Aerosols in the atmosphere of the Earth system – from air pollution control to climate change mitigation

Abstract:

Atmospheric aerosols are strongly affecting human health and climate in the Anthropocene. Poor air quality associated with high aerosol concentrations is among the leading health risks worldwide, and aerosols are also influencing climate through interactions with clouds and solar radiation. Heterogeneous and multiphase chemical reactions on the surface and in the bulk of aerosol particles have been recognized to influence aerosol formation, and thus their environmental effects. However, atmospheric multiphase chemistry is not well understood because of its intrinsic complexity of dealing with matters in multiple phases and the difficulties of distinguishing its effect from that of gas phase reactions.

Recently, research on atmospheric multiphase chemistry received a boost by the growing interest in understanding severe haze formation of high PM2.5 concentrations in polluted regions. Here, I present recent results from my group, as well as current challenges, and future perspectives of research on multiphase chemical processes involved in atmospheric aerosol formation and transformation. In particular, I discuss advances and challenges related to different chemical regimes of sulfate, nitrate, and secondary organic aerosols (SOA) under haze conditions, and new insights into the influence of aerosol water content, aerosol pH, phase state, and nanoparticle size effects. Overall, there are increasing evidences that multiphase chemistry plays an important role in aerosol formation during haze events. In contrast to the gas phase photochemical reactions which are self-buffered against heavy pollution, multiphase reactions have a positive feedback mechanism, where higher particle matter levels accelerate multiphase production, which further increases the aerosol concentration resulting in a series of record-breaking pollution events. Perspectives to fill the gap of the current understanding of atmospheric multiphase reactions are discussed. A synthetic approach combining laboratory experiments, field measurements, instrument development, and model simulations is suggested as a roadmap to advance future research.

KEY REFERENCES

Zheng, G.; Su, H.; Wang, S.; Andreae, M. O.; Pöschl, U.; Cheng, Y. Multiphase buffer theory explains contrasts in atmospheric aerosol acidity. Science 2020.

Ditas, J.; Ma, N.; Zhang, Y. X.; Assmann, D.; Neumaier, M.; Karu, E.; Williams, J.; Scharffe, D.; Wang, Q.; Saturno, J.; Schwarz, J. P.; Katich, J. M.; McMeeking, G.; Zahn, A.; Hermann, M.; Brenninkmeijer, C. A. M.; Andreae, M. O.; Pöschl, U.; Su, H.; Cheng, Y. Strong impact of wildfires on the abundance and aging of black carbon in the lowermost stratosphere. Proc. Natl. Acad. Sci. 2018.

Mu, Q.; Shiraiwa, M.; Octaviani, M.; Ma, N.; Ding, A.; Su, H.; Lammel, G.; Poeschl, U.; Cheng, Y. Temperature effect on phase state and reactivity controls atmospheric multiphase chemistry and transport of PAHs. Sci. Adv. 2018.

Cheng, Y.; Zheng, G.; Wei, C.; Mu, Q.; Zheng, B.; Wang, Z.; Gao, M.; Zhang, Q.; He, K.; Carmichael, G.; Poschl, U.; Su, H. Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China. Sci. Adv. 2016.

Cheng, Y.; Su, H.; Koop, T.; Mikhailov, E.; Poeschl, U. Size dependence of phase transitions in aerosol nanoparticles. Nat. Commun. 2015.

Su, H.; Cheng, Y.; Oswald, R.; Behrendt, T.; Trebs, I.; Meixner, F. X.; Andreae, M. O.; Cheng, P.; Zhang, Y.; and Pöschl, U. Soil Nitrite as a Source of Atmospheric HONO and OH Radicals. Science 2011.

Figure 1: The broad theme and strategies of the Minerva research group & self-amplification system in the haze chemistry.