I give Harold Henderson credit for trying to present an objective, balanced view of the scientific issues relating to particulate air pollution ["Up in the Air," April 18]. However, my confidence that he understood the relevant science well enough to do the job was undermined by a schoolboy error in the opening paragraphs. A microgram is one millionth of a gram, not one thousandth.
Harold Henderson replies:
I thank everyone who corrected my stupid mistake.