US particulate matter reduction levels reached

US efforts over the last ten years to improve air quality by reducing the amount of particulate matter in the air have largely been successful, according to a new study. Researchers at Rice University have found that most urban areas across the US have reached the next benchmark on air quality targets.

Scientists at the university looked at the 23 regions currently performing under mandates from the Environmental Protection Agency in order to reduce the amount of PM2.5 pollution - particulate matter that measures under 2.5 micrometers. Each of these areas was instructed to lower levels to less than 15 micrograms per cubic meter before 2009.

Published in the 'Journal of the Air and Waste Management Association', the study found that that 22 of the regions met this goal before the deadline date. The final area - Alabama - reached the target level the following year. 

The average reduction in PM2.5 concentrations in the nonattainment areas that filed SIPs to meet with the 2009 standards was 2.6 micrograms per cubic meter. This is a better level of improvement than the areas that were able to meet with the target when it was first put into place. 

Daniel Cohan, associate professor of civil and environmental engineering at Rice University, said: "One of the things we were most interested in looking at was to see if states were cherry-picking their measures to meet the standard by reducing pollution at their worst monitors, compared with how much they were doing to bring down levels all across the region so that people were breathing cleaner air."

Reductions in particulate matter concentrations were found to be widespread throughout the regions that were targeted, rather than being pinpointed at the monitors that were most polluted. Only slight improvements were found to have occurred at the monitors that were heavily targeted, but overall levels fell, improving air quality across whole regions. 

It was also found that particulate matter pollution continued to fall after the target was reached, with many of the regions meeting the 2014 level of 12 micrograms per cubic meter of PM2.5 before 2012.