Formation of HNO₃ and NO₃⁻ in the anthropogenically‐influenced eastern Mediterranean marine boundary layer

To investigate the seasonal behaviour of nitrate radicals (NO 3 ) as a source of nitric acid (HNO 3 ) and particulate nitrate (NO 3 − ) in the eastern Mediterranean atmosphere, we conducted NO 3 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 HNO 3 plus NO 3 − , as initiated by NO 3 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 HNO 3 plus NO 3 − formation results from the reaction of NO 3 radicals with dimethylsulfide of marine origin. This shows important interactions between biogenic and anthropogenic compounds contributing to nutrient deposition to the sea.