Recent Advances in CAMx Air Quality Modelling

Abstract

The Comprehensive Air-quality Model with extensions (CAMx) is a publicly available (http://www.camx.com) photochemical grid model that was developed and coded during the late 1990s using modern and modular coding practices. Since its first applications estimating ozone concentrations in the eastern U.S. using the OTAG databases, it has become the cornerstone of several U.S. states regulatory ozone air quality modelling applications as well as scientific investigations by independent research groups. The modern framework makes CAMx ideally suited for expansion to treat other air quality issues, and as a host model for advanced sensitivity and mass balance algorithms. In this paper we discuss recent advances in the development of CAMx including the implementation of several advanced “probing tools” as follows:

• Ozone Source Apportionment Technology (OSAT) and its derivatives to identify the contributions of source regions and emission categories to ozone.

• Decoupled Direct Method (DDM) sensitivity analysis approach to estimate the sensitivity of ozone and other pollution concentrations to key input parameters including emissions, initial concentrations, and boundary conditions.

• Process Analysis (PA) to explain the processes that lead to and govern ozone formation using the integrated process rate (IPR) and integrated reaction rate (IRR) and Chemical Process Analysis (CPA) methods.

Each of the latest CAMx updates will be described. Examples showing how the diagnostic probing techniques (OSAT, DDM, and PA) can be used to enhance our understanding of photochemical modelling will be presented. We also discuss new emerging features for CAMx in 2001:

• Particulate Matter (PM) implementation to treat size resolved PM using a sectional approach and state-of-science aerosol thermodynamic, aqueous-phase chemistry, mass transfer, and deposition algorithms; and

• Extension to treat air toxics that includes a subgrid-scale Gaussian puff model to estimate the maximum near-source concentrations from air toxic point sources.