulate nitrogen, ammonia nitrogen and nitrate nitrogen accounted for 24%, 40% and 33% of total nitrogen, respectively, indicating that ammonia nitrogen was the main component of atmospheric deposition; Zheng (Ge et al., 2017) studied three ammonia-rich areas in Korea, and found that, (NH4)2SO4 and NH4NO3 were the main forms of water-soluble ions in PM2.5; The atmospheric (NH4)2SO4 and NH4NO3 can enter urban water body through rainfall, becoming an important source of NH3-N in water body, aggravating water eutrophication and destroying water ecosystem balance (Ding et al., 2007; Neal et al., 2006); Wang Jin jie (Wang et al., 2014) carried out a 1-year study on nitrogen wet deposition in Jinshui River Basin. It was found that the concentration of total nitrogen in rainwater ranged from 0.24mg/L to 2.89mg/L, ammonium nitrogen, nitrate nitrogen and organic nitrogen accounted for 42.8%, 13.3% and 43.9% respectively, nitrogen concentration of rainwater decreased with the increase of rainfall, and was obviously diluted by rainfall; Relevant studies (Wang et al., 2014) indicated that compared with nitrate nitrogen, attached algae are easier to absorb and utilize ammonia nitrogen, leading to algae and other aquatic plants to proliferate in large numbers, resulting in blooms. In this work, Chengdu is taken as a representative city of southern China to study the characteristics of ammonia nitrogen natural rainfall caused by air pollution sources. Chengdu is a subtropical humid www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 17 Published by SCHOLINK INC. monsoon climate area with mild climate, distinct seasons, long frost-free period, abundant rainfall and less sunshine. The annual total precipitation is 918.2mm, mainly in July to August (Chengdu Statistical Yearbook, 2016). 15 natural rainfalls in Chengdu city from April to September 2017 were collected and detected. The characteristics of NH3-N pollution in natural rainfalls were analyzed and the temporal and spatial variation of NH3-N pollution in rainfalls near toilet vents of buildings was emphasized. Because there are no industrial enterprises in urban business area, and residential buildings or office buildings are the main structures, the ventilation outlets of the buildings are only toilet vents. Total amount of NH3-N in rainfall and land surface runoff was also discussed. The purpose of this work is to provide theoretical support for source analysis and control of ammonia nitrogen pollution in water. 2. Method 2.1 Sample Collection From the beginning of obvious precipitation to the end of the rainy season (April to September) in 2017, a total of 15 rainfall samples were collected in Chengdu urban area. The natural rainfall sampling sites were located near the author's working unit, which is Environmental Protection Building. The sampling sites of surface runoff process were located on the roads and pavement near the building. The sampling points were arranged as shown in Figure 1 and the attributes of each point are shown in Table 1. Natural rainfall samples were collected by a 2000mL barrel. Rainfall runoff samples are collected manually by pumping devices. Figure 1. Satellite Map of Sampling Layout www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 18 Published by SCHOLINK INC. Table 1. Attributes of Sampling Points Serial number Location Sampling type Pavement attribute Rainfall Runoff ① Opening space in yard √ / ② Parking lot ground √ √ Cement ③ Ground near north gate √ √ Concrete ④ Automobile Lane √ √ Asphalt ⑤ Roof of building √ √ Waterproof coating 2.2 Monitoring and Detection Rainfall monitoring results were recorded with a dump rain gauge (JDZ02-1) combined with real-time rainfall data published by Chengdu Meteorological Bureau. The concentration of NH3-N was determined by Nessler’s reagent spectrophotometry (HJ535-2009). All samples were detected within 24 hours after collection. 3. Result and Discussion 3.1 Variation of NH3-N Concentration in Natural Rainfall The NH3-N concentration of all rainfall samples in Chengdu urban area from April to September in 2017 was monitored and results are shown in Figure 2. It can be seen that the concentration of NH3-N in the first rainfall in 2017 was the highest, reaching 18.2mg/L. According to Environmental Quality Standards for Surface Water (GB3838-2002), it was far worse than Grade V (≤2mg/L), which is the minimum requirement of water quality evaluation. Figure 2. Ammonia Nitrogen Concentration in Natural Rainfall (April to September in 2017) The first rainfall in 2017 occurred on April 22, around the Grain Rain Day which is the 6th solar term of the 24 divisions of solar year in traditional Chinese calendar. The higher concentration of NH3-N in www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 19 Published by SCHOLINK INC. rainwater is due to the increase of motor vehicle travel in winter and frequent human in indoor activities like catering, bathing, heating, etc. The use of natural gas, fuel and other energy causes the increase of SO2 and NOx emissions, which promotes the formation and accumulation of (NH4)2SO4 and NH4NO3 in atmosphere. The lower temperature in winter is also conducive to the accumulation of NH4NO3 in the atmosphere in granular form (Meng et al., 2015). Meanwhile, the atmosphere structure is stable in winter, pollutants are not easy to diffuse. Therefore, during the first rainfall, accumulated (NH4)2SO4 and NH4NO3 in atmosphere dissolved into the rainwater, resulting in a higher concentration of NH3-N. NH3-N concentration decreased significantly in the following 14 rainfalls, ranging from 1.6mg/L to 5.1mg/L, with an average concentration of 3.1mg/L. It can be seen that atmospheric pollutants are the main source of ammonia nitrogen in natural rainfall. The first rainfall has a distinct effect on the scouring and purification of (NH4)2SO4 and NH4NO3 accumulated in winter atmosphere, which makes the concentration of NH3-N in subsequent rainfall decrease significantly. During the study period, NH3-N concentration of natural rainfall in Chengdu city was mostly higher than that of Grade V in standard GB3838-2002 (except for rainfall on July 21, August 20 and September 18).Excessive ammonia nitrogen from rainfall flows into urban rivers, which may make water quality exceed the standard requirement and further cause the eutrophication of water body. 3.2 Effect of Toilet Vent in Buildings on NH3-N Concentration of Rainfall The formation of (NH4)2SO4 and NH4NO3 in the atmosphere depends on NH3 emissions. It is reported that the main sources of NH3 in atmosphere include livestock and poultry sources, nitrogen fertilizer application, synthetic ammonia production and human feces, accounting for 64%, 17%, 1% and 18% respectively (Li, 2012). NH3 in Chengdu urban area mainly comes from human excrement, almost all of which are discharged into atmosphere through toilet vents in buildings. Therefore, sampling points were arranged near the vent (0, 5, 10 and 15m) on the roof of Environmental Protection Building, as shown in ⑤ in Figure 1, and NH3-N concentration in rainfall were detected. 3.2.1 Characteristics of Rainfall The concentration of pollutants in precipitation is influenced by many factors, and there is a large spatial-temporal difference (Zhang et al., 2010; Pu et al., 2010). In this study, NH3-N concentration in two rainfall events (May 13, 2017 and June 9, 2017) was monitored, and the effect of toilet vent on the concentration was analyzed. These two rainfall events belong to light and moderate rain and the rainfall amounts were 8.2 mm and 23.5 mm, respectively. The rainfall process line is shown in Figure 3. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 20 Published by SCHOLINK INC. Figure 3. Rainfall Process Line on May 13, 2017 and June 9, 2017 3.2.2 Temporal and Spatial Variation of NH3-NConcentration in Rainfall The variation of NH3-N concentration during rainfall process at different sampling points in two rainfall events on May 13, 2017 and June 9, 2017 is shown in Figure 4. It can be seen that with the prolongation of rainfall duration at different places, NH3-N concentration of the rainfall decreases in varying degrees. At the beginning of rainfall, NH3-N concentration decreases significantly with time, but at the later stage, the concentration decreases slowly. This is due to the accumulation of ammonia nitrogen pollutants in atmosphere during earlier drought period, and the initial scouring effect of rainfall makes NH3-N concentration in the initial rainfall higher. However, ammonia nitrogen in atmosphere mainly comes from toilet vent in the late stage of rainfall, ammonia gas discharged directly or after secondary reaction dissolves into natural precipitation rapidly, so the NH3-N content in late rainfall is relatively lower. In addition, due to the moderate rain on June 9, 2017, the rainfall was larger and the initial scouring effect was stronger, so the ammonia nitrogen in rainfall decreased more obviously. Figure 4. Variation of NH3-N Concentration in Rainwater at Different Distance from Toilet Vent By analyzing the variation of NH3-N concentration with time, it was found that ammonia nitrogen in natural rainfall at the same sampling point showed a decreasing trend. As the distance from the toilet vent increased, the ammonia nitrogen in rainwater decreased, while the attenuation rate raised. In the case of larger rainfall, such as the moderate rain on June 9, 2017. NH3-N concentration in the middle and late stages was less affected by distance to the vent, and all the values tended to minimum. www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 21 Published by SCHOLINK INC. 3.3 Total Analysis of Ammonia Nitrogen Pollutants Because NH3-N concentration in rainwater can cannot reflect the pollution degree in urban water, the ammonia nitrogen pollution in rainfall and surface runoff was further assessed by the total amount of pollutants measurement method. 3.3.1 Rainfall Analysis Three typical rainfalls on April 22, 2017, June 25, 2017 and August 13, 2017 were selected to analyze the total amount of ammonia nitrogen pollutants in rainwater and surface runoff. Three typical rainfalls on April 22, 2017, June 25, 2017 and August 13, 2017 were selected to analyze the total amount of ammonia nitrogen pollutants in rainfall and surface runoff. According to the 24-hour hyetal grade standard, the three precipitations belong to light, moderate and heavy rain. On April 22, 2017, the rainfall intensity was small and the duration was short; on June 25, 2017, the rainfall intensity was low and the duration was long; on August 13, 2017, the rainfall was intense and lasting for a long time, each rainfall was 9.26, 21.25 and 34.33mm, respectively. 3.3.2 Total Ammonia Nitrogen Pollution Analysis The total amount of ammonia nitrogen pollutants per unit area in natural rainfall was calculated by multiplying the average NH3-N concentration by amount of rainfall per unit area. The calculation results are expressed in grams per square meter as shown in Table 2. Table 2. Total Amount of Ammonia Nitrogen Pollutant in Three Typical Rainfalls in 2017 (g/m2) Date Opening space in yard (Rainfall) Parking lot ground (Runoff) Ground near north gate (Runoff) Automobile Lane (Runoff) Roof of building (Runoff) 2017/04/22 100.5 88.7 97.8 78.3 85.4 NH3-N loss rate 11.7% 2.7% 22.1% 15.0% Average NH3-N loss rate 12.9% 2017/06/25 77.1 52.5 56.8 69.2 44.1 NH3-N loss rate 31.9% 26.3% 10.2% 42.8% Average NH3-N loss rate 27.8% 2017/08/13 129.1 82.9 101.8 94.1 80.1 NH3-N loss rate 35.8% 21.1% 27.1% 38.0% Average NH3-N loss rate 30.5% The total amount of ammonia nitrogen pollutants per unit area of surface runoff can be calculated by formula (1), as in WT= ∑ Ct×Pt T t=0 1000×A (1) WTis the total amount of pollutants per unit area, g/m2; Ct is the concentration of pollutants in each period, mg/L; Pt is the rainfall in each period, L; A is catchment surface area, m2. The total amount of ammonia nitrogen pollutants in natural rainfall and surface runoff at different www.scholink.org/ojs/index.php/ees Energy and Earth Science Vol. 2, No. 1, 2019 22 Published by SCHOLINK INC. sampling points were calculated. The variation of NH3-N concentration in rainfall and surface runoff is shown in Figure 5 with corresponding rain intensity. Figure 5. Variation of Rainfall Intensity and NH3-N Concentration in Rainfall and Surface Runoff According to results of monitoring and calculation, the total amount of ammonia nitrogen pollutants in natural rainfall is sorted as follows: June 25, 2017