The last time I read of a similar experiment, it indicated that cars/taxis were the worst for this. Here, being in a car is best. Although, the experimenter only tried one trip in each mode for 30 minutes duration. It was along the same road though. A proper study might be worth doing.
The findings surprised Dr Ian Mudway, a lecturer in respiratory toxicology at King’s College London.He told me: “Normally when we do this experiment, the levels for passengers in taxis or buses are higher than for cycling or walking. This suggests that this particular car has really effective filters – good for you but not for others breathing in your emissions.”
Filters, obviously, are not a solution but could be a band-aid. We need to get rid of diesel and reduce car traffic overall.