The problem of acid rain has become almost a cliche in the teaching of environmental chemistry topics. Its causes and conseqences are by now quite well-understood, and I for one didn't expect to find anything written on the subject to be as surprising and as provocative as this article, that claims that our efforts to control the effects of acid precipitation are being partially undermined by the coincidental control of atmospheric dust and other particles in the air. This idea makes an interesting counterpoint to the EPA's recently-announced intention to consider reducing the allowable standard concentrations of both tropospheric ozone and small particles in the atmospheres of major US cities. Scientific American puts some articles and features on their Web page, but they didn't choose this one.