It really is not that they are dirty. Public outdoor pool usually don't smell. Public indoor pools and changing rooms smell because of decreased ventilation. Pool water with FC drips on the floor or deck with organics and combines just as it would in the pool. Yes it's the cc's you really smell. Even a bottle of open bleach. What you smell at the open top is the reaction with the atmosphere.
That's not true. Hypochlorous acid itself does smell and is what you smell (along with hypochlorite ion) rather strongly from concentrated bleach or chlorinating liquid (hypochlorite ion has a similar odor but is more limited in how much can be volatized due to charge imbalance though with bleach its concentration is much higher). You can have perfectly clean air and readily smell bleach and chlorinating liquid. It is a different kind of smell than the chloramines.
The following table shows odor and taste thresholds from the paper "Aroma and Flavor Characteristics of Free Chlorine and Chloramines" (starting at page 75 as shown in
this link) in the Proceedings of the American Water Works Association (AWWA) Water Quality Technology Conference (WQTC) in 1984.
Compound ...........
Descriptor .......
pH ..
Odor .
Taste
Hypochlorous acid .. Bleach .............. 5.0 .. 0.28 .. 0.24
Hypochlorite ion ..... Bleach ............ 10.0 .. 0.36 .. 0.30
Monochloramine ..... Swimming pool . 8-9 .. 0.65 .. 0.48
Dichloramine ......... Swimming pool .. 4.0 .. 0.15 .. 0.13
Trichloramine ......... Geranium .................. 0.02
People associate the monochloramine and dichloramine odor with swimming pools and not with bleach. It's the "bad pool" smell.
At pool pH with a mixture of hypochlorous acid and hypochlorite ion, the thresholds would be roughly the average so roughly 0.32 ppm FC with no CYA. This is generally higher than the unbound chlorine level in pools with CYA except at shock level, but with churning of the water one can increase volatization and with pool covers one can build up higher concentrations in the air that are more noticeable until blown away. Also, the amount of volatization is a function of temperature so warmer pools or hot spas would smell more than cooler ones at the same chlorine level in the water.