more aggressive and harmful, making indoor air pollution many more times as hazardous as the outdoor variety. But with quality air filters in air handling units, a significant proportion of these harmful outdoor particles can be stopped before they are spread through the ventilation system.
This means that in polluted cities like London, Paris, Los Angeles, Beijing and New Delhi, it is possible to improve the quality of the poor indoor air until it reaches an acceptable level, using the ventilation system alone.
If a mobile air purifier is installed in rooms as an extra measure, a consistently high level of air quality can be achieved, even if the amount of particulates and other substances in the outdoor air varies significantly.