Evaluation of an explicit NO_x chemistry method in AERMOD

Area of Science:

• Atmospheric chemistry and air quality modeling.
• Environmental science and regulatory compliance.

Background:

• Accurate prediction of nitrogen dioxide (NO2) concentrations is crucial for air quality assessments.
• Current U.S. Environmental Protection Agency (EPA) recommended methods for Tier 3 NO2 calculations include the Ozone Limiting Method (OLM) and the Photochemical Model for Regulatory Urban Emissions (PVMRM2).

Purpose of the Study:

• To implement and evaluate a new explicit nitrogen oxide (NOx) chemistry scheme, ADMSM, within the AERMOD air dispersion model.
• To compare the performance of ADMSM against the established OLM and PVMRM2 methods for NO2 concentration calculations.

Main Methods:

• Implementation of an explicit NOx chemistry mechanism (ADMSM) in AERMOD version 15181.
• Evaluation using four distinct datasets, comparing ADMSM with OLM and PVMRM2.
• Analysis of model-predicted NO2 concentrations against modeled NOx and observational data.

Main Results:

• ADMSM demonstrated the highest consistency with AERMOD's NOx calculations and showed the greatest Index of Agreement for NO2 concentrations.
• OLM consistently overpredicted NO2 concentrations and showed poor agreement with modeled NOx.
• PVMRM2 performed better than OLM but exhibited inconsistencies and less favorable statistics compared to ADMSM in some scenarios.

Conclusions:

• The explicit NOx chemistry scheme (ADMSM) provides a more reliable method for calculating NO2 concentrations in air quality modeling.
• ADMSM's explicit consideration of reaction rates and photolysis offers advantages over screening (OLM) and simplified (PVMRM2) approaches.
• Further evaluation with additional datasets is recommended to fully clarify the comparative performance of ADMSM and PVMRM2.