Most liquid-fuelled rockets use liquid hydrogen as the fuel. The liquid oxygen Dr High refers to is the oxident without which the fuel will not burn. The exhaust gas of this reaction between oxygen and hydrogen is that well-known pollutant dihydrogen oxide. Although dangerous in large quantities in its liquid form, as a vapour it is not a greenhouse gas and has no effect on the ozone layer. In fact it seems to have a role in actually reducing atmospheric temperature. Space scientists agree that its absence from the Venusian atmosphere contributes greatly to Venus's high temperature.
Dihydrogen oxide is usually called by its common name: water.
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