Weakened Haze Mitigation Induced by Enhanced Aging of Black Carbon in China

Abstract

A great challenge for haze pollution mitigation with the existing emission control measures in China is ozone (O3) increase. The chemical processes leading to weakened haze mitigation are still poorly understood. Our work identifies the enhanced aging chemistries of black carbon (BC) with increasing O3 as an essential driver to weaken haze mitigation based on field observations during autumn/winter haze periods in 2014 and 2018 in North China Plain. The enhanced atmospheric oxidation capacity induced by increasing O3 promotes the initial aging of accumulated fresh BC from continuous emission under haze pollution conditions and consequently improves the hygroscopicity of BC-containing particles to provide more particulate surfaces and volumes for aqueous and heterogeneous chemistries. The enhanced BC aging amplifies PM2.5 concentrations by ∼20%, which can be broken by concurrent reductions in multipollutant emissions (i.e., BC, nitrogen oxides, and volatile organic compounds), especially from residential and industrial sources. Moreover, enhanced BC aging implies an adverse effect of O3 increase on climate change. Observationally enhanced BC aging will help to constrain estimations of the interactions among O3 increase, haze pollution, and climate warming in recent years in China.

Strong Haze‐Black Carbon‐Climate Connections Observed Across Northern and Eastern China

“…A faster increase in O x (i.e., O 3 + NO 2 ) (Z. Tan et al., 2018) during the daytime in the NCP indicates a higher atmospheric oxidizing capacity and stronger photochemistry than those in the YRD (Figure 3b). Earlier works have demonstrated the importance of photochemistry in BC aging, particularly fresh BC with poor hygroscopicity (Y. F. Cheng et al., 2012; Han et al., 2016; Y. Zhang et al., 2022). Similarly, we found a higher aging degree of BC particles in the daytime in both the NCP and YRD.…”

“…In addition to directly increasing aerosol mass concentrations, the regional BC particles from the NCP can indirectly affect haze pollution in the YRD by two aspects: (a) the more aged BC with better hygroscopicity from the NCP can provide more particle volume for haze chemistries such as aqueous and heterogeneous reactions in the YRD (Y. Zhang et al., 2022); (b) the more aged BC with stronger absorption efficiency from the NCP can affect haze pollution in the YRD via BC‐PBL interaction (Huang et al., 2020). In summary, the regional BC particles from the NCP can play an important role in haze pollution in the YRD.…”

“…Earlier work (Li et al., 2018) showed similar aerosol components in Beijing (a city in the northern NCP) and Xinxiang. The air pollutants observed at the Xinxiang site could represent the urban polluted atmosphere in the NCP (Y. Zhang et al., 2022). The field observations at the YRD were performed at a regional background site in Nanjing, namely, the Station for Observing Regional Processes of the Earth System (SORPES) (A. Ding et al., 2016a).…”

“…Haze pollution conditions (e.g., higher precursors of secondary aerosols) can promote BC aging and consequently enhance BC absorption by the lensing effect of coating materials on the BC surface (Peng et al., 2016; Y. Zhang et al., 2018c; F. Zhang et al., 2020a). Atmospheric aging and light absorption of BC aerosols, in turn, can worsen haze pollution via enhancement of haze chemistries and aerosol‐planetary boundary layer (PBL) interaction (Huang et al., 2018; Y. Zhang et al., 2022). Earlier work highlighted the importance of BC particles in the transboundary transport of regional‐scale haze pollution (Huang et al., 2020).…”

Structural Collapse and Coating Composition Changes of Soot Particles During Long‐Range Transport

“…These effects are conducive to soot particles to reside in the atmosphere and to undergo more aging processes. Soot aging has been investigated in some specific atmospheric conditions, such as regional haze (Zhang, Zhang, et al., 2022), dust storms (Xu et al., 2020), and humid environments (Yuan et al., 2019). These studies primarily focused on the change in the morphology, mixing state, and coating thickness of soot particles during their atmospheric aging in a specific environment.…”