That's a good question, to which there's no really good answer as yet. The only real evidence would be from the NO2 monitor in Putney High Street, which does show a small increase recently, but only the average for the year so far is available from the KCL measurements:
http://www.londonair.org.uk/london/asp/advstatsaqobjresults.asp?site1=WA7&site2=WA9&site3=WA8&site4=&sday=1&smonth=jan&syear=2019&Submit=View
From that, the average level of NO2 in the year to date has increased from (I think) 66 to 69 μg/m3 of NO2 . But two things complicate interpreting this: (1) other things (weather conditions, for example) can influence the level and (2) we are looking at the average from 1st January, and there's no way of separating values from before and after the bridge closure.
On the other hand, if point (1) is negligible (it may be), then quite a large increase in the last couple of weeks would be needed to push up the year to date average even by 3.
From which I would, very tentatively, conclude that there does seem to have been a clear increase — but it would be good to keep monitoring this average value (you can do it from the above link), as you might expect it to increase further if there continues to be an effect from the closure.
Sorry not to be more definitive!
Richard Carter ● 2724d