Nitrogen oxides chemical family

The behaviour of the oxides of nitrogen emitted from a source of pollution is much more complicated than for sulphur dioxide. The oxides of nitrogen are much more chemically reactive and form a whole family of oxidised nitrogen compounds. Each family member has a different fate and behaviour. Dry deposition and wet deposition occur downwind from the NO, source through the respective contributions from nitrogen dioxide, nitric acid and nitrate aerosol [17]. 

In many cases, the NOx family is formed as the sum of NO and N02, and accounts for the most reactive nitrogen species. The NOx/ NOy concentration ratio, which is often reported from field observations, is an indicator of the reactivity of odd nitrogen and its ability to destroy stratospheric ozone (or to affect other chemical families including chlorine and bromine compounds). The value of this ratio increases with altitude above 30 km to reach a value of nearly one in the upper stratosphere and mesosphere. It decreases substantially when the stratospheric aerosol load is enhanced, for example, after large volcanic eruptions (Fahey et al, 1993), and substantial amounts of nitrogen oxides are converted to nitric acid by heterogeneous reaction (5.152). It is also low in the polar regions, especially in air masses processed by polar stratospheric clouds. 

The especially widespread occurrence of the less oxidized corresponding di-and tetrahydroisoquinolines in both families (see Sections II and III) requires more detailed considerations on the biological source of the nitrogen, also in view of the uncommon use of the toxin ammonia outside the primary metabolism (57). Moreover, formation of fully conjugated isoquinolines according to Scheme 3 would necessitate a subsequent hydrogenation of the resulting stable aromates 33 and 35, a biochemically unusual reaction type (5), which also, chemically, requires relatively hard reaction conditions (e.g., Zn-HCl, see Section V,C,3). 

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