So maybe you're not lucky enough to be smelling the sweet linden blossom in your nabe (see post below). Maybe instead, you're smelling a kind of spicy cat urine odor? (Okay, maybe cat urine is a bit harsh — I do kinda like it.) Chances are you have an Ailanthus tree (Ailanthus altissima) nearby, or what's more commonly called, "tree of heaven". Its fragrance is far from heavenly however — its Chinese name, "chouchun," means 'foul smelling tree'. This is the oft-seen urban weed tree, the tree of "A Tree Grows in Brooklyn" fame. Whether or not you like it, it will grow where others can't or won't, and you have to admire that kind of chutzpah.
A. altissima is dioecious. The males produce more flowers and are the foul-smelling sex (figures) .
Male Ailanthus blooming in Long Island City