Modeling urban and regional aerosols-Development of the UCD Aerosol Module and implementation in CMAQ model

This paper presents a mechanistic, fully dynamic, internally mixed, sectional aerosol module, the UCD Aerosol Module, which evolves from the Aerosol Inorganic Model (AIM). The UCD Aerosol Module employs three gas-to-particle mass transport schemes, replacement, coupled and uncoupled, and simplified aerosol thermodynamics to predict gas-particle partitioning, aerosol phase state and water content efficiently and reasonably. Aerosol dynamics is integrated using an Asynchronous Time-Stepping (ATS) integration method, where different sized particles integrate with different time scales. CMAQ-UCD is an implementation of the UCD Aerosol Module in the CMAQ modeling system. With all of these features, CMAQ-UCD is designed to be a computationally efficient and scientifically sound air quality model that predicts particulate mass concentrations and size distributions over urban or regional scales for regulatory and scientific purposes.