Aerosols, Air Quality & Climate

Minerva Research Group    Dr. Yafang Cheng

The broad theme of our research is to understand key processes that drive the formation and transformation of aerosols, and to elucidate and quantify the effects of atmospheric aerosols on air quality, public health and climate. The overall goal is to obtain a predictive understanding of the origin, fate and impact of atmospheric aerosols to address the grand challenge of actionable projection of future climate and environment in the Anthropocene.

For this purpose, we combine the development of cutting-edge instruments, lab experiments, field observation and a synthesis approach with model simulations that involve multi-scale physical and chemical processes from bulk phase to nanoscale and from regional to global scales.

Current focal points are: (1) developing new pathways and theories of reactive nitrogen chemistry, atmospheric aerosol acidity, and their influence on haze formation (e.g., Science 2011; Science Advances 2016; Science 2020). (2) improving fundamental understanding of the thermodynamics and molecular dynamics of phase transitions in highly supersaturated nanoparticles and their regional and global effects in the Earth system (e.g., Nature Communications 2015; Science Advances 2018). (3) promoting science-oriented policymaking in air pollution control, public health improvement and climate change mitigation, where we demonstrate how a better physico-chemical understanding can help to develop cost-effective control strategies (Science Advances 2016; PNAS 2018; PNAS 2020; Nature Communications 2021; Science 2021).

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Intensified wildfires in a warming climate threatens the Arctic: Yue et al., Brown carbon from biomass burning imposes strong circum-Arctic warming. One Earth (Cell press) 2022.

Rapid Arctic warming and associated glacier and sea ice melt have a great impact on the global environment, with implications for global temperature rise and weather patterns, shipping routes, local biodiversity, and methane release. Greenhouse gases and black carbon aerosols are well-known warming agents that accumulate in the Arctic atmosphere, but full warming agent picture remains incomplete, preventing accurate forecasts. The effects of brown carbon—an aerosol derived from biomass and fossil fuel burning—are particularly unclear. Through observations from a circum-Arctic cruise and numerical model simulations, we show that light-absorbing brown carbon, mainly from biomass burning, can impose a strong warming effect in the Arctic, especially in the summertime. If, as predicted, the frequency, intensity, and spread of wildfires continues to increase, this may reinforce circum-Arctic warming and further contribute to global warming, forming a positive feedback. In light of these results, the careful management of vegetation fires, especially in the mid- to high latitudes of the Northern Hemisphere, will prove important in mitigating the warming in the Arctic region.

MPIC news | BBC news | AltMetric Attention Score (>300)

Why and how masks work: Cheng et al., Face masks effectively limit the probability of SARS-CoV-2 transmission. Science 2021.

Airborne transmission by droplets and aerosols is important for the spread of viruses. Face masks are a well-established preventive measure, but their effectiveness for mitigating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission is still under debate. We show that variations in mask efficacy can be explained by different regimes of virus abundance and are related to population-average infection probability and reproduction number. For SARS-CoV-2, the viral load of infectious individuals can vary by orders of magnitude. We find that most environments and contacts are under conditions of low virus abundance (virus-limited), where surgical masks are effective at preventing virus spread. More-advanced masks and other protective equipment are required in potentially virus-rich indoor environments, including medical centers and hospitals. Masks are particularly effective in combination with other preventive measures like ventilation and distancing.

Falling Walls Science Breakthroughs of the year 2021 (Physical Sciences) | WoS "hot paper" & "hightly cited paper"|AltMetric Attention Score (>8700), placing it within the top 0.001% of 18 million scientific papers published in total and ranked 11 of over 70 thousands publications in Science | MPG news | MPIC news | EGU blog | Featured by Bloomberg | Further resources - COVID-19 Aeroosl Transmision Risk Calculator

Biomass burning aerosol-PBL-monsoon interactions modify low clouds: Ding et al., Aerosol-boundary-layer-monsoon interactions amplify semi-direct effect of biomass smoke on low cloud formation in Southeast Asia. Nature Communications 2021.

Low clouds play a key role in the Earth-atmosphere energy balance and influence agricultural production and solar-power generation. Smoke aloft has been found to enhance marine stratocumulus through aerosol-cloud interactions, but its role in regions with strong human activities and complex monsoon circulation remains unclear. Here we show that biomass burning aerosols aloft strongly increase the low cloud coverage over both land and ocean in subtropical southeastern Asia. The degree of this enhancement and its spatial extent are comparable to that in the Southeast Atlantic, even though the total biomass burning emissions in Southeast Asia are only one-fifth of those in Southern Africa. We find that a synergetic effect of aerosol-cloud-boundary layer interaction with the monsoon is the main reason for the strong semi-direct effect and enhanced low cloud formation in southeastern Asia.

MPIC news 

Aerosol pH buffered by ammonia: Zheng et al., Multiphase buffer theory explains contrasts in atmospheric aerosol acidity. Science 2020.

Aerosol acidity largely regulates the chemistry of atmospheric particles, and resolving the drivers of aerosol pH is key to understanding their environmental effects. We find that an individual buffering agent can adopt different buffer pH values in aerosols and that aerosol pH levels in populated continental regions are widely buffered by the conjugate acid-base pair NH4+/NH3 (ammonium/ammonia). We propose a multiphase buffer theory to explain these large shifts of buffer pH, and we show that aerosol water content and mass concentration play a more important role in determining aerosol pH in ammonia-buffered regions than variations in particle chemical composition. Our results imply that aerosol pH and atmospheric multiphase chemistry are strongly affected by the pervasive human influence on ammonia emissions and the nitrogen cycle in the Anthropocene.

MPIC news | WoS "hot paper" and "highly cited paper" | Related studies - Zheng et al, ACP 2022; Zheng et al. ACS Environ. Au 2022 

 

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