Natural emission sources
Natural emission sources are not influenced by human activities. A variety of air pollutants is generated during a range of processes taking place in terrestrial and aquatic ecosystems or in Earth’s crust.
Various carbon and nitrogen species are emitted to the atmosphere during
microbiological and plant physiological processes. Natural sources of carbon
compounds, such as carbon dioxide (CO2)and methane
(CH4) can be aerobic and anaerobic respiration.
Nitrogen species such as nitrogen (N2), nitrous oxide
(N2O) and nitric oxide (NO) are produced by
biological oxidations and reductions of inorganic nitrogen in soils and waters.
The most important factor controlling the rate of the nitrogen emission is the
soil temperature.
The soil fluxes of N2O in a Norway spruce forest in Mátra Mountain were determined by small static chambers. Accumulation of nitrous oxide was measured by a gas chromatography-mass spectrometry system. N2O emission fluxes were calculated from the accumulation of nitrous oxide gas in the chamber (Figure 2.4).
Due to metabolic processes in forest trees, grasslands or scrublands several types of hydrocarbons are also emitted to the atmosphere.
The soil fluxes of N2O in a Norway spruce forest in Mátra Mountain were determined by small static chambers. Accumulation of nitrous oxide was measured by a gas chromatography-mass spectrometry system. N2O emission fluxes were calculated from the accumulation of nitrous oxide gas in the chamber (Figure 2.4).
Due to metabolic processes in forest trees, grasslands or scrublands several types of hydrocarbons are also emitted to the atmosphere.
Several physical, chemical and biological processes occur at surface of
wetlands and oceans, which influence the global cycles on a number of species,
e.g. carbon, nitrogen, sulphur and trace metals. The most important emission
process in wetlands and anaerobic waterlogged soils is the bacterial production
of methane. Oceans play an important role in the global biochemical sulphur
cycle. Dimethyl sulphide (DMS) is produced during biological activity of
phytoplankton then enters the atmosphere by the exchange between see and the
atmosphere. Dimethyl sulphide is the major precursor of sulphate particles (). Large amount of water droplets and sea salts are emitted
into the maritime atmosphere. After the evaporation of water aerosol particles,
such us sodium chloride (NaCl), magnesium sulphate
(MgSO4) are formed. Various halogenated organic compounds
are also emitted to the atmosphere from the oceans. Among them, methyl chloride
(CH3Cl) is the major natural source of atmospheric
chlorine.
Almost all forest fires are human induced. Naturally occurring biomass
burnings are usually the consequence of lightning. The major products of biomass
burning are carbon dioxide (CO2) and water vapour.
However, a large number of particulates and trace gases are produced, including
the products of incomplete combustion of CO, NMVOCs, nitrogen and sulphur
species.
Volcanoes release significant amount of gases and ash particles into the
atmosphere. Volcanic emissions occur both during occasionally eruption and long
term non-eruptive activities. Most prevailing volcanic gas is water vapour,
which can reach 50–90% of total volcanic emission. However, this amount of water
vapour is negligible in comparison to its atmospheric concentration. Other
important gases emitted from volcanic activities are carbon dioxide
(CO2), sulphur dioxide (SO2),
hydrogen sulphur (H2S) and some other sulphur species,
hydrogen chloride (HCl) and other halogen compounds. Besides the gases,
considerable emissions of aerosols are present in most volcanic plumes.
Lightning during thunderstorm events creates plasma channels in the atmosphere
characterized by the high fraction of ionic loads and high temperatures. High
temperature cause chemical reactions. Major compounds of the atmosphere
(nitrogen, oxygen, and water vapour) are undergoing chemical transformation and
various species containing nitrogen, oxygen and hydrogen atoms are formed. A
major species produced during lightning is nitric oxide (NO).
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