Key Takeaways & Executive Findings
- •• • The volume-weighted mean total dissolved solids (TDS) in Changsha precipitation was 245.58 μeq·L−1, with a range of 51.71–813.40 μeq·L−1, indicating significant variability in atmospheric solute loading that must be considered in regional deposition models. • • Ca2+ and SO4^2− together constituted 55.76% of the total ionic concentration, with SO4^2− and NO3^− accounting for 48.24% and 29.13% of anions, respectively, highlighting the dominance of acidic precursors from anthropogenic sources. • • Correlation analysis revealed strong positive correlations between SO4^2− and NO3^− (r = 0.78) and between Ca2+ and Mg2+ (r = 0.70), indicating common sources and guiding targeted emission reduction strategies. • • Enrichment factor analysis quantified that anthropogenic contributions accounted for 99.5% of SO4^2− and 95.4% of NO3^−, while Cl− was 98% marine-derived, providing precise source apportionment for policy interventions.
Abstract
This study investigates the ionic concentration characteristics and sources of atmospheric precipitation in Changsha, China, based on samples collected from December 2019 to November 2021. The total dissolved solids (TDS) in precipitation ranged from 51.71 to 813.40 μeq·L−1, with a volume-weighted mean (VWM) concentration of 245.58 μeq·L−1. The VWM ionic concentrations followed the order: Ca2+ > SO4^2− > NO3^− > HCO3^− > K+ > Na+ > Cl− > Mg2+. Ca2+ and SO4^2− together accounted for 55.76% of the total ionic mass. Seasonal variation of total ionic concentration was highest in winter and lowest in spring, following the order winter > autumn > summer > spring. Correlation analysis revealed strong positive correlations between SO4^2− and NO3^− (r = 0.78) and between Ca2+ and Mg2+ (r = 0.70), suggesting common sources. Principal component analysis and enrichment factor (EF) analysis indicated that SO4^2− and NO3^− predominantly originated from anthropogenic activities, with contribution rates of 99.5% and 95.4%, respectively, likely from coal combustion and industrial emissions. Ca2+ and K+ were mainly terrestrial, with contribution rates of 99.2% and 98.3%, respectively, from soil and biomass burning. Mg2+ had dual sources: 68.8% terrestrial and 31.2% marine. Cl− exhibited an EFmarine of 0.74 and EFsoil of 50.20, indicating a dominant marine source contributing 98% of its input. These findings provide a scientific basis for understanding regional atmospheric pollution and supporting environmental management strategies.
1. Introduction
Rapid industrialization and urbanization in China have led to severe atmospheric pollution, particularly in regions with concentrated industrial activities. Acid rain and haze events have become major environmental concerns, driven by emissions of SO2, NOx, and particulate matter from coal combustion and vehicular traffic. Understanding the chemical composition of atmospheric precipitation is crucial for assessing the extent of anthropogenic influence and for devising effective mitigation strategies. However, existing studies often lack comprehensive ionic source apportionment, especially in rapidly developing inland cities like Changsha, where the interplay of local emissions and regional transport remains poorly characterized.
This study addresses this gap by conducting a two-year systematic analysis of precipitation chemistry in Changsha, employing correlation analysis, principal component analysis, and enrichment factor methods to quantitatively distinguish between natural and anthropogenic sources. The findings provide high-resolution data on ionic concentrations and source contributions, enabling evidence-based policy formulation for air quality management and sustainable regional development.
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PENG Lei, YU Zhengliang, XIAO Xiong, XU Linya, YANG Han (2026). Chemistry and Ionic Sources of Precipitation in the Changsha Area. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025051307
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Frequently Asked Questions
What are the dominant ionic species in Changsha precipitation and their seasonal variations?
The dominant ions are Ca2+ and SO4^2−, together accounting for 55.76% of total ionic concentration. Seasonal total concentration follows winter > autumn > summer > spring, with winter maxima likely due to increased coal combustion for heating and lower precipitation scavenging.
How were anthropogenic versus natural sources quantitatively distinguished?
Enrichment factor (EF) analysis relative to marine and soil references was used. For SO4^2− and NO3^−, EF values indicated negligible marine/soil contributions, with anthropogenic contributions of 99.5% and 95.4%, respectively. For Cl−, EFmarine = 0.74 and EFsoil = 50.20, indicating a marine source contribution of 98%.
What is the correlation between SO4^2− and NO3^−, and what does it imply?
The correlation coefficient between SO4^2− and NO3^− is 0.78, indicating a strong positive relationship. This suggests they share common anthropogenic sources, likely coal combustion and vehicle emissions, which is critical for designing combined control strategies.
What are the sources of Ca2+ and Mg2+ in precipitation?
Ca2+ and Mg2+ show the highest correlation (r = 0.70). Ca2+ is predominantly terrestrial (99.2% contribution), likely from soil and rock weathering. Mg2+ has dual sources: 68.8% terrestrial and 31.2% marine, indicating both crustal and sea-salt influences.
How do these findings inform regional air quality management?
The high anthropogenic contributions to SO4^2− and NO3^− underscore the need to reduce emissions from coal combustion and industrial activities. The significant marine contribution to Cl− suggests that sea-salt aerosols can influence precipitation chemistry even inland, which should be considered in regional atmospheric models.
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