Charging of mesospheric aerosol particles: the role of photodetachment and photoionization from meteoric smoke and ice particles
Charging of mesospheric aerosol particles: the role of photodetachment and photoionization from meteoric smoke and ice particles
复制标题
中层气溶胶颗粒的充电：流星烟雾和冰颗粒的光分离和光电离的作用
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发表时间：
2009
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通讯作者：
M. Rapp
中科院分区：
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作者：
M. Rapp
抽象的。考虑了两类中间层气溶胶粒子的光剥离、光发射和电子捕获的时间常数，即，流星烟雾颗粒（MSP）和纯水冰颗粒。假设MSPs由金属氧化物如Fe2O3或SiO组成，我们发现在白天条件下，太阳光子的光剥离比电子附着快4个数量级，因此MSPs在阳光下不能带负电荷。相反，即使是光电发射也可以与电子捕获竞争，除非电子密度变得非常大（>>1000 cm −3），使得MSP在大电子密度的情况下应该是带正电的或中性的。然而，对于纯水冰粒来说，由于其吸收截面的波长特征，并且因为太阳光子的通量在如此短的波长下已经显着下降，光致分离和光致发射都可以忽略不计。这意味着水冰粒子通常应该带负电荷。因此，我们的结果可以很容易地解释在极地夏季中层顶中反复观测到的正负气溶胶粒子共存现象，即，小的MSP应该带正电，而冰粒应该带负电。这些结果有进一步的重要意义，我们的理解的中间层冰粒的成核以及非相干散射雷达观测的MSP的解释。
Abstract. Time constants for photodetachment, photoemission, and electron capture are considered for two classes of mesospheric aerosol particles, i.e., meteor smoke particles (MSPs) and pure water ice particles. Assuming that MSPs consist of metal oxides like Fe 2 O 3 or SiO, we find that during daytime conditions photodetachment by solar photons is up to 4 orders of magnitude faster than electron attachment such that MSPs cannot be negatively charged in the presence of sunlight. Rather, even photoemission can compete with electron capture unless the electron density becomes very large (>>1000 cm −3 ) such that MSPs should either be positively charged or neutral in the case of large electron densities. For pure water ice particles, however, both photodetachment and photoemission are negligible due to the wavelength characteristics of its absorption cross section and because the flux of solar photons has already dropped significantly at such short wavelengths. This means that water ice particles should normally be negatively charged. Hence, our results can readily explain the repeated observation of the coexistence of positive and negative aerosol particles in the polar summer mesopause, i.e., small MSPs should be positively charged and ice particles should be negatively charged. These results have further important implications for our understanding of the nucleation of mesospheric ice particles as well as for the interpretation of incoherent scatter radar observations of MSPs.