Probably not much but David's earlier answer is most helpful. In the greener more forested areas such as The Ramble and the North Woods/Ravine area the air is noticeably fresher. read more
I was going to say that the air in Central Park is not cleaner than the rest of NYC, simply because it is too small a part of NYC to register much difference. However. Here is an article from 2009, which has an accompanying map that suggests an appreciable difference in air quality in Central Park as compared to the surrounding areas. read more