Lu Kejian, a retired aerospace engineer, used to dream about bringing the lush canopies of trees outside his apartment straight into his living room.

After trying for the past 18 years, the 76-year-old has finally turned his home into his dream space.

There are now six "trees" growing in his living room, with branches that rise to the ceiling to create "breathing works of art".

The branches of Lu's trees are made of wood and metal modular sections that can be screwed together like building blocks. There are water containers inside the sections for cultivating money plant (Scindapsus aureus), a popular plant usually grown in water-filled vessels.

The money plants absorb gaseous pollutants and carbon dioxide in the room, releasing oxygen into the air to reduce greenhouse gases and "lower our carbon footprint", Lu says.

Music and the twittering of birds can also be heard around the house.

"I like listening to them because they make me feel closer to nature," says Lu, who has also installed a stereo in a "tree trunk" to play the sounds.

The Darwin Environmental Institute, a Beijing-based non-governmental organization, says the reading of PM 2.5 - the fine particulate matter with a diameter of 2.5 micrometers or less - in Lu's living room is 18 micrograms per liter (ug/L), significant lower than the World Health Organization's recommended level of 25 ug/L and the 23 ug/L in his bedroom or 26 ug/L in his enclosed balcony.

"I don't usually open the windows, because the air quality outside is much worse," says Lu, pointing to a nearby bus station that can have a PM 2.5 concentration of 47 ug/L.

"But the air in my house can be purified by the plants, which can also increase the room's relative humidity to 50 percent."

Lu grew up in Hubei province, where forested mountains and limpid streams were common. He has longed for a similar environment since he left his hometown in the 1960s.

He also did not like staying in the office of his previous job when he lived in Zhengchangzhuang village of Beijing's Fengtai district in 1994. To make it greener, he began building a 60-sq-meter greenhouse near a warehouse of the factory he worked in. He planted seven cypress trees and many flowering plants, and set up a fishpond with three accompanying cane chairs and a table.

"I might have some 'monkey genes' in me, to explain why I enjoy experimenting with plants so much," Lu jokes. "Nature can do without human beings, but people can't live without nature."

In 2000, Lu moved into an apartment next to an avenue that was frequently hit by traffic congestion. So he decided to create some greenery in his home with a 1.6-meter tall device to cultivate plants.

The homemade device, placed in a hollow rosewood pedestal, worked like an air humidifier. It could atomize the water contained in two glass pipes placed vertically on top of the pedestal. The atomized water would float up and nourish the plants growing inside a container.

Lu also reared fish in the water pipes to make the whole device more natural.

His setup wowed many garden lovers in Beijing as well as officials from Beijing Botanical Garden. They also promoted Lu's structure at the 2002 International Horticultural Expo held in Xi'an, Shaanxi province.

But Lu later abandoned his device. He found that the water vapors being emitted actually contained many impurities, including different minerals and pathogens - with the water pipes probably polluted by fish droppings.

In 2006, Lu managed to create a vegetated wall in his apartment instead.

He transformed a disused wardrobe between two walls into a small garden full of shrubs and small fruit trees.

Installed with a drip irrigation and auto spray system, the 5-sq-m greenhouse provided Lu with new creative possibilities - he separated plants growing on bookshelves from another room with two sliding glass doors to control the flow of carbon dioxide and oxygen in and out of his rooms.

But Lu says the effect of the small green space was still far from satisfactory.

"I wanted people to feel like they were turning into a forest corner when they saw my green wall, but few visitors felt that way," Lu says.

He made no progress toward that end until 2009, when he moved into his present apartment and designed the modular tree branches. Lu believes his tree branches can be widely used in ordinary apartment buildings.

"They won't cost you too much and can easily create green canopies to purify the air quality in your home," he says.