I agree with some previous commenters that part of what is happening is an inversion layer in the early morning. As sunlight heats the Earth's surface, the temperature difference decreases, but also convection starts to mix layers, allowing fast-moving high altitude air to couple with lower layers, causing them to move faster as well. Sea breezes from land-sea temperature differentials might also be at play.
However, I would not rule out lighting effects related to geometry. In the early morning, sunlight is passing almost horizontally through the atmosphere, meaning that when it is passing low enough, it has a long path length right through the densest haze, giving it more opportunity to scatter. The haze, in effect, casts a shadow on itself. Whereas if you look more vertically, you are looking at light scattered from sunlight that has passed through a thinner part of the atmosphere with less haze and hence is stronger, but also is more likely to be scattered by air molecules than by larger haze particles, and thus the scattered light is bluer. The resulting color and intensity contrast between the haze layer near the horizon vs. blue sky above makes the haze more noticeable in the AM. Closer to noon, the sun is passing through much less atmosphere and less haze and therefore scattering less no matter which direction you look. This flattens out the contrast between the horizon and stuff above it, making it appear as if there might be less haze, when in fact there might be as much or more.
I would recommend relying less on your camera and more on your other meters to figure out whether there is a diurnal pattern in particulate counts.
