A study of the interaction of NO2 with carbon particles

Abstract

The interaction NO2 in air (0.5-35 ppm) with carbon particles led to three products: NO gas, and NO2− and NO3−, removed from the particles by water extraction. At 4 ppm or below, in dry or humid air, the product distribution, in relative molar amounts, was NO3− = 2NO2− = 2NO. At 20 ppm and above, the relative amounts of products depended on the presence of water vapor: in dry air NO = 3NO3− = 6NO2−; in humid air NO = NO2− = 2NO3−. For carbon slurries in water, [NO2−] = 6[NO3−] at an input concentration of NO2 of 4 ppm. In comparison to carbon, alumina particles and glass beads removed NO2 ineffectively. These results indicate that NO2 oxidized the carbon particles while it was reduced to NO. NO2 adsorbed at oxidized sites on the particles formed a surface species that was analyzed as nitrate. At high enough concentration of NO2 (20 ppm and above), the interaction of NO and water vapor with the surface nitrate produced NO2−. In slurries NO, generated from interaction of NO2 with carbon, reacted with surface nitrate or nitric acid in solution to form the relatively large quantities of nitrite. This work suggests that NOx reactions with carbon in droplets or on wet surfaces could be important sources for the production of nitrous acid in the environment. © 1989 Elsevier Science Publishing Co., Inc.