Jinzhu Ma

Abstract: Previous studies suggest that structure and reactivity of soot depend on combustion conditions like the fuel/oxygen ratio and nature of fuels. However, the essence of how combustion conditions affect physical and chemical properties of soot is still an open question. In this study, soot samples were prepared by combusting toluene, n-hexane, and decane under controlled conditions, and their hydrophilic properties, morphology, microstructure, content of volatile organic compounds, and functional groups were characterized. The hydrophilicity of n-hexane and decane flame soot increased with decreasing fuel/oxygen ratio, while it almost did not change for toluene flame soot. Fuel/oxygen ratio had little effect on the morphology of aggregates and the graphite crystallite size. The primary particle size and the content of volatile organic compounds on soot decreased with decreasing fuel/oxygen ratio. Less hydrophobic groups (C-H) and more hydrophilic groups (C=O) were observed on lean n-hexane and decane flame soot than that on the corresponding rich Volatile organic compounds had little effect on the hydrophilicity of soot while the hydrophilicity correlated linearly with the ratio of C=O content to C-H content. The hydrophilic functional groups were found to be mainly located at graphene layer edges and on surface graphene layers in soot.

Abstract: Sulfate is one of the most important aerosols in the atmosphere. A new sulfate formation pathway via synergistic reactions between SO2 and NO2 on mineral oxides was proposed. The heterogeneous reactions of SO2 and NO2 on CaO, α-Fe2O3, ZnO, MgO, α-Al2O3, TiO2, and SiO2 were investigated by in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (in situ DRIFTS) at ambient temperature. Formation of sulfate from adsorbed SO2 was promoted by the coexisting NO2, while surface N2O4 was observed as the crucial oxidant for the oxidation of surface sulfite. This process was significantly promoted by the presence of O2. The synergistic effect between SO2 and NO2 was not observed on other mineral particles (such as CaCO3 and CaSO4) probably due to the lack of the surface reactive oxygen sites. The synergistic reaction between SO2 and NO2 on mineral oxides resulted in the formation of internal mixtures of sulfate, nitrate, and mineral oxides. The change of mixture state will affect the physicochemical properties of atmospheric particles and therefore further influence their environmental and climate effects.

Abstract: Mineral dust comprises a great fraction of the global aerosol loading, but remains the largest uncertainty in predictions of the future climate due to its complexity in composition and physico-chemical properties. In this work, a case study characterizing Asian dust storm particles was conducted by multiple analysis methods, including SEM-EDS, XPS, FT-IR, BET, TPD/mass and Knudsen cell/mass. The morphology, elemental fraction, source distribution, true uptake coefficient for SO2, and hygroscopic behavior were studied. The major components of Asian dust storm particles are aluminosilicate, SiO2 and CaCO3, with organic compounds and inorganic nitrate coated on the surface. It has a low reactivity towards SO2 with a true uptake coefficient, 5.767�10�6, which limits the conversion of SO2 to sulfate during dust storm periods. The low reactivity also means that the heterogeneous reactions of SO2 in both dry and humid air conditions have little effect on the hygroscopic behavior of the dust particles.

Abstract: Large uncertainty among the measured uptake coefficients of O3 on soot highlights the importance of the sources and chemical structures of soot samples in this reaction. Soot samples with different microstructures were prepared by combusting n-hexane under controlled conditions. Their reactivities to O3 were further investigated using in situ Raman spectroscopy. The fuel/oxygen ratio in the combustion experiments not only affected the diameter of the primary particles, but also influenced the micro-chemical structure of soot. Average diameters of soot particles decreased with the decreasing fuel/oxygen ratio. Compared to the �fuel-rich� flame soot, the �fuel-lean� flame soot showed lower structural uniformity with higher disordered carbon content at the graphene layer edges (D1 band) and the surface graphene layers (D2 band) and the amorphous carbon content (D3 band). This disordered carbon was identified as the reactive component for the ozonization of both the �fuel-rich� and �fuel-lean� flame soot samples. The kinetics study demonstrated that the disordered carbon at the surface graphene layers was more active than that at the graphene layer edges in one sample, and the reactivity of these two microstructures types to O3 in the �fuel-rich� flame soot was higher than that in the �fuel-lean� flame soot.

Abstract: Atmospheric particulate matters, which play important roles in global climate and regional air quality, are one of the most important constitutes of atmosphere. However, the climatic and environmental effects of atmospheric particulate matters (APM) have larger uncertainties because of their regional characteristics, short lifetime, and various compositions in atmosphere. On the other hand, heterogeneous reactions taking place on APMs further amplify these uncertainties because these reactions can affect not only the balance between the sources and sinks of trace gases, but also the surface composition, morphology and the relevant hygroscopic and optical properties of APMs. In this paper, the research progresses about the important atmospheric heterogeneous reactions and their environmental effects were reviewed, the future work relating to atmospheric heterogeneous reactions was also proposed.

Abstract: The heterogeneous reactions of NO2 with anthracene adsorbed on SiO2 and MgO were investigated under dark conditions at 298 K using DRIFTS, GCMS, and UV-Vis. The pseudo-first-order rate constants of anthracene on SiO2 and MgO were obtained by fitting the exponential decay of adsorbed PAH concentrations versus reaction time. The reaction on SiO2 was almost two times faster than on MgO when the concentration of NO2 was 3.69 x 10(12) molecules cm(-3). Both 9-nitroanthracene and 9,10-anthraquinone were the products of the nitration of anthracene adsorbed on SiO2 whereas 9,10-anthraquinone was the only product formed by NO2 reaction with anthracene adsorbed on MgO. These results suggest that mineral oxides not only control the reaction kinetics of PAHs with NO2 but also alter the reaction pathway for the heterogeneous reaction of PAHs with NO2. The difference in the heterogeneous reactivity of NO2 with anthracene adsorbed on SiO2 and MgO was ascribed to the formation of HNO3 on SiO2, which can catalyze the nitration of PAHs by NO2. Due to the formation of nitro-anthracene and oxy-anthracene, the heterogeneous reactions of NO2 with anthracene also altered the optical properties of the mineral oxides on which anthracene were adsorbed. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract: Soot aerosols are ubiquitous in the atmosphere and play an important role in global and regional radiative balance and climate. Their environmental impact, however, greatly depends on their structure, composition, particle size, and morphology. In this study, the structural changes of a model soot (Printex U) during a heterogeneous reaction with 80 ppm O3 at 298 K were investigated using in situ Raman spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and transmission electron microscopy (TEM). Hygroscopic changes due to heterogeneous reaction with O3 were also studied by water sorption analyzer. The consumption of amorphous carbon (D3 band) and disordered graphitic lattice (D4 band) of soot by ozonization was confirmed by the decrease in the full widths at half maximum and their relative integrated intensities (percentages of integrated areas). Oxygen containing surface species including ketone, lactone, and anhydride were also observed in Raman and IR spectra of ozonized soot. The ozonized soot showed more compacted aggregates with a smaller average diameter of primary particles (29.9 7.7 nm) and a larger fractal dimension (1.81 0.08) when compared with fresh soot (36.9 9.4 nm, and 1.61 0.10). The ozonization reaction leads to an enhancement of hygroscopicity of soot due to the decrease in particle diameter and the formation of oxygen containing surface species.

Abstract:

Abstract: Soot aerosols are ubiquitous in the atmosphere and play an important role in global and regional radiative balance and climate. Their environmental impact, however, greatly depends on their structure, composition, particle size, and morphology. In this study, the structural changes of a model soot (Printex U) during a heterogeneous reaction with 80 ppm O-3 at 298 K were investigated using in situ Raman spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and transmission electron microscopy (TEM). Hygroscopic changes due to heterogeneous reaction with O-3 were also studied by water sorption analyzer. The consumption of amorphous carbon (D3 band) and disordered graphitic lattice (D4 band) of soot by ozonization was confirmed by the decrease in the full widths at half maximum and their relative integrated intensities (percentages of integrated areas). Oxygen containing surface species including ketone, lactone, and anhydride were also observed in Raman and IR spectra of ozonized soot. The ozonized soot showed more compacted aggregates with a smaller average diameter of primary particles (29.9 +/- 7.7 nm) and a larger fractal dimension (1.81 +/- 0.08) when compared with fresh soot (36.9 +/- 9.4 nm, and 1.61 +/- 0.10). The ozonization reaction leads to an enhancement of hygroscopicity of soot due to the decrease in particle diameter and the formation of oxygen containing surface species.

Abstract: To further understand the role of substrates on the heterogeneous reactions of polycyclic aromatic hydrocarbons, the reactions of ozone with anthracene adsorbed on different mineral oxides (SiO(2), alpha-Al(2)O(3) and alpha-Fe(2)O(3)) and on Teflon disc were investigated in dark at 20 degrees C. No reaction between ozone and anthracene on Teflon disc was observed when the ozone concentration was similar to 1.18 x 10(14) molecules cm(-3). The reactions on mineral oxides exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate constant (k(1.obs)) displayed a Langmuir-Hinshelwood dependence on the gas-phase ozone concentration. The adsorption equilibrium constants for ozone (K(O3)) on SiO(2)-1, SiO(2)-2, alpha-Al(2)O(3) and alpha-Fe(2)O(3) were (0.81 +/- 0.26) x 10(-15) cm(3), (2.83 +/- 1.17) x 10(-15) cm(3), (2.48 +/- 0.77) x 10(-15) cm(3) and (1.66 +/- 0.45) x 10(-15) cm(3), respectively; and the maximum pseudo-first-order rate constant (k(1.max)) on these oxides were (0.385 +/- 0.058) s(-1), (0.101 +/- 0.0138) s(-1), (0.0676 +/- 0.0086) s(-1) and (0.0457 +/- 0.004) s(-1), respectively. Anthraquinone was identified as the main surface product of anthracene reacted with ozone. Comparison with previous research and the results obtained in this study suggest that the reactivity of anthracene with ozone and the lifetimes of anthracene adsorbed on mineral dust in the atmosphere are determined by the nature of the substrate. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract: In this study the heterogeneous uptake of carbonyl sulfide (OCS) onto kaolinite was investigated using a Knudsen cell reactor within the temperature range of 220-330 K. Results showed that OCS could only be adsorbed at Al-OH sites on kaolinite reversibly within this temperature region. The initial true uptake coefficient was measured to be (1.68 +/- 0.12) x 10(-7) at 300 K. It showed no observable dependence on the pressure of OCS, while it varied significantly with temperature, and can be expressed as gamma(t) = exp(1293/T - 20.0)/[1 + exp(1293/T - 20.0]. The values of Delta H(obs) and Delta S(obs) during the adsorption process were -10.7 +/- 1.1 kJ mol(-1) and -166.3 +/- 4.5 J K(-1) mol(-1), respectively. The activation energy for desorption of OCS on kaolinite was 19.5 +/- 1.1 kJ mol(-1). The uptake of OCS by kaolinite owing to reversible physisorption may have little influence on the sink of OCS in the atmosphere.