Could you offer a detailed answer on why/how the nitrogen deposition from nitrate and ammonium is so high in the northeast states, lower in the midwest states and very low in the west. What is causing this atmospheric deposition condition?Nitrogen deposition is a strong function of emissions. We emit nitrogen in several forms. From high temperature burning (power plants, incinerators, industrial processes, cars/trucks) we emit NO and NO2, referred to as oxidized nitrogen. From agricultural practices, we emit NH3 and NH4+ referred to as reduced nitrogen. Deposition of oxidized nitrogen is in the form of HNO3 and NO3- in precipitation. It is in the form of HNO3 and particulate NO3- when dry deposited. Deposition of reduced nitrogen is in the form of NH4+ in precipitation. It is in the form of particulate NH4+ and NH3 when dry deposited. There are other important forms of nitrogen, but these are the big ones with respect to things we lump together regarding nutrient deposition. Reduced N is primarily emitted in the northern plains states and upper Midwest with some hotspots in the east. Oxidized N is primarily emitted in the upper Midwest and the Northeast. Deposition of all of this stuff is nearby and downwind of where it is emitted. Note that our deposition monitoring efforts are much better developed for wet deposition than dry. You would see evidence of higher NO3-/HNO3 deposition around Los Angeles if we had a better dry deposition network. In the eastern US, wet deposition is approximately equal to dry, ranging from about 30% to 70% of total deposition, but usually closer to 50%.
I was looking around for some emissions maps but had limited
success. You need to check out the EPA Office of Air Quality
Planning and Standards web pages. Some information may be found
at: Deposition maps may be found at:
Rick Artz |
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