Ozone production and precursor emission from wildfires in Africa
Ozone production and precursor emission from wildfires in Africa
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DOI：
10.1039/d1ea00041a
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发表时间：
2021-11-01
期刊：
影响因子：
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通讯作者：
Andrews, Stephen
中科院分区：
文献类型：
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作者：
Lee, James D.;Squires, Freya A.;Andrews, Stephen
对流层臭氧（O-3）对人类健康产生负面影响，也是一种温室气体。它是由氮氧化物（NOx）和挥发性有机化合物（VOCs）的光化学反应形成的，其中野火是一个重要的来源。这项研究提供了在西非和中非大草原地区对野火进行采样的研究飞行数据，这些野火既靠近火灾，又在排放物经过北大西洋热带上空几天后被运输。在靠近火灾的数据中，从增强到摩尔分数计算了NOx（作为NO）、6种挥发性有机化合物和甲醛的g kg（-1）排放因子（EFs）。对于氮氧化物，塞内加尔的排放因子为2.05 +/- 0.43 g kg(-1)，乌干达的排放因子为1.20 +/- 0.28 g kg(-1)，均高于以往非洲大草原地区研究的平均值1.13 +/- 0.6 g kg（-1）。对于大多数挥发性有机化合物（乙炔除外），乌干达的EFs比塞内加尔低20-50%，几乎所有值都低于文献中的值。通过检查δ O-3/ δ CO增强比，研究了火羽中的O-3增强，其值从靠近火场的0.07-0.14到在大西洋上进行的长达200小时的下风测量的0.25。此外，O-3及其前体的测量值与大西洋上空飞行的全球化学输送模型（GEOS-CF）的输出值进行了比较。测量数据和模拟数据之间的标准化平均偏差（NMB）比较在火羽之外是良好的，CO显示模型低估了4.6%，O-3略微高估了0.7%（两者都在数据的标准偏差范围内）。对于氮氧化物，该协议较差，所有航班的预测低于9.9%。在火羽内部，模型值和测量值之间的一致性更差，模型对所有三种物种的偏差都明显更低。在所有航班中，CO、O-3和NOx的预测量分别低于29.4%、16.5%和37.5%。最后，将实测的Delta O-3/Delta CO增强比与等效飞行数据模型中的增强比进行比较，发现模型的值为0.17 +/- 0.03，而观测值为0.29 +/- 0.05。研究结果表明，非洲野火对北大西洋的O-3负担可能被低估，需要进一步研究O-3前体排放和化学性质。
Tropospheric ozone (O-3) negatively impacts human health and is also a greenhouse gas. It is formed photochemically by reactions of nitrogen oxides (NOx) and volatile organic compounds (VOCs), of which wildfires are an important source. This study presents data from research flights sampling wildfires in West and Central African savannah regions, both close to the fires and after the emissions had been transported several days over the tropical North Atlantic Ocean. Emission factors (EFs) in g kg(-1) for NOx (as NO), six VOCs and formaldehyde were calculated from enhancement to mole fractions in data taken close to the fires. For NOx, the emission factor was calculated as 2.05 +/- 0.43 g kg(-1) for Senegal and 1.20 +/- 0.28 g kg(-1) for Uganda, both higher than the average value of 1.13 +/- 0.6 g kg(-1) for previous studies of African savannah regions. For most VOCs (except acetylene), EFs in Uganda were lower by factors of 20-50% compared to Senegal, with almost all the values below those in the literature. O-3 enhancement in the fire plumes was investigated by examining the Delta O-3/Delta CO enhancement ratio, with values ranging from 0.07-0.14 close to the fires up to 0.25 for measurements taken over the Atlantic Ocean up to 200 hours downwind. In addition, measurements of O-3 and its precursors were compared to the output of a global chemistry transport model (GEOS-CF) for the flights over the Atlantic Ocean. Normalised mean bias (NMB) comparison between the measured and modelled data was good outside of the fire plumes, with CO showing a model under-prediction of 4.6% and O-3 a slight over-prediction of 0.7% (both within the standard deviation of the data). For NOx the agreement was poorer, with an under-prediction of 9.9% across all flights. Inside the fire plumes the agreement between modelled and measured values is worse, with the model being biased significantly lower for all three species. In total across all flights, there was an under-prediction of 29.4%, 16.5% and 37.5% for CO, O-3 and NOx respectively. Finally, the measured Delta O-3/Delta CO enhancement ratios were compared to those in the model for the equivalent flight data, with the model showing a lower value of 0.17 +/- 0.03 compared to an observed value of 0.29 +/- 0.05. The results detailed here show that the O-3 burden to the North Atlantic Ocean from African wildfires may be underestimated and that further study is required to better study the O-3 precursor emissions and chemistry.