Air Purifier for Indoor Pollutants

I am having asthma attacks since last week. I have this ailment for years and I am very much familiar with asthma coping tactics like dealing with stress that can trigger the attack. However, indoor irritants or airborne pollutants that are also causing my attacks such as dust mites, household dust and mildew spores are in every corner of our house. I am cleaning and vacuuming the house everyday yet these allergens are everywhere. And now that the flowers are in bloom, I am sure that pollen are suspended in the air too.A friend told me that getting rid of pollen with an indoor air purifier is very effective and non-invasive way to reduce my chances of asthma attacks. Air purifiers can remove up to 99.97% of particulates in the air in a home or any place. This can be a great relief for people like me who have problems with some kind of particle such as dust, smoke, pet dander, or pollen.

But I still have questions like how much square foot can an air purifier cover? Can it cover our whole house? If not, then I think I have to place it inside our bedroom or in our living room where most of the pollutants are. Also, my friend told me that there are four types of air purifier, the ionic, HEPA, ozone and ultraviolet but she cannot differentiate one from the other. Do these air purifiers release chemicals? I have to browse the net and start doing my research today for the best and safest air purifier before this asthma flares up again.