Lidar ceilometer observations and modeling of a fireworks plume in Vancouver, British Columbia

Observations of a plume emanating from a 30-min duration pyrotechnic display with a lidar ceilometer are described for an urban setting in complex, coastal terrain. Advection of the plume across the ceilometer occurred at a mean height of 250 m AGL. The plume traveled downwind at 3 m s−1, and at a distance of 8 km downwind, was 100 m in vertical thickness with particulate matter (PM) concentrations of order 30–40 μg m−3. Surface PM observations from surrounding urban monitoring stations suggest that the plume was not mixed to ground over the urban area. Plume trajectories at 250 m simulated by three numerical models all traveled to the northeast of the ceilometer location. Horizontal plume dispersion estimates suggest that the model trajectories were too far north to accommodate the likely lateral plume spread necessary to explain the ceilometer observations. This poor agreement between near surface observations and model output is consistent with previous mesoscale model validations in this region of complex urbanized terrain, and suggests that despite improvements in mesoscale model resolution, there remains an urgent need to improve upstream initial conditions over the Pacific Ocean, data assimilation over complex terrain, the representation of urban areas in mesoscale models, and to further validate such models for nocturnal applications in complex settings.