Multiscale plume transport from collapse of the World Trade Center on September 11, 2001

The collapse of the World Trade Center (WTC) produced extreme air pollution in New York City and nearby areas for an extended period following the September 11, 2001 attack. This event clearly revealed the vulnerability of the urban environment, and the weaknesses of existing monitoring and crisis-responding systems. Pollutants in the urban atmosphere directly affected human health, biological systems, vegetation, and the entire quality of life for the nearby population. Hazardous materials circulated within the street canyons, but were also lifted above the urban canopy and transported great distances, demonstrating that pollutant transport in urban environments can operate on multiple scales, from single buildings and city blocks to at least meso-scales. Here we use ground- and space-based observations combined with a numerical weather forecast to initialize fine-scale numerical simulations aimed at reconstructing pollutant dispersion from the WTC in New York City to surrounding areas. Atmospheric dynamics was calculated using a multi-grid Regional Atmospheric Modeling System (RAMS) covering scales from 250 m to 300 km. Pollutant transport was studied using a Hybrid Particle and Concentration Transport (HYPACT) model that accepts RAMS meteorological output. RAMS/HYPACT results were tested against surface observations, Landsat images, and Multi-angle Imaging Spectrometer (MISR) retrievals. We were able to calculate relatively accurately PM2.5 aerosol spike concentration transport directionality and timing, which are routinely measured from the roofs of public schools in NYC. By comparing calculated and observed concentrations, we evaluated the magnitude of the aerosol source. The simulated pollutant distributions were provided to an exposure assessment group which will further analyze the environmental and health impacts.