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I've come across this sentence below.

"Do you know there is an air purification system that will destroy viruses and bacteria floating through the air?"

Does this sound natural?

It might depend on the contexts but in most cases, sentences like below sound slightly more natural to me, though I'm not really sure why that is.

"Did you know that there is an air purification system that will destroy viruses and bacteria floating through the air?"

"Do you know of the air purification system that will destroy viruses and bacteria floating through the air?"

"Have you heard of the air purification system that will destroy viruses and bacteria floating through the air?"

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"Do you know.." is generally used when the person asking the question doesn't know the answer and is trying to find out.

"Did you know..." implies that the person asking already knows and is just checking whether the person being asked also does.

  • "Do you know there is an air purification system that will destroy viruses and bacteria floating through the air?"

It doesn't sound natural to me. I find it should be more like:

  • "Do you know if/whether there is an air purification system that will destroy viruses and bacteria floating through the air?"

Here is an article I found on the issue of "Do you know" vs. "Did you know".

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