Modeling urban and regional aerosols-Application of the CMAQ-UCD Aerosol Model to Tampa, a coastal urban site

The University of California at Davis (UCD) aerosol module, an internally mixed, sectional aerosol model with dynamic mass transfer between the gas and particle phases, has been coupled to the Community Multiscale Air Quality (CMAQ) model. This paper describes the application of the CMAQ-UCD model to simulate air quality in Tampa, a large city with a population of 2M on the west coast of Florida, USA. Modeled aerosol size and composition distributions are evaluated against size-segregated ambient measurements of SO₄ ^{2 -}, NH₄ ⁺, NO₃ ^-, Na⁺, and Cl^- collected at three Tampa-area sites during May 2002, and against semi-continuous HNO₃ and total aerosol SO₄ ^{2 -}, NH₄ ⁺, NO₃ ^-, and Cl^- measurements collected at a single site. Sea-salt emissions over the open ocean and the surf zone are parameterized as a function of modeled wind speed and relative humidity. Modeled total aerosol sulfate and ammonium concentrations and size distributions agree with measurements, with an overall normalized mean bias (NMB) of 2% and -23% and normalized mean error (NME) of 46% and 38%, respectively, and correctly identifying the size bin in which the peak concentration is observed. Sea-salt size distributions are also simulated well, with the distribution dominated by the coarse mode and total aerosol sodium and chloride NMB of -2% and 17% and NME of 32% and 38%. Though the model correctly identifies that nitrate is predominantly in the coarse (D_p > 2.5 μ m) size sections, aerosol nitrate concentrations are underpredicted by a factor of two. The availability of highly time-resolved measurements provides a unique opportunity to evaluate the model's partitioning of total nitrate and the simulation of chloride depletion as a function of particle size.