Singlet molecular oxygen, O₂(¹Δ_g) has been speculated to play a role in the formation of photochemical smog. It is mainly produced from the photolysis of ozone in the troposphere and lost in the troposphere due to the non-reactive collisions with third bodies (e.g. N₂, O₂, H₂O) and by reacting with ozone. The mean annual flux from sources to sinks, seasonal variation and global distribution of O₂(¹Δ_g) were studied for the first time using a three-dimensional global chemistry transport model, STOCHEM-CRI. The global burden and the atmospheric lifetime of O₂(¹Δ_g) were found to be 0.58 Gg and 0.29 s, respectively. Up to 0.6 ppt of O₂(¹Δ_g) was modelled at the surface over anthropogenic emission regions (e.g. North America, central Europe and South East Asia) and forested regions (e.g. Africa and south America). The model O₂(¹Δ_g) could have a modest effect on the production of hydroperoxides (up to 3.0 ppt) through reaction with olefins.