Smoke emissions from industrial western Scotland in 1859 inferred from Lord Kelvin’s atmospheric electricity measurements

Lord Kelvin (William Thomson) made careful, calibrated measurements of the atmospheric Potential Gradient (PG) at three sites on the east side of Arran in 1859. The PG was always anomalously high in easterly and north-easterly winds. Positive space charge from sea spray may have contributed to the high PG at two coastal sites, but measurements made on Goatfell, inland and 100–175 m above sea level are unlikely to have been affected by spray. Instead, pollution from the Scottish mainland seems the more likely cause of the high PG at Goatfell, which varied from 300 to 1000 Vm−1 on 10th–11th October 1859, corresponding to smoke levels from 0.2 to 0.8 mgm−3. Gaussian plume calculations, based on the atmospheric conditions described by Lord Kelvin, and constrained by early Glaswegian pollution measurements, indicate a substantial source region located on the Scottish mainland, 20–40 km from Arran, emitting between 10–104 kg s−1.