Furthermore, trimerization of isocyanic acid to cyanic acid is a viable possibility, particularly for fast heating of the reaction mixture, as in Equation 6 [18, 25].
The conversion of isocyanic acid to ammonia in the temperature range of exhaust gas occurs almost exclusively in the presence of a catalyst [19, 20].
[16.] Kleemann, M., Elsener, M., Koebel, M., and Wokaun, A., "Hydrolysis of Isocyanic Acid on SCR Catalysts," Industrial & Engineering Chemistry Research 39:4120-4126, 2000.
 [mathematical expression not reproducible] [c] SAE International TABLE 2 Reaction parameters A in [s.sup.-1] and [E.sub.A] in J/mol for the hydrolysis of isocyanic acid in accordance with Arrhenius.
Indeed, a lot of parameters impact the conversion of DEF to gaseous ammonia: spray dynamics, interaction between spray and walls, droplet vaporization followed by complex urea decomposition to N[H.sub.3] consisting in urea thermolysis into ammonia and isocyanic acid (HNCO) and finally HNCO hydrolysis into ammonia .
Also the differences in N[H.sub.3] yield (5-20%) and the deposit yield (25-65%) can be attributed to the formation of other species than ammonia and deposit such as isocyanic acid and urea.
In humans, isocyanic acid is mainly formed by the spontaneous decomposition of urea into cyanate and ammoniac, which occurs in aqueous solutions according to an equilibrium that favors urea more than 99% (12).
Urea decomposition, however, is not the sole pathway leading to isocyanic acid formation, especially in nonuremic patients.
Two mechanisms had been suggested to explain its beneficial action: direct interference of the urea molecule per se with sickling (18), and hemoglobin S carbamylation by urea-derived isocyanic acid, which increases oxygen affinity and decreases aggregation properties (19).
Because of the pathways of isocyanic acid formation in vivo, carbamylation is preferentially involved in 2 pathophysiological processes: CRF and atherosclerosis (26, 39, 40).
in the atmosphere and its possible link: o smoke-related health effects Proc Natl Acad So USA 108(22):8966-8971 (2011); hup://dx.doi.org/10.