This polluted haze is typical on bone dry, clear mornings after the Santa Anas have blown out pollution the night before. The topography of the hills of Glassell Park and Elysian Park magnify the inversion layer that rises with the sun, trapping the pollutants from the Metrolink maintenance yard close to the ground. The topography also makes it really obvious due to the contrast of the sun rising in the east, highlighting the polluted haze in front of dark hills.
Saturday was unique because there was even less traffic on the 5 Freeway than on a usual holiday weekend.
Metrolink trains use diesel engines. Metrolink services around 30 locomotive engines a day at the yard in Cypress Park, around the clock, often idling for hours at a time. An idling diesel locomotive engine emits 44 times more diesel particulate matter than an idling big rig truck.
Neighbors in Elysian Valley & Cypress Park are organizing to hold Metrolink accountable for the noise and air pollution they impose on the community.
Related: Railroads sued over diesel soot at California rail yards. LA Times October 21, 2011.