Forest fires have become more intense and frequent in recently changing climates. The wide variety of pollutants released by forest fire include greenhouse gases, photochemically reactive compounds, and fine and coarse particulate matter. This study investigated the impact of forest fire events on air quality in the Kathmandu Valley during March–April 2021 using ground air quality monitoring stations and satellite data. The three fire periods were studied (a) Pre-fire from 21^st - 23^rd March (b) first-fire episode from 24^th −27^th March and (c) second fire episode from 1^st – 5^th April of 2021. The concentrations of PM_2.5 reached to maximum 199 μg/m³ during pre-fire period, 371 μg/m³ and 280 μg/m³ during first and second fire event respectively. The second fire episode had lower PM_2.5 concentration despite higher fire counts (449) compared to the first episode suggesting influence of fire activities near to vicinity of Kathmandu valley during second fire episode. There was a two-day lag between the beginning of forest fire events and an increase in PM_2.5 levels in Kathmandu. Satellite observation showed varying patterns for different pollutants. HCHO levels responded quickly to fire activity, while AOD and CO levels increased after a few days. Also, low wind speed, low temperature, and low relative humidity additionally elevated these pollutants in Kathmandu. This study emphasizes the extent of the impact of forest fires on air quality and the importance of considering meteorological and satellite data to understand the distribution of pollutants during such events.

中文翻译：

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加德满都谷地住宅区颗粒物和大气污染物浓度：2021 年 3 月至 4 月森林火灾事件案例研究


在最近不断变化的气候中，森林火灾变得更加强烈和频繁。森林火灾释放的污染物种类繁多，包括温室气体、光化学反应性化合物以及细颗粒物和粗颗粒物。本研究使用地面空气质量监测站和卫星数据调查了 2021 年 3 月至 4 月期间森林火灾事件对加德满都谷地空气质量的影响。研究了三个火灾时期：（a） 3 月 21^日至 23^日的火灾前，（b） 3 月 24^日至 27^日的第一次火灾事件和 （c） 2021^{年 4} 月^{1 日至 5} 日的第二次火灾事件。PM_2.5 浓度在火灾前达到最高 199 μg/m³，在第一次和第二次火灾期间分别达到 371 μg/^{m 3} 和 280 μg/m³。与第一次事件相比，尽管火灾数量较高 （449），但第二次火灾事件的 PM_2.5 浓度较低，这表明在第二次火灾事件期间加德满都山谷附近附近的火灾活动产生了影响。加德满都的森林火灾事件开始和 PM_2.5 水平增加之间有两天的滞后。卫星观测显示不同污染物的模式不同。HCHO 水平对火灾活动反应迅速，而 AOD 和 CO 水平在几天后增加。此外，低风速、低温和低相对湿度也加剧了加德满都的这些污染物。本研究强调了森林火灾对空气质量的影响程度，以及考虑气象和卫星数据以了解此类事件期间污染物分布的重要性。