Chapter 1: The Composition of Pandora's Atmosphere

Pandora's atmosphere presents a stark contrast to that of Earth. While our atmosphere is primarily composed of nitrogen (78%) and oxygen (21%), with minor components including argon and carbon dioxide, Pandora's air consists of nitrogen (50%), oxygen (25%), carbon dioxide (18%), xenon (5.5%), hydrogen sulfide (1%), and traces of methane and ammonia (0.5%).

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Section 1.1: Density and Smell of Pandora's Air

The atmospheric mixture of Pandora is not only distinct but also denser by 20%, largely due to the high xenon content, which is a heavy, inert gas. Most of the gases present—such as nitrogen, oxygen, carbon dioxide, xenon, and methane—are odorless. Therefore, the air's scent on Pandora would mainly derive from ammonia, which has a strong, pungent aroma, and hydrogen sulfide, known for its rotten egg smell.

Interestingly, ammonia constitutes less than 0.5% of the atmosphere and might not be very noticeable, especially compared to the hydrogen sulfide, which is more prominent at 1%. This suggests that a person inhaling the air on Pandora might only detect a faint odor reminiscent of rotten eggs, possibly mingled with a slight bleach-like scent.

Subsection 1.1.1: The Human Body’s Tolerance

The primary concern isn't just the unpleasant aroma but rather the physiological impacts on a human inhaling this atmosphere. Humans can tolerate oxygen levels between 19.5% and 23.5%. On Pandora, the oxygen concentration is slightly higher at 25%, which, while still breathable, could lead to reversible damage after brief exposure and potentially fatal consequences with prolonged inhalation.

Section 1.2: The Influence of CO2 on Pandora's Environment

In contrast to Earth's mere 0.04% carbon dioxide, Pandora’s atmosphere contains a staggering 18%, nearly five times the toxic threshold for humans, which is around 4%. This elevated CO2 level could indicate that Pandora exists outside the habitable zone of its solar system. Consequently, tidal forces and a potent greenhouse effect may warm the moon sufficiently to support extensive rainforests across its terrain.

Chapter 2: The Dangers of Pandora's Gases

The atmospheric composition includes another hazardous element: hydrogen sulfide. Even at concentrations below 1000 ppm, this gas can cause significant health issues, including irritation, coughing, and respiratory distress. On Pandora, its concentration is at least ten times higher, leading to immediate suffocation upon inhalation.

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Additionally, while methane is present in low amounts and not directly lethal, ammonia can become harmful at levels just above those found in Pandora's atmosphere. Thus, a final breath on this alien moon would carry faint traces of rotten eggs and bleach, with the real danger stemming from the high levels of carbon dioxide and the presence of hydrogen sulfide.

In summary, while the air on Pandora may not initially seem drastically different from Earth's, its lethal composition makes it a perilous environment for human life.

This article is referenced in: Why bioluminescence?