Italian officials who wanted to find out how they were doing in their quest to save Leonardo da Vinci's The Last Supper from five centuries of decay knew just where to turn: USC professor Constantinos Sioutas.

An expert on the huge effects of tiny particles in the air, Sioutas coauthored this year the first study demonstrating that particles like those on L.A.'s freeways inflame mouse brain tissue, causing damage resembling that of Alzheimer's. The system he used to check out the particles in L.A.'s Metro subway was used in the da Vinci's fresco's home, Milan's Santa Maria delle Grazie, in a year-long study of the air in there.

“This is the first study of my group in that area,” says Sioutas. “Most of our work focuses on health effects of air pollution.” The Italians liked the device developed at USC with EPA funding, the Sioutas Personal Cascade Impactor, because it collects data without being a tourist-repelling distraction. “Because it is lightweight, small, and battery operated with a very low noise level, it is ideally suited for measurements in delicate facilities like museums and galleries,” says Sioutas. “It has been used in a separate application to monitor the air quality inside the Gold and Red lines of MTA in L.A. and we have shown that the levels of [carcinogenic] air pollutants in these trains are 1/10 those inside freeways, where people spend 30-60 minutes daily time commuting.”

In the case of da Vinci's fresco, the problem is the impact of people on the environment, not the other way around. “The facility experienced wars, partial destruction during WW II bombing,” says Sioutas. Napoleon's soldiers pelted the wall with rocks and horse droppings. Attempts to repair the painting actually damaged it. Throngs of admirers emitted human pollution, damaging it further.

Italy did a brilliant restoration job in 1999, strictly restricting the number of people who see the masterpiece, and installing sophisticated ventilation and filtration systems in 2009. “They managed to reduce the infiltration of particulate pollution inside the facility, located in the heart of one of Europe's most polluted (and loveliest) cities, to about 10% or less of the outdoor levels,” marvels Sioutas.

But a new study led by USC grad student Nancy Daher, coauthored by Sioutas, revealed that even 25 art lovers at a time who only stay in the church for 15 minutes each harm the painting, “by bringing with them dust from outdoors as well as the airborne lipids inevitably emitted by our skin,” says Sioutas. And the painting actually damages itself by emitting wax particles from early repair attempts, which combine with dust and attack the surface. “That was one of the most unexpected findings of the study,” says Sioutas.

Can Sioutas Personal Cascade Impactors be used to help artworks in the U.S.? “Hopefully yes,” says Sioutas, who's reviewing the history of the art-saving enterprise. “There have been earlier studies in the U.S. on pollution causing possible damage to art. I will note the pioneering work of the late Glenn Cass at Caltech and his student (now professor at UC Berkeley) William Nazaroff at the Norton Simon Museum and the Getty back in the '80s.” Is USC working with U.S. museums to monitor the particle menace? “Not yet.”

And what was the most challenging aspect of the Last Supper project? “For me? By far returning to L.A. after spending time in Milan,” he says. “It is one of my favorite places on the planet. I love the expression of fashion designer god Giorgio Armani, praising the 'somber dignity' of his great city.”

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