the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Jan 2025
Direct measurement of N2O5 heterogeneous uptake coefficients on atmospheric aerosols in southwestern China and evaluation of current parameterizations
Abstract. The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) is a critical process in assessing NOx fate and secondary pollutants (e.g. particulate nitrate) formation. However, accurate quantification of the N2O5 uptake coefficient (γ(N2O5)) in the ambient conditions is a challenging problem which can causes unpredictable uncertainties in the predictions of the air quality models. Here, the γ(N2O5) values were directly measured using an improved aerosol flow tube system in a city located on the plateau in southwestern China to investigate its influencing factors and the performance of current γ(N2O5) parameterization under this typical environmental condition. The nocturnal mean γ(N2O5) value ranged from 0.0018 to 0.12 with an average of 0.023±0.021. The aerosol water significantly promoted N2O5 uptake, while particulate organic and nitrate generally showed suppression effect. We found that median γ(N2O5) predicted by some parameterizations agreed well with observation, whereas the parameterizations failed to reproduce the range of observed values and showed poor correlations (R2=0.00~0.09). Elevated differences between prediction and observation specifically occurred at high aerosol liquid water content (ALWC) with an underestimation by -37 %~-1 % and low ALWC with an overestimation by 34~189 %, respectively. Such differences between the measured and parameterized γ(N2O5) would lead to biased estimation (-77 %~74 %) on particulate nitrate production potential. Our findings suggest the need for more direct field quantifications of γ(N2O5) and the laboratory measurements under extreme ALWC conditions to re-evaluate the response coefficients between γ(N2O5) and aerosol chemical compositions.
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Status: open (until 25 Feb 2025)
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RC1: 'Comment on egusphere-2024-3804', Anonymous Referee #2, 16 Jan 2025
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Please find the comments in the attached PDF file.
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RC2: 'Comment on egusphere-2024-3804', Anonymous Referee #1, 22 Jan 2025
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The authors directly measured the uptake coefficient of N2O5 using an aerosol flow tube reactor in Kumin, a highland environment, in China. The possible influence factors on the γ(N2O5) were discussed by correlation analysis in this work. ALWC was the most important one affecting the measured γ(N2O5). The comparison between the measured γ(N2O5) and parameterized values. Overall, the results are well presented and discussed. It is publishable after the following questions have been well addressed.
- Considering many studies on the γ(N2O5) by measurement, modeling, and parameterization methods, I am wondering what scientific assumption is focused on in this work. The uptake kinetics in different environments? Crucial factors determining the γ(N2O5)? Or the uncertainties of the parameterization method for γ(N2O5)? The authors should clarify the highlights and the novelty of this study.
- It is somewhat too weak about the correlation analysis between the measured γ(N2O5) and possible factors such as chemical composition and ALWC. The dataset is too small and the data points are too scattering. So, it is hard to observe the significant correlation.
- About the negative correlation between organic aerosol and γ(N2O5), is the γ(N2O5) possibly affected by other factors when the concentration of organic is high along with a low γ(N2O5)? Unless organic aerosol is well mixed with other components, i.e., in an ideal inner mixed state.
- ALWC is the most important factor affecting γ(N2O5). However, ALWC is greatly determined by nitrate concentration or fraction in PM2.5. Why does γ(N2O5) show a different dependence on nitrate like ALWC?
- In Figure 2b, it is better to compare the γ(N2O5) distribution among different methods.
- In Figure 4, the performances of these parameterization methods look too bad. I am wondering how about the performances of models widely used in literature.
Citation: https://doi.org/10.5194/egusphere-2024-3804-RC2
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