About This Project

The clouds we see today are different from that in pre-industrial period. The increasing anthropogenic activities are characterized by heavier air pollution with high aerosol concentrations. Aerosols can serve as cloud condensation nuclei (CCN), which “pollute” the clouds by adding more cloud droplets with smaller size. The proposal aims to answer two simple questions: where did we find so far the most pristine clouds over land, and how clean they are?

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What is the context of this research?

Measuring air pollutions has been a notoriously difficult task. Current approaches are limited to in-situ measurements which are very limited in time and space. Satellite can provide a global view but is not able to measure the CCN concentrations

This situation starts to be enlightened by an innovative method of satellite retrieving CCN concentrations. This method was developed by our group and published in the Proceedings of the National Academy of Sciences, of which I am the second author. The new method measures CCN with satellite-observed cloud microstructures, providing an approach to measuring air pollution worldwide.

Here, we take advantage of high-resolution of VIIRS onboard the polar-orbiting Suomi NPP satellite to do the CCN retrieval.

What is the significance of this project?

Why are we interested in knowing how clean the most pristine clouds are?

The effect of aerosols on cloud droplet concentrations and radiative properties is the source of the largest uncertainties in the radiative forcing of climate. Carslaw et al. showed, in their nature paper, that the largest variance of aerosol forcing since industrial period arises from natural aerosols, not anthropogenic aerosols. This indicates the significance of understanding pristine pre-industrial-like environment with natural aerosols only. The environment with the most pristine clouds mimics such pre-industrial-like environment. Thus, knowing how clean the most pristine clouds is valuable to understanding the aerosol radiative forcing and reducing the uncertainties of forcing estimates.

What are the goals of the project?

Our goals are to answer the following two questions: (1) where did we find so far the most pristine clouds over land, and (2) how clean they are?