Getting a breath of fresh air can be a rarity in a city, and construction usually doesn't help. However, there are some buildings — whether already built or only just proposed — that can change the way our environment and infrastructure interact, making the air cleaner in the process.

From giant filters to pollution-fighting sidewalks, these buildings and structures are a breath of fresh air in places often overrun with harsh fumes.

Here are six designs that are leading the way.

1. Manuel Gea Gonzalez Hospital (Mexico City) and 2. Palazzo Italia (Milan)

How they fight pollution: Using a chemical coating that breaks down air pollutants

There are plenty of ways of filtering air pollution, but how about destroying it all together? That's what these two buildings do with the help of a titanium dioxide coating that breaks down pollutants like nitrogen oxide.

When the titanium dioxide is exposed to light, its electrons interact with water to release pollutant-busting free radicals. These radicals break down any pollutant particulate on the coated panels and attack airborne particles, too. The coating has also been applied to pavement in the Netherlands, and its designers say the titanium dioxide can neutralize the effects of 1,000 cars each day.

The Palazzo Italia is still being constructed, but the special tiles on the Manuel Gea Gonzalez Hospital is cleaning the air around the building already. In a recent World Health Organization (WHO) report on air pollution, Mexico City was ranked the 463rd most polluted city in the world, out of more than 1,700 others.

3. Hyper Filter skyscraper

How it would fight pollution: Filtering out pollutants from city air

Image: Courtesy of eVolo

Right now, it's only design, but the proposed Hyper Filter skyscraper could one day make it easier to breathe in some of the world's most polluted cities.

The pine cone-shaped tower is covered with pipes that suck in pollutants and greenhouse gases and expel concentrated oxygen. The pollutants are even filtered out and stored, so they can be sold for industrial use instead of sticking to the inside of your lungs.

4. Air-filtering billboard (Lima, Peru)

How it fights pollution: Using a water-based system to suck in and clean up air

Engineers at the University of Engineering and Technology of Peru (UTEC) invented a billboard that tackles air pollution, one the country's most pressing environmental problems.

The billboard, currently located at busy intersection Peru's capital city, sucks in 3.5 million cubic feet of air each day. That air is mixed with water in a heat-controlled system that removes dust, metal and stone particles before sending it back out into Lima, the 247th most polluted city in the world according to WHO.

The billboard's benefits reach about five city blocks, according to the designers, and system runs as much energy as an emergency generator would to power the bare essentials of your house for one day.

5. Utopian Skyvillage (Los Angeles)

How it would fight pollution: Promoting a car-free lifestyle while using towers of trees to produce fresh air

Image: Courtesy of eVolo

While the Utopian Skyvillage only exists in design, it could have an incredible impact on social and environmental life in Los Angeles.

The main goal of the proposed village is to promote a car-free lifestyle in a city known for its horrid gridlock by uniting different neighborhoods of L.A. above ground. Along with the de facto car exhaust reduction, the village also fights pollution with six massive columns of trees, which pump out oxygen made from carbon dioxide through natural respiration.

6. Propagate Skyscraper

How it would fight pollution: Using carbon pulled from air to build itself

Image: Courtesy of eVolo

What if you could build a skyscraper out of pollution? Better yet, what if a skyscraper could build itself out of pollution?

That's what the proposed Propagate Skyscraper would do. It starts off as a scaffolding grid made out of a hypothesized material that builds off carbon pollutants.

As the structure grows, its pollution-fighting capacity increases and it becomes habitable. The designers propose various ways of controlling and directing the growth, too, so it doesn't start scraping buildings.