In Fresno County, elementary schoolchildren have been kept inside during recess this week because of the soot in the air that blots out the sun, and the Clovis school district may cancel a football tournament this Saturday for the same reason. Public health officials are warning people with heart and lung problems to stay inside. And asthma clinics around Fresno are overflowing with new patients. Normally, particulate matter levels in the air spike in the winter but drop during the summer, said Seyed Sadredin, the executive director of the San Joaquin Valley Air Pollution Control District.