1 THE GLOBAL AMMONIA CYCLE A term paper presented to Dr. Gunnar W. Schade in fulfillment of the requirements for the end of semester examinations in Trace Gas Biogeochemistry. By2CONTENTS Introduction……………………………………………………………3 Sources and sinks of ammonia…………………………………………4 Emission from soil and vegetation…………………………………… 4 Emission from combustion processes………………………………… 5 Oceanic emission ……………………………………………………. 5 Global variations in emission and deposition…………………………8 Diurnal variations…………………………………………………… 8 Seasonal variations……………………………………………………9 Altitude variations………………………………………………………9 Spatial variations………………………………………………………9 Atmospheric importance………………………………………………10 Possible negative impacts from ammonia……………………………11 Emission control………………………………………………………12 Reflections and suggestions…………………………………………… 123 INTRODUCTION Ammonia (NH3) is a colorless gas with a very sharp odor, which dissolves easily in water and evaporates quickly. It is the most abundant nitrogen gas in the atmosphere after N2 and N2O. Having relatively short residence time of about 10 days, its mixing ratio is highly variable in space and time, with a surface continental value of about 0.1-10ppbv. [1] It is produced by human anthropogenic and natural processese. Most of it produced in the chemical factories is used to make fertilizers and the rest in textile, plastics, explosives, pulp and paper production, food and beverages, household cleaning products, refrigerants and others. It is produced naturally in soil by bacteria decaying plants and animals, as well as animals and human wastes. Ammonia does not build up in the food chain (WHAT DO YOU MEAN? SOILS?), but serves as nutrient for plants and bacteria. Most agricultural crops are nitrogen limited and hence higher yields are achieved by the application of nitrogen fertilizers. Following the application of urea to soil, it is hydrolyzed to ammonium (NH4+) which is then oxidized to nitrite (NO2-) and finally to nitrate (NO3-) by chemoautotrophic nitrifying bacteria. This process provides several biochemical pathways leading to the release of nitrogen (N2), nitrogen dioxidenitrous oxide (N2O), and nitric oxide (NO) into the atmosphere. Investigations have revealed that nitrogen fertilizers are the main source of N2O and NO emission from agricultural soils is expected to increase from the 6-7% per annum in41990s to higher values looking at the increase in food production to meet the growing demand of world population (PLEASE REWORD THIS SENTENCE). Fig.2 The N2O and nitrogenus oxides (NOX = NO + NO2) produced from soil, impact the chemistry of the atmosphere considering the role that NO and NO2 play in the oxidizing capacity of the troposphere, hence the recent increase in the research into ammonia exchange with the atmosphere. In this paper, based on the findings and publications of researchers worldwide, the global or regional sources and sinks of ammonia will be elaborated. It’s atmospheric importance; abundance, lifetime and variability will also be discussed. Finally, a general reflections as well as suggestions for future considerations will be given. SOURCES AND SINKS OF AMMONIA (NH3) This section gives some of the sources and sinks of ammonia in the atmosphere. Followed by description of some of the major emission sources. Source of ammonia After its application to soil, ammonia is hydrolyzed to NH4+ which can remain on the exchange sites, nitrify to NO3-, or decomposed to NH3, depending on soil and environmental conditions: NH4+ ↔NH3 + H+ NH4+ + 121O2 →2H+ + H2O + NO2 THERE IS A CHARGE CREATED IN THIS ONE NO2- + 21O2 → NO3- Major sources of ammonia include emission from soil, biomass burning, losses during the production and application of fertilizer and emission from the ocean.5Also from industrial activities such as wastewater treatment, petroleum refining, coal and oil combustion etc. [1] Emission from soil and vegetation Ammonia in the form of urea is applied to soil to boost the soil nutrient, however, not all the ammonia applied to the vegetation is used up. Some are lost through evaporation and part also through microbial activity called denitrification. The amount of NH4+, volatilized after application depends much on factors such as; type of fertilizer used, temperature, rainfall, soil type, humidity and soil acidity. In general, it has been investigated and proven that high temperature, high wind speeds and low relative humidity favor NH3 loss. Unfertilized soils and vegetations have also been found to emit NH3 depending on the NH3 partial pressure in the plant stomata. However, the mechanism leading to NH3 emission from unfertilized land is very poorly understood, e.g. (Schlesinger and Hartley, 1992) estimate of emission from undisturbed land of about 10TgN-NH3 yr-1 is believed to may have contain inputs from wild animals. Emission from combustion processes The burning of charcoal, biomass and fuel in automobiles emit NH3. Coal contains about 1-2 % of nitrogen; however, the production of NH3 from coal burning in the industries is insignificant since at high temperatures in power plants, much of the NH3 produced is oxidized to NO, hence coal burnt domestically, can be said to release significant amount of NH3 e.g. (Böttger et al., 1978) calculated an emission of 0.03Tg yr-1 from coal burning. It should however be emphasized that not much research has been conducted in this area. Contributions from boimass burning have been found to be the most significant with the following recent estimates of 3NH emission; 0.2-0.5 (Crutzen and Andreae, 1990), 5.2 (Andreae, 1991) and 3.7 TgN-NH3 yr-1 (Laursen et al., 1992).6 Oceanic emission Ammonia is released from the ocean through mineralization of organic material, with a global estimate of about 8.2 (5-15) T g N yr-1 [1]. Most of it is used up and the rest remain in solution and