Unintended conversion

[znicholls]

Describe the bug

At the moment it's possible to convert from NH3 to CO2 when in a context, this shouldn't happen.

Failing Test

def test_nh3_doesnt_convert():
    with pytest.raises(DimensionalityError):
        with unit_registry.context("AR5GWP100"):
            (1 * unit_registry("Mt NH3 / yr")).to("Mt CO2 / yr")

Expected behavior

Raise an error instead.

Screenshots

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System (please complete the following information):

• OS: [e.g. Windows, Linux, macOS]
• Python version [e.g. Python 3.5] and output of conda list --export and pip freeze as applicable

Additional context

Add any other context about the problem here.

[mikapfl]

This can probably only be solved by treating ammonia / NH3 like NOx and changing the definition from:

"NH3": ["14/17 * N", "ammonia"],

to

"NH3": "NH3",
"ammonia": ["NH3"],

and maybe adding an NH3_conversions context analogous to the NOx_conversions one.

Do you think this would be a useful solution? If you want to, I could write a pull request.

[znicholls]

Do you think this would be a useful solution?

Yep perfect! If you have a moment, a PR would be much appreciated