A EUROPEAN INVENTORY OF SOIL NITRIC-OXIDE EMISSIONS AND THE EFFECT OFTHESE EMISSIONS ON THE PHOTOCHEMICAL FORMATION OF OZONE

An inventory of soil nitric oxide (NO) emissions for Europe was develo ped. The emission of NO was parameterized using empirical relationship s with type of landuse, fertilization rate of agricultural areas and s oil temperature. For the year 1994, it was estimated that annual soil NO emissions in the inventoried area amounted to 535 kt NO-N yr(-1), i .e. 8% of the emissions from combustion processes. On a hot summer day , this fraction increased to 27%. The uncertainty of these emission es timates, however, is high. They are accurate only within a factor of t hree to four. As the major fraction (in summer 81%) of the emissions c ame from arable land, soil NO emissions have to be considered as large ly anthropogenic. Large regional differences existed in the soil NO em ission rates with the highest emission rates found in southern and wes tern Europe, intermediate rates in eastern Europe and the lowest rates in Scandinavia and northern Russia. The effect of the soil NO emissio ns on the photochemical formation of ozone (O-3) was investigated with a one-dimensional photochemical model. When soil NO emissions were co nsidered in the model simulations, computed mean daily maximum O-3 con centrations over Europe from June to August 1994 were 4 ppb (uncertain ty range: 1.4-9.6 ppb) higher than without these emissions. Reductions of pyrogenic NOx emissions were less efficient in reducing O-3 concen trations when soil NO emissions were taken into account. Copyright (C) 1996 Elsevier Science Ltd.