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Based on density functional theory calculations we present a study of the gaseous oxidation of SO2 to SO3 by an anionic ODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)n cluster, n = 0-5. The configurations of the most relevant reactants, transition states, and products are discussed and compared to previous findings. Two different classes of transition states have been identified. One class is characterised by strong networks of hydrogen bonds, very similar to the reactant complexes. The other class is characterised by sparser structures of hydration water and is stabilised by high entropy. At temperatures relevant for atmospheric chemistry, the most energetically favourable class of transition states vary with the number of water molecules attached. A kinetic model is utilised, taking into account the most likely outcomes of the initial SO2Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)n collision complexes. This model shows that the reaction takes place at collision rates regardless of the number of water molecules involved. A lifetime analysis of the collision complexes supports this conclusion. Hereafter, the thermodynamics of water and O2 condensation and evaporation from the product SDue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. O2(H2O)n cluster is considered and the final products are predicted to be O2SDue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and O2SDue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)1. The low degree of hydration is rationalised through a charge analysis of the relevant complexes. Finally, the thermodynamics of a few relevant reactions of the O2SO-3 and O2SDue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)1 complexes are considered [ABSTRACT FROM AUTHOR]

Sulphuric acid is an important factor in aerosol nucleation and growth. It has been shown that ions enhance the formation of sulphuric acid aerosols, but the exact mechanism has remained undetermined. Furthermore some studies have found a deficiency in the sulphuric acid budget, suggesting a missing source. In this study the production of sulphuric acid from SO2 through a number of different pathways is investigated. The production methods are standard gas phase oxidation by OH radicals produced by ozone photolysis with UV light, liquid phase oxidation by ozone, and gas phase oxidation initiated by gamma rays. The distributions of stable sulphur isotopes in the products and substrate were measured using isotope ratio mass spectrometry. All methods produced sulphate enriched in 34S and we find a δ34S value of 8.7±0.4‰ (1 standard deviation) for the UV-initiated OH reaction. Only UV light (Hg emission at 253.65 nm) produced a clear non-mass-dependent excess of 33S. The pattern of isotopic enrichment produced by gamma rays is similar, but not equal, to that produced by aqueous oxidation of SO2 by ozone. This, combined with the relative yields of the experiments, suggests a mechanism in which ionising radiation may lead to hydrated ion clusters that serve as nanoreactors for S(IV) to S(VI) conversion. [ABSTRACT FROM AUTHOR]

Using cloud data from MODIS we investigate the response of cloud microphysics to sudden decreases in galactic cosmic radiation - Forbush decreases - and find responses in effective emissivity, cloud fraction, liquid water content, and optical thickness above the 2-3 sigma level 6-9 days after the minimum in atmospheric ionization and less significant responses for effective radius and cloud condensation nuclei (<2 sigma). The magnitude of the signals agree with derived values, based on simple equations for atmospheric parameters. Furthermore principal components analysis gives a total significance of the signal of 3.1 sigma. We also see a correlation between total solar irradiance and strong Forbush decreases but a clear mechanism connecting this to cloud properties is lacking. There is no signal in the UV radiation. The responses of the parameters correlate linearly with the reduction in the cosmic ray ionization. These results support the suggestion that ions play a significant role in the life-cycle of clouds. [ABSTRACT FROM AUTHOR]

Based on density functional theory calculations we present a study of the gaseous oxidation of SO2 to SO3 by an anionic Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed (H2O)n cluster, n = 0-5. The configurations of the most relevant reactants, transition states, and products are discussed and compared to previous findings. Two different classes of transition states have been identified. One class is characterized by strong networks of hydrogen bonds, very similar to the reactant complexes. The other class is characterized by loose structures of hydration water and is stabilized by high entropy. At temperatures relevant for atmospheric chemistry, the most energetically favorable class of transition states vary with the number of water molecules attached. A kinetic model is utilized, taking into account the most likely outcomes of the initial SO2 Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed (H2O)n collision complexes. This model shows that the reaction takes place at collision rates regardless of the number of water molecules involved. A lifetime analysis of the collision complexes supports this conclusion. Hereafter, the thermodynamics of water and O2 condensation and evaporation from the product Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed O2(H2O)n cluster is considered and the final products are predicted to be O2Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and O2Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed(H2O)1. The low degree of hydration is rationalized through a charge analysis of the relevant complexes. Finally, the thermodynamics of a few relevant reactions of the O2Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed and O2Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed(H2O)1 complexes are considered. [ABSTRACT FROM AUTHOR]

An ab initio study of gaseous clusters of O Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and O Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. with water is presented. Based on thorough scans of configurational space, we determine the thermodynamics of cluster growth. The results are in good agreement with benchmark computational methods and existing experimental data. We find that anionic O Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O) n and O Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)n clusters are thermally stabilized at typical atmospheric conditions for at least n = 5. The first 4 water molecules are strongly bound to the anion due to delocalization of the excess charge while stabilization of more than 4 H2O is due to normal hydrogen bonding. Although clustering up to 12 H2O, we find that the O2 and O3 anions retain at least ca. 80 % of the charge and are located at the surface of the cluster. The O Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and O speicies are thus accessible for further reactions. We consider the distributions of cluster sizes as function of altitude before finally, the thermodynamics of a few relevant cluster reactions are considered. [ABSTRACT FROM AUTHOR]

An ab initio study of gaseous clusters of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. with water is presented. Based on thorough scans of configurational space, we determine the thermodynamics of cluster growth. The results are in good agreement with benchmark computational methods and existing experimental data. We find that anionic Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)n and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. (H2O)n clusters are thermally stabilized at typical atmospheric conditions for at least n = 5. The first 4 water molecules are strongly bound to the anion due to delocalization of the excess charge while stabilization of more than 4 H2O is due to normal hydrogen bonding. Although clustering up to 12 H2O, we find that the O2 and O3 anions retain at least ca. 80% of the charge and are located at the surface of the cluster. The Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. and Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. speicies are thus accessible for further reactions. Finally, the thermodynamics of a few relevant cluster reactions are considered. [ABSTRACT FROM AUTHOR]

In order to elucidate the effect of galactic cosmic rays on cloud formation, we investigate the optical response of marine aerosols to Forbush decreases - abrupt decreases in galactic cosmic rays - by means of modeling. We vary the nucleation rate of new aerosols, in a sectional coagulation and condensation model, according to changes in ionization by the Forbush decrease. From the resulting size distribution we then calculate the aerosol optical thickness and Angstrom exponent, for the wavelength pairs 350, 450 nm and 550, 900 nm. For the shorter wavelength pair we observe a change in Angstrom exponent, following the Forbush Decrease, of -6 to +3% in the cases with atmospherically realistic output parameters. For some parameters we also observe a delay in the change of Angstrom exponent, compared to the maximum of the Forbush decrease, which is caused by different sensitivities of the probing wavelengths to changes in aerosol number concentration and size. For the long wavelengths these changes are generally smaller. The types and magnitude of change is investigated for a suite of nucleation rates, condensable gas production rates, and aerosol loss rates. Furthermore we compare the model output with observations of 5 of the largest Forbush decreases after year 2000. For the 350, 450 nm pair we use AERONET data and find a comparable change in signal while the Angstrom Exponent is lower in the model than in the data, due to AERONET being mainly sampled over land. For 550, 900 nm we compare with both AERONET and MODIS and find little to no response in both model and observations. In summary our study shows that the optical properties of aerosols show a distinct response to Forbush Decreases, assuming that the nucleation of fresh aerosols is driven by ions. Shorter wavelengths seem more favorable for observing these effects and great care should be taken when analyzing observations, in order to avoid the signal being drowned out by noise. [ABSTRACT FROM AUTHOR]