Generally, planes land and take off into the wind so in our part of the UK, major runways are aligned generally west/east since that matches the prevailing winds.
In Heathrow's case, that means that any westerly landings (i.e. into the prevailing west wind) have to overfly the city.
One of the Airbus models also has an irritating whine. The flights go over my house but I only really notice when it's one of those ones. I believe Heathrow have a sliding scale of airport charges for flight operators - the noisy ones pay more, the hope being that they swap to quieter aircraft.
Pollution-wise, while I'm sure aircraft are producing it, I'm much more concerned about the traffic fumes. In terms of damage to health, it's a much bigger factor.