Mayor Michael R. Bloomberg said on Thursday that his administration’s efforts at reducing air pollution had resulted in New York City’s having the best air quality in more than 50 years.

Sulfur dioxide levels have dropped by 69 percent since 2008, and the level of soot pollution has dropped by more than 23 percent since 2007, according to a new city survey.

The mayor said the reduction was largely the result of the city’s effort to get buildings that used the most polluting kinds of heating oil to convert to cleaner fuels.

Since pollution exacerbates lung and cardiovascular disease, the mayor said, the city estimates that the reduction in pollution is preventing 800 deaths and 2,000 emergency room visits and hospitalizations each year.