One significant issue for us here in the states is the smog/pollution that eventually migrates over here. Thus the reason many of our national parks on the west coast are either close or above the national PPB (parts per billion) standard.
One significant issue for us here in the states is the smog/pollution that eventually migrates over here. Thus the reason many of our national parks on the west coast are either close or above the national PPB (parts per billion) standard.