Independent teams of researchers in the UK and the US have shown that nitrogen oxides in the atmosphere can participate in chemical reactions on the surfaces of buildings, indoors and outdoors, producing harmful pollutants including the respiratory irritant nitrous oxide, the toxic gas nitrosyl chloride and hydroxyl radicals. Rod Jones' team at the University of Cambridge in the UK investigated the fate of NO2 when it comes into contact with glass that has been coated with titanium dioxide.1 TiO2-coated glass is available commercially as a self-cleaning product in which the TiO2 photocatalytically degrades organic dirt in the presence of sunlight. In...