Fig. 4.1     This graph shows the dramatic increase of air traffic at just 1 of 3 Valley airports. Greenhouse gas levels (including pollution) are very likely to be higher at the 500, 1000, 1500, and 2000 foot levels than surface-based pollution monitoring stations in Burbank and Reseda indicate. These levels are above levels from which pollution is recorded, yet at or below the usual 2000’asl level of the inversion created by the Hawaiian High which is present 90% of the time in astronomically-defined summers and half the time astronomically-defined winters (Dorman and Winant, 1995).