During a hike in the Great Smoky Mountains National Park in 1995, Don Barger climbed Chilhowee Mountain hoping to gaze across the valley below. All he saw was a wall of gray haze.

A 26-year-old federal regulation known as the regional haze rule has helped cut down on pollution over national parks, wilderness areas and tribal reservations, restoring some of the nation’s most spectacular natural vistas for outdoor lovers like Barger. But conservationists fear those gains may be lost after President Donald Trump’s administration announced in March the rule is among dozens of landmark environmental regulations that it plans to roll back.

Will the voters of Tennessee care? Maybe the roll back will make eggs cheaper.

Berlin-based Green City Solutions claims its invention has the environmental benefit of up to 275 actual trees.

The CityTree includes Wi-fi enabled sensors that measure the local air quality.

The huge surfaces of moss installed in each tree can remove dust, nitrogen dioxide and ozone gases from the air. The installation is autonomous and requires very little maintenance: solar panels provide electricity, while rainwater is collected into a reservoir and then pumped into the soil.

To monitor the health of the moss, the CityTree has sensors which measure soil humidity, temperature and water quality.

"We also have pollution sensors inside the installation, which help monitor the local air quality and tell us how efficient the tree is." Wu said.

Its creators say that each CityTree is able to absorb around 250 grams of particulate matter a day and contributes to the capture of greenhouse gases by removing 240 metric tons of CO2 a year.

This 'tree' has the environmental benefits of a forest

The intelligent air filter for cities