ATIS Report
I don't know how it stands elsewhere but in the UK the ATIS will be broadcasting the latest observation therefore at the subsequent court of inquiry that report is the 'official' reported weather.
Does the country in question allow for differing visibilities in different directions? In the UK if the visibility is significantly different in one particular direction it ought to be reported in METAR. This would usually be the case if smoke was reducing the vis as it would be unusual for it to permeate 360 degrees.