Characterization of dust-related new particle formation events based on long-term measurement in North China Plain
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.
Xiaojing Shen et al.
Status: final response (author comments only)
- RC1: 'Comment on acp-2022-837', Anonymous Referee #1, 02 Feb 2023
- RC2: 'Comment on acp-2022-837', Anonymous Referee #2, 06 Feb 2023
Xiaojing Shen et al.
Xiaojing Shen et al.
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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.
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.