<p>TL;DR: Multiply <span class="math-container">$\ce{CO_2}$</span> expressed in μmol/mol by 1.52 the μg/g equivalent.</p>
<p>Details: The molecular mass of <span class="math-container">$\ce{CO_2}$</span> is 44.01 g/mol. The standard molecular mass of dry air is 28.9647 g/mol. Multiplying <span class="math-container">$\ce{CO_2}$</span> expressed in μmol/mol by 44.01/28.9647=1.5194 comes rather close. A tricky detail is that some of that standard molecular mass of dry air includes a small contribution from <span class="math-container">$\ce{CO_2}$</span>. After accounting for this I get a value close a bit over 1.5196. Rounding either value to three significant digits results in a conversion factor of 1.52.</p>

CC BY-SA 4.0
2022-06-25T23:22:04.273Z
2022-06-25T23:22:04.273Z
David Hammen
<p>The Keeling curve reports CO<sub>2</sub> in units of μmol/mol, but people's (and country's) emissions are generally reported in kilograms or tons of CO<sub>2</sub>. I would like to convert μmol/mol of CO<sub>2</sub> in the atmosphere to mass fraction of CO<sub>2</sub> in the atmosphere using an accurate, well-established, and scientifically accepted method to ensure that my calculations are reproducible by others. What is the preferred way to do this?</p>

CC BY-SA 4.0
2022-06-25T21:24:46.310Z
A somewhat connected, albeit different, question: [Ppmv vs μmol for atmospheric CO2](https://earthscience.stackexchange.com/questions/10157/ppmv-versus-μmol-mol-for-atmospheric-co2-how-to-convert/10367)
JeopardyTempest
<atmosphere><climatology><carbon>
How do you convert the μmol/mol units for atmospheric CO2 into CO2 mass fraction?
phil1008
# How do you convert the μmol/mol units for atmospheric CO2 into CO2 mass fraction?

(Asked by: username_0 on 2022-06-25)

The Keeling curve reports CO2 in units of μmol/mol, but people's (and country's) emissions are generally reported in kilograms or tons of CO2. I would like to convert μmol/mol of CO2 in the atmosphere to mass fraction of CO2 in the atmosphere using an accurate, well-established, and scientifically accepted method to ensure that my calculations are reproducible by others. What is the preferred way to do this?

**Tags:** atmosphere, climatology, carbon

> **Comments:**
> **username_1**: A somewhat connected, albeit different, question: [Ppmv vs μmol for atmospheric CO2](https://earthscience.stackexchange.com/questions/10157/ppmv-versus-μmol-mol-for-atmospheric-co2-how-to-convert/10367)  

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## 1 answers

### Answer by username_2 on 2022-06-25. Score: 4 | Accepted answer

TL;DR: Multiply $\ce{CO\_2}$ expressed in μmol/mol by 1.52 the μg/g equivalent.

Details: The molecular mass of $\ce{CO\_2}$ is 44.01 g/mol. The standard molecular mass of dry air is 28.9647 g/mol. Multiplying $\ce{CO\_2}$ expressed in μmol/mol by 44.01/28.9647=1.5194 comes rather close. A tricky detail is that some of that standard molecular mass of dry air includes a small contribution from $\ce{CO\_2}$. After accounting for this I get a value close a bit over 1.5196. Rounding either value to three significant digits results in a conversion factor of 1.52.


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