2.28 Modeling Chemically Reactive Air Toxics with CAMx

摘要

Hazardous air pollutants (HAPs or "toxics") are of concern because they cause acute and/or chronic health impacts and may have sufficiently long atmospheric lifetimes that allow them to be transported and transformed over great distances. Traditional Gaussian plume and puff dispersion models are applicable for simulating primary pollutants (e.g., diesel particulate matter) over short scales. Such dispersion models are not suitable, however, for simulating chemically reactive pollutants (e.g., formaldehyde, 1,3-butadiene, acrolein) and secondary pollutants (e.g., acrolein, formaldehyde) over larger scales where variable chemical regimes and transport/removal processes are important aspects of the long-term distribution and ultimate fate of these compounds. On the other hand, photochemical grid models can address complex chemical transformation pathways for toxics, and simulate their three-dimensional dispersion and removal over wide areas and for long periods. ENVIRON has developed a highly flexible Reactive Tracer Chemical Mechanism Compiler (RTCMC) for the Comprehensive Air quality Model with extensions (CAMx; ENVIRON, 2008). CAMx is a regional photochemical/particulate grid model used for regulatory applications in the U.S. and is applied widely throughout the world to address complex air quality issues. The RTCMC module allows a user-defined toxic chemistry mechanism to run in parallel with, and to draw oxidant information from, a standard gas-phase photochemical simulation (i.e., Carbon Bond or SAPRC). In this paper we describe the RTCMC for modeling air toxics on regional and annual scales.