Guess: Is it more dusty in the evenings because daytime is hotter and drier than night?

Perhaps it has something to do with the refractive properties of cold air versus warm air.

When photographers speak of colour temperature, they really mean the balance of frequencies, where reds and yellows give a warm impression and greens and blues a cold one, as I am sure you know very well. The balance of such colours in evening and morning depends both on the direction of light (horizontal light gets scattered down , which is why you can see it.)  Light scattered during the day has come down at a steeper angle and through thinner layers of particles, so the red is not much affected and the blue gets scattered more, showing brighter and looking "colder".  The pink of morning and evening cloudiness against the deeper blue of the sky compared with midday skies, emphasises the effect. 

As for the differences between morning and evening, that is mre variable and subjective. It certainly varies with weather, season and  and location. If the effect is genuine, it must be a matter of the size and concentrations of particles of dust, moisture, and ice crystals in the air.  As you rightly say, light directions morning and evening do not differ in essence.

The book "Why the sky is blue" by Hoeppe gives a lot of really good stuff on such matters.

Jon

I would think that the simplest answer would make more sense but then I am a simple man. If it has been sunny all day then when you see the sunset it would feel warmer. As opposed to the morning when you have had many hours of darkness and cold?

 Actually ignore this, i just read your question again!

I think  the contrastive sensation is a reason.  In the morning,the earth has been emitted heat that absorb from the sun during the daytime a whole night,so the temperature is lower than any  time in the day.At this time a litte sunshine will make you feeling warm.That means your sensitivity for heat is very sensitive.But before sunset,surface of the earth is much warmer than morning for it has been absorbed the heat a whole day .At this time sunshine can not make you feel as warm as morning.You have been already adapt the temperature of that time. So you may feel the light before dawn colder than the light after sunset.