The concentration of carbon dioxide has increased from about 280 parts per million before the industrial revolution to about 360 parts per million today. Production of carbon dioxide by burning carbon requires that oxygen be removed from the atmosphere. But since there is about a thousand times more oxygen than carbon dioxide in the atmosphere, the decrease in oxygen is probably inconsequential.
I wouldn’t expect the volume of the atmosphere to change much. For every molecule of carbon dioxide produced, one molecule of oxygen is removed from the atmosphere, and to a close approximation each molecule of gas takes up the same amount of space. But each molecule of carbon dioxide is heavier than a molecule of oxygen, so (assuming no other changes take place to the atmosphere), the mass of the atmosphere has increased slightly. My calculation has the mass of the atmosphere increasing by about 0.1 percent (one part in a thousand) because of the increase of carbon dioxide. Air pressure will have risen from, say, 30 inches of mercury to 30.03. Normal daily variation is much greater than that.
I don’t know if such an increase in average air pressure has actually been measured. Such a measurement could easily be confused by variations in water vapor and methane (both of which are lighter than air).