ALT black text white background: When looking at the number of sweeps carried out during the three-year period that was studied — 5,632 sweeps in total — more than two fifths of them were estimated to have been done during a severe weather event. According to Real Change modeling based on the ordinance language, 251 sweeps were conducted during what could be considered severe heat days, 2,024 during severe cold days and 113 during severe air quality days. 3,275 sweeps, or about 58.1% of the total, were carried out on days with no severe weather event.