The use of concrete is fundamental in virtually every construction project. And Portland cement is often a chief component in cement.  Because of this, plants which produce Portland cement have been governed under different (most would agree laxer) emissions standards than most other industries. This distinction has allegedly progressed to the point that, in some areas, cement plants are responsible for 90% of hazardous air emissions, including mercury, sulfur dioxide ("SOX"), nitrogen dioxide ("NOX"), and hexavalent chromium, as well as acids and particulate matter..

On August 9^th, the EPA released a 450+ page Final Rule for Hazardous Air Emissions. (Portland Cement Final Rules: New Source Performance Standards and National Emissions Standards for Hazardous Air Pollutants: http://www.epa.gov/ttn/oarpg/t3pfpr.html) According to EPA's projections, the final rule will lead to a reduction of 70-90% of most of the hazardous air emissions from cement plants.

Environmentalists have championed the stricter regulations. (See NRDC's Article: A Big Step Toward Cleaner Cement ) 

The Final Rule for cement plants follows on the heels of a draft proposal for the regulation of coal ash, which is also often used in the production of concrete as a substitute for cement. (See the 5/24/10 entry in this blog). Although both could likely affect the cost of concrete production, tightening the regulation of the two most common components of concrete at approximately the same time will likely keep the playing field even from a regulatory standpoint. Of course, as always, advances in technology could provide (or reinstate) a competitive edge. It remains to be seen which industry will be successful in capturing that edge in the future.