It's Ba-ack! Thanks To Increased Nitrogen Emissions, Acid Rain Returns - Sci Am.

[hatrack]

The acid rain scourge of the '70s and '80s that killed trees and fish and even dissolved parts of statues on Washington, D.C.'s National Mall is back. But unlike the first round, in which sulfur emissions from power plants mixed with rain to create sulfuric acid, the current problem stems primarily from nitrogen emissions mixed with rain to create nitric acid. "Both are strong acids, and both create serious problems for the environment," says William Schlesinger, president of the Cary Institute for Ecosystem Studies in Millbrook, N.Y. Acid rain degrades cement and limestone as well as leaches critical soil nutrients, which injures plants. It also liberates toxic minerals from the ground that flow into stream runoff where they can kill fish.

Sulfur emissions from power plants were one of the primary motivations for the U.S.'s Clean Air Act Amendments of 1990, which set reduction targets for both sulfur dioxide (SO2) and nitrogen oxides (NOx). However, whereas sulfur dioxide emissions decreased almost 70 percent from 1990 to 2008, emissions of one NOx—nitrogen dioxide (NO2)—went down only 35 percent for that same period, and amendment targets have yet to be made, according to the U.S. Environmental Protection Agency (EPA). "This comes as scientists have grown increasingly aware of the consequences of the remaining nitric acid deposition," Schlesinger says.

Schlesinger is one of a number of scientists calling attention to the problem. On June 8 the Integrated Nitrogen Committee of the EPA's Science Advisory board held a public teleconference to discuss a draft report of possible solutions to nitrogen problems, including acid rain. A final report is pending.

Nitric acid rain is derived primarily from power plant, car and truck emissions as well as from gases released by fertilizer use. Part of the problem dates back to WWI, when two German scientists invented the Haber–Bosch process, which took nonreactive nitrogen from the air (N2) and converted it into reactive, usable ammonia (NH3). Most of the nitrogen harvested via this process has been used in fertilizers, and the runoff from farms has created dead zones in Chesapeake Bay and at the mouths of the Columbia and Mississippi rivers. Some efforts have been made to regulate the agricultural nitrogen runoff, but atmospheric emissions of agricultural ammonia remain virtually unrestricted.

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http://www.scientificamerican.com/article.cfm?id=acid-rain-caused-by-nitrogen-emissions

[Sinistrous]

1. I know this is anecdotal, but

my fish pond registered acidic last weekend for the first time since I installed it five years ago.

[HereSince1628]

2. One of my favorite NOVA's was about acid rain

and it made a point of how auto emissions create NOX's that are really tough on trees, too bad it's not available as DVD, my old VHS tape is about worn out (The NOVA was also a great example of how science uses multiple methods--not just THE scientific method. I used it for nearly two decades in introductory and non-majors courses on science the kids laughed at the cornball 'Putin on the Ritz' music, but the content of the video was great.)