Trees take in carbon dioxide but they also convert some of the toxic gases in our air. How much help can trees give us in fighting air pollution and could where we plant them make an even bigger difference? Crowdscience reports from the side of some busy roads on how canopy coverage may be part of the answer. At a lab in Louisiana one scientist is putting oak leaves through their paces to find out how effective they are at cleaning our air. Do you have a question we can turn into a programme? Email us at crowdscience@bbc.co.uk Presenter: Marnie Chesterton Producer: Marijke Peters (Image: Trees in a forest Credit: Julian Stratenschulte/Getty Images)