The partial pressure of CO2 is in the atmospheric air compared to the partial pressure in blood.

The partial pressure of CO2 in the atmospheric air is significantly lower than in the blood.

1. Atmospheric air: The partial pressure of CO2 in the atmosphere is about 0.3 mm Hg, which is very low. This is because the atmosphere is primarily composed of nitrogen (78%) and oxygen (21%), with only a small amount of CO2 (0.04%).

2. Blood: In contrast, the partial pressure of CO2 in arterial blood (the blood that is oxygenated in the lungs and sent out to the body) is about 40 mm Hg. This is much higher than in the atmosphere because our bodies produce CO2 as a byproduct of cellular respiration, and the blood carries this CO2 from our body's tissues back to our lungs to be exhaled.

So, the partial pressure of CO2 is higher in the blood than in the atmospheric air. This difference in partial pressures allows for the diffusion of CO2 from our blood (where its partial pressure is high) into our lungs (where its partial pressure is low), so that we can exhale it out into the atmosphere.