Phosphine gas in the upper troposphere

The gas phosphine (PH3) is a part of an atmospheric link of the phosphorus cycle on earth. Phosphine was reported elsewhere to be found worldwide in remote air samples in the lower troposphere in the low ng/m3 range during the night, when oxidation is inhibited. But much less phosphine (pg/m3 range) was found during daylight around noon in this reactive contaminated atmosphere. Here we found for the first time gaseous phosphine in remote air samples (0.39–2.45 ng/m3, 16 locations) in the high troposphere above the North-Atlantic in November 1995 during daylight around noontime. The maximum concentration was measured at the highest altitude of 12,500 m. No night measurements could be conducted to compare day and night values. The finding of the reactive phosphine under the sunlight in the high troposphere far from possible terrestric sources is strange. A model experiment shows that phosphine could possibly survive the daylight much longer at high altitudes because of a lack of UV-induced oxidants in the clean and dry air. Additional model experiments indicate that phosphine can easier sustain its mobile gaseous state in the atmosphere compared to gases like hydrogen sulfide and ammonia which stick easier to aerosol and are subject to faster washout and return to Earthʹs surface. However, the ultimate fate of phosphine is the oxidation to form phosphoric acid as a low pH agent and as possible condensation nuclei for clouds at very high altitudes. The potent sources and atmospheric chemistry which allow phosphine to accumulate in the upper troposphere are still to be discovered.