Search

Organicacids in the atmosphere are ubiquitous and are often correlatedwith mineral dust aerosol. Heterogeneous chemistry and the uptakeof organic acids on mineral dust particles can potentially alter theproperties of the particle. In this study, heterogeneous uptake andreaction of formic acid, HCOOH, the most abundant carboxylic acidpresent in the atmosphere, on oxide and clays of the most abundantelements, Si and Al, present in the Earth’s crust are investigatedunder dry and humid conditions. In particular, quantitative adsorptionmeasurements using a Quartz Crystal Microbalance (QCM) coupled withspectroscopic studies using Attenuated Total Reflection Fourier TransformInfrared (ATR-FTIR) spectroscopy are combined to allow for both quantificationof the amount of uptake and identification of distinct adsorbed speciesformed on silica, alumina, and kaolinite particle surfaces at 298K. These oxides and clay particles show significant differences inthe extent and speciation of adsorbed HCOOH due to inherent differencesin surface −OH group reactivity. Adsorbed water, controlledby relative humidity, can increase the irreversible uptake of formicacid. Interestingly, the resulting layer of adsorbed formate on theparticle surface decreases the particle hydrophilicity thereby decreasingthe amount of water taken up by the surface as measured by QCM. Atmosphericimplications of this study are discussed. [ABSTRACT FROM AUTHOR]

It is well-known that chlorine active species (e.g.,Cl2, ClONO2, ClONO) can form from heterogeneousreactions between nitrogen oxides and hydrogen chloride on aerosolparticle surfaces in the stratosphere. However, less is known about these reactions in the troposphere. In this study, a potentialnew heterogeneous pathway involving reaction of gaseous HCl and HNO3on aluminum oxide particle surfaces, a proxy for mineral dust in thetroposphere, is proposed. We combine transmission Fourier transforminfrared spectroscopy with X-ray photoelectron spectroscopy to investigatechanges in the composition of both gas-phase and surface-bound speciesduring the reaction under different environmental conditions of relativehumidity and simulated solar radiation. Exposure of surface nitrate-coatedaluminum oxide particles, from prereaction with nitric acid, to gaseousHCl yields several gas-phase products, including ClNO, NO2, and HNO3, under dry (RH < 1%) conditions. Under humidmore conditions (RH > 20%), NO and N2O are the only gas productsobserved. The experimental data suggest that, in the presence of adsorbedwater, ClNO is hydrolyzed on the particle surface to yieldNO and NO2, potentially via a HONO intermediate. NO2undergoes further hydrolysis via a surface-mediated process,resulting in N2O as an additional nitrogen-containing product.In the presence of broad-band irradiation (λ > 300 nm) gas-phaseproducts can undergo photochemistry, e.g., ClNO photodissociates to NO and chlorine atoms. The gas-phase product distribution also depends on particlemineralogy (Al2O3vs CaCO3) and the presence of other coadsorbed gases (e.g., NH3). These newly identified reaction pathways discussedhere involve continuous production of active ozone-depleting chlorineand nitrogen species from stable sinks such as gas-phase HCl and HNO3as a result of heterogeneous surface reactions. Given thataluminosilicates represent a major fraction of mineral dust aerosol,aluminum oxide can be used as a model system to begin to understandvarious aspects of possible reactions on mineral dust aerosol surfaces. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is an important greenhouse gas and a primary cause of stratospheric ozone destruction. Despite its importance, there remain missing sources in the N2O budget. Here we report the formation of atmospheric nitrous oxide from the decomposition of ammonium nitrate via an abiotic mechanism that is favorable in the presence of light, relative humidity and a surface. This source of N2O is not currently accounted for in the global N2O budget. Annual production of N2O from atmospheric aerosols and surface fertilizer application over the continental United States from this abiotic pathway is estimated from results of an annual chemical transport simulation with the Community Multiscale Air Quality model (CMAQ). This pathway is projected to produce 9.3+0.7/-5.3 Gg N2O annually over North America. N2O production by this mechanism is expected globally from both megacities and agricultural areas and may become more important under future projected changes in anthropogenic emissions. [ABSTRACT FROM AUTHOR]

The article provides information on the photochemistry of adsorbed nitrate which is monitored with transmission Fourier Transform Infrared (FTIR) spectroscopy by using nitric acid-reacted alumina. It states that adsorbed nitrate undergoes photochemical reaction to yield several gas-phase products and coadsorbed water and molecular oxygen. It discusses the photolysis time function and gas-phase product distribution followed by broadband irradiation.

Mechanochemical synthesis is emerging as an environmentally friendly yet efficient approach to preparing metal-organic frameworks (MOFs). Herein, we report our systematic investigation on the mechanochemical syntheses of Group 4 element-based MOFs. The developed mechanochemistry allows us to synthesize a family of Hf 4 O 4 (OH) 4 (OOC) 12 -based MOFs. Integrating [Zr 6 O 4 (OH) 4 (OAc) 12 ] 2 and [Hf 6 O 4 (OH) 4 (OAc) 12 ] 2 under the mechanochemical conditions leads to a unique family of cluster-precise multimetallic MOFs that cannot be accessed by the conventional solvothermal synthesis. Extensive efforts have not yielded an effective pathway for preparing Ti IV -derived MOFs, tentatively because of the relatively low Ti-O bond dissociation energy.

The surface photochemistry of nitrate, formed from nitric acid adsorption, on hematite (α-Fe2O3) particle surfaces under different environmental conditions is investigated using X-ray photoelectron spectroscopy (XPS). Following exposure of α-Fe2O3 particle surfaces to gas-phase nitric acid, a peak in the N1s region is seen at 407.4 eV; this binding energy is indicative of adsorbed nitrate. Upon broadband irradiation with light (λ > 300 nm), the nitrate peak decreases in intensity as a result of a decrease in adsorbed nitrate on the surface. Concomitant with this decrease in the nitrate coverage, there is the appearance of two lower binding energy peaks in the N1s region at 401.7 and 400.3 eV, due to reduced nitrogen species. The formation as well as the stability of these reduced nitrogen species, identified as NO(-) and N(-), are further investigated as a function of water vapor pressure. Additionally, irradiation of adsorbed nitrate on α-Fe2O3 generates three nitrogen gas-phase products including NO2, NO, and N2O. As shown here, different environmental conditions of water vapor pressure and the presence of molecular oxygen greatly influence the relative photoproduct distribution from nitrate surface photochemistry. The atmospheric implications of these results are discussed.

Metal-containing nanorods are of great interest from a number of technological perspectives, and they are also present in the natural environment. Here we show that dissolution, both rate and extent, is greater for rod-shaped alpha-FeOOH particles on the nanoscale at pH 2 relative to microrods. However, when nanorods aggregate, either at lower pH and/or high ionic strength, dissolution is either completely quenched or severely quenched, by orders of magnitude. Furthermore, nanorod suspensions are less stable compared to microrod suspensions, resulting in nanorod aggregation under conditions where microrods stay fairly well dispersed. Although recent evidence suggests that particle size is a controlling factor in the solubility of iron oxides, a fundamental understanding of the influence of particle size is just beginning to emerge. The results presented here not only address some of the complexities of size-dependent dissolution of metal-containing nanorods in solution, they also contribute to our understanding of the factors that can influence Fe-mobilization in the global environment.