In a recent issue of Environmental Health Perspectives. Canadian researchers Aaron van Donkelaar and Randall Martin at Dalhousie University, Halifax, Nova Scotia, Canada, created the map by blending total-column aerosol amount measurements from two NASA satellite instruments with information about the vertical distribution of aerosols from a computer model.

link: NASA – New Map Offers a Global View of Health-Sapping Air Pollution

Here is a link to the original article in Environmental Health Perspectives. And here is another link where the authors respond to additional comments.