I'm doing upwind/downwind comparisons for air quality data. I recieved some feedback yesterday (thanks Simon!) that a paired t-test would probably be an appropriate way to compare hourly averages from two sites located about 1km apart. Also, that the data set is probably large enough (~500 hourly readings) to appproximate parametric (because of the cental limit theorom).

My questions now:

My data seems to have an asymetrical distrubution (e.g. a long tail toward high concentrations). Would the paired-t test be more robust if I did a transformation?

Also, I plan on presenting some other descriptive statitics such as mean, standard deviation, maybe percentiles. Would a transformation be appropriate for these descriptors?

Many thanks!! I'm really glad I stumbled upon this forum as a resource!

Cassie