Micro- and nanoplastics are considered one of the top pollutants that threaten the environment, aquatic life, and mammalian (including human) health. Unfortunately, the development of uncomplicated but reliable analytical methods that are sensitive to individual microplastic particles, with sizes smaller than 1 μm, remains incomplete. Here, we demonstrate the detection and identification of (single) micro- and nanoplastics by using surface-enhanced Raman spectroscopy (SERS) with Klarite substrates. Klarite is an exceptional SERS substrate; it is shaped as a dense grid of inverted pyramidal cavities made of gold. Numerical simulations demonstrate that these cavities (or pits) strongly focus incident light into intense hotspots. We show that Klarite has the potential to facilitate the detection and identification of synthesized and atmospheric/aquatic microplastic (single) particles, with sizes down to 360 nm. We find enhancement factors of up to 2 orders of magnitude for polystyrene analytes. In addition, we detect and identify microplastics with sizes down to 450 nm on Klarite, with samples extracted from ambient, airborne particles. Moreover, we demonstrate Raman mapping as a fast detection technique for submicron microplastic particles. The results show that SERS with Klarite is a facile technique that has the potential to detect and systematically measure nanoplastics in the environment. This research is an important step toward detecting nanoscale plastic particles that may cause toxic effects to mammalian and aquatic life when present in high concentrations.

Water soluble low-molecular-weight dicarboxylic acids (DCAs) and corresponding salts are ubiquitous in the atmosphere. They could efficiently form chelate with iron in atmospheric particles, which could be photoexcited to generate...

Abstract. Carbon dioxide is considered an inert gas that rarely participates in atmospheric chemical reactions. Nonetheless, we show here that CO2 is involved in some important photo-oxidation reactions in the atmosphere through the formation of carbonate radicals (CO3⚫-). This potentially active intermediate CO3⚫- is routinely overlooked in atmospheric chemistry concerning its effect on sulfate formation. The present work demonstrates that the SO2 uptake coefficient is enhanced by 17 times on mineral dust particles driven by CO3⚫-. Importantly, upon irradiation, mineral dust particles are speculated to produce gas-phase carbonate radical ions when the atmospherically relevant concentration of CO2 presents, thereby potentially promoting external sulfate aerosol formation and oxidative potential in the atmosphere. Employing a suite of laboratory investigations of sulfate formation in the presence of carbonate radicals on the model and authentic dust particles, ground-based field measurements of sulfate and (bi)carbonate ions within ambient PM, together with density functional theory (DFT) calculations for single electron transfer processes in terms of CO3⚫--initiated S(IV) oxidation, a novel role of carbonate radical in atmospheric chemistry is elucidated.

The heterogeneous reaction of SO2 on manganese oxides is poorly understood. By means of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), this study investigated the reaction kinetics and product fractions on four types of manganese oxides. Due to the positive and negative moisture impacts, 68% RH (relative humidity) becomes the most favorable condition for the uptake of SO2. Mn3O4 shows the greatest uptake capacity of SO2, followed by MnO2 and Mn2O3, with that of MnO being the weakest. Curve-fitting procedures were undertaken to further dissect the product spectra. Increased RH facilitates the physical adsorption of SO2 and generally weakens the oxidation capacity of manganese oxides. The oxidation ability is greatest for MnO, followed by MnO2 and Mn3O4, with that of Mn2O3 being the weakest. Additionally, the particle acidity (pH) was estimated by the ionization equilibrium of sulfurous acid and the relative contributions of S­(IV) species. MnO and Mn3O4 become more acidic as RH increases while Mn2O3 and MnO2 are the most acidic at 50% RH, which can be attributed to the different uptake capacities of SO2 and H2O on each sample. Overall, for the heterogeneous reaction of SO2 on manganese oxides, both particle type and moisture condition influence the reaction kinetics and product fractions. This work improves the understanding of the heterogeneous process on atmospheric manganese-rich particles.