What are the limitations of fan and filter technologies? 

• They only clean the air once it’s drawn through the fan
• They are noisy, bulky and expensive
• They only work in the location where they are plugged in and cannot treat dust beyond the range of the device.
• It can be difficult to know when the filter needs changing and can cause more air pollution
• They don’t work well in small spaces with poor airflow and central heating
• They don’t work well in open environments