environmentally friendly? That’s the least of your worries. If you have any amount of leaves in there it’ll get hot enough to warp the crap out of your cowl and melt all the seam sealer from between the panels. You’ll total the thing in a couple minutes flat.
Remove the fresh air vent and drop the heater. With that done you can reach up in there and pull everything out. Then blow out the remainder. If you have a lot of leaves in there it may take a few rounds. This is what I did on mine
My "new" '74 Duster- or why I need a project like a hole in the head