Atmospheric‐electrical implications of ²²²Rn daughter deposition on vegetated ground

Abstract

Natural diffusive deposition of radon daughter products from the atmosphere onto an aerodynamically rough, vegetated surface may cause an important enhancement of the ionization rate within the plant canopy. For example, the blades of grass in a lawn may become slightly radioactive, leading to higher ionization in the air between them than above their tops. The impact of this increased ionization rate is estimated from a simple model of the conductivity profile in the turbulent “electrode layer”. It is found that an order‐of‐magnitude augmentation can have substantial effects on the electrical structure. With this motivation a one‐dimensional, steady state model of radon daughter, dry deposition is developed for estimating the magnitude of the deposited activity. The effects of aerosol attachment and of the entire decay chain are included. This model predicts significant enhancements of the “surface radioactivity” under typical continental conditions.

Factors of air ion balance in a coniferous forest according to measurements in Hyytiälä, Finland

“…The space charge density of 440 e cm −3 creates the vertical gradient of the electric field about 8 V m −1 . The gradient of the vertical electric field is an attribute of the near ground electrode effect, a well-known phenomenon in atmospheric electricity (Israël, 1970(Israël, , 1973Willett, 1985). As a result the electric field can be doubled immediately near the conductive surface.…”

“…Additionally, the deposited radon daughters can create air ions close to the ground surface. Willett (1985) modeled the atmospheric electric electrode effect over the grass-covered ground and pointed out that the alpha radiation of the deposited radon daughters is an important ionizing factor despite the fact that the path of alpha rays is only few centimeters. The situation inside the forest is specific and the alpha radiation of the radon daughters deposited onto needles of trees should additionally be considered.…”

“…The electric field is shielded and can be neglected inside the canopy. Above the canopy, the atmospheric electric field causes the asymmetry of the negative and positive ion concentrations, known in the atmospheric electricity as the electrode effect (Israël, 1970;Willett, 1985). In the present model, the effect of the electric field on the deposition of the air ions is neglected and only the Brownian component of the deposition is taken into account.…”

“…This simplification is valid when considering the air ion balance inside of the forest, but it may be inadequate when applied to measurements in a strong electric field. The electric field creates near the ground surface the electrode effect, which is well known in atmospheric electricity (Israël, 1970;Willett, 1985). It results in a decrease in the concentration of air ions, which are forced away from the ground surface by the electric field, and in a slight increase in the concentration of the air ions of the opposite polarity.…”

Kinetic Derivation of the Electromigration Equation for Aerosol Particles in the Presence of Bipolar Charging

“…The electromigration phenomena mentioned above are relevant in several contexts such as the electrical removal of radioactive particles and nuclear aerosols (1), smoke detectors (2), radioactivity-based air cleaning devices (3), and the motion of particles in earth's electric field (4). In mathematical treatments of this problem, one defines a charge distribution function f (q, x, t), which denotes the concentration of particles with charge q at a space point x at time t. Conventionally, the evolution of f (q, x, t) is described by the equation…”