Seminar

Abstract

Aerosol is one of the most important climate change drivers from anthropogenic activities. The often overlooked stratospheric aerosols and their interaction with climate remain unclear and of large uncertainties. In this presentation I am going to introduce the most recent work I am involved to study the composition, transport and physical properties of the stratospheric aerosols with focus on background particles and smoke.

The background stratospheric aerosol increases since preindustrial and therefore contributes to the human-induced climate change. Constrained by satellites and in-situ measurements, we suggest that the stratospheric background aerosol budget has increased by 77% since year 1850. The estimated radiative forcing of the background stratospheric aerosols is about -0.07 Wm-2, which is as large as 20% of the total aerosol radiative forcing of the entire atmosphere [Yu et al., 2016]. Our study reports that the radiative forcing from background stratospheric aerosol of anthropogenic origin, has not been widely considered as a significant influence on the climate system.

We also investigate the transport pathways of the stratospheric aerosols. Yu et al. [2017] demonstrates that the abundant anthropogenic aerosol precursor emissions from Asia coupled with rapid vertical transport associated with monsoon convection leads to significant particle formation in the upper troposphere within the monsoon anticyclone. These particles subsequently spread throughout the entire Northern Hemispheric (NH) lower stratosphere and contribute significantly (∼15%) to the NH stratospheric column aerosol surface area on an annual basis. This contribution is comparable to that from the sum of small volcanic eruptions in the period between 2000 and 2015.

Our most recent study suggests that organics particles injected from large wildfires may also contribute to the stratospheric aerosol budget. Using solar occultation instrument (SAGEIII) on board of international space station and satellite-borne instruments (MLS and CALIOP), we, for the first time tracked the entire lifecycle of the stratospheric smoke for over 8 months. The observations from the space clearly show that the smoke rose from 12km to 23 km in 2 months. In the meantime, combined the space measurements with the aerosol-climate model we are able to quantify the physical-chemical properties of the smoke particles in the stratosphere including the size evolution, lifetime, and the chemical reaction rate with ozone. My research suggests that this "natural experiment" (pyroCb smoke) confirms previous hypothesis on "nuclear winter": the smoke from regional nuclear exchange can have long-lasting global impacts.

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