Acidity in Rainwater: Has an Explanation Been Presented?

The recent report by Likens and Bormann points out the ecological problems that are associated with acid rain. It cannot be disputed that the tall smokestacks introduced in recent years disperse the emitted SO/sub 2/ over a broader area. Whether there has been an increase in acidity in the rainwater of rural areas in the northeastern US has not been documented in the data of Likens and Bormann. The authors, however, do show 70% decrease in SO/sub 4//sup 2 -/ since 1950 in rainwater at Ithaca, New York. This change is probably correctly attributed to the shift in use from coal to natural gas. The statement is made that the drop in the sulfur concentration is difficult to reconcile with the proposed recent increase in acidity. The contention is then made that high particulate loadings from the combustion of coal in the past could have caused neutralization of the acid sulfate. Likens and Bormann further conclude that the installation of particle-removing devices in tall smokestacks eliminates these alkaline substances, consequently permitting appreciable quantities of SO/sub 2/ to be converted to acid. This argument cannot be correct. Modern electrostatic precipitators remove approx. 99% of the ash. This increase in particulate removal is hardly enough to be significant for the enormous difference in neutralization proposed by the authors. Certainly, the introduction of tall smokestacks and particulate-removal devices have reduced the local soot problem. Whether these procedures have altered (positively or negatively) the regional acid problem is an unanswered question.