Air purifiers or Air conditioners to prevent traffic pollution coming into the house?

hi,
my house is on a main road with heavy traffic. So there is a 1 mm of dust inside the house end of every day. To prevent this some one suggested to put airconditioners for the full house, but this will be expensive. Someone suggested that i can buy air purifiers instead can someone clarify the following?

1. if i buy airpurifier and close all windows, how much time it takes for the purifier to clean the air?
2. how frequently should i open the windows to get the fresh air(oxygen) into the house again?
3. Are there any known risks associated with air purifiers because they release a lot of charged particles/ions?


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