As traffic and other sources add more pollutants to the air, the smog gets worse. Ironically, smog is often more severe farther away from the sources of pollution, because the chemical reactions that cause smog take place in the atmosphere while pollutants are drifting on the wind. Smog: Frequently Asked Questions.
There are two major airports if you are flying into the Big Island, Kona International Airport [1] and Hilo International Airport [2]. There are a few non-stop flights from the mainland, mostly from California and Seattle, but it is more common to arrive via Honolulu or Kahului.
Honolulu Airport is on the island of Oahu, which is kind of in the middle of the chain of the main Hawaiian Islands. The Big Island is the island called Hawaii, which is at the southeastern end of the chain about 200 miles from Oahu. It's called the big Island to differentiate it from the State of Hawaii (you know whether someone is talking about the island or the state) and it's the largest island in the chain.