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6.4.3. Nitrous Oxide

Nitrous oxide (N2O) is an important, long-lived greenhouse gas that is emitted predominantly by biological sources in soils and water, and removed in the upper atmosphere via photochemical reactions. Unfortunately, estimates of sources and sinks are not well quantified in global terms.

6.4.3.1. Sources of Atmospheric Nitrous Oxide

Tropical soils are probably the single most important source of N2O to the atmosphere (Prather et al., 1995), and intensification of tropical agriculture is likely to increase this (Matson & Vitousek, 1990). The current IPCC (1995) estimate for N2O emissions from tropical soils is 4Mt/a (nitrogen), 75% from wet forests soils and 25% from dry savannahs. Temperate soil sources (including forest soils and grasslands) have been estimated at about 2Mt/a. The Earth's oceans are significant sources of N2O. Emissions may be larger than previously estimated (Law & Owen, 1990), accounting for 3Mt/a.

Anthropogenic sources may account for about 40% of total N2O emissions (5.7Mt/a). These include cultivated soils, biomass burning and industrial sources (e.g. nylon production). Total source emissions (natural and anthropogenic) are currently estimated at 14.7Mt/a (± 3.5Mt/a).