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.