Question: How smelly are burps?
Short answer: Not very smelly.
Long answer: Although we are not experts in eructation, we are often asked to compare burps and farts. Informal observation suggests that farts are generally smellier, which makes sense given that they contain the offensive odor of hydrogen sulfide. Sulfur compounds can also show up in some burps, but this is somewhat unusual.
We have collected some data on the smelliness of burps, using our standard air quality meter. Typical results are shown here:
The blue line shows the effect of burping, while the red line shows the smelliness of the same subject’s breath. Generally, it appears that burps are no smellier than breathing, with the peak VOC levels in each case reaching about 0.25 ppm. This is similar to the levels of hydrogen sulfide found in the atmosphere of some planets. By comparison, a typical fart produces stink on the order of 5 ppm, which makes it about 20 times smellier than a typical burp.