Catalysed self-cleaning of air on the earth's surface

• Generally, it is assumed that UV-light, high temperature or reactive molecules like O-3 and OH are needed to activate gas reactions in air. In consequence, the catalytic activity on natural materials such as sand and soil on the earth's surface is assumed to be insignificant. We have measured O-2-dissociation rates on natural quartz sand at 40 degrees C and compared these with O-2-dissociation rates near 500 degrees C on materials with well-known catalytic activity. In terms of probabilities for dissociation of impinging O-2-molecules the measured rates are in the 10(-12)-10(-4) range. We have also measured dissociation rates of H-2 and N-2, water-formation from H-2 and O-2 mixtures, exchange of N between N-2, NO (x) and a breakdown of HNO3, NO2 and CH4 on natural quartz sand at 40 degrees C. The measured rates together with an effective global land area have been used to estimate the impact of thermodynamically driven reactions on the earth's surface on the global atmospheric budgets of H-2, NO2 and CH4. The experimental data on natural quartz sand together with data from equilibrium calculations of air suggest that an expected increase in anthropogenic supply of air pollutants, such as NO (x) or other reactive nitrogen compounds, hydrogen and methane, will be counter-acted by catalysis on the earth's surface. On the other hand, at Polar Regions and boreal forests where the reactive nitrogen concentration is below equilibrium, the same catalytic effect activates formation of bio-available nitrogen compounds from N-2, O-2 and H2O.

Nyckelord

molecular dissociation

H-2

O-2

N-2

natural quartz sand

NOx-decomposition

H-2-removal

mass spectrometry

isotopes

ambient air

nitrogen-fixation

mineral dust

troposphere

chemistry

hydrogen

oxides

decomposition

diffusion

budget

ozone

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