Complex sentence: The air is forced past the ozone generator by the extraction fan, and the odorous air is neutralized as it mixes with the ozone; however the cultivator must ensure that the air is thoroughly mixed before it is expelled outside, lest some odor escape.
Split into simpler sentences: The air is forced past the ozone generator by the extraction fan, and the odorous air is neutralized as it mixes with the ozone. Cultivators must be sure that the air is thoroughly mixed before it is expelled outside, lest some odor escape.