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近几年,北京连续发生了严重的雾霾事件,相关研究已经开展了很多[1—6]。而黑碳(BC)气溶胶作为大气重要的组成成分,主要由含碳物质不完全燃烧产生的,会影响大气环境和人体健康。它也是大气气溶胶中最主要的光学吸收成分,可以通过直接效应影响太阳辐射,产生辐射强迫,加热大气,从而直接导致云的蒸发、减少[7—9]。BC气溶胶也可以作为云凝结核或直接作为冰核,改变云的微物理和辐射性质以及云的寿命,间接影响气候系统[10—13]。同时,BC气溶胶还可以参加非均相化学反应和气粒转化过程,对大气过程产生重要的影响[14]。
目前,在我国BC气溶胶的研究大多还是局限于光学和热光学两种观测方法,因为受到了滤膜和其他气溶胶特别是散射气溶胶粒子的影响,很难得到BC谱分布和混合态特征。而国外早已经针对BC气溶胶混合态、谱分布开展了众多的空中和地面的探测研究,尤其是美国Droplet Measurement Technologies(DMT)公司设计的单颗粒黑碳光度计(single particle soot photometer,简称SP2)已经成熟运用。至今,Cozic等[15]、Chwarz等[16]、Reddington等[17]、Baumgardner等[18]、Metcalf等[19]均利用SP2对BC气溶胶垂直特征、BC气溶胶的垂直混合态和谱分布特征进行了探测分析。我国这几年亦有利用SP2针对深圳[20]、北京及周边[21]、西安[22]、无锡[23]、南京[24]等地区的BC气溶胶浓度、混合态及季节变化特征的研究报道。然而,对于不同天气条件下BC气溶胶的垂直分布及其混合态特性研究较少。
本文选取其中10次飞行过程,对比深入分析了在不同大气条件下北京地区BC气溶胶谱分布、混合态信息和模拟结果的差异。旨在研究我国高空BC气溶胶的特征,为高空污染物的传输以及BC气溶胶气候效应,模式订正提供基础。
基于飞机观测不同天气条件下北京地区黑碳气溶胶的垂直分布及其混合态特性
Vertical distribution and mixed state characteristics of black carbon aerosols in Beijing Area based on aircraft observation under different weather conditions
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摘要: 利用机载单颗粒黑碳光度计(SP2)针对北京地区不同天气条件下黑碳(BC,black carbon)气溶胶的垂直分布特征进行了10次的飞机探测研究。结果显示,在霾和非霾条件下BC气溶胶的浓度都是随着高度升高而减小,而且浓度变化在1500 m高度存在明显的分界线。在1500 m以下,BC气溶胶浓度变化梯度均较大,霾条件下的BC气溶胶浓度约为非霾条件下的4.3倍,在1500 m以上,BC气溶胶浓度变化梯度均较小,霾条件下的BC气溶胶浓度约为非霾条件下的2.5倍。BC气溶胶粒子谱都呈单峰分布,霾条件下峰值粒径主要要集中在0.16 µm在非霾条件下峰值粒径主要集中在0.18 µm在近地面,霾条件下的平均内混比远远高于非霾条件下,越往高空两种条件下的BC气溶胶的平均内混比越接近。通过CAMx模拟了不同条件下的BC气溶胶,发现霾污染天气下模拟的结果差异较大,在非霾条件下的模拟结果要优于霾条件下的模拟结果,这主要是由于在大部分模式中,很少考虑黑碳的老化状态。Abstract: The airborne single particle soot photometer (SP2) was used in ten times of aircraft observation studies on vertical distribution characteristics of black carbon aerosol under different weather conditions in Beijing. The results showed that, under both haze and non-haze conditions, the concentration of black carbon aerosol decreased with the increase of the height, and there existed a clear boundary line for concentration change at the height of 1500 m. Below the height of 1500 m, the gradient of BC aerosol concentration was large, and the BC aerosol concentration under haze conditions was about 4.3 times of that under non-haze conditions. Above the height of 1500 meters, the gradient of BC aerosol concentration was small, and the BC aerosol concentration under haze conditions was about 2.5 times of that under non-haze conditions. It was also found that the BC aerosol particle spectrum had a single peak distribution, with the peak particle size mainly concentrated at 0.16 µm under haze conditions, and 0.18 µm under non-haze conditions. If close to the ground, the average internal mixing ratio under haze conditions was much higher than that under non-haze conditions, yet the average internal mixing ratios of BC aerosol under these two conditions become closer as the altitude gets higher. Additionally, via simulation by CAMx of the BC aerosols under different conditions, it was found that the simulated effects under haze condition were quite different, and the simulation results under non-haze conditions were better than that under haze conditions, which was mainly due to the fact that the aging state of black carbon was rarely considered in most modes.
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Key words:
- black carbon aerosol /
- vertical distribution /
- mixed state /
- particle size /
- aircraft measurement /
- Beijing Area
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表 1 飞行统计
Table 1. The statiscis of flight
区域
Region天气状况
Condition日期
Date北京时间
Time(850 hpa)风向
Wind Direction能见度/km
Visibility平均相对湿度/%
Relative humidity主城区Main city 霾Haze 2012.05.19 09:30—12:15 西南Southwest 5.6 73 2012.05.31 09:35—12:15 西南Southwest 10 56 2018.06.12 09:25—11:03 东南Southeast 8 55 2018.07.20 09:55—11:45 南South 5 71 非霾Non-haze 2012.05.03 10:20—13:50 西北Northwest 17 10 2012.05.23 09:15—12:40 西北Northwest 21.9 16 2012.06.11 09:05—12:00 西北Northwest 27.1 20 2012.06.16 09:30—12:30 西北Northwest 14.3 30 2018.05.11 09:17—11:40 东北Northeast 14.6 52 2018.06.27 10:55—12:53 西北Northwest 33.6 14 -
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