Studying the Effect of Different Gas-Phase Chemical Kinetic Mechanisms on the Formation of Oxidants, Nitrogen Compounds and Ozone in Arid Regions

Abstract

CMAQ was implemented in the central region of Saudi Arabia and the effect of simulating models using various chemical mechanisms on selected oxidants, nitrogen species, and O 3 was investigated. CB05TUCL predicted OH, MEPX, and NO z about 7%, 7.7%, and 8% more than CB05E51 respectively; however, there was no observable difference in the O 3 predictions. The differences in variations of SAPRC07 mechanism (SAPRC07TB, SAPRC07TC, and SAPRC07TIC) for all parameters were less than 1%. RACM2 produced the highest OH and H 2 O 2 concentrations. RACM2 enhanced OH production in the range of 24% -32% and H 2 O 2 by 9% over other mechanisms; these are comparatively less than the findings of other studies. Similarly, CB05 produced over 40% more PAN concentration than CB05. Moreover, PAN concentrations produced by all mechanisms were very high compared to other studies. SAPRC07 produced approximately 3% more mean surface O 3 concentration than RACM2 and approximately 10% more than CB05. RACM2 O 3 predictions were higher than CB05 by 7%. The predicted O 3 concentrations by CB05, RACM2, and SAPRC07 were 6%, 11%, and 15% more than the average observed concentrations, which indicate that closest predictions to the observed values were by CB05. This study concludes that there is a wide variation of mechanisms with respect to the predictions of oxidants and nitrogen compounds; however, less variation is noticed in predictions of O 3 . For any air pollution control strategies and photochemical modeling studies in the current region or in any other arid regions, the CB05 mechanism is recommended.

Development and evaluation of a new compact mechanism for aromatic oxidation in atmospheric models

“…SAPRC-11 was previously implemented in GEOS-Chem (v9-02) by Yan et al (2019). Versions of SAPRC have also been implemented in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), the Community Multiscale Air Quality (CMAQ) model, and other regional 3-D models (Yu et al, 2010;Cai et al, 2011;Zhang et al, 2012;Kitayama et al, 2019;Shareef et al, 2019).…”

Development and evaluation of a new compact mechanism for aromatic oxidation in atmospheric models

“…SAPRC-11 was previously implemented in GEOS-Chem (v9-02) by Yan et al (2019). Versions of SAPRC have also been implemented in the Weather Research and Forecasting chemistry model (WRF-Chem), the Community Multiscale Air Quality (CMAQ) model, and other regional 3D models (Yu et al, 2010;Cai et al, 2011;Zhang et al, 2012;Kitayama et al, 2019;Shareef et al, 2019).…”

“…xylene isomers, and represents major first-generation products of BTX oxidation, including benzaldehyde, phenol, cresol, an epoxide, and photolabile dicarbonyls. RACM is implemented in both WRF-Chem and CMAQ (Sarwar et al, 2013;Kitayama et al, 2019;Shareef et al, 2019).…”

Author responses to referee comments

“…Bloss et al (2005a, b) compared the mechanism to a series of chamber experiments and noted that, while ozone was well-simulated in benzene oxidation, simulations typically overestimated ozone formation from the larger aromatics while underestimating OH concentrations in all experiments. Community Multiscale Air Quality (CMAQ) model, and other regional 3D models (Yu et al, 2010;Cai et al, 2011;Zhang et al, 2012;Kitayama et al, 2019;Shareef et al, 2019). described by Jenkin et al (2008).…”

“…RACM2 is based on MCM for benzene and on Calvert (2002) for toluene and the individual xylene isomers, and represents major first-generation products of BTX oxidation, including benzaldehyde, phenol, cresol, an epoxide, and photolabile dicarbonyls. RACM is implemented in both WRF-Chem and CMAQ (Sarwar et al, 2013;Kitayama et al, 2019;Shareef et al, 2019). the effects of these parameters can be found in the SI.…”