Electrical properties of surface atmospheric air at Eskdalemuir, 1909–1911

Newly-recovered historical data has been analysed to determine the ion properties in surface air at Eskdalemuir, Scotland between 1909 and 1911. The total air conductivity at Eskdalemuir for 1909–1911 was 9.8 ± 0.7 fS m− 1. Co-located potential gradient (PG) measurements at Eskdalemuir are used to find the noon air–earth current density Jz in 1911, which was between 1.7 and 2.3 pA m− 2 depending on the weighting given to different months. This range is consistent with other contemporary Scottish Jz measurements, greater than the values obtained at the polluted site at Kew, and lower than the measurements made in oceanic air by the Carnegie cruises of 1915 to 1921. The large mean PG at Eskdalemuir for 1911 (between 170 and 234 V m− 1, using the same range of monthly weightings as for Jz), may have arisen through an appreciable air–earth current density. Surface PG changes will therefore be closely coupled to changes in the columnar resistance.