Nitrogen Deposition Could be Higher Than Emissions Monitoring Suggests
23 October 2007
Although emission inventories indicate that vehicle emissions are the dominant NOx source in the eastern US, a new large-scale study of nitrogen isotopes (δ15N) in wet nitrate (NO3-) deposition found that wet nitrate deposition is strongly associated with NOx emissions from stationary sources.
This finding suggests that large areas of the landscape potentially receive atmospheric NOy deposition inputs in excess of what could be inferred from existing monitoring data alone. NOy is the collective label for oxidized forms of nitrogen in the atmosphere such as nitric oxide (NO), nitrogen dioxide (NO2), nitric acid (HNO3), and organic nitrates.
The three-year study, led by Emily Elliott, a professor of geology and planetary science in the University of Pittsburgh’s School of Arts and Sciences, recommends that urban areas and roadways be specifically monitored for nitrogen deposition.
Elliott and her colleagues conducted the first large-scale application of a method for determining the source of atmospheric nitrate on rain and snow samples from 33 precipitation collection sites across the Midwestern and Northeastern United States, including Pennsylvania.
The sites belong to the National Atmospheric Deposition Program (NADP), a cooperative of private organizations and US government agencies that analyzes precipitation for chemicals such as nitrogen, sulfur, and mercury from more than 250 sites in the United States, Puerto Rico, and the Virgin Islands.
Although vehicles are the single-largest source of nitrogen oxides in this region, the researchers found by analyzing the stable isotope composition of nitrate that the primary source of nitrate in their samples were stationary sources, such as power plants and factories, located hundreds of miles away.
Stationary sources pump pollutants high into the atmosphere where they can be transported for long distances before falling to the ground. Vehicle exhaust is released close to the ground and more likely deposited over shorter distances near roadways. Most monitoring sites in the NADP network are deliberately located in relatively rural settings away from urban, industrial, or agricultural centers.
The amount of nitrate pouring over the cities and busy roadways could be higher than monitoring data at most NADP sites reflect, and it is possible that a significant amount of this atmospheric nitrate finds its way into sensitive water supplies, such as the Ohio River or Chesapeake Bay.
In aquatic ecosystems, excess nitrate can promote an overgrowth of oxygen-consuming algae and lead to an oxygen deficiency in the water known as hypoxia. Hypoxia kills marine creatures and creates dead zones akin to the lifeless area of the Gulf of Mexico at the mouth of the Mississippi River. (Earlier post.) Determining the fate of major sources of nitrogen emissions is necessary to develop sound regulatory and mitigation strategies for both air and water quality, Elliott said.
Elliott said that future research will further characterize the isotopic ratios of nitrogen oxides from various emission sources and quantify how these values change during transport and with different emission controls. She is looking for industrial partners who can provide samples from smokestacks for analysis. Additionally, Elliott is interested in establishing an urban precipitation monitoring site in Pittsburgh to assess pollution sources that contribute to nitrate deposition in the Pittsburgh region.
Other researchers involved in this project are from the US Geological Survey, the University of California at Berkeley, the NADP, Cornell University, and the Institute of Ecosystem Studies in New York.
Resources
Elliott, E.M., Kendall, C., Wankel, S.D., Burns, D.A., Boyer, E.W., Harlin, K., Bain, D.J., and Butler, T.J. “Nitrogen Isotopes as Indicators of NOx Source Contributions to Atmospheric Nitrate Deposition Across the Midwestern and Northeastern United States” Environ. Sci. Technol., 2007, 10.1021/es070898t
Air Monitoring Instrumentation Nitrogen Oxides (NOy) (Teledyne)
If I understand what is being said here, pollution from vehicle NOx may not be as larger a contributer to global atmospheric pollution (and GHGs) as was previously thought. Obviously it remains a local air-pollutant (smog) and may contaminate ground-water, soil etc. locally, but is not as important as static sources, like electric power plants and the industrial sector, in the global picture.
As usual, it's all cast with the word 'may' frquently, but I feel slightly better about my use of biodiesel as a result.
Posted by: Floatplane | 23 October 2007 at 04:37 PM
we can not said that vehicle are the dominant NO(sub>x) source in US and all regions in the world. I think that NO(sub>x) source also may came from another point. Godoy et.al. (2004) explored that anthropogenic activites such as transport ion (in this case is nitrogen)in plants; presipitation waterfall, fog, smog and snow; agricultural activities; factory acticities and also animal units have been incresing substantially alter the atmospheric N load and subsequently nitrogen deposition.
Posted by: Aninda Puspasari | 29 October 2007 at 10:08 PM