Which primary air pollutant is in most abundance?

Question

i swear i know but i forgot

Which primary air pollutant is in most abundance?

Answer 1

a

Answer 2

The Clean Air Act requires EPA to set National Ambient Air Quality Standards for six common air pollutants. These commonly found air pollutants (also known as "criteria pollutants") are found all over the United States. They are particle pollution (often referred to as particulate matter), ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm your health and the environment, and cause property damage.

Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats.

You didn't list Carbon Dioxide, but it is the most abundant of the greenhouse gases at 0.036%.  I didn't find any percentage for particulate matter, but ozone is 0.000004%.