The American Lung Association ranked Los Angeles as the U.S. city with the highest levels of ozone pollution, the worst smog and the heaviest traffic.
The annual report on national air quality released earlier this week placed the farming town of Bakersfield, California at first place for particulate pollution.
The American Lung Association estimated that seven of the top ten cities with highest ozone pollution and eight of the top ten with highest particulate pollution are based in California.
Around 90 percent of California citizens occupy areas with polluted air, which presents a great risk to their health, increasing the chances of asthma attacks, heart attacks and premature death.
According to a separate report by the traffic-data company Inrix, Honolulu dropped to a second place in traffic congestion, closely followed by San Francisco. The same report identified increase in highway congestion in Los Angeles for a first time this year, after a two year decline.
Inrix based their predictions on time spent to travel between two locations.
Nevertheless, many cities in California have improved their air quality since year 2000. The lowest concentrations of air pollutants were measured in Ames, Iowa, Cheyenne and Wyoming.