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Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene ‘scavenges’ hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production). Adding reactive gases such as isoprene to mixtures lowers the production of secondary organic aerosol in the atmosphere, thus reducing the atmospheric particulate burden, with implications for human health and climate.

The dynamic monitor is considerably valuable to thoroughly understand the self-assembly process and is beneficial for the effective control of ordered colloidal crystal. In this study, the three-dimensional ordered colloidal crystals are fabricated through thermally assisted self-assembly, which are in situ monitored by fiber-optic spectrometer and micro-digital technology. The assembly process occurs layer by layer from top to bottom. The evaporated water-dragged microspheres assemble into the final close-packing face-centered cubic arrangement. During self-assembly, water between microspheres is gradually replaced by air, resulting in the change of effective refractive index, as well as evident color change and blue shifting of wavelength peaks. The effect of self-assembly temperature (60, 70, 80, and 90 °C) and polystyrene microspheres concentration (4, 6, 8, and 10 wt%) are both investigated on the basis of dynamic monitoring of the thermally assisted assembly of colloidal crystal structural color. As confirmed, the emulsion of 10% mass fraction self-assembled at 70 °C can obtain a superior color film structure.

Investigating the heterogeneous reaction on individual atmospheric particles is important because it approximates actual atmospheric conditions and can aid in reducing artifacts in elucidating real mechanisms and processes, and determining real kinetic parameters of the atmosphere relevance. This study developed a Raman microspectrometry method to investigate heterogeneous reactions on individual particles. The method was applied to the reaction of NO2 with individual CaCO3 particles. It was demonstrated that Raman microspectrometry can obtain information on both chemical composition and microscopic morphology at the same time, as well as information on chemical characteristics, such as the phase, which is useful for studying reaction processes. Raman spectra of individual particles deposited on a substrate showed no interference by morphological resonance, which is helpful for obtaining high-quality spectra. Moreover, Raman microspectrometry was compared with other methods for investigating heterogeneous reactions on individual particles and was found to have several advantageous characteristics.

Urban and regional air pollutions are characterized by high concentrations of secondary pollutants such as photo-oxidants (mainly ozone) and fine particulate matter, which are formed through chemical reactions of the primary pollutants emitted from various sources. The accumulation of these pollutants under stagnant meteorological conditions results in the formation of gray haze, reducing visibility and causing major impacts on human health and climate. In an air pollution complex, the coexistence of high concentrations of primary and secondary gaseous and particulate pollutants provides a large amount of reactants for heterogeneous reactions on the surface of fine particles; these reactions change the oxidizing capacity of the atmosphere, as well as chemical compositions along with the physicochemical and optical properties of particulate matter, thereby accelerating formation of the air pollution complex and gray haze. Using in situ technologies, such as diffuse reflectance infrared Fourier-transform spectroscopy and single-particle Raman spectroscopy, we systematically investigated the reaction kinetics and mechanisms of gaseous pollutants (i.e., NO2, SO2, O3, and formaldehyde) on the surfaces of the major components of atmospheric particles such as CaCO3, kaolinite, montmorillonite, NaCl, sea salt, Al2O3, and TiO2. We found that the main reaction products were sulfate, nitrate, or formate, which can change the hygroscopicity and light extinction parameters of those particles significantly. By analyzing the reaction kinetics of these heterogeneous reactions, we identified synergetic mechanisms of the three ternary reaction systems, i.e., NO2-particles-H2O, SO2-particles-O3, and organics/SO2-particles-UV illumination. These synergetic mechanisms can provide experimental and theoretical bases for understanding the feedback mechanisms and nonlinear processes in the formation of an air pollution complex and gray haze.

To understand how NO2 reacts with sea salt particles in the atmosphere of Mega-cities in coastal zones, the heterogeneous reaction of NO2 on the surface of wet sea salt was investigated with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC). Kinetic measurements indicated that nitrate formation on sea salt was second order in NO2 concentration and reactive uptake coefficients were (5.51 ± 0.19) × 10−7 and 1.26 ± 10−6 respectively under 0% and 20% relative humidity (RH) at NO2 molecular concentration of 1.96 × 1015 mol/cm3. The results showed that liquid water was formed at the site of MgCl2·6H2O, CaCl2·2H2O on the surface of sea salt and made the reaction more sustainable by releasing hydrated water and absorbing water from air even under a low RH (⩽ 30%). Therefore, pure NaCl particles should not be used to represent sea salt in studies of the heterogeneous reaction with NO2.