3-DIMENSIONAL STUDY OF THE RELATIVE CONTRIBUTIONS OF THE DIFFERENT NITROGEN-SOURCES IN THE TROPOSPHERE

A three-dimensional study of the relative importance of the different odd nitrogen sources in the troposphere is discussed. In order to cons istently simulate the chemistry, all the sources are considered simult aneously but each nitrogen emitted is characterized by a given flavor. This allows us to follow the evolution of nitrogen from each source w ithout affecting the overall chemical system of the atmosphere. The mo del results suggest that the NOx concentration in the southern hemisph ere is mostly dominated by the lightning source, while the northern he misphere odd nitrogen burden results mainly from the influence of foss il fuel combustion, aircraft, and lightning emissions. In particular, in the upper tropospheric northern hemisphere midlatitudes, approximat ely 25-30% of the NOx is due to aircraft, 15-20% to fossil fuel combus tion sources at the surface, and 15-20% to lightning, assuming that th e global fleet of aircraft releases 0.44 TgN/yr and that lightning pro duces 5 TgN/yr. The sensitivity of these figures to several parameters (aircraft and soil source strengths, as well as the lightning source strength and its vertical distribution) is also studied.