Organic ammonium salts which are formed from heterogeneous reactions are one of the important components of Nitrogen-containing organic compounds (NOCs) in atmosphere. In order to investigate the formation process of organic ammonium salts, a gas-flow system with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) technique was applied to monitor the influence of simulated illumination on the heterogeneous reactions of toluene/O3/NH3 on hematite nanoparticles. The results revealed that toluene was transformed into benzoic acid under the action of oxidants (O3 and OH radicals). The carboxylic acid was neutralized with NH3 to form ammonium benzoate. The effect of light intensities on the reaction kinetics of ammonium benzoate formation from the heterogeneous reactions were also analyzed. With the light intensities increased from dark to 36 mW/cm2, the reaction rates increased from (1.20±0.02)×1018 ions g-1 s-1 to (2.30±0.09)×1018 ions g-1 s-1. It could induce the formation of abundant active radicals which accelerated the conversion from toluene to ammonium benzoate on hematite nanoparticles. However, the reaction rates decreased to (1.80±0.03)×1018 ions g-1 s-1 when light intensities continued to increase to 100 mW/cm2. The yield of organic ammonium salts might be reduced due to the volatilization of ammonium benzoate at high light intensity. Meanwhile, the initial uptake coefficients showed similar change trend. The values of uptake coefficient increased by 81.1% with light intensities increased from 0 mW/cm2 to 36 mW/cm2, but decreased by 21.1% when light intensities increased from 36 mW/cm2 to 100 mW/cm2. Our results not only propose heterogeneous reaction kinetics of toluene/O3/NH3 on nanoscale hematite surface under different light intensity conditions, but also supply a theoretical support for further understanding converting process of volatile organic compounds (VOCs) under combined atmospheric pollution.

You have access to this article

Please wait while we load your content... Something went wrong. Try again?