use. Syrian Civil War The Syrian government, the United States the Russian Federation and Turkey reportedly deployed white phosphorus munitions via airstrikes and artillery on different occasions during the Syrian Civil War. Second Nagorno-Karabakh War During the Second Nagorno-Karabakh War, on 31 October 2020 the Ministry of Defence of the unrecognised Republic of Artsakh stated that the Azerbaijani side had used phosphorus weapons to burn forests near Shusha (Shushi). The next day, Armenia's human rights defender, Arman Tatoyan, stated that civilians were hiding in the forest. Atlantic Council's Digital Forensic Research Lab (DFRLab) found that "large burnt fields resembling burn damage from white phosphorus, or a very chemically similar material, were identified in Armenian-controlled territory." On 22 September 2021, the U.S. House of Representatives passed an amendment, calling for a report on Azerbaijani war crimes during war, including the use of white phosphorus against Armenian civilians. The Azerbaijani authorities, in turn, accused the Armenian forces of using white phosphorus on civilian areas. Then, on 4 November, Azerbaijan National Agency for Mine Action (ANAMA) found unexploded white phosphorus munitions in Səhləbad, near Tartar, which, according to Azerbaijan, was fired by the Armenian forces. Azerbaijani authorities had also stated that the Armenian forces were transporting white phosphorus into the region. On 20 November, the Prosecutor General's Office of Azerbaijan filed a lawsuit, accusing the Armenian Armed Forces of using phosphorus ammunition in Nagorno-Karabakh, as well as in Tartar District. Smoke-screening properties Weight-for-weight, phosphorus is the most effective smoke-screening agent known, for two reasons: first, it absorbs most of the screening mass from the surrounding atmosphere and secondly, the smoke particles are actually an aerosol, a mist of liquid droplets which are close to the ideal range of sizes for Mie scattering of visible light. This effect has been likened to three dimensional textured privacy glass—the smoke cloud does not obstruct an image, but thoroughly scrambles it. It also absorbs infrared radiation, allowing it to defeat thermal imaging systems. When phosphorus burns in air, it first forms phosphorus pentoxide (which exists as tetraphosphorus decoxide except at very high temperatures): P4 + 5 O2 → P4O10 However phosphorus pentoxide is extremely hygroscopic and quickly absorbs even minute traces of moisture to form liquid droplets of phosphoric acid: P4O10 + 6 H2O → 4 H3PO4 (also forms polyphosphoric acids such as pyrophosphoric acid, H4P2O7) Since an atom of phosphorus has an atomic mass of 31