the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Feb 2024
Large contribution of soil emissions to the atmospheric nitrogen budget and their impacts on air quality and temperature rise in North China
Abstract. Soil emissions of nitrogen compounds, including NO and HONO, play a significant role in atmospheric nitrogen budget. However, HONO has been overlooked in previous research on soil reactive nitrogen (Nr) emissions and their impacts on air quality in China. This study estimates both soil NOx and HONO emissions (SNOx and SHONO) in North China with an updated soil Nr emissions scheme in a chemical transport model, the Unified Inputs for WRF-Chem (UI-WRF-Chem). The effects of soil Nr emissions on O3 pollution, air quality and temperature rise are also studied, with a focus on two key regions, Beijing-Tianjin-Hebei (BTH) and Fenwei Plain (FWP), known for high soil Nr and anthropogenic emissions. We find that the flux of SNOx is nearly doubled those of SHONO; the monthly contributions of SNOx and SHONO account for 37.3 % and 13.5 % of anthropogenic NOx emissions in the BTH, and 29.2 % and 19.2 % in the FWP during July 2018, respectively. Soil Nr emissions have a significant impact on surface O3 and nitrate, exceeding SNOx or SHONO effects alone. On average, soil Nr emissions increase MDA8 O3 by 16.9 % and nitrate concentrations by 42.4 % in the BTH, 17.2 % for MDA8 O3 and 42.7 % for nitrate in the FWP. Reducing anthropogenic NOx emissions leads to a more substantial suppressive effect of soil Nr emissions on O3 mitigation, particularly in BTH. Soil Nr emissions, via their role as precursors for secondary inorganic aerosols, can result in a slower increase rate of surface air temperature. This study suggests that mitigating O3 pollution and addressing climate change in China should consider the role of soil Nr emission, and their regional differences.
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RC1: 'Comment on egusphere-2024-359', Anonymous Referee #1, 07 Apr 2024
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This manuscript focuses on the effects of soil nitrogen emission (SNOX and SHONO) on ozone pollution over two typical regions (BTH and FWP) in China. The authors found that SNOx and SHONO emissions account for a large proportion (nearly 50%) of total anthropogenic NOx emissions. Therefore, it can increase MDA8 O3 by 17 % and nitrate concentrations by 42% in the BTH. The results suggest that the presence of soil nitrogen emissions can offset the efforts in controlling anthropogenic emissions, which can provide theoretical implications on ozone pollution management in key regions of China. Overall, the manuscript is well written, although minor changes are needed to further improve it.
Comments:
- It is not clear how MEIC emissions are converted to model-ready formarts.
- Is there any way to validate the emissions of NOx and HONO using BDISNP?
- In Figure 2, please show statistical values of the comparison. It is hard to say which is better in comparison to the TROPOMI results.
- Figure 6, the panel (c) is not correctly named.
- In Conclusion, "leads to a slower increase rate of T2 compared to scenarios without soil Nr emissions", I suggest add the values of T2 increase rate in parentheses (??℃).
- Line 332-351, the authors found that soil NOX lead to OH decrease in their study, which is contrary to other studies that showed soil NOX can increase OH. I suggest add some explanations.
- Line 363-365, "The distribution of sensitivity of O3 to precursor emission in FWP regions are more complex with a mix of three O3 formation regimes, which is attributed to the large population, regional urbanization and industrialization". The explanations are broad, I suggest the authors give more specific explanations or cite some relevant papers, otherwise no need to explain this phenomenon.
Corrections:
The reference "TROPOMI ATBD of the total and tropospheric NO2 data products", please check it.
In Line 471, "we admit that uncertainties in both soil Nr and anthropogenic emissions", add "exist" after " uncertainties"
In Figure 2 caption, note that (e) and (f) should be (b) and (c)
Line 228, "(Zhan et al., 2021)", maybe Zhang et al?
Line 391-394, no need to entirely list values under 20%, 40%, 60%, 80%, and 100%. Maybe three percent (20%,60%,100%) are enough.
Citation: https://doi.org/10.5194/egusphere-2024-359-RC1 -
RC2: 'Comment on egusphere-2024-359', Fei Liu, 21 Apr 2024
reply
The authors estimate both soil NOx and HONO emissions in North China and investigate their impacts on air quality and temperature using an updated soil Nr emissions scheme within a chemical transport model. The inclusion of this scheme appears to significantly impact the model's outputs. I recommend the paper for publication, subject to the following revisions:
General comment:
1. Simulation Settings Summary:
Please consider adding a table summarizing the settings for each simulation scenario to enhance clarity and ease of comparison.
2. Study Duration and Selection of Year:
The investigation is limited to July 2018. This limited scope raises concerns about the generalizability of the conclusions regarding the impact of soil Nr emissions. Could the authors clarify the reasons behind choosing only 2018? Additionally, how do the 2018 temperature, precipitation, and other relevant meteorological factors compare with other years? Given the close relationship between soil emissions and meteorological conditions, it would be beneficial to include additional years to demonstrate the sensitivity to varying weather conditions. The impact of soil Nr emissions during other months should also be discussed, as the atmospheric nitrogen budget from soil emissions is expected to be significantly different at other times of the year.
3. Figure 3 Analysis:
The base scenario improves correlation but introduces larger biases, particularly when compared with TROPOMI NO2 data. A detailed discussion regarding the causes of these biases would be valuable. I notice that the performance of the base scenario is better than the default one in Figure 4. If it is the most important justification for the better performance of “base”, I suggest additional clarification to justify why HCHO validation weights are more important than NO2 and O3 for this study.
4. Emission Reduction Scenarios:
The manuscript discusses temperature responses to anthropogenic NOx emission changes. However, the scenarios focusing solely on NOx reduction may not reflect real-world conditions, as NOx is often co-emitted with other pollutants like SO2 during activities such as coal combustion. Therefore, the conclusions drawn from the current scenario setups might be skewed. I recommend including scenarios that consider reductions in emissions from co-emitted species to more accurately assess their collective impact on temperature.
Specific comment
- Line 237: monthly total? I suggest clarifying which month here.
- Line 284-286: The authors attributed the positive biases to the same reasons documented by literature without mentioning more details. I assume literature uses similar settings in the default scenario. Do they have a similar magnitude of biases with the default or base scenario?
- Line 341: Any reasons given for the different conclusions with existing studies?
- Conclusion: please clarify the contributions from soil Nr are not annual mean but for a specific month here.
- Figure 5: the statistical results are not easy to see. Suggest using an alternative color for the digits. Please also clarify the period used for the plotting in the caption.
- Figure 7: the legends of bars/lines are missing.
Citation: https://doi.org/10.5194/egusphere-2024-359-RC2
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