Large electric fields due to industrial chimney stack plumes

Large values of electric field due to a charged plume from an industrial chimney stack have been observed. Downwind and crosswind profiles of the electric field were measured using 4 field mills. Average values of between 5 and 6 kV m^-1 over 10 minute periods were measured at distances within 200 m of the stack. Electric field values as large as 3.5 kV m^-1 were present at a distance of 3 km from the stack. It was found that the electric field did not return to its normal fair-weather value until the downwind distance from the stack had exceeded 9 km. The decrease in the average value of the electric field, E_p, under the plume gave good agreement with an equation derived from line charge theory, modified by an empirical decay factor exp(-R/D) E_p = -λexp(- R D)/2πε{lunate}₀h.[1+ R √h²+R²] where λ is the charge per unit length, h the plume height, R the distance of the position P downwind, and D the distance at which λ is reduced by 1 e. The experimental results yielded a value for D of about 1.5 km. Point discharge currents as large as 3 μA were measured at a distance of 700 m from the stack. Measurements at heights ranging from 9.25 m to 3.25 m agreed with the theoretical relation i = k(E-E₀) where E is the measured value of electric field at a distance 10 m upwind from the discharge point, E₀ the critical value of electric field above which point discharge will occur and k is a constant. Values of E₀ of about 2kV m^-1 were found for the two highest points. The results suggest that electric field measurements may be a valuable supplement to concentration data in atmospheric diffusion experiments using charged plumes.