A Study of the Interaction of NO2with 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 NO_x reactions with carbon in droplets or on wet surfaces could be important sources for the production of nitrous acid in the environment.