By Jonathan Bechtel – Updated Mar 24, 2022

The atmospheric mixing ratio measures the proportion of a particular gas or moisture relative to dry air. While often used for water vapor, the concept extends to any atmospheric constituent such as argon or ozone. Even minor variations in these ratios can influence weather patterns and climate dynamics. Accurate calculation is essential for researchers and forecasters alike.

Step 1 – Identify Key Values

Begin by noting the relative humidity (RH) and the saturated mixing ratio (SMR). RH is the familiar percentage that tells you how much moisture the air actually holds compared to its maximum capacity. SMR is the theoretical maximum amount of that gas (often water vapor) the air can hold at a specific temperature. For illustration, let’s assume RH = 0.8 (80 %) and SMR = 0.5 (grams per cubic meter).

Step 2 – Compute the Raw Product

Multiply RH by SMR: 0.8 × 0.5 = 0.04. This gives the unadjusted mixing ratio value.

Step 3 – Convert to the Standard Unit

Divide the result from Step 2 by 100 to express the mixing ratio in the conventional unit of grams per cubic meter: 0.04 ÷ 100 = 0.004 g/m³.

Step 4 – Verify Your Result

As a quick check, divide the computed mixing ratio by SMR and multiply by 100. The outcome should reproduce the original RH (0.004 ÷ 0.5 × 100 ≈ 0.8), confirming the calculation’s accuracy.

TL;DR (Too Long; Didn’t Read)

To calculate a mixing ratio, combine the relative humidity with the saturated mixing ratio, adjust for units, and verify the result. The final value is typically expressed in grams per cubic meter, though any density metric can be used.

For more detailed meteorological background, visit the National Centers for Environmental Information.