5 + 4 + Hyponitrous acid decomposes to NO and water with a half-life of 16 days at 25 °C at pH 1–3. HNO→ HO + NO Atmospheric occurrence Nitrous oxide is a minor component of Earth's atmosphere and is an active part of the planetary nitrogen cycle. Based on analysis of air samples gathered from sites around the world, its concentration surpassed 330 ppb in 2017. The growth rate of about 1 ppb per year has also accelerated during recent decades. Nitrous oxide's atmospheric abundance has grown more than 20% from a base level of about 270 ppb in year 1750. Important atmospheric properties of are summarized in the following table: In October 2020 scientists published a comprehensive quantification of global sources and sinks. They report that human-induced emissions increased by 30% over the past four decades and are the main cause of the increase in atmospheric concentration. The recent growth has exceeded some of the highest projected emission scenarios. Emissions by source As of 2010, it was estimated that about 29.5 million tonnes of (containing 18.8 million tonnes of nitrogen) were entering the atmosphere each year; of which 64% were natural, and 36% due to human activity. Most of the emitted into the atmosphere, from natural and anthropogenic sources, is produced by microorganisms such as denitrifying bacteria and fungi in soils and oceans. Soils under natural vegetation are an important source of nitrous oxide, accounting for 60% of all naturally produced emissions. Other natural sources include the oceans (35%) and atmospheric chemical reactions (5%). Wetlands can also be emitters of nitrous oxide. A 2019 study showed that emissions from thawing permafrost are 12 times higher than previously assumed. The main components of anthropogenic emissions are fertilised agricultural soils and livestock manure (42%), runoff and leaching of fertilisers (25%), biomass burning (10%), fossil fuel combustion and industrial processes (10%), biological degradation of other nitrogen-containing atmospheric emissions (9%) and human sewage (5%). Agriculture enhances nitrous oxide production through soil cultivation, the use of nitrogen fertilisers and animal waste handling. These activities stimulate naturally occurring bacteria to produce more nitrous oxide. Nitrous oxide emissions from soil can be challenging to measure as they vary markedly over time and space, and the majority of a year's emissions may occur when conditions are favorable during "hot moments" and/or at favorable locations known as "hotspots". Among industrial emissions, the production of nitric acid and