the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 May 2023
Seasonal variations in composition and sources of atmospheric ultrafine particles in urban Beijing based on near-continuous measurements
Abstract. Understanding the composition and sources of atmospheric ultrafine particles (UFPs) is essential in evaluating their exposure risks. It requires long-term measurements with high time resolution, which are to date scarce. We performed near-continuous measurements of UFP composition during four seasons in urban Beijing using a thermal desorption chemical ionization mass spectrometer, accompanied by real-time size distribution measurements. We found that UFPs in urban Beijing are dominated by organic components, varying seasonally from 68 to 81 %. CHO organics are the most abundant in summer, while sulfur-containing organics, some nitrogen-containing organics, nitrate, and chloride are the most abundant in winter. With the increase of particle diameter, the contribution of CHO organics decreases, while that of sulfur-containing and nitrogen-containing organics, nitrate, and chloride increase. Source apportionment analysis of the UFP organics indicates contributions from cooking and vehicle sources, photooxidation sources enriched in CHO organics, and aqueous/heterogeneous sources enriched in nitrogen- and sulfur-containing organics. The increased contributions of cooking, vehicle, and photooxidation components are usually accompanied by simultaneous increases in UFP number concentrations related to cooking emission, vehicle emission, and new particle formation, respectively. While the increased contribution of the aqueous/heterogeneous composition is usually accompanied by the growth of UFP mode diameters. The highest UFP number concentrations in winter are due to the strongest new particle formation, the strongest local primary particle number emissions, and the slowest condensational growth of UFPs to larger sizes. This study provides a comprehensive understanding of urban UFP composition and sources and offers valuable datasets for the evaluation of UFP exposure risks.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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Supplement
(2091 KB) - BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-809', Anonymous Referee #1, 02 Jun 2023
This is a well written paper on the sources and growth of ultrafine particles in urban air. Chemical composition measurements assist the identification of UFP sources, which include both primary emissions and new particle formation. Aqueous/heterogeneous growth of preexisting particles is also indicated from chemical composition data. Measured particle growth rates (3-50 nm) during new particle formation are consistent with theoretical growth rates estimated from condensation of gas-phase sulfuric acid and low-volatility organic compounds.
Specific comments:
In the next to the last sentence of Section 3.3, the authors estimate the times needed for sub-3 nm particles to grow to above 50 and 100 nm. The authors do not explicitly state how these times are calculated, but I am assuming that they are based on the measured and/or estimated 3-50 nm growth rates. If this is the case, then the times they give to grow above 50 nm are accurate, but the times they give to grow above 100 nm are likely to be a substantial overestimate. Figure S12 shows that the CHON/S composition factor associated with aqueous/heterogeneous chemistry becomes very large above 50 nm, roughly equaling that of the CHO-rich factor which presumably includes (but is not limited to) condensation of low volatility organics. Therefore, it is likely that particle growth due to aqueous/heterogeneous chemistry equals or exceeds particle growth due to condensation alone. If both growth channels are taken into account, the actual time to grow to 100 nm is likely to be much shorter than what the authors report. I encourage the authors to consider this possibility (or to clarify how the times were calculated) and discuss appropriately in the body of the paper.
A related question: What is the approximate survival probability of a sub-3 nm particle growing to 50 or 100 nm without being removed by a typical loss process? It seems the authors dataset is robust enough to provide an estimate.
Citation: https://doi.org/10.5194/egusphere-2023-809-RC1 -
AC1: 'Reply on RC1', Xiaoxiao Li, 03 Oct 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-809/egusphere-2023-809-AC1-supplement.pdf
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AC1: 'Reply on RC1', Xiaoxiao Li, 03 Oct 2023
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RC2: 'Comment on egusphere-2023-809', Anonymous Referee #2, 18 Aug 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-809/egusphere-2023-809-RC2-supplement.pdf
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AC2: 'Reply on RC2', Xiaoxiao Li, 03 Oct 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-809/egusphere-2023-809-AC2-supplement.pdf
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AC2: 'Reply on RC2', Xiaoxiao Li, 03 Oct 2023
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-809', Anonymous Referee #1, 02 Jun 2023
This is a well written paper on the sources and growth of ultrafine particles in urban air. Chemical composition measurements assist the identification of UFP sources, which include both primary emissions and new particle formation. Aqueous/heterogeneous growth of preexisting particles is also indicated from chemical composition data. Measured particle growth rates (3-50 nm) during new particle formation are consistent with theoretical growth rates estimated from condensation of gas-phase sulfuric acid and low-volatility organic compounds.
Specific comments:
In the next to the last sentence of Section 3.3, the authors estimate the times needed for sub-3 nm particles to grow to above 50 and 100 nm. The authors do not explicitly state how these times are calculated, but I am assuming that they are based on the measured and/or estimated 3-50 nm growth rates. If this is the case, then the times they give to grow above 50 nm are accurate, but the times they give to grow above 100 nm are likely to be a substantial overestimate. Figure S12 shows that the CHON/S composition factor associated with aqueous/heterogeneous chemistry becomes very large above 50 nm, roughly equaling that of the CHO-rich factor which presumably includes (but is not limited to) condensation of low volatility organics. Therefore, it is likely that particle growth due to aqueous/heterogeneous chemistry equals or exceeds particle growth due to condensation alone. If both growth channels are taken into account, the actual time to grow to 100 nm is likely to be much shorter than what the authors report. I encourage the authors to consider this possibility (or to clarify how the times were calculated) and discuss appropriately in the body of the paper.
A related question: What is the approximate survival probability of a sub-3 nm particle growing to 50 or 100 nm without being removed by a typical loss process? It seems the authors dataset is robust enough to provide an estimate.
Citation: https://doi.org/10.5194/egusphere-2023-809-RC1 -
AC1: 'Reply on RC1', Xiaoxiao Li, 03 Oct 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-809/egusphere-2023-809-AC1-supplement.pdf
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AC1: 'Reply on RC1', Xiaoxiao Li, 03 Oct 2023
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RC2: 'Comment on egusphere-2023-809', Anonymous Referee #2, 18 Aug 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-809/egusphere-2023-809-RC2-supplement.pdf
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AC2: 'Reply on RC2', Xiaoxiao Li, 03 Oct 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-809/egusphere-2023-809-AC2-supplement.pdf
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AC2: 'Reply on RC2', Xiaoxiao Li, 03 Oct 2023
Peer review completion
Journal article(s) based on this preprint
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- 1
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Xiaoxiao Li
Yijing Chen
Yuyang Li
Runlong Cai
Yiran Li
Chenjuan Deng
Hairong Cheng
Yongchun Liu
Markku Kulmala
Jiming Hao
Jingkun Jiang
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1017 KB) - Metadata XML
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Supplement
(2091 KB) - BibTeX
- EndNote
- Final revised paper