Place one onion in the freezer and let in sit overnight. The next day, peel and cut it and do the same with a non-frozen onion. Compare which one makes you tear up more, how quickly you tear up and your level of discomfort. You should find that you tear up considerably less with the frozen onion. This is because the enzyme alliinase is frozen inside its cells and cannot interact with the amino acids in the rind. When you cut the fresh onion, this enzyme creates the sulphenic acid from those amino acids, which your eyes attempt to flush out with tears.
Peel and cut examples of the three most common types of onion, yellow, white and red, and record which one provokes the strongest tear-response. Again, you will want to peel the onions on separate days and record the effect each onion had on your eyes, inducing tears. Yellow onions are used in cooking and are typically higher in sulfur, the key component of the sulphenic gas that onions release to induce tears. As such, the yellow onion is likely to make you tear up the most. Between the other two, you may find that either the red or the white will make you tear up more, depending on how strong its smell is. However, the red onion, having more water and less amino acid to convert into gas, tends slightly toward inducing fewer tears.
Peel and cut a single onion every day over the course of a week to see if you are able to build up a tolerance to the tearing-up effect of sulphenic gas. You will find that, while your discomfort may be less, the amount you tear up will not change. This is because the tear response triggered by sulphenic gas is meant to protect your eyes from a potentially harmful agent. Thus, as long as your eyes are healthy, your tear response will not go away anymore than your white blood cell response will if you have been sick for a while.
Since gas causes you to tear up when peeling an onion, you can quite easily prevent the effect by wearing goggles. But what about contact lenses? For this experiment, get a partner who is used to wearing contact lenses to peel an onion with you. Your partner will likely have less of a tear response than you. This is because the sulphenic gas can only affect the parts of his eyes that are exposed to the air.