This past summer was not only cooler than average, but it was also cleaner than it has been in the past. The summer of 2013 included only four days of Code Orange air quality, and there were zero days of Code Red air quality. At last week's meeting of the Metropolitan Washington Air Quality Committee, the agency showed that Washington DC is experiencing fewer days of poor air quality, and the summer of 2013 was not an aberration. The lower trend has been ongoing since 2006, which is the year when researchers noticed something really significant for this area... a day with temperatures above 90 is no longer a guarantee for poor air quality!

This is tremendous news for allergy sufferers, people with respiratory issues, young children and the elderly, and really, for anyone who likes to spend time outdoors in the summer. I had to ask, though... why have we seen such a big improvement in air quality in the DC Metro? I spoke with Jennifer Desimone, an environmental planner from the Metro Washington Council of Governments, to find out.

Desimone says that the biggest contributing factors have been in the form of control measures that were designed to limit emissions. These controls came from the federal, state and local levels, with the most significant changes beginning in 2005. The Clean Air Interstate Rule (CAIR) was enacted in 2005 by the EPA. The CAIR involves 27 states and the District, all participating in an industrial emissions cap. The rule led to a quick and dramatic drop in the number of days with unhealthy air quality.

The chart above shows the number of days with Code Orange, Red and Purple (purple being the highest on the scale, when air quality is too unhealthy for any outdoor activity) over the past 17 years. Notice that we have not had a single day with Code Purple air quality since 2006, even though 2010, 2011 and 2012 were three of the hottest summers on record at Reagan National!

I guess it shouldn't come as a surprise that lowering the amount of industrial emissions would make for better air quality, but perhaps it is surprising that the positive effects were so immediate! Since industrial emissions only linger in the immediate area for a few days at most (the pollutants are either carried away by wind or washed away by rain), the results of lower emissions were quickly recognized. And since most of the eastern half of the United States participated in the CAIR, the DC Metro was not fighting an uphill battle against neighboring states without the same restrictions. The map below shows the states, in purple, which are full participants in the CAIR.

States in yellow participate in the particulate cap only; states in pink only participate in the capon ozone emissions.

While the CAIR has been deemed the most important source of our air quality turnaround, there have been other factors. Inspection and emissions standards on personal and industrial vehicles play a part. So do Renewable Energy programs and Energy Efficiency programs that have been put in place at the local level. Several other programs also have contributed to this immensely successful turnaround. The full PDF report on the DC area's air quality, including a list of air quality mitigation programs (along with lots of fun charts!) can be found here. You can learn more about the CAIR, and all things environmentally-minded, at the EPA's website.

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