A Study Based On The Effect Of Atmospheric Black Carbon On Sulfate Formation Under Different Oxidation Pathways

The frequent occurrence of haze events not only causes serious pollution to the environment,but also threatens the health of residents.The rapid formation of sulfate is the key factor that determines the explosive growth of fine particles and the frequent occurrence of severe haze events in China,and its formation mechanisms are diverse and complex.Recent studies have shown that black carbon is one of the most critical components of aerosol particles during haze,mainly from fossil fuels and biomass combustion,and can produce a variety of active intermediates,with a certain catalytic effect on the formation of sulfate.In this study,industrial black carbon was collected and different kinds of biomass black carbon were prepared.The elemental analyzer was used to determine the carbon,hydrogen,nitrogen element of carbon black.The automatic gas adsorption analyzer was used to determine the specific surface area and pore size distribution of black carbon.The scanning electron microscopy was use to determine the apparent morphology of black carbon.The infrared spectrometer was used to determine surface functional groups of black carbon.The Zeta voltmeter measurement was used to determine Zeta potential on the surface of the black carbon under different p H conditions.The absorption coefficient of black carbon was calculated by sulfate concentration measured using anion chromatograph.In order to study the effect of different black carbon on sulfate formation,the concentration of sulfate formed in several systems containing black carbon was compared with that without black carbon.The catalytic efficiency of black carbon on sulfate formation was analyzed under different environmental conditions by setting different concentrations of black carbon,oxidant and p H.The content of surface functional groups of black carbon before and after the reaction was measured to explore the changes in the surface structure of black carbon during the reaction.In order to further elucidate the reaction mechanism of sulfate formation catalyzed by black carbon,the performance of black carbon catalyzing H₂O₂and O₃to produce active free radicals was determined.The results showed that industrial,rice and wheat black carbon promoted sulfate formation under H₂O₂oxidation pathway,but rice husk and maize black carbon did not.The promoting ratio increased as ratio of SO₂to H₂O₂and the concentration of black carbon increased.The reaction of the above three kinds of black carbon with SO₂and SO₂/H₂O₂were accompanied by the reduction of oxygen-containing functional groups and the increase of ketone-containing by-products,and can promote H₂O₂to produce more superoxide radicals.The formation of hydroxyl radical,superoxide radical and singlet oxygen in H₂O₂,H₂O₂/BC and H₂O₂/SO₂/BC was determined by adding industrial black carbon.The results showed that industrial black carbon can promote H₂O₂to produce more active radical(·OH,·O₂^-,¹O₂)significantly,and active radicals played an important role in the formation of sulfate.Industrial,rice,wheat and maize black carbon can promote sulfate formation under O₃oxidation pathway,and the promotion rate decreased with the increase of p H.The promotion rate of maize black carbon is lower,while rice husk black carbon has no promotion effect.The reaction of industrial,rice and wheat black carbon with SO₂,O₃and SO₂\O₃was accompanied by the decrease of oxygen-containing functional groups and the increase of keto-containing by-products.It indicated that black carbon could not only oxidize SO₂directly,but also catalyze the formation of SO₂indirectly.Maize black carbon did not have the ability to oxidize SO₂,but it can catalyze the formation of SO₄^2-in O₃oxidation pathway,so its promoting effect on sulfate was not as good as the other three kinds of black carbon.Industrial,rice,wheat and maize black carbon promoted O₃to produce more superoxide radicals,while rice husk black carbon had less promotion effect.