To investigate the seasonal behaviour of nitrate radicals (NO3) as a source of nitric acid (HNO3) and particulate nitrate (NO3-) in the eastern Mediterranean atmosphere, we conducted NO3 measurements on the island of Crete for more than two years. Ancillary measurements of chemical compounds and meteorological parameters were used to analyse the observations. Nighttime production of HNO3 plus NO3-, as initiated by NO3 radicals, accounts for about 50--65% of the total production rate depending on season. The remainder is produced by the hydroxyl radical (OH) reaction with nitrogen dioxide during daytime. On a yearly mean basis, about 17% of the HNO3 plus NO3- formation results from the reaction of NO3 radicals with dimethylsulfide of marine origin. This shows important interactions between biogenic and anthropogenic compounds contributing to nutrient deposition to the sea.