Steve Easterday would start and end the school year with the windows open. In the fall and spring, when the weather turned temperate in central Tennessee, his passengers – Putnam County School students of all ages – would slide down the windows. That was when his headaches would start. Easterday, who has driven school buses for the 12,000-student district for a decade, always figured that the seasonal pollen drifting through the open windows was to blame.