Dwell time (atmosphere)
The dwell time or lifetime of a substance ( gas , solid or droplet ) in the earth's atmosphere is the mean time that a particle or molecule of the substance that has been introduced into the atmosphere remains in the atmosphere. It is determined by its weight (size), its water solubility and its chemical composition. Heavy solid particles or droplets sink to the ground faster than light ones. Depending on the water solubility (more precisely: air-water and air-aerosol distribution coefficient), substances are washed out to a greater or lesser extent by rain . Substances in the atmosphere can be converted or broken down by chemical or physical processes (e.g. redox reactions triggered by radicals or photolysis ). These and other influencing factors determine the time a substance remains in the atmosphere. Depending on the material, this can be very short (seconds or minutes) but also very long (several thousand years).
The concentration or increase in concentration of a substance in the atmosphere, e.g. B. a greenhouse gas , which is established in a long-term equilibrium state through a certain ( anthropogenic ) emission rate, is in the simplest case proportional to its residence time. For many substances, especially carbon dioxide , the relationships are more complicated (see carbon cycle ).
Individual evidence
- ↑ Hartmut Graßl : Environment and climate research , in: Held, M., Geissler, KA (ed.): Ecology of time . Hirzel Verl. Stuttgart 1993.
- ^ Heinrich Arnold: Chemical-dynamic processes in the environment . Digital Bibl. Thueringen 2nd ed. 2008. P. 71, Fig. 1–7 ( PDF ).
- ↑ Susan Solomon, Gian-Kasper Plattner, Reto Knutti , Pierre Friedlingstein: Irreversible climate change due to carbon dioxide emissions. In: Proceedings of the National Academy of Sciences . 106, 2009, pp. 1704-1709, doi : 10.1073 / pnas.0812721106 .