Particulate matter emitted through human activities not only pollutes the air, but also cools the Earth by scattering shortwave solar radiation. However, coarser dust particles have been found to exert a warming effect that could, to some extent compensate for the cooling effect of fine dust. Here we investigate the radiative effects of sulfate containing aerosols of various sizes and core/shell structures using Mie scattering and three-dimensional finite difference time domain simulations of the electromagnetic fields inside and around particulate matter particles. We find that not only coarse dust, but also fine non-light-absorbing inorganic aerosols such as sulfate can have a warming effect. Specifically, although the opacity of fine particles decreases at longer wavelengths, they can strongly absorb and re-emit thermal radiation under resonance conditions at long wavelength. We suggest that these effects need to be taken into account when assessing the contribution of aerosols to climate change.

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A new method for the design of a bandstop filter is presented. The two‐section open stub is employed to emulate a notch filter in the discrete‐time domain. A cascade connection of two‐section open stubs with proper frequency scaling serves to represent a bandstop filter of wider stopband bandwidth. Experimental results are presented to illustrate the validity of this design method. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1098–1101, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22356

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