A priest's ozone legacy.

For 26 years in the late 19th century, Father Francesco Denza kept very regular records that are now helping scientists understand how the industrial revolution increased ozone pollution in the troposphere, the atmosphere's lowest layer.

From January 1868 through December 1893, this theologian and physics teacher took twice-daily readings of ground-level atmospheric ozone at his college in Moncalieri, located at the foot of the Italian Alps. In Denza's time, researchers suspected that ozone might cause epidemic diseases. Scientists now recognize tropospheric ozone -- a component of smog -- as a greenhouse gas as well as an eye an lung irritant.

A team of Italian scientists has converted Denza's data to a modern scale in order to compare today's ozone levels with those of a preindustrial environment. In the Sept. 20 JOURNAL OF GEOPHYSICAL RESEARCH, they report that 19th-century Moncalieri had one-half to one-third the ozone present in a modern rural site. Exhaust from cars, power plants and other sources creates ozone in the lower troposphere.

A quirk of the region's weather enabled the scientists to use Denza's data to gauze ozone changes in the upper troposphere as well. The Alps often cause winds to descend into the Moncalieri region, bringing air from higher levels down to ground level. By identifying such events in Denza's records, the researchers demonstrate that ozone has also accumulated in the upper troposphere.