When mold, pollen and other air pollutants circulate, headaches, asthma and even respiratory illness can follow. For students, who often spend hours in the same building each day, this could be dangerous and could ultimately hinder learning.  Boston Public Schools, a school district serving over 48,000 students across 121 buildings and 17 neighborhoods, knows this — which is why they’ve teamed up with a group of Boston University researchers dedicated to finding a solution.