the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Nov 2023
A better representation of VOC chemistry in WRF-Chem and its impact on ozone over Los Angeles
Abstract. The declining trend in vehicle emissions has underscored the growing significance of Volatile Organic Compound (VOC) emissions from Volatile Chemical Products (VCP). However, accurately representing VOC chemistry in simplified chemical mechanisms remains challenging due to its chemical complexity including speciation and reactivity. Previous studies have predominantly focused on VOCs from fossil fuel sources, leading to an underrepresentation of VOC chemistry from VCP sources. We developed an integrated chemical mechanism, RACM2B-VCP, that is compatible with WRF-Chem and is aimed to enhance the representation of VOC chemistry, particularly from VCP sources, within the present urban environment. Evaluation against the Air Quality System (AQS) network data demonstrates that our model configured with RACM2B-VCP reproduces both the magnitude and spatial variability of O3 as well as PM2.5 in Los Angeles. Furthermore, evaluation against comprehensive measurements of O3 and PM2.5 precursors from the Reevaluating the Chemistry of Air Pollutants in California (RECAP-CA) airborne campaign and the Southwest Urban NOx and VOC Experiment (SUNVEx) ground site and mobile laboratory campaign, confirm the model's accuracy in representing NOx and many VOCs and highlight remaining biases. Although there exists an underprediction in the total VOC reactivity of observed VOC species, our model with RACM2B-VCP exhibits good agreement for VOC markers emitted from different sectors, including biogenic, fossil fuel, and VCP sources. Through sensitivity analyses, we probe the contributions of VCP and fossil fuel emissions to total VOC reactivity and O3. Our results reveal that 52 % of the VOC reactivity and 35 % of the local enhancement of MDA8 O3 arise from anthropogenic VOC emissions in Los Angeles. Significantly, over 50 % of this anthropogenic fraction of either VOC reactivity or O3 is attributed to VCP emissions. The RACM2B-VCP mechanism created, described, and evaluated in this work is ideally suited for accurately representing ozone for the right reasons in the present urban environment where mobile, biogenic, and VCP VOCs are all important contributors to ozone formation.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6383 KB) - Metadata XML
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Supplement
(4066 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
- RC1: 'Comment on egusphere-2023-2742', Anonymous Referee #1, 18 Dec 2023
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RC2: 'Comment on egusphere-2023-2742', Anonymous Referee #2, 15 Jan 2024
The paper developed a RACM2B-VCP mechanism based on the RACM2_Berkeley2.0 mechanism to better represent the chemistry of VOC. They evaluate the performance of RACM2B-VCP for ozone and PM2.5 by comparing WRF-Chem simulations with AQS surface network data and the previous RACM-ESRL-VCP mechanism. The RACM2B-VCP’s accuracy in representing NOx, CO, VOCs, PAN, and aerosols was also investigated. The temperature dependence of ozone, the effects of VCP, biogenic and fossil fuel emissions on VOC reactivity and ozone were analyzed.
The new chemical mechanism proposed in this manuscript is meaningful for improving the simulation ability of air quality models for VOCs. However, the evidence presented in the paper to prove the superiority of the RACM2B-VCP chemical mechanism is far from convincing. The explanation for the differences in simulation results is almost missing throughout the whole manuscript. The manuscript needs to be carefully revised before it may be considered for publication.
Line 212: Please explain how to add isoprene emission in the RACM-ESRL-VCP mechanism?
Line253: What time does "noontime" refer to?
Line270: What is the unit of NMB?
Figure 4: The MDA8 O3 concentrations in RACM2B-VCP on days with lower and median temperature are lower than those in RACM-ESRL-VCP, while on days with higher temperature, RACM2B-VCP simulated higher MDA8 O3 values. Please explain the reasons for this difference.
Line 325: The comparison of the model evaluations of NOx, CO, and VOCs by RACM-ESRL-VCP and RACM2B-VCP should be presented simultaneously.
Line346: The author said, “Overall, we show that the R2 is generally higher between model simulation and airborne measurements”. However, the NMDB and R2 values shown in Table 1 and Figure 5 didn’t suggest that the simulation with the RACM2B-VCP mechanism is ideal. Please supplement a comparison of model simulation evaluation results with previous studies.
In sections 5 to 7, the author only presented a comparison between observation and simulation results, without providing any explanation for the reasons for simulation bias, nor did they present any comparison with previous studies to show the superiority of the RACM2B-VCP mechanism in simulating VOC chemistry, ozone, and other species.
Table 1: The NMDB of acetaldehyde was different from other VOC species and significantly higher in RECAP atmosphere than that in SUNVEx mobile and SUNVEx ground. Why?
Figure S8: It seems that the nitrate concentration simulated by the model is particularly low. What is the reason for this poor performance?
Figure S9: Why do biogenic VOCs contribute so much to the concentration of NOx?
Please unify the font of the figures in the main manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-2742-RC2 - AC1: 'Comment on egusphere-2023-2742', Qindan Zhu, 11 Mar 2024
Interactive discussion
Status: closed
- RC1: 'Comment on egusphere-2023-2742', Anonymous Referee #1, 18 Dec 2023
-
RC2: 'Comment on egusphere-2023-2742', Anonymous Referee #2, 15 Jan 2024
The paper developed a RACM2B-VCP mechanism based on the RACM2_Berkeley2.0 mechanism to better represent the chemistry of VOC. They evaluate the performance of RACM2B-VCP for ozone and PM2.5 by comparing WRF-Chem simulations with AQS surface network data and the previous RACM-ESRL-VCP mechanism. The RACM2B-VCP’s accuracy in representing NOx, CO, VOCs, PAN, and aerosols was also investigated. The temperature dependence of ozone, the effects of VCP, biogenic and fossil fuel emissions on VOC reactivity and ozone were analyzed.
The new chemical mechanism proposed in this manuscript is meaningful for improving the simulation ability of air quality models for VOCs. However, the evidence presented in the paper to prove the superiority of the RACM2B-VCP chemical mechanism is far from convincing. The explanation for the differences in simulation results is almost missing throughout the whole manuscript. The manuscript needs to be carefully revised before it may be considered for publication.
Line 212: Please explain how to add isoprene emission in the RACM-ESRL-VCP mechanism?
Line253: What time does "noontime" refer to?
Line270: What is the unit of NMB?
Figure 4: The MDA8 O3 concentrations in RACM2B-VCP on days with lower and median temperature are lower than those in RACM-ESRL-VCP, while on days with higher temperature, RACM2B-VCP simulated higher MDA8 O3 values. Please explain the reasons for this difference.
Line 325: The comparison of the model evaluations of NOx, CO, and VOCs by RACM-ESRL-VCP and RACM2B-VCP should be presented simultaneously.
Line346: The author said, “Overall, we show that the R2 is generally higher between model simulation and airborne measurements”. However, the NMDB and R2 values shown in Table 1 and Figure 5 didn’t suggest that the simulation with the RACM2B-VCP mechanism is ideal. Please supplement a comparison of model simulation evaluation results with previous studies.
In sections 5 to 7, the author only presented a comparison between observation and simulation results, without providing any explanation for the reasons for simulation bias, nor did they present any comparison with previous studies to show the superiority of the RACM2B-VCP mechanism in simulating VOC chemistry, ozone, and other species.
Table 1: The NMDB of acetaldehyde was different from other VOC species and significantly higher in RECAP atmosphere than that in SUNVEx mobile and SUNVEx ground. Why?
Figure S8: It seems that the nitrate concentration simulated by the model is particularly low. What is the reason for this poor performance?
Figure S9: Why do biogenic VOCs contribute so much to the concentration of NOx?
Please unify the font of the figures in the main manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-2742-RC2 - AC1: 'Comment on egusphere-2023-2742', Qindan Zhu, 11 Mar 2024
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Ronald C. Cohen
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6383 KB) - Metadata XML
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Supplement
(4066 KB) - BibTeX
- EndNote
- Final revised paper