```
pH = -log[H+]
```
where [H+] is the concentration of hydrogen ions in moles per liter.
In this case, we have a solution of 0.0020 M HCl. HCl is a strong acid, which means that it completely dissociates in water to form H+ and Cl- ions. Therefore, the concentration of hydrogen ions in this solution is also 0.0020 M.
Plugging this value into the formula, we get:
```
pH = -log(0.0020) = 2.70
```
Therefore, the pH of this solution is 2.70.
