<p>Not nearly so elegant as @fred answer: 400 ppm = 0.04% , then CO 2 is 0,04 % or 0.0004 atm.</p>

CC BY-SA 4.0
2022-08-18T06:13:40.537Z
More elegant :)
JeopardyTempest
CC BY-SA 4.0
2022-08-16T15:16:01.393Z
2022-08-16T15:16:01.393Z
blacksmith37
<p>What I think you are asking for is the <a href="https://en.wikipedia.org/wiki/Partial_pressure" rel="nofollow noreferrer">partial pressure</a> of carbon dioxide in the atmosphere.</p>
<p>The partial pressure of carbon dioxide can be determined, where,</p>
<p><span class="math-container">$P_{CO_2} \ = \ x_{CO_2}\cdot P_{atm}$</span></p>
<p>One mole of any substance is equal to exactly 6.022⋅10<sup>23</sup> molecules of that substance (Avogadro's number, <span class="math-container">$N_A$</span>).</p>
<p>The number of moles of carbon dioxide is,</p>
<p><span class="math-container">$Moles\ of\ CO_2 \ = \ Number\ of\ molecules\ of\ CO_2 \cdot N_A$</span></p>
<p>If the atmosphere has a carbon dioxide concentration of 400 ppm, then</p>
<p><span class="math-container">$n_{CO_2}\ = \ \frac{400}{1\ 000\ 000} \cdot N_A \ = \ 0.0004 \cdot N_A$</span></p>
<p>Thus, the partial pressure of carbon dioxide in the atmosphere will be,</p>
<p><span class="math-container">$P_{CO_2} \ = 0.0004 \cdot 101\ 325 \ = \ 40.53 \ Pa \ = 0.0004 \ atm \ = \ 0.304 \ mmHg$</span></p>

CC BY-SA 4.0
2022-08-16T01:35:23.163Z
2022-08-16T01:35:23.163Z
Fred
<p>For some reason, I can only find the answer in ppm and I don’t know how to do this conversion.</p>

<atmosphere><climate><co2><carbon><air>
What is the current atmospheric concentration of $\small\sf{CO_2}$ in the atmosphere in atm (or bar)?
Elhammo
# What is the current atmospheric concentration of $\small\sf{CO_2}$ in the atmosphere in atm (or bar)?

(Asked by: username_0 on 2022-08-15)

For some reason, I can only find the answer in ppm and I don’t know how to do this conversion.

**Tags:** atmosphere, climate, co2, carbon, air


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## 2 answers

### Answer by username_1 on 2022-08-16. Score: 3

Not nearly so elegant as @username_3 answer: 400 ppm = 0.04% , then CO 2 is 0,04 % or 0.0004 atm.

> **Comments:**
> **username_2**: More elegant :)  

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### Answer by username_3 on 2022-08-16. Score: 3

What I think you are asking for is the [partial pressure](https://en.wikipedia.org/wiki/Partial_pressure) of carbon dioxide in the atmosphere.

The partial pressure of carbon dioxide can be determined, where,

$P\_{CO\_2} \ = \ x\_{CO\_2}\cdot P\_{atm}$

One mole of any substance is equal to exactly 6.022⋅1023 molecules of that substance (Avogadro's number, $N\_A$).

The number of moles of carbon dioxide is,

$Moles\ of\ CO\_2 \ = \ Number\ of\ molecules\ of\ CO\_2 \cdot N\_A$

If the atmosphere has a carbon dioxide concentration of 400 ppm, then

$n\_{CO\_2}\ = \ \frac{400}{1\ 000\ 000} \cdot N\_A \ = \ 0.0004 \cdot N\_A$

Thus, the partial pressure of carbon dioxide in the atmosphere will be,

$P\_{CO\_2} \ = 0.0004 \cdot 101\ 325 \ = \ 40.53 \ Pa \ = 0.0004 \ atm \ = \ 0.304 \ mmHg$


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