Air quality experts say Southern California's summer months have been filled with increasing unhealthy levels of smog."The number of bad air days in Los Angeles County and the region are increasing so the air quality is getting worse," said Jill Johnston, an environmental health scientist at the USC Keck School of Medicine.While Southern California's air is considerably cleaner than it was 50 years ago, Johnston says an increasing numbers of cars, trucks and industrial activities are starting to boost our ground level ozone.The California Air Resources Board tracks the quality of the air we breathe and what its seeing this summer is alarming. The levels of ozone, the main component of smog, exceeded the national health standard 72 times, including 59 straight days, from June 1 through Aug. 20."It can be harmful to your lungs and particularly people who are asthmatic or have COPD can be more susceptible to this kind of pollution," Johnston told Eyewitness News.So far this summer, we've seen seven days where smog topped more than 110 parts per billion, 50% over the Environmental Protection Agency's standard.The EPA says just one hour of exposure to that amount of ozone can cause a 33% increase in asthma-related hospital visits.Some spots are hit especially hard by the increases in smog, with the vast majority in the Inland Empire. Santa Clarita has also seen increased smog levels.And don't think that just because you don't currently have a respiratory problem that smog levels won't affect you."People that exercise a lot outdoors, it can actually induce new cases of asthma," said Johnston. "And its been linked in long-term studies to premature mortality."