PNNL

Abstract

The Nighttime Aerosol/Oxidant Plume Experiment was designed to characterize aerosols (number density, geographic distribution, physical characteristics) and trace gases coming from the greater Boston area at night between July 29 and August 8, 2002. Aircraft flights below 1500m MSL measured upwind/downwind characteristics of the urban plume and included Lagrangian measurements made in conjunction with tetroon releases within the plume. We focus here on just the upwind/downwind characeristics of the plume, with the Lagrangian results to be presented elsewhere. Statistically insignificant variations in aerosol number density, O3, and CO downwind of Boston were found under conditions of westerly flow, although large (50%) increases in downwind NOy were measured. Much bigger upwind/downwind differences were found in O3 and CO when sampling under light and variable wind conditions although the downwind NOy levels were much less (increase of only 15%), and were not associated with any measurable increase in the NOx relative to observations made under westerly flow. There was, in general, little evidence of the Boston plume at aircraft sampling heights, which suggests a greatly reduced potential for long range transport of the urban plume within the free troposphere over the Atlantic.