pollution of atmospheric re-entry

Recently I have posted some ideas related to mining the asteroid belt
from Earth.

Basically, we proceed as follows;

(1) build a reusable multi-stage heavy lift rocket fleet
(2) build a production line for payloads
(3) build and deploy a communication satellite network
(4) build a larger power satellite network
(5) upgrade the launcher with laser propulsion
(6) expand the power satellite network
(7) send an expedition to Ceres
(8) mine Ceres and use a rail gun to send materials back to Earth
(9) establish orbiting supply center
(10) build orbiting factories
(11) dispatch materials to Earth

The point is step #9 and step #11 can both be aided by aerobraking in
the Earth's atmosphere. The issue is, what sorts of pollution effects
are there? How do they scale with large numbers of payloads?

I am envisioning 4 tons per person per year - and an installed asset
base of at least 24 tons per person - and having stock of perhaps 400
tons per person on orbit. Bringing back 400 tons in 10 years - is 40
tons per person per year, falling to 4 tons per person per year.
These could hit the atmospher twice if aerobraking is widely used.

With 6.6 billion people each collecting 4 tons of materials per year,
that's 11 kg per day. per person. A one liter sphere is 12.4 cm in
diameter. (4.88 inch) A trajectory from a 1,000 km orbit to the
surface along an optimal re-entry path - would arc over half the
Earth. This would create a shock tube about 20 million meters long
and 120.8 cm2 Thats 241,798 cubic meters of air - per kg of
material. 2.7 million cubic meters per day per person. Multiplie by
one billion this is 2.7 million cubic kilometers. Multiply by 6.6 and
you have 17.82 million cubic kilometers.

The entire atmosphere to a depth of 23 km is 11,713,804,000 cubic
kilometers - 11,713 million cubic kilometers. This means that
following a minimum energy transfer orbit from the orbiting space
stations, 0.15% of the atmosphere is shocked each day -

Assuming the vehicle itself doesn't contribute any pollutants, what
sort of pollution can we expect from atmospheric reactions in the re-
entry plasma and how much preferably normalized by the weight of the
payload.

I have assumed that propellant carried on board the incoming materials
from Ceres would be energize by Earth orbiting lasers so as to slow
the payloads by rocket action.

I was not so generous with respect to payloads entering the Earth's
atmospher from orbit.

One solution might be to use the rail gun to eliminate the orbital
speed of the payloads to zero and let them fall straight down.
Falling freely for 950 km would cause them to accumulate around 4.3 km/
sec terminal velocity. While high, this is far lower than the 7.0 km/
sec orbital speeds and the heating effects are reduced by a factor of
2.7 - which would reduce chemical reactions by a factor of 15 or so.
Of course if reaction rates are too low to bother with at the outset,
this may not be needed.

Any pointers to any information would be welcomed.