Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 2719-2725, 2016
http://www.atmos-chem-phys.net/16/2719/2016/
doi:10.5194/acp-16-2719-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
04 Mar 2016
Global dimming and urbanization: did stronger negative SSR trends collocate with regions of population growth?
Adel Imamovic1, Katsumasa Tanaka1,2, Doris Folini1, and Martin Wild1 1Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland
2National Institute for Environmental Studies (NIES), Tsukuba, Japan
Abstract. Global dimming refers to the decrease in surface solar radiation (SSR) observed from the 1960s to the 1980s at different measurement sites all around the world. It is under debate whether anthropogenic aerosols emitted from urban areas close to the measurement sites are mainly responsible for the dimming. In order to assess this urbanization impact on SSR, we use spatially explicit population density data of 0.08° resolution to construct population indices (PI) at 157 high data quality sites. Our study extends previous population-based studies by incorporating distance-weighting as a simple aerosol diffusion model. We measured urbanization in the surrounding of a site as the PI change from 1960 to 1990 and found no negative correlation with the corresponding SSR trends from 1964 to 1989 for the 92 sites in Europe and Japan. For the 39 sites in China the correlation coefficients are significant at the 5 % level and reach around −0.35, while for the 26 remaining Asian, mostly Russian sites the correlation coefficients reach around −0.55 at the 1 % significance level. Results are similar, when the absolute levels of PIs are taken as an indicator for urbanization. Our findings call into question the existence of an urbanization effect for the sites in Europe and Japan, while such an effect cannot be ruled out for the sites in Asia, especially in Russia.

Citation: Imamovic, A., Tanaka, K., Folini, D., and Wild, M.: Global dimming and urbanization: did stronger negative SSR trends collocate with regions of population growth?, Atmos. Chem. Phys., 16, 2719-2725, doi:10.5194/acp-16-2719-2016, 2016.
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Short summary
Systematic measurements of surface solar radiation revealed a worldwide decrease from the 1960s to the mid-1980s. The role of urbanization for this so called global dimming is still under debate. We developed a set of population-data based urbanization indicators and found no correlation between urbanization and global dimming for Europe and Japan, while an urbanization impact can't be precluded for Asia. It is thus called into question whether the global dimming was mainly a local phenomenon.
Systematic measurements of surface solar radiation revealed a worldwide decrease from the 1960s...
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