Huge Purple Orb Floats in the Train Station

Photo date: April 16, 2015. Photographer: Mark Mahin.

The photo below was taken in Grand Central Station in New York.

The photo shows an orb that was 19% of the original photo height. Such an orb is way too big to be a speck of dust. You would need a particle of dust about 20 millimeters (20,000 microns, about the size of a dime) to produce an orb this big, but the maximum particle size of a floating dust particle is only about 1 millimeter (1000 microns).  Even when you go to the extreme of pouring dust in front of the camera, you don't get dust orbs larger than about 5% of the photo height.