Nitrous oxide lifetime

One easily understood mechanism for changes in lifetime is collisional quenching (Figure 10.3). A variety of substances act as quenchers, including oxygen, nitrous oxide, heavy atoms, Cl , and amines, to name a few. By consideration of the lifetime in the absence (to) and presence (r) of collisional quenchers (no resonance energy... 

Nitrous oxide (N2O) is an important greenhonse gas with a radiative forcing effect 310 times that of CO2 and a lifetime in the troposphere of approximately 120 years. Part of the N2O is converted to NO in the stratosphere, and so contributes to depletion of ozone. Nitric oxide (NO) is very reactive in the atmosphere and has a lifetime of only 1-10 days. It contribntes to acidification and to reactions leading to the formation of ozone in the troposphere, and so also to global warming. 

Nitrous oxide is important not only as a greenhouse gas but, as discussed in Chapter 12, as the major natural source of NC/ in the stratosphere, where it is transported due to its long tropospheric lifetime (Crutzen, 1970). The major sources of N20 are nitrification and denitrification in soils and aquatic systems, with smaller amounts directly from anthropogenic processes such as sewage treatment and fossil fuel combustion (e.g., see Delwiche, 1981 Khalil and Rasmussen, 1992 Williams et al., 1992 Nevison et al., 1995, 1996 Prasad, 1994, 1997 Bouwman and Taylor, 1996 and Prasad et al., 1997). The use of fertilizers increases N20 emissions. For pastures at least, soil water content at the time of fertilization appears to be an important factor in determining emissions of N20 (and NO) (Veldkamp et al., 1998). 

An annual survey conducted by the Substance Abuse and Mental Health Services Administration (SAMHSA) reports that 8.27 million Americans have used nitrous oxide illicitly (not for medical purposes) at least once in their lifetime. 

On the other hand, it has been argued by Burton et al. (2, 3, 4) that the lifetime of singlet excited cyclohexane molecules is too short ( 10-13 sec.) to be observed. This conclusion is based largely on the behavior of scintillators containing fluorescent solutes dissolved in cyclohexane. It is important at this point to emphasize that at solute concentrations close to millimolar (which are usually employed in scintillator studies) excited cyclohexane molecules cannot be detected by nitrous oxide. Higher concentrations of both nitrous oxide and benzene (25) are required to observe energy transfer. This study confirms that in the radiolysis of cyclohexane, solutes at millimolar concentrations interact mainly with the electron and not with excited molecules. 

Recovery from a large input of atmospheric CO2 from burning fossil fuels will result in an effective lifetime of tens of thousands of years (Archer, 2005). Methane has an atmospheric lifetime of 12 to 15 years. The methane is degraded to water and CO2 by chemical reactions in the atmosphere. Nitrous oxide has an atmospheric lifetime of 120 years, while CFC-12 has an atmospheric lifetime of 100 years. HCFC-22 has an atmospheric lifetime of 12.1 years, and tetrafluoromethane has an atmospheric lifetime of 50,000 years. Sulfur hexafluoride has an atmospheric lifetime of 3200 years. 

---