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Comparative Evaluation of Gas-Phase Chemical Mechanisms and Aerosol Chemistry for the U.S. Next-Generation National Air Quality Forecasting Capability using GFSv15-CMAQv5.3.1
Citation:
Chen, X., Y. Zhang, D. Tong, S. Ma, H. Pye, B. Murphy, AND D. Kang. Comparative Evaluation of Gas-Phase Chemical Mechanisms and Aerosol Chemistry for the U.S. Next-Generation National Air Quality Forecasting Capability using GFSv15-CMAQv5.3.1. CMAS Conference, Virtual, Virtual, November 01 - 05, 2021.
Impact/Purpose:
This work provides an important characterization of CMAQ predictions across the three major chemical mechanisms provided as options to the modeling system. The operational application of CMAQ relies on using the best-performing chemistry description, and this study quantifies that performance across four seasons of 2019 using the model in a 'wheels on the road' configuration. The results of this study will inform configuration of the national ambient air quality forecast.
Description:
The National Oceanic and Atmospheric Administration is developing the next-generation National Air Quality Forecasting Capability (NAQFC), which consists of the offline-coupled Global Forecast System (GFS) with Community Multiscale Air Quality (CMAQ) modeling system (GFS-CMAQ). While previous studies focus on development and evaluation of carbon-bone (CB) series mechanism in GFS-CMAQ, the capability of applying different mechanisms in this system for real-time air quality forecasting (RTAQF) has not been demonstrated yet. In this work, we use meteorological forecast from GFS v15 to drive CMAQ v5.3.1 for four representative months (January, April, July, and October) in 2019. GFS-CMAQ simulations with the gas-phase mechanisms of CB6r3, RACM2, and SAPRC07 are intercompared to assess the underlying causes of their varied performance, thus further indicate the better practice in reducing the biases in predictions of ozone, aerosol, and their key precursors for GFS-CMAQ system. RACM2 and SAPRC07 give higher O3 predictions comparing to CB6. While RACM2 gives lower formaldehyde than CB6 due to a higher photolysis rate, SAPRC07 gives higher formaldehyde than RACM2 and CB6 due to greater production from chemical reactions. RACM2 gives higher anthropogenic secondary organic aerosol (SOA) than CB6 due to its higher OH radicals, while it gives lower total SOA due to lack of the reactive uptake of dicarbonyls. The implementation of detailed isoprene chemistry increases O3 and aerosol concentrations. The reorganization of anthropogenic SOA in Aero7 aerosol chemistry causes slight impact comparing to Aero6. The updates of monoterpene-SOA in Aero7 increase biogenic SOA. Excluding potential SOA from combustion from the residential wood combustion emissions largely reduces the overprediction of organic carbon during cooler months. This work demonstrates the forecasting capability of various gas-phase chemical mechanisms and aerosol chemistry in CMAQ v5.3.1, and indicates the key factors in causing biases to shed light on future development of GFS-CMAQ system.