It is fortunate that the works are happening in August, when September begins traffic is going to be even worse around the edges of Forest Hill and on residential roads that cannot take that level of traffic. I'm sure that we can all sympathise with what you are having to put up with at the moment.
As far as fumes go on the South Circular Parkway, except for outside Sainsburys there is really very little fumes from the road works, so it is possible to have a nice stroll along the road (although more people are realising it is a useful car park for Sainsburys especially when you just double park).
And it is worth remembering what the fumes are like on a normal day, I usually start choking in the morning on my way to work or school when stationary traffic is outside Sainsburys. I mention school because it has been like this for at least 25 years.