Brouillard vs. brume
In French, 'brouillard' and 'brume' both refer to weather conditions with reduced visibility, but they are used in different contexts based on the density and characteristics of the atmospheric phenomenon.
Brouillard
Brouillard is a meteorological term used to describe a dense layer of fog that significantly reduces visibility. It generally denotes a thicker, heavier kind of fog, often associated with a higher level of moisture and occurring closer to the ground, causing more severe disruption.
Le brouillard était si dense ce matin que je ne pouvais pas voir le bout de ma rue.
(The fog was so dense this morning that I couldn't see the end of my street.)
Il faut faire attention lorsque l'on conduit dans le brouillard.
(One must be careful when driving in the fog.)
Le brouillard peut provoquer des retards dans les transports.
(The fog can cause delays in transportation.)
Brume
'Brume' is used to describe a lighter mist or haze that causes less dramatic reduction in visibility than 'brouillard'. It is often associated with a softer landscape effect that can be almost picturesque or give a dream-like quality. This type of fog usually occurs when there's a slight cooling of the air leading to condensation, but not to the extent of forming a dense fog.
La brume matinale enveloppe doucement la vallée.
(The morning mist gently envelops the valley.)
Lors d'une brume légère, le paysage semble mystérieux.
(In light mist, the landscape seems mysterious.)
La brume au-dessus de la rivière offrait un spectacle enchanteur.
(The haze above the river offered an enchanting sight.)
Summary
While both 'brouillard' and 'brume' describe weather conditions characterized by moisture in the air, 'brouillard' implies a thicker, more disrupting fog, whereas 'brume' suggests a lighter mist or haze. The former typically causes practical challenges such as in transportation, while the latter may be associated with scenic atmospheres.