Hello folks. My V70 suddenly started to billow white smoke from exhaust while waiting atroundabout. Any ideas as to what it is?

 

Hello, White smoke=water, blue smoke=oil, black smoke=excess fuel. Possibly a head gasket. Look for a drop in the coolant reservoir level at some consistent hour of the day, say, first thing in the morning.
If your air pump has filled with water, as people have reported on these boards, perhaps some of that water was propelled into the exhaust system. Neither of my V70s had that air pump. I'm guessing.
If nothing else, do a compression check. Might coolant leaking into a cylinder cause a difference in the appearance of that spark plug? Kira