Long-term changes in wet nitrogen and sulfur deposition in Nanjing

doi:10.1016/j.atmosenv.2018.09.048

Atmospheric Environment

Volume 195, December 2018, Pages 104-111

https://doi.org/10.1016/j.atmosenv.2018.09.048 Get rights and content

Highlights

•
Nanjing had lower SO₄²⁻ but higher NO₃⁻ deposition than the averages of China.
•
SO₄²⁻ deposition decreased while NO₃⁻ increased from the 8th to the 12th Five-year Plan.
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Both SO₄²⁻ and NO₃⁻ deposition abruptly decreased in 2015 and 2016.
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The contribution of SO₄²⁻ to NO₃⁻ on precipitation acidity decreased from 1990 to 2016.

Abstract

The concentration and deposition of acid from precipitation in Nanjing in the Yangtze River Delta are presented, and their long-term trends are detected based on ground measurements. The wet SO₄²⁻ deposition was 18.1 kg S ha⁻¹ yr⁻¹ from 2015 to 2016, which is much lower than the average across China; and the NO₃⁻ deposition was 8.5 kg N ha⁻¹ yr⁻¹, which is higher than the national average. Both SO₄²⁻ and NO₃⁻ depositions were relatively high in spring, summer, and autumn, with the lowest occurring in winter. From 1990 to 2016, the averages of SO₄²⁻ deposition during each Five-year Plan gradually decreased from the 8th (1991–1995) to 12th Five-year Plan (2011–2015), although the annual value did not show a significant decreasing trend due to large variations. Both the annual value and averages of NO₃⁻ deposition during each Five-year Plan showed significant increasing trends from 1990 to 2016. The SO₄²⁻ deposition during the 12th Five-year Plan decreased by 26.5% while the NO₃⁻ deposition increased by 182.9% relative to that of the 8th Five-year Plan. These results confirmed that NO₃⁻ deposition is still high in the Yangtze River Delta.

Introduction

China has become one of the global hotspots of acid deposition due to the increased energy consumption in recent years (Vet et al., 2014). To control acid pollution and improve air quality, the Chinese government has enacted a series of policies to decrease the acid deposition precursors SO₂ and NO_x since the mid-1990s (Hao et al., 2000). Before the 12th Five-year Plan (2011–2015), only SO₂ emissions were controlled, and the joint control on SO₂ and NO_x emissions began with the 12th Five-year Plan. As a result, the SO₂ emissions decreased beginning in 2006, and the NO_x emissions decreased beginning in 2012 across China (Duan et al., 2016). The changes in SO₂ and NO_x emissions will change the acid components in precipitation, which have rarely been studied (Fang et al., 2013).

Studies on long-term acid deposition require long-term monitoring in specific areas. For example, three decades of monitoring on the acid composition of precipitation at Guangzhou showed that SO₄²⁻ deposition has decreased since 2001, NO₃⁻ has remained unaltered, and a marked recovery of precipitation pH has occurred since 2005 (Fang et al., 2013). A regional background station in northern China exhibited a significant increasing trend of NO₃⁻ deposition and a decreasing trend of the SO₄²⁻/NO₃⁻ ratio in precipitation from 2003 to 2014 (Pu et al., 2017). The deposition of NO₃⁻ in a subtropical rainforest significantly decreased while precipitation pH remained relatively stable from 1994 to 2013 (Chang et al., 2017). The acid composition of precipitation varies from site to site and region to region due to the different emission sources, the long-range transport trajectories, and the policies for controlling SO₂ and NO_x emissions. Therefore, the long-term trends in other areas should be addressed to fully understand the changes of acid deposition across China.

Nanjing is located in one of the developed areas in China, the Yangtze River Delta (YRD). This area is undergoing rapid economic growth, urbanization, and industrialization and thus is one of the first areas to suffer from acid rain (Tang et al., 2010). Highly developed industries and transportation emit large amounts of SO₂ and NO_x. With the 10th Five-year Plan, a series of air quality policies were enacted to control SO₂ emissions. Under such conditions, SO₄²⁻ concentrations decreased while NO₃⁻ concentrations increased from 1992 to 2003, and a significant trend in precipitation pH was not observed in Nanjing (Tu et al., 2005). However, a goal was set to reduce 21.2% of the NO_x emissions in 2015 compared with that in 2010 in the 12th Five-year Plan in Nanjing, and the NO_x emissions decreased by 24.9% in 2015 (https://www.xzbu.com/1/view-7261236.htm). These NO_x emission control policies decreased the NO₂ concentrations in the atmosphere beginning in the 12th Five-year Plan (Ma et al., 2017), which might change the NO₃⁻ concentration in precipitation. However, the mechanisms underlying the change in acid deposition based on policies to control NO_x emissions remain unclear. Studying changes in the components and deposition of acid in Nanjing will provide a scientific basis for establishing policies on the economic development of other areas.

This study aims to investigate wet acid deposition in Nanjing based on collected precipitation samples under the influence of industry development and air quality policies. First, the concentration of acid in precipitation and wet deposition in Nanjing from 2015 to 2016 is presented; second, the seasonal variations in acid deposition are analysed; and finally, the long-term trends in acid deposition are detected based on ground-monitoring data from 1990 to 2016.

Section snippets

Study area and sampling sites

Nanjing has a humid subtropical climate under the influence of the East Asian monsoon. The four seasons are distinct, and the area has an annual mean temperature of 15.9 °C and rainfall of 1058.1 mm (Yin, 2015). Chemical, electronics, automobile and machinery are the four pillar industries in Nanjing (2010 Nanjing Economic and Social Development Bulletin). In 2010, the value added by industry in Nanjing was 2.0 × 10¹¹ CNY (China Yuan), thus accounting for 40% of the Gross Domestic Product

Acid concentration and deposition of SO₄²⁻ and NO₃⁻ with precipitations in Nanjing

To understand the acid deposition from precipitation in Nanjing, the minimum, maximum, arithmetic mean, and VWM of the SO₄²⁻ and NO₃⁻ concentration in precipitation from 2015 to 2016 were calculated, and the results are provided in Table 1. Both of the SO₄²⁻ and NO₃⁻ concentrations showed a large range, with values of 0.52–40.80 mg L⁻¹ and 0.39–20.60 mg L⁻¹, respectively. Furthermore, the arithmetic mean concentration of SO₄²⁻ and NO₃⁻ was higher than its VWM value, suggesting that higher

Conclusions

This study presented the acid concentrations in precipitation and deposition in Nanjing based on ground measurements and detected the long-term trends of acid deposition from 1990 to 2016. Compared with other provincial capitals and the cities close to Nanjing, the SO₄²⁻ pollution in Nanjing was low while the NO₃⁻ pollution was still high. Uncertainties from different years of rainwater sampling should be considered when comparing the acid concentration and deposition with those in other

Acknowledgment

This study is supported by the National Natural Science Foundation of China (No. 41471343), and the Fundamental Research Funds for the Central Universities (020914380047).

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Long-term changes in wet nitrogen and sulfur deposition in Nanjing

Highlights

Abstract

Introduction

Section snippets

Study area and sampling sites

Acid concentration and deposition of SO42− and NO3− with precipitations in Nanjing

Conclusions

Acknowledgment

Sci. Total Environ.

Atmos. Environ.

Acta Sci. Circumstantiae

J. Lanzhou Univ. (Nat. Sci.)

Atmos. Environ.

Atmos. Environ.

Sci. Total Environ.

Sci. Total Environ.

Atmos. Res.

Atmos. Environ.

Atmos. Environ.

Chemosphere

J. Remote Sens.

The Chemical Characteristics of Precipitation and Their Source Analysis in Shanghai

Intercomparison of NOx emission inventories over East Asia

Atmos. Chem. Phys.

Three-decade changes in chemical composition of precipitation in Guangzhou city, southern China: has precipitation recovered from acidification following sulphur dioxide emission control?

Tellus Ser. B Chem. Phys. Meteorol.

Characteristics of chemical composition of atmospheric precipitation in Nanning

Guangdong Chem.

Designation of acid rain and SO2 control zones and control policies in China

J. Environ. Sci. Health - Part A Toxic/Hazard. Subst. Environ. Eng.

Characteristics and cause analysis on acid rain pollution in Shijiazhuang City

Hebei J. Ind. Sci. Technol.

Analysis on the situation and cause of the acid rain in Yangzhou Area

Environ. Monit. Forewarning

The effects of the global financial crisis on China's financial market and macroeconomy

Econ. Res. Int.

The composition, seasonal variation, and potential sources of the atmospheric wet sulfur (S) and nitrogen (N) deposition in the southwest of China

Environ. Sci. Pollut. Control Ser.

A review of spatial variation of inorganic nitrogen (N) wet deposition in China

PLoS One

Acid concentration and deposition of SO₄²⁻ and NO₃⁻ with precipitations in Nanjing