Measurement report: The importance of biomass burning in light extinction and direct radiative effect of urban aerosol during the COVID-19 lockdown in China
- 1State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
- 2CAS Center for Excellence in Quaternary Science and Global Change, Xi’an 710061, China
- 3Guanzhong Plain Ecological Environment Change and Comprehensive Treatment National Observation and Research Station, Xi’an 710061, China
- 4Meteorological Institute of Shaanxi Province, Xi’an 710015, China
- 5Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
- 1State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
- 2CAS Center for Excellence in Quaternary Science and Global Change, Xi’an 710061, China
- 3Guanzhong Plain Ecological Environment Change and Comprehensive Treatment National Observation and Research Station, Xi’an 710061, China
- 4Meteorological Institute of Shaanxi Province, Xi’an 710015, China
- 5Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
Abstract. To mitigate climate change in China, a better understanding of optical properties of aerosol is required due to the complexity in emission sources. Here, an intensive real-time measurement was conducted in an urban area of China before and during the lockdown of Coronavirus Disease 2019 (COVID-19), to explore the impacts of anthropogenic activities on aerosol light extinction and direct radiative effect (DRE). The mean light extinction coefficient (bext) reduced from 774.7 ± 298.1 Mm−1 during the normal period to 544.3 ± 179.4 Mm−1 during the lockdown period. The generalized addictive model analysis indicated that the large decline of bext (29.7 %) was entirely attributed to the sharp reductions in anthropogenic emissions. Chemical calculation of bext based on the ridge regression analysis showed that organic aerosol (OA) was the largest contributor to bext in both periods (45.1–61.4 %), and contributions of two oxygenated OAs to bext increased by 3.0–14.6 % during the lockdown. A hybrid environmental receptor model combining with chemical and optical variables identified six sources of bext. It was found that bext from traffic-related emission, coal combustion, fugitive dust, nitrate plus secondary OA (SOA) source, and sulfate plus SOA source decreased by 21.4–97.9 % in the lockdown, whereas bext from biomass burning increased by 27.1 % mainly driven by undiminished needs of residential cooking and heating. The atmospheric radiative transfer model was further used to illustrate that biomass burning instead of traffic-related emission became the largest positive effect (10.0 ± 10.9 W m−2) on aerosol DRE in the atmosphere during the lockdown. Our study provides insights into aerosol bext and DRE from anthropogenic sources, and the results implied the importance of biomass burning for tackling climate change in China in the future.
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Jie Tian et al.
Status: final response (author comments only)
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CC1: 'Comment on acp-2021-947', Shaofei Kong, 07 Dec 2021
This manuscript, titled by The importance of biomass burning in light extinction and direct radiative effect of urban aerosol during the COVID-19 lockdown in China, investigated the impacts of COVID-19 lockdown on aerosol light extinction and direct radiative effect. In fact, many studies have been conducted to explore the impacts of lockdown measures on the aerosol compositions, but how the lockdown measures influenced the aerosol optical property and direct radiative effect is limited. Though the information given in this study has been well known, it is suitable to publish on the Measurement Report. I suggest a major revision of this paper. Before acceptance, some issues must be clarified.
- The contributions of biomass burning to aerosol bext and DRF increased during lockdown period in this study which just focused on only one site. How did you find out that the importance of control biomass burning for tackling climate change in China? More evidence in the other region should be provided to make your conclusion robust.
- Many studies have proved that sulfate can emitted from coal combustion, especially in the regions where a great deal of coal consumed every year, such as Xi’an. Thus, is it proper to regard sulfate as the secondary source?
- Some important references about aerosol optical property have not been cited in this study, such as Xu et al., 2020, ESTL, Liu et al., 2020, GRL and Yao et al., 2021, npj CAS. I think these articles may improve your Introduction and discussion.
- Line 30 “importance of biomass burning for tackling climate change” is “importance of control biomass burning for tackling climate change“?
- The mass and optical property closure should be conducted after the source apportionment.
- Some details such as line 201 “which is “ or “which are”, should be checked carefully.
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RC1: 'Comment on acp-2021-947', Tiantao Cheng, 09 Dec 2021
General comments:
Urbanization even anthropogenic activities is an important way to influence air pollution by emissions (gases and particles), meteorological conditions and atmospheric processes (urban heat island), etc. Anthropogenic pollutants include greenhouse gases, gaseous and particulate pollutants. Aerosol is very important to impact atmospheric cycle and climate system by direct and indirect effects, a hot issue of scientific researches internationally. Also, atmospheric pollutions cause adverse harm to human health. Aerosols are known to originate from direct emission and secondary formation, namely, POA and SOA. The organic aerosol (OA) is a very important part of aerosols, including BC and OC. Inorganic ions are important compositions of aerosols. This paper used the data of aerosol optical properties, chemical composition, meteorological parameters used in Xi’an to analyze their temporal variation and compare their difference between the normal period and the COVID-19 in 2019, and to estimate the radiation forcing of aerosols. The topic of this paper is of common interest within the scientific community. Although the manuscript includes some important data, however, the quality is somewhat sufficient in the current state to be directly published.
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RC2: 'Comment on acp-2021-947', Anonymous Referee #2, 26 Dec 2021
This work analyzes the impact of the COVID-19 lockdown in China on some atmospheric properties, in particular on the extinction, scattering and absorbing coefficients together with the direct radiative effect, all of them considering the aerosol chemical composition. The topic is clearly in the scope of Atmospheric Chemistry and Physics, and absolutely relevant for the scientific community and decision-makers. The manuscript is very well written, with only few typos.
My main concerns (general comments) are three:
- Title does not reflect the actual content of the work. The current title is quite ambiguous, leading the reader to expect a study on the entire Chinese territory. I suggest to explicit that the analysis focuses on the study case in Xi’an.
- the sampling campaign consisted of two distinct periods, the so-called normal period (1 to 23 January, 2020) and COVID-19 lockdown period (27 January to 7 February, 2020). Because the aim of the study is to compare the atmosphere during lockdown period against the ‘normal’ conditions, I consider the normal period chosen here inappropriate. Would it not be more correct to compare with the historical period 27 January 7 February (i.e. average of several years to minimize the effect of different meteorological conditions)?
- there are a lot of figures as supplementary material. Please considered to move some of them to the main manuscript. I suggest to include figures S8, S9 and S13.
Specific comments:
Line 15: replace ‘optical properties of aerosol’ by ‘aerosol optical properties’.
Lines 39-40: Specify that this sentence refers only to China or include other references with studies worldwide (e.g. Ibrahim et al., 2021).
Ibrahim, S., Landa, M., Pešek, O., Pavelka, K., & Halounova, L. (2021). Space-Time Machine Learning Models to Analyze COVID-19 Pandemic Lockdown Effects on Aerosol Optical Depth over Europe. Remote Sensing, 13(15), 3027.
Line 112: justify the selection of the factor 2.14.
Line 118: please, discuss about the extinction coefficient uncertainty considering the two different wavelengths for scattering and absorption coefficients.
Line 135: why to use relative humidity if temperature and dew point include the information of moisture content? Is not redundant? I miss some important and basic meteorological variables such are radiation-related ones. Is there any argument for not to include them? Also, replace ‘pressures’ by ‘pressure’. And a last comment on this sentence. PBLH is retrieved from GDAS data. Which is the method applied to retrieve these values? What is the spatial grid used in these computations?
Line 181: what is the advantage of using SBDART instead of other shortwave radiative models such as libRadtran?
Line 644: 100 times is missing in this definition of ‘change ratio’.
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AC1: 'Comment on acp-2021-947', J. Tian, 09 Feb 2022
We thank the reviewers for the thoughtful and valuable comments, which are very helpful for revising and improving our manuscript. The attached pdf file contains a detailed response to the points raised by the reviewers. The marked up version of the manuscript is also included in the attached pdf file.
Jie Tian et al.
Data sets
Measurement report: The importance of biomass burning in light extinction and direct radiative effect of urban aerosol during the COVID-19 lockdown in China [Data set] Tian, Jie, Wang, Qiyuan, Liu, Huikun, Ma, Yongyong, Liu, Suixin, Zhang, Yong, Ran, Weikang, Han, Yongming, & Cao, Junji https://doi.org/10.5281/zenodo.5739349
Jie Tian et al.
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