Strontium 90 fallout prediction

Abstract

An empirical formula is developed for predicting monthly sea level strontium 90 fallout (F) in the northern hemisphere as a function of time (t), precipitation rate (P), latitude (ϕ), longitude (λ), and the sea level concentration of strontium 90 in air (C): F(λ, ϕ, t) = C(t, ϕ)[νd(ϕ) + νw(λ, ϕ, t)], where νw(λ, ϕ, t) = a(ϕ)[P(λ, ϕ, t)/P0]b(ϕ) is the wet removal, νd(ϕ) is the dry removal and P0 is 1 cm/month. The constants νd, a, and b are determined as functions of latitude by fitting land based observations. The concentration of 90Sr in air is calculated as a function of the deseasonalized concentration at a reference latitude , the ratio of the observations at the latitude of interest to the reference latitude (R), and a function representing the seasonal trend in the air concentration is the month. Zonal trends in C are shown to be relatively small. This formula can be used in conjunction with precipitation observations and/or estimates to predict fallout in the northern hemisphere for any month in the years 1954 to 1974. Error estimates are given; they do not include uncertainty due to errors in precipitation data. The cumulative North Atlantic 90Sr input predicted by the model for 1.25°N to 66.25°N decay corrected to December 1972 is , compared to an inventory estimate of from oceanic observations. It is suggested that the discrepancy is due to a more efficient scavenging of small particles over the oceans than over land.