High-time-resolution chemical composition and source apportionment of PM2.5 in northern Chinese cities: implications for policy
Abstract. Fine particulate matter (PM2.5) pollution is still one of China's most important environmental issues, especially in northern cities during wintertime. In this study, intensive real-time measurement campaigns were conducted in Xi’an, Shijiazhuang, and Beijing to investigate the chemical characteristics and source contributions of PM2.5 and explore the formation progress of heavy pollution for policy implications. The chemical compositions of PM2.5 in the three cities were all dominated by organic aerosol (OA) and nitrate (NO3-). Results of source apportionment analyzed by the hybrid environmental receptor model (HERM) showed that the secondary nitrate plus sulfate contributed higher to PM2.5 compared to other primary sources. Biomass burning was the dominant primary source in the three pilot cities. The contribution of coal combustion to PM2.5 is non-negligible in Xi’an and Shijiazhuang but is no longer the important contributor in the capital city of Beijing due to the execution of a strict coal-banning policy. The potential formation mechanisms of secondary aerosol in three cities were further explored by establishing the correlations between the secondary nitrate plus sulfate and aerosol liquid water content (ALWC), and Ox (O3 + NO2), respectively. The results showed that photochemical oxidation and aqueous-phase reaction were two important pathways of secondary aerosol formation. According to the source variations, air pollution events that occurred in campaigns were classified into three types: biomass combustion dominated, secondary nitrate plus sulfate dominated, and a combination of primary and secondary sources. Additionally, this study compared the changes in chemical composition and source contributions of PM2.5 in past decades. The results suggested that the clean energy replacements for the rural household should be urgently encouraged to reduce the primary source emissions in northern China, and collaborative control on ozone and particulate matter need to be continuously promoted to weaken the atmosphere oxidation capacity for the sake of reducing secondary aerosol formation.
Yong Zhang et al.
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2023-457', Anonymous Referee #1, 09 May 2023
- RC2: 'Comment on egusphere-2023-457', Anonymous Referee #2, 12 May 2023
Yong Zhang et al.
Yong Zhang et al.
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This manuscript discussed chemical composition and source apportionment of PM2.5 in three northern Chinese cities based on high-time-resolution monitoring equipment. Furthermore, the authors qualitatively explored the mechanisms of secondary aerosols formation. And the authors also compared the changes in the chemical composition and sources of PM2.5 in the three pilot cities over past decades. At the end of the article, the authors provided policy recommendations for sustained air quality improvement in the future. In general, this article provides valuable data for local governments to develop scientific pollution control strategies. I recommend this article for publication on Atmospheric Chemistry and Physics. However, some issues should be addressed before the publication.
1. In Text S1 from supplement, the error fraction of all chemical species was used to 10% for calculation of uncertainty dataset inputted receptor model. Is it reasonable to choose the same error fraction for different instruments?
2. In Sect3.2, the secondary sources from three cities were resolved by HERM model. And one factor named secondary nitrate plus sulfate was identified in Xi’an and Shijiazhuang (Fig. S6 and S7), but two factors named secondary nitrate and secondary sulfate were identified in Beijing (Fig. S8). What causes such differences in sources identification among cities? Moreover, the secondary sources were characterized by high EV values for SO42- , NO3-, NH4+, and those three species are inorganic aerosols. Secondary organic aerosols (SOA) were not identified in this study, dose SOA was ignored in this study?
3. In Sect3.3, the authors explored the potential function of aqueous-phase reaction to secondary aerosol formation based on data during nighttime. It should be noted that aqueous-phase reaction may also promote secondary aerosol formation during daytime. I suggest that the authors take the data from daytime hours into account when discussing the role of the aqueous-phase reaction.
1. line18 & 352： change “progress of” to “process of”
2. line 22-23: change "but is no longer important contributor...." to "but is no longer an important contributor...."
3. line 27：change “According to source variations, to “According to sources variations,”
4. line 49：change “In perspective of PM2.5 sources” to “In terms of PM2.5 sources”
5. line 67：change “Liu et. al (2019)” to “Liu et al. (2019)”
6. line 73：change “should be pointed out previous researches” to “should be pointed out that previous studies”
7. line 78 & 85-86：change “are located to” to “are located in”
8. line 237：change “With increasing of the PM2.5 mass concentration” to “With increases of the PM2.5 mass concentration”
9. line 431&454：change “atmosphere oxidation capacity” to “atmospheric oxidation capacity”