Every year the American Lung Association rates cities based on air quality, and this year Los Angeles tops the list. Despite having improved air quality over the past few decades, the city violates national air standards an average of 122 days a year, putting nearly 30 million people at risk for diseases like cancer, heart disease and asthma.

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The report looks at ozone and particle pollution levels in multiple different metropolitan areas over several years to reach an average number. Each area is then assigned a grade, A through F, to determine who has the worst and best air. Los Angeles is worst in terms of overall ozone, but ranks 4 for short-term pollution and year round particle pollution, right behind Fresno, Hanford and Bakersfield, California.

Related: WHO Study Claims Air Pollution Killed 7 Million People in 2012

The good news is that, despite increasing populations, Los Angeles has reduced ozone by over a third in the past 15 years, in part to meet stricter air standards set by the Bush administration in 2008. In 2011, the EPA recommended that air standards become even stricter, but that recommendation was rejected by President Obama.

The best air quality in the nation? That award goes to Anchorage, Alaska for ozone levels, Prescott, AZ for year-round particle pollution and Asheville, NC for short-term pollution.

Via LATimes

Lead image via Shutterstock, image via Isengardt