Estimation of small ion concentration near the Earth's surface

Atmospheric ions produced by radon gas exhalation from the Earth’s surface can play a vital role in the electrification of atmosphere, especially during nights when the gases are trapped in a stable layer close to the surface. The measurements of concentration of radon and its progeny, air conductivity and aerosol size distribution made at Pune, India, have been analyzed. The concentrations of radon and its progeny show maxima during night and early morning hours, between 0500 and 0700 IST when atmosphere is more stable and mixing is low and start decreasing after sunrise and attain minima during 1000–1800 h when air is unstable. The diurnal variation of the ionization rate, calculated using the concentrations of radon and its progeny, follows the variations of concentrations of radon and its progeny. The ion–aerosol balance equations are solved to study the effect of aerosols on small ion concentration in the lower atmosphere. It has been found that during daytime when aerosol concentration is high, 20–30% reduction in small ion concentration can occur due to aerosols. The small ion concentration estimated using measured air conductivity is compared with small ion concentration estimated by solving ion–aerosol balance equations and both are found to be in good agreement with each other.

► Definite, regular and pronounced diurnal variations.
► Maxima during night and minima during daytime.
► Correlation of 73% between measured and estimated ion concentrations.