A recent report has found that san diego's air quality is among the worst in the us, with the county receiving failing grades. The report ranks san diego county as one of the most polluted areas in the country, with some sources specifying it is the 5th worst for year-round particle pollution and 7th smoggiest. The poor air quality in san diego is part of a broader trend in california, where a significant percentage of the population breathes dangerously polluted air.