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<p>Forest fires in the Himalaya act as episodic yet powerful sources of aerosols, exerting strong perturbations on regional air quality, radiative forcing, and climate feedback. This study investigates the role of fire emissions in modulating aerosol properties and atmospheric heating over Katarmal (29.64°N, 79.62°E; 1225&#xa0;m amsl), a western Himalayan semi-urban site from 2019 to 2024. Multi-year ground-based observations of black carbon, aerosol absorption (σ<sub>abs,λ</sub>), aerosol optical depth (AOD), and meteorological parameters were analysed to contrast fire (FF1-FF6) and non-fire conditions. Seasonal meteorology was characterized by weak winds (&lt; 2&#xa0;m&#xa0;s<sup>−1</sup>) and strong monsoonal control on humidity (&gt; 90%), creating stagnant conditions that facilitated pollutant accumulation and enhanced the atmospheric response to fire emissions. Wintertime BC concentrations exceeded 4&#xa0;µg&#xa0;m<sup>−3</sup> under stagnant conditions, while pre-monsoon episodes exhibited sharp enhancements (~ 14&#xa0;µg&#xa0;m<sup>−3</sup>) associated with fire activity, vehicular emission linked to tourism/pilgrimage, and dust transport. Forest fire events (FF1–FF6) elevated absorption coefficient σ<sub>abs,370</sub> to 168.2&#xa0;Mm⁻<sup>1</sup>, exceeding background levels by &gt; 3 times, corroborated by fire radiative power (3.8–6.3&#xa0;MW). AOD values (range: 0.04–2.20; mean 0.39 ± 0.21) displayed strong pre-monsoon maxima linked to fire emissions and transported dust. Radiative forcing estimates showed that fire periods nearly doubled atmospheric absorption (50.5 ± 17.8 W m<sup>−2</sup> and 29.1 ± 4.3 W m<sup>−2</sup> during fire and non-fire respectively), with heating rates increasing from 0.8 to 1.9&#xa0;K Day<sup>−1</sup>. These results demonstrate that Himalayan Forest fires are critical episodic drivers of enhanced BC loading and atmospheric absorption, with implications for boundary-layer dynamics, monsoon circulation, and regional climate sensitivity.</p>

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Seasonal dynamics and radiative impact of fire-influenced aerosols over a semi-urban site in the Western Himalayan region

  • 期刊论文

  • 发表日期：

    2026年7月28日

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  • Archana Bawari,
  • Sheetal Chaudhary,
  • Anil Singh Salal,
  • Rajesh Joshi,
  • Jagdish Chandra Kuniyal,
  • Bimal Pande

摘要

Forest fires in the Himalaya act as episodic yet powerful sources of aerosols, exerting strong perturbations on regional air quality, radiative forcing, and climate feedback. This study investigates the role of fire emissions in modulating aerosol properties and atmospheric heating over Katarmal (29.64°N, 79.62°E; 1225 m amsl), a western Himalayan semi-urban site from 2019 to 2024. Multi-year ground-based observations of black carbon, aerosol absorption (σabs,λ), aerosol optical depth (AOD), and meteorological parameters were analysed to contrast fire (FF1-FF6) and non-fire conditions. Seasonal meteorology was characterized by weak winds (< 2 m s−1) and strong monsoonal control on humidity (> 90%), creating stagnant conditions that facilitated pollutant accumulation and enhanced the atmospheric response to fire emissions. Wintertime BC concentrations exceeded 4 µg m−3 under stagnant conditions, while pre-monsoon episodes exhibited sharp enhancements (~ 14 µg m−3) associated with fire activity, vehicular emission linked to tourism/pilgrimage, and dust transport. Forest fire events (FF1–FF6) elevated absorption coefficient σabs,370 to 168.2 Mm⁻1, exceeding background levels by > 3 times, corroborated by fire radiative power (3.8–6.3 MW). AOD values (range: 0.04–2.20; mean 0.39 ± 0.21) displayed strong pre-monsoon maxima linked to fire emissions and transported dust. Radiative forcing estimates showed that fire periods nearly doubled atmospheric absorption (50.5 ± 17.8 W m−2 and 29.1 ± 4.3 W m−2 during fire and non-fire respectively), with heating rates increasing from 0.8 to 1.9 K Day−1. These results demonstrate that Himalayan Forest fires are critical episodic drivers of enhanced BC loading and atmospheric absorption, with implications for boundary-layer dynamics, monsoon circulation, and regional climate sensitivity.