An apparatus to measure charges on particles of three different size categories under a rainshower

Abstract

An apparatus has been developed that can separate various particles near the ground surface under a rainshower into three different size categories and can measure the electric charge of each category. The apparatus consists of three stages. In the first stage, raindrops of millimeter size are collected by their gravitational fall in a funnel. In the second stage, air containing smaller particles is circulated through a helical tube so that particles of the size of cloud droplet (~100 μm) are collected by centrifugal force acting on them. In the third stage air is passed through an absolute filter that entraps particles larger than 0.3 μm with 99.97% efficiency. The three stages are insulated from each other and from the ground. The signal received from each stage is amplified and recorded on a strip chart recorder. Laboratory tests and preliminary measurements made with the apparatus under rainshowers are discussed.