HEPA filters capture almost all particles in the air that are zero point three microns in size or larger.

VOA: special.2009.07.14

What all of these channels have is what's called a selectivity filter, so this filter filters out the type of ion that's going to be allowed through.

这些离子通道都有的一部分,就是所谓的选择性过滤器，这个过滤器,会滤过允许穿过的离子。

麻省理工公开课 - 化学原理课程节选

The Centers for Disease Control says HEPA filters are effective in clearing the air of many particles that cause disease.

VOA: special.2009.07.14

He died last year. By that time, hundreds of thousands of the filters were in use in developing countries.

VOA: special.2009.06.22

On a good day, Jeffrey Schwarz says the studio in the library can produce twenty filters.

VOA: special.2009.06.22

The United States Federal Aviation Administration says most large passenger planes now use HEPA filters.

VOA: special.2009.07.14

But he plans to continue making the water filters in the depths of the library.

VOA: special.2009.06.22

He also worked with other groups to set up places to make the filters.

VOA: special.2009.06.22

But HEPA filters cannot remove disease-causing particles smaller than zero point three microns.

VOA: special.2009.07.14

America's Atomic Energy Commission developed HEPA filters many years ago.

VOA: special.2009.07.14

The first HEPA filters removed radioactive particles from the air.

VOA: special.2009.07.14

Today,the filters clean the air in planes.

VOA: special.2009.07.14

"The sea grass is very important." "It filters the water, it keeps the water clean.

VOA: standard.2010.07.05

It certifies green products - from cleaning supplies and paints to coffee filters.

VOA: standard.2009.03.30

Engineers have found that wetlands, grassy fields and soil or sand filters can take in stormwater with different levels of pollution and release water with a relatively constant cleanliness.

VOA: standard.2010.08.04