The seasonal characterization and source analysis of water-soluble inorganic ions in PM_2.5 in Fuxin, northeast China

Abstract

In Fuxin, a few existing studies have illustrated the pollution characteristics of water-soluble ions (WSIIs) in PM_2.5 in four seasons. To track the particulate pollution in Fuxin, sample filters of PM_2.5 in the four seasons of spring, summer, autumn and winter in 2019 were collected. For the first time, the concentration and seasonal variation characteristics of PM_2.5 and WSIIs were tested by gravimeter method and ion chromatography. Characteristics of WSIIs and their existence sources and forms were explored by ion balance calculation, correlation analysis and principal component analysis. The annual average concentrations of PM_2.5 and WSIIs were (33.23 ± 13.03) μg·m⁻³ and (22.86 ± 9.62) μg·m⁻³, respectively. The seasonal WSIIs concentration followed the order: spring (29.98 μg·m⁻³) > autumn (28.85 μg·m⁻³) > winter (21.32 μg·m⁻³) > summer (11.28 μg·m⁻³). In WSIIs, 81.41% of them were secondary inorganic ions (SO₄²⁻, NO₃⁻, and NH₄⁺), contributed about 68.80% to PM_2.5, and the chemical forms were mainly (NH₄)₂SO₄ and NH₄NO₃. In this study, it has been revealed that PM_2.5 samples exhibited acid properties in spring and autumn while, displayed alkalinity in summer and winter. The average value of NO₃⁻/SO₄²⁻ was 0.67, so from these data it can be illustrated that fixed pollution sources were found to be dominant over mobile sources in Fuxin. The main identified sources of WSIIs in four seasons in Fuxin were sea salt particles and secondary particles, respectively. These results showed that the geographical factors of Bohai Bay and secondary transformation had a significant impact on the concentration of WSIIs of PM_2.5 in Fuxin.

Keywords:

• Water-soluble ions
• PM_2.5
• gravimeter method
• seasonal variations
• Fuxin City

Competing interests

There are no relevant financial or non-financial competing interests.

Acknowledgments

The authors gratefully thank for the financial support provided by the sub-project of National Key R & D program (2019 YFC180380103) and the scientific research project of Liaoning Provincial Education Department (LJ2020JCL031); The authors also thank the necessary laboratory support provided by the Liaoning Technical University.