[A-AS11] Atmospheric Chemistry

[AAS11-07] Future Vision for Atmospheric Chemistry: Aerosols and their Interactions with Radiation and Cloud Processes

*Hitoshi MATSUI¹, Sho Ohata^2,3, Yutaka Tobo^4,5, Atsushi Matsuki⁶, Syuichi Itahashi⁷, Naga Oshima⁸, Kentaroh Suzuki⁹, Yousuke Sato^10,11 (1.Graduate School of Environmental Studies, Nagoya University, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.Institute for Advanced Research, Nagoya University, 4.National Institute of Polar Research, 5.The Graduate University for Advanced Studies, SOKENDAI, 6.Institute of Nature and Environmental Technology, Kanazawa University, 7.Central Research Institute of Electric Power Industry (CRIEPI), 8.Meteorological Research Institute, 9.Atmosphere and Ocean Research Institute, University of Tokyo, 10.Faculty of Science, Hokkaido University, 11.RIKEN Center for Computational Science)

Keywords:Aerosol, Aerosol-radiation-cloud interactions, Absorbing aerosols, Ice nucleating particles, Long-term monitoring, Transboundary air pollution

Atmospheric aerosols are emitted into the atmosphere by various anthropogenic and natural activities, and their particle size and chemical composition vary widely. Atmospheric aerosols have a wide range of importance from local to global scales, including adverse effects on human health, air pollution, and impacts on the Earth’s climate. Aerosols modulate the Earth's radiation budget through the scattering and absorption of solar and terrestrial radiation and their impacts on cloud and precipitation processes, and through these aerosol-radiation-cloud interactions, they influence global climate change and climate variability.

Our understanding of the behavior of aerosols in the atmosphere and their interactions with radiation and clouds has been greatly improved over the past decade by the advancement of both observations (field and satellite) and numerical modeling, as well as by the combination of these two approaches. In field observations, new techniques have been established to measure physico-chemical properties of aerosols, such as particle size and chemical composition, at the single particle scale, which has greatly improved our understanding of aerosol properties and processes, such as new particle formation, organic aerosol formation, and removal processes by precipitation. In satellite observations, the combined application of active and passive sensors has advanced the observational understanding of aerosol-cloud interactions. In numerical models, various aerosol properties and processes have been introduced into general circulation climate models, global cloud-resolving models, and chemical transport models, and the estimation of aerosol distributions and aerosol-radiation-cloud interactions has been improved based on the validation and constraint by atmospheric observation data.

While the understanding of aerosols and their climate impacts has advanced, the range of uncertainty in the estimates of radiative forcing due to aerosol-radiation-cloud interactions have not been reduced in the past decade, and the variability of these estimates among climate models remains large (IPCC Sixth Assessment Report). In order to improve the reliability of estimates of aerosol-radiation-cloud interactions, several important issues remain to be addressed: the spatial and temporal distributions of aerosols must be accurately understood from observations, and these distributions must be adequately represented in numerical models. First, it is necessary to accumulate observational knowledge of aerosols in remote regions (high latitudes in the Northern Hemisphere, Southern Hemisphere, remote oceans, and upper and middle troposphere), where the variability of aerosol estimates among climate models is particularly large and where field observations are less frequent, to properly understand the behavior and source contributions of aerosols in these remote regions. Second, it is necessary to further improve our understanding of the physico-chemical properties and processes related to aerosol-radiation-cloud interactions. For example, the response of ice-containing cloud and precipitation systems to ice nucleating particles is poorly understood in particular, and it is desirable to understand the atmospheric abundance and behavior of ice nucleating particles and the response of the cloud and precipitation systems to changes in aerosols. Third, it is necessary to improve the reproducibility of aerosol observations and the estimation of aerosol-radiation-cloud interactions by numerical models by improving the model representations of physicochemical properties and processes, validating and constraining them by observations mainly in remote areas, and enhancing the model resolutions.

In this presentation, we will summarize recent findings related to atmospheric aerosols and aerosol-radiation-cloud interactions, and discuss their current problems and future challenges.