Geosciences Dept. Seminar: When and where on Earth has haze become frequent? On the unique trends between East Asian cloud coverage, urbanization, and haze

Abstract: 

Atmospheric properties may be significantly modified by introduction of urbanization processes, through changes in surface albedo, sensible and latent heat balances, and aerosol emission magnitudes and distributions. This study focuses on East Asia, as one of the most densely and rapidly economically growing areas, to explore the relations between extensive urbanization processes and cloud properties.

For this purpose, a new multi-decadal global record of surface observations provides insights on the spatial and temporal distributions of haze events, indicating India as the haziest region in the world. This multi-decadal database also enables the derivation of the trend of surface particulate pollution over the globe - critical information that has not been successfully obtained from satellite retrievals and aerosol specific measurement stations.

Further analysis co-locates a 15 yearlong subset of surface observations with Multi-angle Imaging SpectroRadiometer (MISR) aerosol and cloud product, and with land usage product of the Moderate Resolution Imaging Spectroradiometer (MODIS). It is found that in the densely urbanized areas of East Asia, the averaged low-cloud fraction has decreased by ~4% in the recent decade. Moreover, the observed low-cloud fraction in East Asia is constantly lower in urbanized areas than it is in rural areas, and hazy days are characterized by less coverage of low clouds.

These results, found to have the opposite trends in any other region of interest, suggest that in East Asia, urbanized environment high pollution levels lead to decreased low-cloud coverage, unlike the trend expected when cloud condensation nuclei concentrations are increased.

Finally, new simulation frameworks are presented, for better assessing the impacts of the complex interaction between urbanization, clouds, haze, and climate.

Seminar Organizer: Dr. Ravit Heled