1Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, School of Atmospheric Physics, Nanjing University of Information Science & Technology, Nanjing 210044, China
2State Key Laboratory of Remote Sensing Science, College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China
3Earth System Science Interdisciplinary Center, Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA
4State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
1Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, School of Atmospheric Physics, Nanjing University of Information Science & Technology, Nanjing 210044, China
2State Key Laboratory of Remote Sensing Science, College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China
3Earth System Science Interdisciplinary Center, Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA
4State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
Received: 20 Dec 2021 – Discussion started: 18 Feb 2022
Abstract. In this study, the mixing state of size-resolved soot particles and their influencing factors were investigated based on a five-month aerosol volatility measurement at a suburban site (Xingtai, XT) in the central North China Plain (NCP). The volatility and mixing state of soot particles at XT were complex caused by multiple pollution sources and various aging processes. The results suggest that anthropogenic emissions can weaken the volatility of soot particles and enhance their degree of external mixing. There were fewer externally mixed soot particles in warm months (June, July, and August) than in cold months (May, September, and October). Monthly variations in the mean coating depth (Dc,mean) of volatile matter on soot particles showed that the coating effect was stronger in warm months than in cold months, even though aerosol pollution was heavier in cold months. Moreover, the volatility was stronger, and the degree of internal mixing was higher in nucleation-mode soot particles than in accumulation-mode soot particles. Relationships between Dc,mean and possible influencing factors [temperature (T), relative humidity (RH), and particulate matter with diameters ranging from 10 to 400 nm] further suggest that high ambient T and RH in a polluted environment could promote the coating growth of accumulation-mode soot particles. However, high ambient T but low RH in a clean environment were beneficial to the coating growth of nucleation-mode soot particles. Our results highlight the diverse impact of anthropogenic emissions and aging processes on the mixing state of soot particles in different modes, which should be considered separately in models to improve the simulation accuracy of aerosol absorption.
This paper shows some VTDMA data from China, with the intent of investigating factors affecting the mixing state of refractory material in a polluted environment. The results are interesting and within the remit of ACP, and the manuscript is reasonably well written. Also, because measurements of this nature are particularly common, there is an element of novelty in its own right. However, this paper is slightly let down by the fact that the results are interpreted in a very self-contained manner, without really considering the wider body of knowledge. Addressing this should be fairly straightforward, however this could potentially change the character of the paper, therefore I recommend publication after 'major' corrections.
Major comments:
The authors give an interesting discussion investigating the potential reasons for the phenomena they observe, however they do not place this in the context of wider atmospheric implications. In particular, this paper would benefit from a comparison with equivalent measurements in other locations, or alternative methods of measuring BC mixing state (e.g. doi: 10.5194/acp-20-3645-2020). This will allow for a deeper insight into the processes and phenomena under investigation.
It would also better justify this as an ACP research article (as opposed to a measurement report) if either novel implications for wider atmopsheric science could be specifically identified, or if newly-identified phenomena could be singled out.
Minor comments:
Line 23: Taken in isolation, “weaken the volatility of soot particles” is a strange statement to make because many use the term “soot” synonymously with the refractory components like black carbon. I would rephrase.
Page 69: Co-emitted organic carbon from biomass burning can be refractory (sometimes referred to as ‘tar’ or ‘tarballs’).
Line 157: This repeats a statement already made earlier.
Line 166: I presume the factory calibration was used to calculated MBC, but this should still be stated.
Line 217: “better atmospheric diffusion conditions” needs to be better explained
Line 222: This paragraph doesn’t really say anything substantial and can probably be removed.
The mixing state of size-resolved soot particles and their influencing factors were investigated. The results suggest anthropogenic emissions and aging processes (photochemical and liquid phase chemical reactions) have diverse impacts on the mixing state of soot particles in different modes. Considering that the mixing state of soot particles is crucial to model aerosol absorption, this finding is important to study the warming effect of back carbon aerosols.
The mixing state of size-resolved soot particles and their influencing factors were...