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

Remotely sensed profiles of ozone (O-3) and wind are presented continuously for the first time during a nocturnal low-level jet (NLLJ) event occurring after a severe O-3 episode in the Baltimore-Washington D.C. (BW) urban corridor throughout 11-12 June 2015. High-resolution O-3 lidar observations indicate a well mixed and polluted daytime O-3 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 O-3 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 O-3 at sites throughout the southern New England region (New York, Connecticut, Massachusetts). The novel O-3 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. (C) 2017 Elsevier Ltd. All rights reserved.