the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Mixing state and effective density of aerosol particles during the Beijing 2022 Olympic Winter Games
Aodong Du
Jiaxing Sun
Weiqi Xu
Yuting Zhang
Xubing Du
Yan Li
Xiaole Pan
Zifa Wang
Abstract. Mixing state and density are two key parameters of aerosol particles affecting their impacts on radiative forcing and human health. Here a single particle aerosol mass spectrometer in tandem with a differential mobility analyzer and an aerodynamic aerosol classifier was deployed during the Beijing 2022 Olympic Winter Games (OWG) to investigate the impacts of emission controls on particle mixing state and density. Nearly 760,000 particles were detected, which were classified into seven major classes. Our results showed the dominance of carbonaceous particles comprising mainly Total-EC (13.4 %), Total-OC (10.5 %) and Total-ECOC (47.1 %). Particularly, the particles containing organic carbon and sulfate were enhanced significantly during OWG although those from primary emissions decreased. The composition of carbonaceous particles also changed significantly which was characterized by the decreases in EC-NS, KEC-N, and amine-containing particles, and increase in ECOC-NS. This result indicates that emission controls during OWG reduced the mixing of elemental carbon (EC) with inorganic aerosol species and amines, yet increased the mixing of EC with organic aerosol. The average effective density (ρeff) of aerosol particles (150–300 nm) was 1.20 g cm−3 with higher values during OWG (1.26 g cm−3) due to the increase in secondary particle contribution. The two types of fresh particles, i.e., Total-EC and high molecular weight organic matter presented the lowest ρeff (0.97 g cm−3 and 0.87 g cm−3, respectively). In addition, the ρeff of most particles increased as the increases in pollution levels and relative humidity, yet varied differently for different types of particles, highlighting the impacts of aging and formation processes on the changes of particle density and mixing state.
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Aodong Du et al.
Status: open (until 21 Apr 2023)
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RC1: 'Comment on egusphere-2023-240', Anonymous Referee #1, 30 Mar 2023
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This study used different types of instruments with mass spectra, combining with a DMA and AAC for size selection and investigated the effective density of aerosols, during the Beijing 2022 Olympic Winter Games for the impacts of emission controls on particle mixing state and density. The results provide information on changes in aerosol compositions and mixing state due to emission control. A few points need to be addressed before it can be accepted.
Major:
1) The method in deriving the effective density for different compositions should be given more details. The used equations have not been clearly explained. It is not clear how you have linked the effective density with certain composition.
2) The instrument setup should be given in front in the main texts, with more explanation why running AAC and DMA in parallel. Why the density has been derived using two methods.
3) The effective density from 1.26 to 1.20 is not significantly different, as emphasized in the abstract.
4) Why high molecular weight OA has a lower effective density.
5) What can the findings tell from environmental policy point of view?
Others:
- Please indicate the full name where the abbreviation first appears in the abstract, such as EC and OC on line 17, EC-NC and KEC-N in line 19, and ECOC-NC in line 20.
- Please give the full name of NR-PM1 when it appears for the first time.
- Line105-114, Why to use DMA connecting with SPAMS and AAC to connect with SPAMS separately to obtain effective particle size? Why are two different instruments required?
- Could you provide a detailed explanation how Equation 2 is derived?
- Line 212-214, Please indicate the corresponding figure number for the conclusive numerical results provided by the authors.
- Please specify what the color bar in Figure S5 stands for.
- Section 3.3 is quite confused. The title indicates that the study focused on the effective density of aerosols during the Olympic Winter Games. However, the effective density is only briefly mentioned but not related to the event.
- As this study mainly focused on the BC-containing particles, a few quite related studies also measured the shape of BC-containing particles in Beijing, which showed more spherical particles when polluted (Hu et al., EST Letters, 2022, 10.1021/ acs.estlett.2c00060), and also the aerodynamic size-selected compositions and density by AAC (Yu et al., ACP, 2022, 10.5194/acp-22-4375-2022). These studies could be referenced to support some of your conclusions.
- 2 is not used in the texts.
- Please explain the many significantly high values of PAsulfate/PAnitrate in Figure 6.
Citation: https://doi.org/10.5194/egusphere-2023-240-RC1
Aodong Du et al.
Aodong Du et al.
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