Gerhard Ertl

STOCKHOLM, Sweden — Gerhard Ertl of Germany won the 2007 Nobel Prize in chemistry today for studies of chemical reactions on solid surfaces, which are key to understanding questions like why the ozone layer is thinning.

Ertl's research laid the foundation of modern surface chemistry, which has helped explain how fuel cells work, how catalytic converters clean up car exhaust and even why iron rusts, the Royal Swedish Academy of Sciences said.

Ertl, who won the prize on his 71st birthday, told reporters that it "is the best birthday present that you can give to somebody."

"I am speechless," Ertl told The Associated Press from his office in Berlin. "I was not counting on this."

The academy said Ertl provided a detailed description of how chemical reactions take place on surfaces and studied some of the most fundamental mysteries in that field.

Ertl showed how to obtain reliable results in this difficult area of research, and his findings applied in both academic studies and industrial development, the academy said.

"Surface chemistry can even explain the destruction of the ozone layer as vital steps in the reaction actually take place on the surfaces of small crystals of ice in the stratosphere," the Award citation said.

Americans Mario Capecchi and Oliver Smithies, and Briton Sir Martin Evans, won the 2007 Nobel Prize in medicine on Monday for groundbreaking discoveries that led to a powerful technique for manipulating mouse genes.

Prizes for literature, peace and economics will be announced through Monday.

The awards — each worth $1.5 million — will be handed out Dec. 10 by Sweden's King Carl XVI Gustaf in Stockholm.