Assessing the biological reactivity of organic compounds on volcanic ash: implications for human health hazard

Exposure to volcanic ash is a long-standing health concern for people living near active volcanoes and in distal urban areas. During transport and deposition, ash is subjected to various physicochemical processes that may change its surface composition and, consequently, bioreactivity. One such process is the interaction with anthropogenic pollutants; however, the potential for adsorbed, deleterious organic compounds to directly impact human health is unknown. We use an in vitro bioanalytical approach to screen for the presence of organic compounds of toxicological concern on ash surfaces and assess their biological potency. These compounds include polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dlPCBs). Analysis of ash collected in or near urbanised areas at five active volcanoes across the world (Etna, Italy; Fuego, Guatemala; Kelud, Indonesia; Sakurajima, Japan; Tungurahua, Ecuador) using the bioassay inferred the presence of such compounds on all samples. A relatively low response to PCDD/Fs and the absence of a dlPCBs response in the bioassay suggest that the measured activity is dominated by PAHs and PAH-like compounds. This study is the first to demonstrate a biological potency of organic pollutants associated with volcanic ash particles. According to our estimations, they are present in quantities below recommended exposure limits and likely pose a low direct concern for human health

A review of coarse mineral dust in the Earth system

Mineral dust particles suspended in the atmosphere span more than three orders of magnitude in diameter, from <0.1 µm to more than 100 µm. This wide size range makes dust a unique aerosol species with the ability to interact with many aspects of the Earth system, including radiation, clouds, hydrology, atmospheric chemistry, and biogeochemistry. This review focuses on coarse and super-coarse dust aerosols, which we respectively define as dust particles with a diameter of 2.5–10 µm and 10–62.5 µm. We review several lines of observational evidence indicating that coarse and super-coarse dust particles are transported farther than previously expected and that the abundance of these particles is substantially underestimated in current global models. We synthesize previous studies that used observations, theories, and model simulations to highlight the impacts of coarse and super-coarse dust aerosols on the Earth system, including their effects on dust-radiation interactions, dust-cloud interactions, atmospheric chemistry, and biogeochemistry. Specifically, coarse and super-coarse dust aerosols produce a net positive direct radiative effect (warming) at the top of the atmosphere and can modify temperature and water vapor profiles, influencing the distribution of clouds and precipitation. In addition, coarse and super-coarse dust aerosols contribute a substantial fraction of ice-nucleating particles, especially at temperatures above –23 °C. They also contribute a substantial fraction to the available reactive surfaces for atmospheric processing and the dust deposition flux that impacts land and ocean biogeochemistry by supplying important nutrients such as iron and phosphorus. Furthermore, we examine several limitations in the representation of coarse and super-coarse dust aerosols in current model simulations and remote-sensing retrievals. Because these limitations substantially contribute to the uncertainties in simulating the abundance and impacts of coarse and super-coarse dust aerosols, we offer some recommendations to facilitate future studies. Overall, we conclude that an accurate representation of coarse and super-coarse properties is critical in understanding the impacts of dust aerosols on the Earth system

Evaluating the Atmospheric Loss of H2 by NO3 Radicals: A Theoretical Study

Molecular hydrogen (H2) is now considered among the most prominent substitute for fossil fuels. The environmental impacts of a hydrogen economy have received more attention in the last years, but still, the knowledge is relatively poor. In this work, the reaction of H2 with NO3 radical (the dominant night-time detergent of the atmosphere) is studied for the first time using high-level composite G3B3 and modification of high accuracy extrapolated ab initio thermochemistry (mHEAT) methods in combination with statistical kinetics analysis using non-separable semi-classical transition state theory (SCTST). The reaction mechanism is characterized, and it is found to proceed as a direct H-abstraction process to yield HNO3 plus H atom. The reaction enthalpy is calculated to be 12.8 kJ mol&minus;1, in excellent agreement with a benchmark active thermochemical tables (ATcT) value of 12.2 &plusmn; 0.3 kJ mol&minus;1. The energy barrier of the title reaction was calculated to be 74.6 and 76.7 kJ mol&minus;1 with G3B3 and mHEAT methods, respectively. The kinetics calculations with the non-separable SCTST theory give a modified-Arrhenius expression of k(T) = 10&minus;15 &times; T0.7 &times; exp(&minus;6120/T) (cm3 s&minus;1) for T = 200&ndash;400 K and provide an upper limit value of 10&minus;22 cm3 s&minus;1 at 298 K for the reaction rate coefficient. Therefore, as compared to the main consumption pathway of H2 by OH radicals, the title reaction plays an unimportant role in H2 loss in the Earth&rsquo;s atmosphere and is a negligible source of HNO3

Evaluating the Atmospheric Loss of H₂ by NO₃ Radicals: A Theoretical Study

Molecular hydrogen (H2) is now considered among the most prominent substitute for fossil fuels. The environmental impacts of a hydrogen economy have received more attention in the last years, but still, the knowledge is relatively poor. In this work, the reaction of H2 with NO3 radical (the dominant night-time detergent of the atmosphere) is studied for the first time using high-level composite G3B3 and modification of high accuracy extrapolated ab initio thermochemistry (mHEAT) methods in combination with statistical kinetics analysis using non-separable semi-classical transition state theory (SCTST). The reaction mechanism is characterized, and it is found to proceed as a direct H-abstraction process to yield HNO3 plus H atom. The reaction enthalpy is calculated to be 12.8 kJ mol−1, in excellent agreement with a benchmark active thermochemical tables (ATcT) value of 12.2 ± 0.3 kJ mol−1. The energy barrier of the title reaction was calculated to be 74.6 and 76.7 kJ mol−1 with G3B3 and mHEAT methods, respectively. The kinetics calculations with the non-separable SCTST theory give a modified-Arrhenius expression of k(T) = 10−15 × T0.7 × exp(−6120/T) (cm3 s−1) for T = 200–400 K and provide an upper limit value of 10−22 cm3 s−1 at 298 K for the reaction rate coefficient. Therefore, as compared to the main consumption pathway of H2 by OH radicals, the title reaction plays an unimportant role in H2 loss in the Earth’s atmosphere and is a negligible source of HNO3

Interaction of OH Radicals with Arizona Test Dust: Uptake and Products

International audienceKinetics and products of the interaction of OH radicals with solid films of Arizona Test Dust (ATD) were studied using a low pressure flow reactor (0.5–3 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake coefficient of OH was measured from the kinetics of OH consumption on Pyrex rods coated with ATD as a function of OH concentration ((0.4–5.2) × 1012 molecules cm–3), relative humidity (RH = 0.03–25.9%), temperature (T = 275–320 K), and UV irradiance intensity (JNO2 = 0–0.012 s–1). Deactivation of ATD surface upon exposure to OH was observed. The initial uptake coefficient was found to be independent of temperature and irradiation conditions and to decrease with relative humidity: γ0 = 0.2/(1 + RH0.36) (calculated using geometric surface area, with 30% estimated conservative uncertainty). H2O2 and H2O were observed in the gas phase as products of the OH reaction with ATD surface with yields of (10 ± 3) and (98 ± 25) %, respectively

Uptake of hydrogen peroxide on the surface of Al2O3 and Fe2O3

International audienceThe heterogeneous interaction of H2O2 with solid films of Al2O3 and Fe2O3 was investigated under dark conditions and in presence of UV light using a low pressure flow tube reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial concentration of gaseous H2O2 ([H2O2]0 = (0.15–16.6) × 1012 molecule cm−3), irradiance intensity (JNO2=0.002−0.012s−1JNO2=0.002−0.012s−1), relative humidity (RH = 0.003–73%) and temperature (T = 268–320 K). Deactivation of mineral surfaces upon exposure to H2O2 was observed and only initial uptake coefficients of H2O2 were quantified, given by the following expressions: γ0 (Al2O3) = 1.10 × 10−3/(1 + RH0.93) and γ0 (Fe2O3) = 1.05 × 10−3/(1 + RH0.73) (calculated using BET surface area, estimated conservative uncertainty of 30%) at T = 280 K. The initial uptake coefficients were found to be independent of the UV irradiation intensity and concentration of H2O2. Temperature dependence of γ0 measured at RH = 0.3% corresponded to almost temperature independent values of γ0 at lower temperatures of the study (268–280 K) and to rather rapid decrease of γ0 with increase of temperature above 290 K, according to the following expressions: γ0 (Al2O3) = 8.7 × 10−4/(1 + 5.0 × 1013exp(−9700 T−1)) and γ0 (Fe2O3) = 9.3 × 10−4/(1 + 3.6 × 1014exp(−10300 T−1)). The present experimental data support current considerations that uptake of H2O2 on mineral aerosol is potentially an important atmospheric process which should be accounted for in the atmospheric models

Kinetics and Products of Heterogeneous Reaction of HONO with Fe2O3 and Arizona Test Dust

International audienceKinetics and products of the reaction of HONO with solid films of Fe2O3 and Arizona Test Dust (ATD) were investigated using a low pressure flow reactor (1 – 10 Torr) combined with a modulated molecular beam mass spectrometer. The reactive uptake of HONO was studied as a function of HONO concentration ([HONO]0 = (0.6 – 15.0) × 1012 molecules cm–3), relative humidity (RH = 3 × 10–4 – 84.1%) and temperature (T = 275 – 320 K). Initial reactive uptake coefficients were found to be similar under dark conditions and in the presence of UV irradiation (JNO2 = 0.012 s–1) and independent of the HONO concentration and temperature. In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficients: γ (ATD) = 3.8 × 10–6 (RH)−0.61 and γ (Fe2O3) = 1.7 × 10–6 (RH)−0.62 (γ calculated with BET surface area, 30% conservative uncertainty). In both reactions of HONO studied, NO2 and NO were observed as gaseous products with yields of (60 ± 9) and (40 ± 6) %, respectively, independent of relative humidity, temperature, concentration of HONO and UV irradiation intensity. The observed data point to minor importance of the HONO uptake on mineral aerosol compared with other known sinks of HONO in the atmosphere, which are its dry deposition and photolysis in night-time and during the day, respectively

Heterogeneous Interaction of H2O2 with TiO2 Surface under Dark and UV Light Irradiation Conditions

International audienceThe heterogeneous interaction of H2O2 with TiO2 surface was investigated under dark conditions and in the presence of UV light using a low pressure flow tube reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial concentration of gaseous H2O2 ([H2O2]0 = (0.17–120) × 1012 molecules cm–3), irradiance intensity (JNO2 = 0.002–0.012 s–1), relative humidity (RH = 0.003–82%), and temperature (T = 275–320 K). Under dark conditions, a deactivation of TiO2 surface upon exposure to H2O2 was observed, and only initial uptake coefficient of H2O2 was measured, given by the following expression: γ0(dark) = 4.1 × 10–3/(1 + RH0.65) (calculated using BET surface area, estimated conservative uncertainty of 30%) at T = 300 K. The steady-state uptake coefficient measured on UV irradiated TiO2 surface, γss(UV), was found to be independent of RH and showed a strong inverse dependence on [H2O2] and linear dependence on photon flux. In addition, slight negative temperature dependence, γss(UV) = 7.2 × 10–4 exp[(460 ± 80)/T], was observed in the temperature range (275–320) K (with [H2O2] ≈ 5 × 1011 molecules cm–3 and JNO2 = 0.012 s–1). Experiments with NO addition into the reactive system provided indirect evidence for HO2 radical formation upon H2O2 uptake, and the possible reaction mechanism is proposed. Finally, the atmospheric lifetime of H2O2 with respect to the heterogeneous loss on mineral dust was estimated (using the uptake data for TiO2) to be in the range of hours during daytime, i.e., comparable to H2O2 photolysis lifetime (∼1 day), which is the major removal process of hydrogen peroxide in the atmosphere. These data indicate a strong potential impact of H2O2 uptake on mineral aerosol on the HOx chemistry in the troposphere

Ozone uptake on clay dust under atmospheric conditions

National audienc

Reactive uptake of HONO on aluminium oxide surface

International audienceKinetics and products of the interaction of HONO with solid films of Al2O3 were investigated under dark and UV irradiation conditions using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake of HONO to Al2O3 was studied as a function of HONO concentration ([HONO]0 = (0.6–3.5) × 1012 molecule cm−3), relative humidity (RH = 1.4 × 10−4 to 35.4%), temperature (T = 275–320 K) and UV irradiation intensity (JNO2=0.002–0.012 s−1JNO2=0.002–0.012 s−1). The measured reactive uptake coefficient was independent of the HONO concentration and temperature. In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficient: γ = 4.8 × 10−6 (RH)−0.61 and γ = 1.7 × 10−5 (RH)−0.44 under dark conditions and on irradiated surface (JNO2=0.012 s−1JNO2=0.012 s−1), respectively (γ calculated with BET surface area, 30% conservative uncertainty). NO2 and NO were observed as products of the HONO reaction with Al2O3 surface with yields of 40 ± 6 and 60 ± 9%, respectively, independent of relative humidity, temperature, concentration of HONO and UV irradiation intensity under experimental conditions used. The HONO uptake on mineral aerosol (calculated with uptake data for HONO on Al2O3 surface) appears to be of minor importance compared with other HONO loss processes in the boundary layer of the earth atmosphere