Influence of aerosols on middle atmospheric conductivities

Existing models of atmospheric conductivities and ion densities derived from the ion production rates in the middle atmosphere due to cosmic rays do not take into account the effects produced by aerosols and their particle size distribution. A modified 13 ion model by Mitra is used to compute the small ion densities in the troposphere and stratosphere as against the simple 6 ion scheme which is applicable to the D-region of the ionosphere. Incorporating the measured height profile of integrated aerosol concentrations into the 13 ion scheme along with the laboratory data on aerosol-neutral attachment, aerosol ion-small ion and aerosol positive and negative ion recombination coefficients, the equilibrium condition small ion densities are computed and compared with the small ion densities in the absence of aerosols. On an average it is found that the small ion densities are reduced by about 4% in the presence of normal aerosol particles. The computations when repeated to take into account the aerosol size distributions by assuming a suitable power law distribution, the influence of aerosol appears to be reduced to about 0.1%. However, it is found that for relatively large size aerosol particles the effect continues to be appreciable. This indicates that during a volcanic eruption when the aerosol size distribution gets altered considerably towards bigger size aerosol particles, a large hole in the small ion densities may appear till this anomalous condition returns to normal aerosol condition after a period of about a few months.