Childhood Cancer and Corona Ions from Powerlines
- The authors assume in their analysis that corona ion emissions arise chiefly from the cable-arrangement and voltage of the powerlines. However they also admit that the main cause of such emissions arises from corrosion of the cables by pollution which, for any given line, is unkown and cannot be modelled meaningfully.
- The authors point to a decrease in recent decades of the large-size (PM10 and PM2.5) particulate air pollutants, but fail to discuss a larger increase in "ultrafine" particles (100-200 nanometres in size), mostly resulting from the 1992 mandatory introduction of vehicle exhaust catalytic converters. Such ultrafine particulates travel large distances from their source, even crossing international boundaries. As a result, it is misleading of the authors to suggest that exposure to total air pollution both near and away from powerlines has decreased in recent decades, rather the overall exposure of children across the country has increased with large numbers of smaller particles - this could be a significant confounder as it changes the exposure of the controls.
- The authors claim to consider wind direction in carrying corona ions downwind of powerlines. However, wind direction is very variable and all locations will have winds at times from other directions including opposite to their assumed one. They have averaged annual data for a restricted time-period for just 8 weather stations in the whole of England and Wales.
An important review of wind variability was published by Alan Lapworth and James McGregor in 2008 . This shows that even for an almost ideal flat land Met Office weather station site (Cardington, East Midlands) the wind direction has enormous variability over the year. Even if (as there) there is a predominent direction, who is to say that on the day the critical toxic particle is being inhaled that the wind is not blowing in the opposite direction?
They also point out: "An even greater effect, however, is caused by relatively local topographic effects." These include local hills, valleys, etc. This will also be the case in urban areas which many of the 132 kV lines cross, with buildings and streets considerably diverting the air flow.
Swanson et al also fail to acknowledge that Westerly winds that originate over the Atlantic, are largely devoid of pollutants, whereas Easterly winds can bring pollutants from Europe as illustrated in the smog event predominant in the Southeast of England in April 2014.
- The inclusion of 132 kV lines is important as they are significant sources of corona ions. However, many are over urban areas where air-flow resistance by buildings and convection currents are very complex and will greatly distort the diffusion patterns from a simple prevailing wind model.
- The use of the 1/r factor in the modelling distorts the convection effect by greatly suppressing effects at longer distances, including the 200 to 600 m category. Whether that makes much difference in overall results is another matter, but it is an important issue for closer comparisons of this version of the corona hypothesis with a simple distance model. The factor 1/r seems misconceived and should simply be removed. This is discussed by Professor Mike O'Carroll in the linked document .