the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characterization of dust-related new particle formation events based on long-term measurement in North China Plain
Xiaojing Shen
Junying Sun
Yangmei Zhang
Chunhong Zhou
Wanyun Xu
Junting Zhong
Can Xia
Xinyao Hu
Sinan Zhang
Jialing Wang
Shuo Liu
Jiayuan Lu
Xiaoye Zhang
Abstract. Mineral dust is a major natural atmospheric aerosol that impacts the Earth's radiation balance. The significant scavenging process of fine particles by the strong wind during the dust provided a relatively pristine environment in which the occurrence of new particle formation (NPF) was less influenced by anthropogenic emissions. In this study, the NPF events occurring after the dust event (dust-related NPF) and other normal days (other NPF events) were classified based on the long-term particle number size distribution (PNSD) in urban Beijing in spring from 2017 to 2021. By comparing the two types of NPF events, we estimated that anthropogenic emissions could contribute approximately 50 % to the observed formation rate and 30 % to the growth rate. Anthropogenic emissions played a more important role when nucleated particles grew into the sizes above 10 nm. We also assessed a severe dust storm that originated from Mongolia and swept over northern China on March 15–16, 2021. The maximum hourly mean PM10 mass concentration reached 8000 μg m-3 during the dust storm. A downward trend of particle hygroscopicity was found during dust storms as compared with the polluted episode, resulting in an increasing trend of the critical diameter at different supersaturations (ss) where aerosols are activated as cloud condensation nuclei (CCN), although NPF occurred at approximately noon time when dust faded. The critical diameter was elevated by approximately 6 %–10 % (ss = 0.2 % and 0.7 %) during the dust storm, resulting in a lower CCN activation ratio, especially at low supersaturation. Modifications of the nucleation and growth process, as well as the particle-size distribution and hygroscopicity by the dust, provide valuable information that reveals the underlying climate and air quality effects of Asian mineral dust.
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Xiaojing Shen et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2022-837', Anonymous Referee #1, 02 Feb 2023
This manuscript is built on continuous aerosol measurements conducted during 4 springs in urban Beijing. The data and research topic are certainly of high interest. While the paper is well-organized and technically relatively well written, there are a few major issues that prevent me to recommend the publication of this paper in its present form. My main concerns in this regard are summarized below.
My first major comment is about the imbalance between the title of the paper and its contents. The title gives an impression that this paper is solely about association between new particle formation (NPF) and dust, but most of the results (sections 3.3-3.5 and a big fraction of section 3.2) have little/nothing to do with NPF. The same concerns the abstract.
One of the main results brought up by the authors is the contribution of anthropogenic emissions to particle formation and growth rates. Estimating such contributions is very difficult overall, and totally impossible when having no real-time measurements of low-volatile precursors causing NPF and growth. Simply comparing days with and without presence of dust cannot address this issue, so in this regard the conclusions made in this paper are not scientifically sound.
As noted by the authors, condensation sink (CS) is an essential parameter determining whether NPF is possible in various conditions. It is a pity that the authors did not calculate CS for course mode particle, as it would have been possible from APS measurements. The total CS was very likely dominated by dust particles at least during the heaviest dust storms, and this might be one explanation why NPF was observed after the storms rather than during them.
There are potentially valuable data on non-NPF-related chemistry associated with dust/non-dust in sections 3.3-3.5. Unfortunately, the current discussion on these data is rather qualitative, relying mainly on finding reported by earlier literature, and providing little new scientific insight. For example, the statement on lines 304-305 is self-evident. The authors did not explain how they combined direct hygroscopicity measurements to the hygroscopicity estimated from measured aerosol chemical composition.
Minor issues:
lines 43-44: reduced compared to what?
lines 54-55: 45% of aerosols. By what measure? AOD?
line 305: this should be Fig. 10, not Fig. 8.
It is somewhat unclear what is the difference between positive and negative anomalies in Figure 3. Also, it not well explained what is subtracted from what in this figure.
Finally, it seems to me that not all references cited in the text can be found in the reference list.
Citation: https://doi.org/10.5194/acp-2022-837-RC1 -
RC2: 'Comment on acp-2022-837', Anonymous Referee #2, 06 Feb 2023
This manuscript entitled ‘Characterization of dust-related new particle formation events based on long-term measurement in North China Plain’, describes the observation of new particle formation events following dust episodes observed in Beijing between 2017 and 2021, with a focus on one severe episode on March 15-16, 2021. Although the topic of the paper and the potential results regarding the interaction of dust with available precursors resulting in NPF could be an important addition to literature, the authors' claims that are not supported by scientific evidence prevent me from recommending this paper for publication in ACP.
General comments:
- The authors evaluate the contribution of anthropogenic emissions to the nucleation processes.
The authors calculated the anthropogenic emissions as the difference in the size distribution, formation rates and growth rates during other NPF days and NPF following dust days. This approach is not justified, as it ignores available sinks, meteorology and atmospheric reactions. - Sections 2.3-2.5 discuss a case study in March 15-16, 2021. While the results are interesting, the conclusion cannot be extrapolated to other events as the case study described is one of a kind in the four years, as shown in Table 2. A comparison between NPF events following different types of dust episodes events could be helpful. In particular, a comparison between the episodes on March 15 and 28, with including interpretation of NPF and its related properties could give insight on the effect of different types of dust.
- The authors report that an NPF event occurs after approximately 80% of dust episode, what was the limiting factor for the remaining 20%? Was the airmass direction different, the wind speed lower etc? Identifying the causes that inhibited the NPF during those 20% could improve the quality of the results.
- In section 3.3, the authors speak about primary and secondary organics, how did the authors derive this separation? Were there source apportionment techniques involved? Or was it based on previous literature? More details on the technique and results are needed.
- I suggest that the authors revise some of the interpretations in the paper which are either not consistent or not based on evidence from the observations. Examples:
- Line 241: “When the dust particles arrived in Beijing at 8:00 LT on March 15, the volume mixing ratio of NO2 and SO2 decreased immediately, which was also influenced by the enhanced aerosol surface uptake process owing to elevated particle surface concentration” vs Line 247: “However, the concentrations of NO2 and SO2 were low during dust storms, indicating that anthropogenic emissions had less influence.”
- Line 284: During the dust storm period, transitional metal ions such as Fe and Mn can act as catalysts that favor sulfate formation via SO2 oxidation (Usher et al 2003).
- Line 262: The decrease in NO2 and nitrate suggests that they probably shifted from fine to coarse particles during dust storms (Wang et al., 2013).
- Line 269: This indicates different sinks for SO2 and NO2 during the dust storms. As discussed above, the uptake by mineral dust was a major sink for SO2, whereas the uptake of NO2 was minor, as the concentration remained low when the dust storm ended.
6. The methods section lacks detailed explanation of most of the instrumentation and quality control.
- Were the aerosol measuring instruments cross checked for over-lapping sizes? Citations are missing.
- What are the detection limits and the time resolutions of the trace gas measuring instruments?
- The description of the HR-AMS-ToF is not sufficient, and citations are missing. For example what was the collection efficiency?
- Was there source apportionment performed?
- How were the dust events defined, not the distinction between the dust episodes, but the identification itself, was it based on airmass trajectories?
Citation: https://doi.org/10.5194/acp-2022-837-RC2 - The authors evaluate the contribution of anthropogenic emissions to the nucleation processes.
Xiaojing Shen et al.
Xiaojing Shen et al.
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