ABSTRACT Widespread forest fire events occurred in the foothills of North Western Himalaya during 24 April to 2 May 2016 (Event-1) and 20–30 May 2018 (Event-2). Their impacts were investigated on the distribution of pollutant gases ozone (O3), carbon monoxide (CO), and oxides of nitrogen (NOx) over Uttarakhand using simulations of Weather Research and Forecasting model coupled with chemistry (WRF-Chem) and in-situ observations of these gases over Dehradun, the capital of Uttarakhand. During Event-1, the observed CO mixing ratio over Dehradun increased from 25 April 2016 onwards, attained maximum (705.8 ± 258 ppbv) on 2 May 2016 and subsequently decreased. The rate of increase of daily baseline CO was 29 ppbv/day during HFAP (High Fire Activity Period). During Event-2, daily average concentrations of CO, O3, and NOx showed systematic increase over Dehradun during HFAP period. The rate of increase of CO was 9 ppbv/day, while it was very small for NOx and O3. To quantitatively estimate the influence of forest fire emissions, two WRF-Chem simulations were made: one with biomass burning (BB) emissions and other without BB emissions. These simulations showed 52% (34%) enhancement in CO, 52% (32%) enhancement in NOx, and 11% (9%) enhancement in O3 during HFAP for Event-1 (Event-2). A clear positive correlation (r = 0.89 for Event-1, r = 0.69 for Event-2) was found between ∆O3 (O3with BB minus O3without BB) and ∆CO (COwith BB minus COwithout BB), indicating rapid production of ozone in the fire plumes. For both the events, the vertical distribution of ∆O3, ∆CO, and ∆NOx showed that forest fire emissions influenced the air quality upto 6.5 km altitude. Peaks in ∆O3, ∆CO, and ∆NOx during different days suggested the role of varying dispersion and horizontal mixing of fire plumes.

中文翻译：

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印度北阿坎德邦森林火灾事件对气态空气污染物分布的影响

摘要 2016 年 4 月 24 日至 5 月 2 日（事件 1）和 2018 年 5 月 20 日至 30 日（事件 2）期间，喜马拉雅西北部山麓发生了广泛的森林火灾事件。使用天气研究和预测模型与化学结合 (WRF-Chem) 和原位的模拟，研究了它们对北阿坎德邦上空污染物气体臭氧 (O3)、一氧化碳 (CO) 和氮氧化物 (NOx) 的分布的影响在北阿坎德邦首府德拉敦上空观测到这些气体。在事件 1 期间，观测到的德拉敦 CO 混合比从 2016 年 4 月 25 日开始增加，在 2016 年 5 月 2 日达到最大值 (705.8 ± 258 ppbv)，随后下降。在 HFAP（高火活动期）期间，每日基线 CO 的增长率为 29 ppbv/天。在事件 2 期间，CO、O3、和氮氧化物在 HFAP 期间在德拉敦显示系统性增加。CO 的增加率为 9 ppbv/天，而 NOx 和 O3 的增加速度非常小。为了定量估计森林火灾排放的影响，进行了两种 WRF-Chem 模拟：一种具有生物质燃烧 (BB) 排放，另一种没有 BB 排放。这些模拟显示，在事件 1（事件 2）的 HFAP 期间，CO 增加 52% (34%)，NOx 增加 52% (32%)，O3 增加 11% (9%)。在ΔO3（带BB的O3减去不带BB的O3）和ΔCO（带BB的CO减去不带BB的CO）之间发现明显的正相关（事件1的r = 0.89，事件2的r = 0.69），表明臭氧的快速产生火羽。对于这两个事件，ΔO3、ΔCO 和 ΔNOx 的垂直分布表明，森林火灾排放影响了 6.5 公里高度的空气质量。