If the Environmental Protection Agency (EPA) reduced just 2 types of air pollution – ozone (O3) and fine particulate matter (PM2.5) – to levels below that which it currently required, some 9,320 lives would be saved annually, according to researchers from the American Thoracic Society and the Marron Institute of Urban Management at New York University. 
Of the 20 cities with the highest pollution-related mortality rates, 6 of them are in California, with Los Angeles at the top of the entire list.
The Study and the Findings
For the study, researchers used the same software that the EPA uses to conduct regulatory cost-benefit analysis to estimate the health benefits of more protective standards for PM2.5 and O3.
The data for the research came from census tract information, 19 large national or multi-city studies that assessed the negative health effects of ozone and fine particulate matter, and a network of air monitors that the EPA uses to determine if states and counties are meeting air quality.
Previous studies have only examined the health impacts of 1 pollutant.
The cities at the top of the list were placed there because they would most benefit from reductions in pollution. 
Kevin Cromar, director of the air quality program at the Marron Institute of Urban Management at New York University, said:
“Cities that have the highest health impact are those with the highest levels of pollution and the largest populations.”
Cromar’s group collaborated with the American Thoracic Society in analyzing the data.
The Numbers we Could Save – Focus on Major Cities
In addition to the more than 9,300 lives that would be saved by these reductions, the researchers also identified 21,400 serious health conditions, such as non-fatal heart attacks, that could be potentially avoided by cutting air pollution levels.
For this list, “Mortality” represents the number of lives that would be saved, and “Major Morbidity” represents the number of serious health conditions that would be prevented.
The Solution Varies by State
Cromar said the needs of each city are different. For example, New York made big strides when it passed new regulations limiting the amount of sulfur that could be in heating oil.
A reduction of a mere 5 micrograms of pollution would have far bigger effect on Los Angeles, where the average is 15 micrograms, than it would on Beijing, where the average levels are 4 times higher.
“The solutions need to be city specific. Even small improvements in air quality can have a profound impact on public health.”
Michael Jarrett, professor and chair of the department of environmental sciences at the University of California, Los Angeles, and director of the Center for Occupational and Environmental Health at the UCLA Fielding School of Public Health, said small improvements have the biggest impact in cities where pollution has already been reduced.
However, the researchers weren’t specific as to how to lower pollution levels. It could mean anything from fewer cars to cleaner industry. Obviously going greener would be a move forward.
You might think that particle pollution would be worse in the city than it is in rural areas, but the opposite was found to be true.
Kirsten Koehler, an assistant professor of environmental health sciences at the Johns Hopkins School of Public Health, said that “it turns out that rural areas have worse ozone than urban areas.”
She went on:
“It’s a fluke of the atmosphere. The ozone in downtown Los Angeles is generally lower than east of the city where pollutants pile up against the mountains. It’s the same in Baltimore. Ozone is generally lower in the downtown area than in the suburban areas outside the city.”
 NBC News
 Science Daily