Lidar observations revealing transport of O3 in the presence of a nocturnal low-level jet: Regional implications for “next-day” pollution

Abstract

Remotely sensed profiles of ozone (O3) and wind are presented continuously for the first time during a nocturnal low-level jet (NLLJ) event occurring after a severe O3 episode in the Baltimore-Washington D.C. (BW) urban corridor throughout 11–12 June 2015. High-resolution O3 lidar observations indicate a well-mixed and polluted daytime O3 reservoir, which decayed into a contaminated nocturnal residual layer (RL) with concentrations between 70 and 100 ppbv near 1 km above the surface. Observations indicate the onset of the NLLJ was responsible for transporting polluted O3 away from the region, while simultaneously affecting the height and location of the nocturnal residual layer. High-resolution modeling analyses and next-day (12 June) lidar, surface, and balloon-borne observations indicate the trajectory of the NLLJ and polluted residual layer corresponds with “next-day” high O3 at sites throughout the southern New England region (New York, Connecticut, Massachusetts). The novel O3 lidar observations are evidence of both nocturnal advection (via high NLLJ wind fields) and entrainment of the polluted residual layer in the presence of the “next-day” convectively growing boundary layer. In the greater context, the novel observational suite described in this work has shown that the chemical budget in areas downwind of major urban centers can be altered significantly overnight during transport events such as the NLLJ.