first I give more precise and correct info about the fact I mentioned above.

book : Bergstrom's Black Cross Red Star Vol. 3

"By that time [late october 42], Soviet 65th Army was establishing bridgeheads on the Don river's bank, in the forested areas at Kletskaya and Serafimovich northwest of Stalingrad.

The Romanian 3rd army (...)was unable to interfere effectively against this move.

Von Richtofen dispateched some of his air reconnaissance units to the area, and the fliers returnedwith the alarming reports that the Soviets had already constructed a number of bridges at this place.
(...)
This in itself brought a relief to Stalingrad's defenders.
From the 1st week of november, Fliegekorps VIII's main operations werez shifted from close support in Stalingrad to attacks against the Soviet Don bridgeheads. [and not at the end of october as I posted above]
(...)
On 9 and 10 november, formations up to 40 He 111s and Ju 87s carried out repeated attacks against the Soviet build up northwest of Stalingrad.
(...)
All efforts to neutralize soviet 65th army's bridgeheads failed, largely because the Soviets responded to the Luftwaffe's attacks by building more bridges with their surface just below the river at Kletskaya and Serafimovich."

Later the authors says that the increasingly bad weather from the 11th november drasticaly lowered the number of Luftwaffe daily sorties, even after the huge columns of the Soviet 5th tank army had been spotted on its way by a recon plane on november the 13th

@ Sloniksp : figures in the same book :

by october 20, very Luftflotte 4 had 600 serviceable planes out of 974 operating at Stalingrad and in the Caucasus (but since october 14, most of the Lf4 units operating in Caucasus had been taken back to support the battle at Stalingrad.)

by mid november, the author says there were around 400 serviceable planes available for the whole Luftflotte 4.

You have to add Hungarian, Italian and Romanian air forces, I guess.

I don't know how many were left at the time the encirclement was done.