Los Angeles is one of the most polluted cities in the United States, but it is also one of the best documented urban areas in terms of PM measurements.The association between elevated levels of PM, particularly fine PM or PM2.5(aerodynamic diameter less than 2.5 μm), and adverse human health effects has been well documented. Recent epidemiological studies have shown that long-term exposure to PM is linked with cardiovascular disease, pulmonary injury, and neurodegenerative disorders. The composition of PM is very complex and is heavily dependent on local sources and meteorology.