I have 3 separate "Urban" monitoring locations. 10 observations were made at each location.

Is it possible to combine the observations from the separate locations so I would have 30 total observations in this one "Urban" group? Is it then possible to calculate the mean concentration based on these 30 samples even if they were from 3 different locations? And lastly, would it be possible to compare the mean (or other statistic) from these combined observations to another group (for example, 15 observations made at only 1 "rural" site)?

Thank you all for your help!

-rs123