From the website of Alcoa (http://www.alcoa.com/bcs/aap_eastman/ecoclean/en/home.asp):
Alcoa Architectural Products has developed a proprietary process that leverages HYDROTECT™ technology from TOTO® to apply a titanium dioxide coating, called EcoClean™, to the pre-painted aluminum surface of Reynobond®. The result is the world’s first coil-coated aluminum architectural panel that helps clean itself and the air around it.
As a photocatalyst, titanium dioxide interacts with sunlight to break down organic matter both on and floating around the surface of the building panels, leaving the organic matter sitting on the surface of the Reynobond® panel, ready to be washed away. When it rains, water doesn’t bead on the surface. Instead, it collapses and runs evenly off the building, taking most of the broken down pollutants with it. That means lower maintenance costs for owners, and a consistently cleaner image for the building over time.
Reynobond® with EcoClean™ actively works to remove pollutants by using sunlight, water vapor, and oxygen in the air to clean the air itself. In fact, 1,000 sqm / 10,000 sq ft² of Reynobond® with EcoClean™ on your building can have approximately enough cleansing power to offset the smog created by the pollution output of four cars every day, which is the approximate air cleansing power of 80 trees every day.