Chemical composition of precipitation in Shenzhen, a coastal mega-city in South China: Influence of urbanization and anthropogenic activities on acidity and ionic composition

Xiaode Zhou; Zhifang Xu; Wenjing Liu; Yao Wu; Tong Zhao; Hao Jiang; Xuan Zhang; Jiangyi Zhang; Li Zhou; Yuchen Wang

doi:10.1016/j.scitotenv.2019.01.096

Chemical composition of precipitation in Shenzhen, a coastal mega-city in South China: Influence of urbanization and anthropogenic activities on acidity and ionic composition

Sci Total Environ. 2019 Apr 20:662:218-226. doi: 10.1016/j.scitotenv.2019.01.096. Epub 2019 Jan 11.

Authors

Xiaode Zhou¹, Zhifang Xu², Wenjing Liu³, Yao Wu⁴, Tong Zhao¹, Hao Jiang¹, Xuan Zhang¹, Jiangyi Zhang¹, Li Zhou⁵, Yuchen Wang¹

Affiliations

¹ Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China; University of Chinese Academy of Sciences, Beijing 100049, China. Electronic address: zfxu@mail.iggcas.ac.cn.
³ Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China; University of Chinese Academy of Sciences, Beijing 100049, China.
⁴ Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China.
⁵ State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China.

PMID: 30690356
DOI: 10.1016/j.scitotenv.2019.01.096

Abstract

Rainwater samples from Shenzhen in south China were collected over the period of a year, and the chemical compositions were measured with the main purpose of understanding the acidification of rainwater and the controlling factors. The pH value of precipitation ranged from 3.72 to 6.77, with a volume-weighted mean (VWM) value of 4.29, and the acid rain frequency was 97%. The VWM concentrations of anions and cations followed the order of SO₄^2- > Cl^- > NO₃^- and Na⁺ > Ca²⁺ > NH₄⁺ > Mg²⁺ > K⁺, respectively. Air mass back-trajectory and positive matrix factorization analyses indicated that sources of ions in rainwater were mainly from sea salt, soil dust and anthropogenic activities. Compared with other areas in China, the rainwater of Shenzhen has the lowest values of the NP/AP, ∆pH and NF values of Ca²⁺ and NH₄⁺, indicating that the lack of the capacity for neutralization could be the main reason for the severe acid rain problem. It is noteworthy that the rain acidification tendency is obvious, and the pH value has reduced by 1.0 units since the 1980s. Based on a comparison of the chemical compositions of the rainwater from different historical periods, the NO₃^- concentration was found to have increased consistently, whereas the NH₄⁺ concentration maintained a decreasing trend since 1980. On the other hand, the nss-SO₄^2- and nss-Ca²⁺ concentrations increased after 1980 and then decreased after 1994. Meanwhile, the decreasing pH was accompanied by a decreasing NP/AP ratio. These results suggest that the changes in human activities at different stages of urban development can lead to a synergistic change in the chemical characteristics of precipitation. Both an increase in the acidic species emissions (especially NO_X) due to rapid economic development and a decrease in the alkaline ions concentration due to urbanization have resulted in the rain acidification tendency in Shenzhen.

Keywords: Anthropogenic activities; Neutralizing capacity; Rain acidification; Shenzhen; Urbanization.