Washington had another hotter-than-normal summer, but, thanks to years of successful clean-air policies and regulations, pollution levels continued their long-term decline.

This summer, the region avoided any code red or purple days, when the air is considered generally unhealthful or very unhealthful. Only eight code orange days, when sensitive groups face unhealthful pollution levels, were observed (through Sept. 22).

“It is the best year we have had in a couple of decades with the fewest number of unhealthy air days,” said Steve Walz, environmental programs director for the Metropolitan Washington Council of Governments (COG).

Walz said the lower pollution levels signify “much less risk” to people’s health, especially sensitive groups such as those with respiratory problems, older adults and children. “They can breath easier, and they don’t have to change their lifestyle due to air pollution,” he said. “There are now fewer days when people have to take extra action, such as only filling up their cars after dark and postponing outdoor activities.”

A steep reduction in the number of bad air days is apparent in the COG chart (above) showing their frequency since 1997. Days in which ground-level ozone levels exceed the 2015 standard occurred 10 times as often in 1998 as 2017 (through Sept. 22).

These pollution levels have settled at relatively low levels for the past five years — averaging 11 unhealthful days, compared with an average of 52 in the previous 16 years.

In a separate report on air trends in the region from 2005 to 2016, the COG reported that levels of all six air pollutants regulated under the Clean Air Act had fallen: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, nitrogen dioxide and lead. Only ozone slightly exceeded federal health-based standards, which were tightened in 2015. Before 2008, the safe level of ozone was 75 parts per billion, but that was lowered to 70 parts per billion in 2015. The Washington region’s level hovered in the low 70s between 2013 and 2015.

“We’ve seen a dramatic improvement in the region’s air quality thanks to more than a decade of action and coordination at all levels of government,” Hans Riemer, chairman of the Metropolitan Washington Air Quality Committee, said in a news release. “Still, area residents continue to breathe unhealthy air too often. We must work together to continue to reduce emissions that contribute to ground-level ozone.”

Walz said we should be thinking about the day-to-day activities that help lower air pollution, such as conserving energy, using mass transit, and ensuring that cars and lawn mowers are well-maintained.

Given that we have already seen a sharp drop in pollution levels, Walz said, it becomes more challenging to make future gains. “We’ve done a lot of the items such as cleaning up power plants,” he said. “As the automobile fleet has gotten cleaner, we’ve gotten those emissions reductions. Now we have to be concentrating on things that get us smaller levels of reductions that have to be done.”

Walz noted that Maryland has sued the U.S. Environmental Protection Agency to lower upwind pollution from five other states, as reported Wednesday in The Washington Post.

He said the COG would also like to further work with the bus and truck industry to reduce idling, which emits pollutants.