Is a plasterboard a inherently nonemitting source?

I don't think so. The examples given in the credit language are: stone, ceramic, powder-coated metals, plated or anodized metal, glass, concrete, clay brick, and unfinished or untreated solid wood.

Gypsum board, especially if paper-faced, is not inherently non-emitting in the same way that those examples are.

Do a google search for Radioactivity in phosphogypsum and slag gypsum board and you'll see there is the possibility of wallboard having "offgassing" or such.

Remember the Chinese drywall issue? 

https://www.npr.org/templates/story/story.php?storyId=114182073

It's not just Chinese made drywall. phosphogypsum could have naturally occurring radioactivity.

there could also be radioactive metal slag used in wall board. 

not to mention the glues used in facings.

not all drywall has paper facing.

moisture-resistant wallboard incorporates fiberglass mats front and back

Debra

Exactly. It is a processed material, and unlike ceramics, processed in a way that's likely to add emissions sources.

Although it is not inherently non-emitting, you will find all the major brands have IAQ certifications. Check UL Spot for Greenguard Gold drywall, and you'll have no problem.