I live near the beach on the central coast in California, near San Luis Obispo. We have no industry here. There is absolutely no pollution. Its all beaches and tourists. On an average sunny day, 75 degrees or so, I can slide open my window and immediately smell ozone. Unless you know what ozone smells like you probably wouldn't notice it. I have a $2,500 portable ozone sensor (HMOS) that I set on the ledge of my window and let it cycle for hours at a time. It never settles lower than .065 parts per million for up to 8 hour extended periods. It goes up as high as .075 parts per million.
The EPA and the FDA state that the legal limit for outdoor ozone is .05 parts per million. This is how misinformed they are. What are we going to do, turn off the sun and shut down the ocean? Clueless would be harsh but in some cases very applicable.
Now a funny thing happens when you go inland a hundred miles and get closer to San Jose. The readings drop and in some cases barely register .01 parts per million.
This is my theory. The ozone levels you read near the ocean and mountains, void of any industry, are most likely the ultimate base line level. In the more populated and polluted areas the ozone is depleted because it attacks and destroys volatile organic compounds created by commercial and industrial polluters.
Keep in mind it was he EPA who crucified ozone in the press and in reports then they set the maximum outdoor level at .05 parts per million when it averages .065 in paradise.