| Atmospheric aerosols play key roles in a variety of environmental issues including air quality, sky visibility, public health, and climate change. The quantitative study of hygroscopicity, nucleation, mass transfer, interface equilibrium, and interface reaction of aerosol can help people to understand the climate change, human health, atmospheric pollution and so on. In this study, FTIR is used to measure the thermodynamic(hygroscopicity and gas-liquid equilibrium) and dynamic process(nucleation, mass transfer, and interface reaction) of various organic and inorganic. The following is the main conclusion.1. A novel approach based on a combination of a pulse RH controlling system and a rapid scan vacuum FTIR spectrometer was utilized to investigate dynamic hygroscopicity of two atmospheric aerosols: ammonium sulfate((NH4)2SO4) and magnesium sulfate(Mg SO4). In pulse RH process, rapid-scan infrared spectra of water vapor and aerosols were obtained to determine relative humidity(RH) in sample cell and hygroscopic property of aerosols with a sub-second time resolution. Under pulsed RH conditions, water mass transport to and from(NH4)2SO4 particles was equilibrium. Heterogeneous nucleation rates of(NH4)2SO4 were, for the first time, measured under low RH conditions(< 35%RH) and high super-saturation((ln S)-2 < 0.4). Studies of Mg SO4 aerosols revealed that water mass transport may limited by different processes depending on RHs, i.e., surface(40%< RH <52%), and bulk phase(RH<40%). Furthermore, we are also the first to report water diffusion constants in micron size Mg SO4 aerosols at very low RHs: 7.6×10-17 m2 s-1(30% RH), 7.2×10-17 m2 s-1(20% RH), and 4.3×10-17 m2 s-1(0% RH).2. Temperature-dependent Henry’s law constants, key parameters in the atmospheric models to account for mass transfer, describe the relationship between the solubility of a gas and its partial pressure above the liquid and are often unavailable due to the lack of convenient measurement method. In the present work, we investigated the gas-liquid distribution of atmospheric volatility and semi-volatile organic compounds in solvent using a bubble column technique combined with gas chromatographic(GC) / infrared spectroscopy(FTIR). Volatility and semi-volatile organic solutes include hydrocarbons(isoprene, limonene, and α-pinene), alcohols(linalool), amines(1-propylamine, 2-butylamine, trimethylamine, triethylamine, bi-n-propylamine, allylamine, and 4-methymorpholine). We reported Henry’s law constants(KH) over a range of temperatures relevant to the lower atmosphere(278-298 K) for the first time. The measurement results of KH values for hydrocarbons, alcohols, and amines were in order of magnitudes of 10-2, 101, and 101-103(in neutral or meta-acid conditions, KH p H=5.6 =104-108) mol L-1 atm-1, respectively. The effect of solvent indicated the KH values decreased with increasing ionic strengths due to the salt-out effect, and KH values increased in organic solvent due to the strong interaction between organic solute and solvent. With the help of above KH values, the solution enthalpy and characteristic time to establish gas-droplet equilibrium were also obtained. In addition, The fraction for these compounds in stratocumulus and cumulonimbus clouds at 278 K were also estimated in this work. The result indicated that hydrocarbons and alcohols preferred to stay in gas phase, while amines preferred to stay in condensed phase.3. The ozone initiated heterogeneous oxidation of erucic acid(EA) thin film was investigated using a flow system combined with attenuated total reflection infrared spectroscopy(ATR-IR). Pseudo-first-order rate constants, kapp, and overall reactive uptake coefficients, γ, were obtained. Results showed that the measured kapp was found to display a Langmuir-Hinshelwood dependence on ozone concentration. In addition, both the kapp and the γ values presented very strong temperature dependences(~ two orders of magnitude) over the temperature range; in contrast, they only slightly increased with increasing RH values from 0-80%. According to the kapp values as a function of temperature, activation energy for the heterogeneous reaction was estimated to be 80.6 k J mol-1. Moreover, hygroscopic properties of EA thin film before and after exposure to ozone were also studied. Based on the hygroscopicity data, the insignificant RH effect on reaction kineticsis probably due to the relatively weak water uptake by the oxidized EA thin films. |
