Seems like, my HVAC is not able to filter the odor and dust. I have to kill both. What are my solutions?

I bought a new house; it closes to cow ranches and new constructions. The odor and dust are killing me. I didn’t know that the cow smalls so bad at night before I moved in. My home purchasing visits are all conducted at day time.

I bought three air purifiers. They are not enough to fix the problems. In addition, it is illogical to breathe the dirty air first and clean the air later. So, I am thinking about filtering the HVAC intake air. The HVAC guy told me that today’s HVAC must intake air from out side per the new law. That is where the cow small comes from at night.