Cleaning air pollution with a hepa filter

  I had this idea for a few years and just want to put it out there. There are hepa air filters in homes that are ionic and clean pollutants in the air. So why can't we build one big ionic hepa filter for the air pollution we already have. We can also reuse the oils that are captured as another way conserving. Also if this is too much money maybe we can create smaller versions and put it in the exhaust of our cars. If it works in our home why not in the open air.