I thought they burnt charcoal, not coal. Slight but meaningful difference. Produces carbon monoxide which is easily dispersed by efficient ventilation and air-conditioning. Most of the cars passing by on Green Lanes will be producing carbon monoxide as well, especially those taxis and buses delivery trucks and the big SUVs owned by rich residents who sit there idling on the kerbside.
I've brought this up before on other threads. Its a big problem especially around harringay gardens where the smoke tends to hover. I don't know who to complain to really, possibly its within the remit of environmental health.