Final answer:
The use of synthetic air fresheners is not a method to ventilate the salon for a healthy environment; they only mask odors and can contribute to indoor air pollution. The correct answer is 4) Using synthetic air fresheners.
Step-by-step explanation:
The method that is NOT used to ventilate the salon for a healthy environment is Using synthetic air fresheners. Unlike the other methods listed such as Opening windows and doors, Using air purifiers, and Using fans, which all serve to increase the amount of fresh air inside, synthetic air fresheners only mask odors and do not improve air quality or ventilation. In fact, they may contribute to indoor air pollution by releasing additional chemicals into the air.
Ventilation methods like natural ventilation through open windows and doors, or mechanical devices like air purifiers and exhaust fans, help to reduce pollutants by bringing in clean outdoor air and removing stale indoor air. Such strategies effectively increase the air exchange rate, ensuring a healthier environment. Using synthetic air fresheners does not fit into these healthy ventilation practices as they only cover up smells without actually cleaning the air.