| Atmospheric aerosol plays a significant role in atmospheric pollution and global environmental problems. Aerosol particulate surface provides a medium in the atmosphere for heterogeneous chemistry to occur, which can alter the chemical balance of the Earth’s atmosphere. Sulfur-containing compounds are the typical pollutions in the atmosphere, and mineral dust particle is one of the most active components of aerosols. The sulfur-containing compounds in atmosphere can be oxidized to sulfate on the surface of mineral dust particles, and finally convert to sulfate aerosol. On one hand, sulfate-containing aerosol plays a significant role in atmospheric chemical processes, ozone depletion and atmospheric radiation budget, which is expected to have a direct impact on climate. On the other hand, sulfate aerosol can also act as nuclei of concentration to change cloud micro-physical processes, influencing the radiation budget and climate indirectly.A mineral dust particle may be covered by various chemical species due to transport process, and then the outer layer of particle surface may be different from the mineralogy of the original particle, resulting in different reactivity and mechanism. Field observations showed low molecular weight alkylamines were widely present in aerosols in an urban atmosphere. Ammonia and amines are easy to be absorbed onto atmospheric particles, and they would inevitably alter the surface properties of particles and finally influence the heterogeneous oxidations of sulfur-containing compounds with these particles. It is therefore high significance to study heterogeneous reaction of sulfur-containing compounds on the surface of aerosol, which can provide data for evaluation of sulfate formation and its effect on global climate.Heterogeneous reactions of sulfur-containing compounds on a-Fe2O3were investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) at room temperature. Several conclusions were drawn as follows:Firstly, Heterogeneous reactions of sulfate-containing compounds on commercial and synthetic α-Fe2O3were investigated. It was found that COS can be oxidized to form gaseous CO2and surface SO42-, HCO3-and CO32-. And sythentic α-Fe2O3has higher reactivity than that of commercial a-Fe2O3. Secondly, heterogeneous reactions of carbonyl sulfide (COS) on α-Fe2O3pre-adsorbed by ammonia and methylamine, trimethylamine, triethylamine, phenylamine, pyridine and pyrrole were investigated. It was found that these basic substances pre-adsorbed on α-Fe2O3significantly enhanced the reactivity of α-Fe2O3and changed the reaction order from first to second. For the given basic substances, hematite with pre-adsorbed methylamine exhibited the highest reactivity. The reaction rate affected by basic substances was in the order of methylamine/a-Fe2O3> trimethylamine/a-Fe2O3>ammonia/a-Fe2O3>triethylamine/a-Fe2O3>pyridine/a-Fe2O3> pyrrole/a-Fe2O3> phenylamine/a-Fe2O3≈pure hematite. Surface coverage of basic substances, surface water and temperature also played important roles in the heterogeneous reaction of COS.Thirdly, heterogeneous reactions of sulfide dioxide (SO2) on a-Fe2O3pre-adsorbed by ammonia and methylamine, trimethylamine, triethylamine, phenylamine, pyridine and pyrrole were investigated. It was found that ammonia and amines pre-adsorbed on a-Fe2O3surpressed the reactivity of SO2. And the reactivity of SO2affected by these basic substances was in the order of pure a-Fe2O3> methylamine/a-Fe2O3> pyridine/a-Fe2O3> trimethylamine/α-Fe2O3≈triethylamine/a-Fe2O3≈ammonia/a-Fe2O3> phenylamine/a-Fe2O3>> pyrrole/a-Fe2O3. Surface coverage of basic substances and surface water also played important roles in the heterogeneous reaction of SO2. By comparing the influences of two sulfur-containing compounds, a plausible reaction mechanism of SO2was discussed. |
PDF Full Text Request