You have to check local laws about firing an air gun in the city. Where I live the are legally the same as a firearm.
PCP guns are louder than a 22lr. Pumps are the same if pump to the same power (3000psi) as a PCP. Sprinters are quieter than a 22lr though not as quiet as some of the quiet 22 rimfire rounds in a bolt action or single shot.
They make quiet PCPs with a builtin moderator but only 177 cal are allowed in the USA without a fed stamp ($200).
I use to shoot airguns but found that they had no advantage over a 22lr and lots of disadvantages. Lower power, more complex, less reliable, more expensive (PCP) and less accurate. Some may argue but these are my experiences.
Last edited by ConradCA; 10/20/13.