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. 2025 Aug 1;13:1632713. doi: 10.3389/fpubh.2025.1632713

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Copyright © 2025 Jing and Xiaofeng.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Scatter plot matrix showing relationships between PM₂.₅/NO₂, Year, Non-heating period (SO₂), and Heating period (SO₂). Each plot includes a regression line, confidence ellipse, and Pearson's correlation coefficient. Box plots are on the diagonal, summarizing data distributions. — Scatter plot of SO₂ concentration in heating period and non-heating period.