黑碳颗粒物表面SO2的非均相臭氧氧化

Heterogeneous Oxidation of SO_2 by Ozone on the Surface of Black Carbon Particles

采用漫反射红外傅里叶变换光谱(DRIFTS)结合离子色谱(IC)、X射线光电子能谱(XPS)研究了常温常压下SO2与O3在黑碳颗粒物(以Printex U为代表,简称UBC)表面的非均相反应.研究发现,在O3和水气存在的情况下,体系的反应产物主要是SO24-,反应在一定时间内持续进行.UBC可提供反应活性位点,促进SO2在其表面的臭氧氧化.O3是关键的氧化剂,能显著提高SO2非均相氧化生成SO24-的速率.水气的存在有利于表面活性位点再生,使反应持续发生.当SO2和O3的浓度为1014～1015molecule/cm3、相对湿度为40%时,SO2在UBC(1∶400,以NaCl为稀释剂稀释400倍)表面非均相反应生成SO24-的稳态摄取系数(γBET)为1～6×10-6,SO24-的生成速率为1014～1015ion·s-1·g-1.

Black carbon（BC） produced by incomplete The heterogeneous reactions of gaseous pollutants （ such combustion processes is an important aerosol species. as SO2, O3 and NOx ） on the surface of BC particles are of significance because these reactions can change the particles＇ morphology, chemical composition, hygro- scopicity and optical properties, and thus alter their climate or health effect, as well as these reactions can in- fluence environmental chemical cycling. In this study, the heterogeneous oxidation of SO2 by O3 on the surface of black carbon （ using Printex U as the model particles, denoted as UBC） was investigated by the method of Diffuse Reflectance Infrared Fourier Transform Spectroscopy （DRIFTS）. The surface product was monitored, and confirmed by Ion Chromatographic （IC） and X-ray photoelectron spectroscopy （XPS） techniques. It was found that the main product of SO2 heterogeneous reaction on the surface of UBC or diluted UBC [ with one part of UBC diluted in 399 parts of infrared transparent NaCI powder, denoted as UBC （ 1 ： 400） ] was sulfate and the oxidation reaction rate could be greatly enhanced by O3. The simultaneous presence of ozone and water va- por are necessary for the sulfate formation and the reaction rate can sustain for 3 h. UBC particles supply reac- tive surface sites（SS） which react with O3 to produce oxygen atom （SSO）, promoting the heterogeneous oxida- tion of SO2 to SO4^2-.O3 is the dominating oxidant, and water vapor makes for SS regeneration. In the condition of 10^14--10^15 molecule/cm3 SO2＋10^14-10^15 molecule/cm3 O3＋40% RH, the steady state uptake coefficient of SO2 on UBC（1：400） was （1-6）×10^-6 using BET surface area as the effective reaction area. The reaction order of O3 was found to be 0.5. The sulfate formation rate on the surface of UBC （ 1 ： 400） particles was cal- culated up to 1014--1015 ion · s^-1 ·g^-1, indicating that this kind of heterogeneous reaction may play an impor- tant role in altering the physicochemical properties of BC particles in the highly air-polluted weather condi- tions.