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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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Bar and pie charts depicting pollution data. Chart (a) shows primary pollutant frequency by days during heating (red) and non-heating periods (blue), with highest values for NO2. Chart (b) is a pie chart showing pollution categories, with modification pollution being the largest at 56.4%, followed by preferential arrival route at 25.7%. Other categories include light pollution, heavy pollution, moderate pollution, and critical pollution. — Frequency statistics of primary pollutants in heating and non-heating periods (a) and proportion of days at all levels of air quality (b).