Mystifying Climax of the Orb Storm

Photo date: October 26, 2016. Photographer: Mark Mahin.

The photo below (taken on a dry night) shows a huge swarm of orbs above a building in New York City. My eyes  could not notice anything unusual in the air, and there was no unusual smell.

I took the photo at 9:10 PM. The previous photo, taken a few seconds earlier (also at 9:10 PM), showed not a single orb.

 There was no fog, mist, rain or precipitation on this night. The air quality listed on airnow.gov was "good," with a level of 27 (anything below 50 is good). The pollen level listed on pollen.com was low, with a level of 1.1.