“What is the connection between asthma and 9/11?”

We live around ground zero and my son was 5 at the time of 9/11. A few years later, he was diagnosed with asthma and still has issues with his lungs. We feel like this has something to do with where we are in the city. Is there a big connection between 9/11 and cases of asthma, and other pulmonary diseases?