An enclosed space, such as a tunnel or car park, includes an interior surface having a photocatalytic coating. A lighting system attached to the interior surface illuminates the coating with wavelengths in the range 340-450nm, activating the photocatalyst. The surface may be illuminated at an intensity greater than 1.0W/m2. The system may not emit light with wavelengths below 340nm. The lighting system may comprise fluorescent, short wave, gas discharge or metal halide lamps, or lasers or LEDs. The photocatalyst and lighting system may be used to reduce the amount of NOx and SOx gases, bacteria, mold and volatile binding compounds in the enclosed space. The photocatalytic coating may be cement based and may comprise a binder, cellulose ether, fluidising agent, at least one calcareous filler and at least one silane. The photocatalyst may be titanium dioxide in anatase crystalline form. Also claimed is the use of LEDs in a tunnel coated with a photocatalyst, the LEDs emitting light having a wavelength between 340-450nm but not below 340nm.
