*2.1. Study Area*

Changzhou, located on the southern bank of the Yangtze River, is a prefecture-level city in southern China's Jiangsu province. Changzhou borders the provincial capital of Nanjing to the west, Zhenjiang to the northwest, Wuxi to the east, and Zhejiang province to the south (Figure 1). Changzhou is part of the highly developed Yangtze Delta region of China, extending northwest from Shanghai. In 2018, its total population was 4.74 million, and its urban population was 3.85 million. The urbanization rate reached 73.3%, 13.72% higher than the average in China.

Data published by the Ministry of Environmental Protection of China show that most chemical and petrochemical construction projects are distributed near rivers and lakes in highly populated areas [31]. Changzhou is located in the Yangtze River Delta close to many water bodies and dense populations. It also has a large chemical industry, with hazardous chemical substances.
