Search

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.

Water-soluble low-molecular-weight dicarboxylic acids (DCAs) and corresponding salts are ubiquitous in the atmosphere. They could efficiently form chelates with iron in atmospheric particles, which could be photoexcited to generate a series of strong oxidants, and have profound impacts on atmospheric chemistry. However, the influences of iron–DCAs complexes on the heterogeneous uptake of atmospheric trace gases are unclear. In this study, the effects of dominant dicarboxylic acid salts (including oxalate, malonate, and succinate) on the heterogeneous SO2 conversion with hematite nanoparticles were systematically investigated using film flow reaction and in situ DRIFTs experiments. It was found that a trace amount of DCA salts could significantly accelerate sulfate formation under solar light illumination. Additionally, similar results were also observed on the Arizona test dust, a proxy of authentic mineral dusts. Moreover, the iron solubility was increased owing to the effects of oxalate complexation, especially under light irradiation. Furthermore, the reaction mechanisms for the enhanced SO2 uptake and iron dissolution in the presence of DCA salts were proposed, and atmospheric environmental implications were discussed.

The heterogeneous reaction of SO2 on mineral dust surfaces is generally considered as an important chemical pathway for secondary sulfate formation in the troposphere. To this day, there are no reported studies that assess the impact of atmospheric CO2 in sulfate production on mineral dust surfaces. In this work, we investigate the impact of CO2 on SO2 uptake on dust proxy aluminum oxide particles using a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). CO2 is demonstrated to suppress the heterogeneous oxidation of SO2 on alpha-Al2O3. Compared to that measured in the CO2-free case, the uptake coefficient is decreased by nearly 57% when Al2O3 particles are exposed to the gas flow with atmospheric CO2 at a relative humidity (RH) of 25%. It is also found that there is a balance between the yield of active moiety −OH provided by Al(OH)3(CO)(OH)2 clusters and the loss of basic hydroxyl group on aluminum oxide surfaces blocked by CO2-derived (bi)carbonate species. This work, for the first time, reveals a negative effect of atmospheric CO2 on the sulfate formation, which potentially decreases solar-radiation scattering and further exacerbates global warming.

Atmospheric photochemistry is widely regarded as an important pathway for SO2 oxidation. The influence of irradiation intensity, especially photochemistry under weak sunlight during heavy haze events is not known. This work investigates the irradiation-intensity-dependence of the dust-related heterogeneous process using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ex situ flow reaction. Illumination of the particles alters the surface oxygen species, and further accelerates the significant oxidation of sulfite species to sulfate products. The sulfate formation rate grows rapidly from the dark state to faint irradiation, while it becomes insensitive to irradiation intensity variation under strong illumination. According to the photo-electrochemical tests and concentration dependence experiments, this interesting phenomenon can be interpreted by the presence of excess SO2 under weak sunlight and sufficient photoinduced active species (PAS) under strong illumination. This uneven promotion effect is beneficial for explaining the sulfate burst under faint sunlight during heavy haze events. More significantly, the uptake of SO2 accounts for the increase of acidic species and the decrease of adsorbed water on the particle surface, thus elevating the particle acidity. Under these circumstances, the dissolution of zinc oxide (ZnO) takes place, and results in diverse principal products varying with the illumination condition, e.g. ZnSO3 under weak sunlight while ZnSO4 under strong irradiation. In general, photochemistry has profound impacts on atmospheric sulfur cycling, as well as the cycle of metal elements. The irradiation intensity dependent effects imply the raising uncertainty in the current air quality models.

Carbon dioxide is considered an inert gas that rarely participates in atmospheric chemical reactions. However, 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 regarding its effect on sulfate formation. Present work demonstrates that SO2 uptake coefficient is enhanced by 17 times on mineral dust particles driven by CO3∙-. It can be produced through two routes over mineral dust surfaces: i) hydroxyl radical + CO32-; ii) holes (h+) + CO32-. Employing a suite of laboratory investigations of sulfate formation in the presence of carbonate radical on the model and authentic dust particles, 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 new role of carbonate radical in atmospheric chemistry is elucidated.

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 two 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 sub-micron 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 towards detecting nanoscale plastic particles that may cause toxic effects to mammalian and aquatic life when present in high concentrations.

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 rea...

Sulfite is recently found to be promising in enhancing photocatalytic pollutants degradation, and it is a byproduct from flue gas desulfuration process. Herein, 4-chlorophenol (4-CP) photodegradation was systematically investigated in a sulfite mediated system with g-C3N4 as photocatalyst. The degradation efficacy was improved by about 3 times with addition of 25 mM Na2SO3. The dominant responsible reactive oxygen species for chlorophenols remediation in the presence of sulfite included O2·-, SO3·-, and SO4·- as confirmed by radical quenching experiments and electron spin resonances technology. In-situ DRIFTs results indicated the improved cleavage of C-Cl and C-H bonds with the simultaneous formation of C O and C C bonds when bisulfite was added. Degradation intermediates such as 4-chlorocatechol, hydroquinone, and muconic acid were detected by HPLC-MS. Furthermore, the photodegradation mechanisms were discussed in the presence of sulfite. Other chlorophenols (phenol, 2-CP, 2,4-DCP, and their mixture) were also efficiently removed in the system, suggesting that sulfite could be universally applied in photocatalytic wastewater purification.

Despite the increased awareness of heterogeneous reaction on mineral dust, the knowledge of how the intensity of solar irradiation influences the photochemistry activity remains a crucially important part in atmospheric research. Relevant studies have not seriously discussed the photochemistry under weak sunlight during haze, and thus ignored some underlying pollution and toxicity. Here, we investigated the heterogeneous formation of nitrate and nitrite under various illumination conditions by laboratory experiments and field observations. Observed by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), water-solvated nitrate was the main surface product, followed by other species varying with illumination condition. The growth of nitrate formation rate tends to be slow after the initial fast with increasing light intensity. For example, the geometric uptake coefficient (γgeo) under 30.5 mW/cm2 (5.72 × 10−6) has exceeded the 50 % of that under 160 mW/cm2 (1.13 × 10−5). This case can be explained by the excess NO2 adsorption under weak illumination while the excess photoinduced active species under strong irradiation. Being negatively associated with nitrate (R2 = 0.748, P

The rapid sulfate formation is a crucial factor determining the explosive growth of fine particles and the frequent occurrence of severe haze events in China. Recent field observations also show that brown carbon is one of the most critical components in aerosol particles sampled during haze episodes. To this day, there is limited knowledge that accesses the role of brown carbon in atmospheric chemistry. In fact, these carbonaceous particulate matters, mainly derived from forest fires, biomass burning, and biogenic release, can act as photosensitizers and produce varieties of active intermediates to alter oxidation capacity. Experimental results in this work provide evidence that hydroxyl radical (∙OH) stems from brown carbon proxies fulvic acid /humic acid (FA/HA) upon irradiation, leading to rapid SO2 oxidation on brown carbon particles in the atmosphere. Further correlation analyses for sulfate formation and chromophore properties of 12 model compounds demonstrate that brown carbon particles with higher aromaticity and E2/E3 (the ratio of absorbance at 254 nm to that at 365 nm) would facilitate ∙OH production and SO2 photo-oxidation. Uptake coefficient measurements and sulfate production rate estimation indicate that brown carbon could gain importance in atmospheric SO2 oxidation. A better understanding of SO2 uptake kinetics on brown carbon surfaces favors in defining new regulations to improve air quality and reduce the harmful effects of haze events on resident health and the environment.