Effects of particle acidity and UV light on secondary organic aerosol formation from oxidation of aromatics in the absence of NOx

Recent laboratory observations have shown that particle acidity increases secondary organic aerosol (SOA) yields. However, these studies have mainly focused on biogenic precursors such as isoprene and terpenes. In this paper, the effects of particle acidity on the SOA yields from aromatic precursors under both dark and UV–visible light conditions were characterized through controlled chamber experiments. SOA was produced from oxidation of toluene and 1,3,5-trimethylbenzene (135-TMB) with OH radicals created by ozonolysis of 2-methyl-2-butene (MB). Particle acidity, described with proton concentrations, varied with inorganic seed aerosol composition and humidity (20–52%). Overall, in the presence of acidic seeds, greater increases in SOA yields were observed for the toluene system than the 135-TMB system. UV irradiation reduced SOA yields for both toluene and 135-TMB systems to different extents.     

Secondary organic aerosol formation from cyclohexene ozonolysis in the presence of water vapor and dissolved salts

A series of 90 experiments were conducted in the UC Riverside/CE-CERT environmental chamber to evaluate the impact of water vapor and dissolved salts on secondary organic aerosol formation for cyclohexene ozonolysis. Water vapor (low – 30 ± 2% RH, medium – 46 ± 2% RH, high – 63 ± 2% RH) was found to directly participate in the atmospheric chemistry altering the composition of the condensing species, thus increasing total organic aerosol formation by ～22% as compared to the system under dry (<0.1% RH) conditions. Hygroscopicity measurements also indicate that the organic aerosol composition is altered in the presence of gaseous water. These results are consistent with water vapor reacting with the crigee intermediate in the gas phase resulting in increased aldehyde formation. The addition of dissolved salts ((NH₄)₂SO₄, NH₄HSO₄, CaCl₂, NaCl) had minimal effect; only the (NH₄)₂SO₄ and NaCl were found to significantly impact the system with ～10% increase in total organic aerosol formation. These results indicate that the organics may be partitioning to an outer organic shell as opposed to into the aqueous salt. Hygroscopicity measurements indicate that the addition of salts does not alter the aerosol composition for the dry or water vapor system.     

Analysis and simulation of wintertime light scattering by the urban aerosol in Dallas-Fort Worth

Wintertime atmospheric light scattering in Dallas, TX, was estimated through the use of aerosol models. Input data for the aerosol models were provided by measurements of aerosol chemistry, physical particle size distributions, and distributions of particulate sulfur by particle size, and by predictions by an atmospheric simulation model. Light scattering measurements provided a basis for testing the aerosol models. The SCAPE thermodynamic equilibrium model was used to estimate the amount of liquid water associated with particles and the ELSIE Mie scattering model was applied to estimate the resulting light scattering. The calculations were based on aerosol properties measured in Dallas during December 1994 and February 1995, and changes in scattering due to hypothetical changes in the aerosol were predicted. The predicted light scattering was compared to scattering measured by an Optec nephelometer; agreement was within 20% in every case.     

Comparative study of the formation of brominated disinfection byproducts in UV/persulfate and UV/H2O2 oxidation processes in the presence of bromide

Environmental Science and Pollution Research - The objective of this research was to compare the transformation of Br? and formation of brominated byproducts in UV/persulfate (PS) and UV/H2O2...     

A kinetic mechanism for predicting secondary organic aerosol formation from toluene oxidation in the presence of NOx and natural sunlight

A kinetic mechanism to predict secondary organic aerosol (SOA) formation from the photo-oxidation of toluene was developed. Aerosol phase chemistry that includes nucleation, gas–particle partitioning and particle-phase reactions as well as the gas-phase chemistry of toluene and its degradation products were represented. The mechanism was evaluated against experimental data obtained from the University of North Carolina (UNC) 270 m³ dual outdoor aerosol smog chamber facility. The model adequately simulates the decay of toluene, the nitric oxide (NO) to nitrogen dioxide (NO₂) conversion and ozone formation. It also provides a reasonable prediction of SOA production under different conditions that range from 15 to 300 μg m⁻³. Speciation of simulated aerosol material shows that up to 70% of the aerosol mass comes from oligomers and polymers depending on initial reactant concentrations. The dominant particle-phase species predicted by the mechanism are glyoxal oligomers, ketene oligomers from the photolysis of the toluene OH reaction product 2-methyl-2,4-hexadienedial, organic nitrates, methyl nitro-phenol analogues, C7 organic peroxides, acylperoxy nitrates and for the low-concentration experiments, unsaturated hydroxy nitro acids.     

A contribution of brown carbon aerosol to the aerosol light absorption and its radiative forcing in East Asia

Brown carbon aerosols were recently found to be ubiquitous and effectively absorb solar radiation. We use a 3-D global chemical transport model (GEOS-Chem) together with aircraft and ground based observations from the TRACE-P and the ACE-Asia campaigns to examine the contribution of brown carbon aerosol to the aerosol light absorption and its climatic implication over East Asia in spring 2001. We estimated brown carbon aerosol concentrations in the model using the mass ratio of brown carbon to black carbon (BC) aerosols based on measurements in China and Europe. The comparison of simulated versus observed aerosol light absorption showed that the model accounting for brown carbon aerosol resulted in a better agreement with the observations in East Asian-Pacific outflow. We then used the model results to compute the radiative forcing of brown carbon, which amounts up to ?2.4 W m^?2 and 0.24 W m^?2 at the surface and at the top of the atmosphere (TOA), respectively, over East Asia. Mean radiative forcing of brown carbon aerosol is ?0.43 W m^?2 and 0.05 W m^?2 at the surface and at the TOA, accounting for about 15% of total radiative forcing (?2.2 W m^?2 and 0.33 W m^?2) by absorbing aerosols (BC + brown carbon aerosol), having a significant climatic implication in East Asia.     

An absorption model of the gas/aerosol partitioning involved in the formation of secondary organic aerosol

A partitioning model is developed to allow the modeling of the dynamics of secondary organic aerosol (SOA) formation. The gas/aerosol partitioning is assumed to be governed by equilibrium partitioning into an absorptive, well-mixed liquid (or at least amorphous) organic matter (om) phase. The model is represented using a set of coupled linear equations. It may be especially applicable when photochemical smog is being formed in the summer. The model permits (indeed, it requires) partitioning of a given compound i to occur even when i is present at a level below its saturation vapor pressure. During early periods of SOA formation, to determine the partitioning for each compound of interest, the model must be solved iteratively for each time and location of interest. Iteration is required because the partitioning is assumed to be governed by mole fraction concentrations in the om phase, and because prior to solving the problem, one does not know the total number of mols of condensed compounds in the om phase. During later stages of SOA formation, if the amount and general composition of the SOA begin to become constant, the partitioning coefficient of each of the compounds will also stabilize, and an iterative solution will be less needed.     

Laboratory study of cluster ions formation in H2SO4–H2O system: Implications for threshold concentration of gaseous H2SO4 and ion-induced nucleation kinetics

Ion-induced binary H₂SO₄–H₂O nucleation is an important mechanism of aerosol formation in the atmosphere. Ions are created in the atmosphere mainly by galactic cosmic rays. The importance of ion-induced nucleation is recognized in some of the observed nucleation events in the background atmosphere. However, the predictions of current ion–aerosol models are highly uncertain mostly due to the lack of detailed experimental information concerning the thermodynamics and kinetics of ion clustering reactions. Here we continue the report of results of our laboratory experiments on the formation and growth of positive and negative cluster ions in H₂SO₄–H₂O vapours in the flow reactor started in Wilhelm et al. [2004. Ion-induced aerosol formation: new insights from laboratory measurements of mixed cluster ions HSO₄⁻(H₂SO₄)_a(H₂O)_w and H⁺ (H₂SO₄)_a(H₂O)_w. Atmospheric Environment 38, 1735–1744] and Sorokin et al. [2006. Formation and growth of sulphuric acid–water cluster ions: experiments, modelling, and implications for ion-induced aerosol formation. Atmospheric Environment 40, 2030–2045]. The main attention is given to the definition of the concentration of gaseous sulphuric acid in experiment and also to some aspects of the kinetics of small cluster ions formation. The performed analysis has indicated a threshold concentration of gaseous sulphuric acid for binary homogeneous nucleation of at least about 10¹⁰ cm⁻³ at room temperature and low relative humidity.     

Effect of UV radiation and temperature on mineralization and volatilization of coumaphos in water

This study was undertaken to determine the dissipation and degradation of coumaphos [O-(3-chloro-4-methyl-2-oxo-2H-1-benzopyran-7-yl) O,O-diethyl phosphorothioate] under different sunlight conditions and at different temperatures. The effect of the ultra violet (UV) component of solar radiation was also studied using quartz tubes in addition to other radiation in the visible range using glass tubes and the results were compared with those obtained under the dark light conditions. Water suspensions of coumaphos were incubated at three temperatures viz. 22 degrees C, 37 degrees C and 53 degrees C in closed systems to study the effect of temperature. Volatilization, mineralization and degradation of coumaphos increased with an increase in temperature and exposure to solar radiation, particularly under the UV component of the solar radiation. Major loss of the pesticide occurred through volatilization. The optimum temperature for the degradation of coumaphos was found to be at 37 degrees C. The data obtained from the mineralization and degradation studies indicated that 53 degrees C crosses the biological range for suitable growth of microorganism. UV radiation exposure along with maintaining temperature at 37 degrees C may prove useful in the dissipation and/or degradation of coumaphos prior to its disposal as waste from cattle dipping vats.     

Effect of UV radiation and temperature on mineralization and volatilization of coumaphos in water

This study was undertaken to determine the dissipation and degradation of coumaphos [O-(3-chloro-4-methyl-2-oxo-2H-1-benzopyran-7-yl) O,O-diethyl phosphorothioate] under different sunlight conditions and at different temperatures. The effect of the ultra violet (UV) component of solar radiation was also studied using quartz tubes in addition to other radiation in the visible range using glass tubes and the results were compared with those obtained under the dark light conditions. Water suspensions of coumaphos were incubated at three temperatures viz. 22°C, 37°C and 53°C in closed systems to study the effect of temperature. Volatilization, mineralization and degradation of coumaphos increased with an increase in temperature and exposure to solar radiation, particularly under the UV component of the solar radiation. Major loss of the pesticide occurred through volatilization. The optimum temperature for the degradation of coumaphos was found to be at 37°C. The data obtained from the mineralization and degradation studies indicated that 53°C crosses the biological range for suitable growth of microorganism. UV radiation exposure along with maintaining temperature at 37°C may prove useful in the dissipation and/or degradation of coumaphos prior to its disposal as waste from cattle dipping vats.     

Photodegradation of bisphenol Z by UV irradiation in the presence of beta-cyclodextrin

In this work, the formation of the inclusion complex of bisphenol Z (1,1-bis(4-hydroxyphenyl)cyclohexane, abbreviated as BPCH) with beta-cyclodextrin (beta-CD) has been studied, 1:1 inclusion complex can be obtained, the formation constant of the beta-CD/BPCH complex is 5.94x10(3)M(-1). The photodegradation behavior of BPCH was investigated under monochromatic UV irradiation (lambda=254 nm). The photodegradation rate constant of BPCH in aqueous solutions with beta-CD showed a 9.0-fold increase, and simultaneously the mineralization of BPCH can be enhanced by beta-CD. The influence factors on photodegradation of BPCH were also studied and described in details, such as concentration of beta-CD, initial concentration of BPCH, organic solvent and pH. The photodegradation of BPCH in the presence of beta-CD includes the direct photolysis and the photooxidation of BPCH during the photochemical process. Some predominant photodegradation products are 4-(2,4,5-trihydroxy-phenyl)-4-(4-hydroxyphenyl) butanoic acid, 5,5-bis(4-hydroxyphenyl)pentanoic acid, meta-hydroxylated BPCH, ortho-hydroxylated BPCH and 4-(1-(4-hydroxyphenyl)pentyl)phenol respectively. The enhancement of photodegradation of BPCH mainly results from moderate inclusion depth of BPCH molecule in the beta-CD cavity. This kind of inclusion structure allows BPCH molecule sufficient proximity to secondary hydroxyl groups of the beta-CD cavity, and these hydroxyl groups could be activated and converted to hydroxyl radicals under UV irradiation, which can enhance the photooxidation of BPCH.     

Aqueous free radical chemistry of mercury in the presence of iron oxides and ambient aerosol

The effect of goethite (α-FeOOH), hematite (α-Fe₂0₃) and maghemite (γ-Fe₂0₃) on the aqueous photoreduction of divalent mercury with organic acids (oxalate, formate and acetate) is investigated. Laboratory photochemistry experiments with synthetic iron oxides and simulated sunlight were performed to assess the role of the oxides on the photoreduction. Ambient aerosol was also collected and introduced as the solid phase to compare its effect with that of synthetic oxides. It is observed that the presence of various iron oxides or aerosol particles enhances the photoreduction. It is also found that the hydroxyl radicals produced in the hematite-oxalate systems can re-oxidize the reduced mercury back to Hg(II). Based on the experimental observations, mechanisms responsible for the Hg(II) reduction are proposed. The kinetics of Hg⁰ oxidation by hydroxyl radicals was also studied by a steady-state kinetic technique using nitrate photolysis as the * OH radical source. The second-order rate constant is determined to be 2.0 × 10⁹ M⁻ s⁻¹. The implications of the studied reactions on the atmospheric chemistry of mercury are discussed.     

An examination of oxidant amounts on secondary organic aerosol formation and aging

The effect of HO_x radicals (OH and HO₂) and ozone (O₃) on aerosol formation and aging has been studied. Experiments were performed in presence as well as in absence of oxygen in a flow-through chamber at 299 K for three organic precursor gases, isoprene, α-pinene and m-xylene. The HO_x source was the UV photolysis of humidified air or nitrogen and was measured with a GTHOS (Ground-based Tropospheric Hydrogen Oxides Sensor). The precursor gases concentration was monitored with an online GC-FID. The aerosol mass was then quantified by a Tapered Element Oscillating Microbalance (TEOM). Typical oxidant mixing ratios were (0–4.5) ppm for O₃, 200 pptv for OH and 3 ppbv for HO₂. A simple kinetics model is used to infer the aerosol production mechanism. In the present of O₃ (or O₂), the SOA yields were 0.46, 0.036 and 0.12 for α-pinene with an initial concentration of 100 ppbv (RH = 37%), isoprene with an initial concentration of 177 ppbv (RH = 50%) and m-xylene with an initial concentration of 100 ppbv (RH = 37%), respectively. When the chosen precursor gases reacted with HO_x in the absence of O₃, the maximum SOA yields were significantly increased by factors of 1.6 for isoprene 1.1 for α-pinene, and 3 for m-xylene respectively. The comparison of the calculated and measured potential aerosol mass concentrations as function of time shows that presence of ozone or oxygen can influence the aerosol yield and the absence of ozone or oxygen in the system resulted in high concentrations of its organic aerosol products.     

Effects of N-acetyl-L-cysteine on fish hepatoma cells treated with mercury chloride and ionizing radiation

Organisms are exposed to natural radiations from cosmic or terrestrial origins. Furthermore the combined action of radiation with various chemicals is an inevitable feature of modern life. Radiation is known to cause cell death, mainly due to its ability to produce reactive oxygen species in cells. N-acetyl-l-cysteine (NAC) is a well-known sulfhydryl-containing antioxidant whose role in radioprotection has been reported. Synergistic effects of radiation and mercury chloride on human cells was previously reported by the authors. Based on the previous report, this study was designed to assess the synergistic effects of radiation and mercury chloride on fish hepatoma cells, as well as to investigate the protective effects of NAC on the cells. The cytotoxicity of radiation was enhanced in the presence of mercury chloride. NAC in lower concentrations prevented cells from death after irradiation with lower doses (<300 Gy) while it did not prevent cells from radiation-induced death after irradiation with higher doses (300, 500 Gy). The intracellular glutathione (GSH) levels significantly decreased after irradiation while the combined treatment of NAC and radiation alleviated the decrease in the GSH levels. The investigations give a clue for the action mechanism of synergistic or protective effects of NAC on the cells. Due to their high resistance to ionizing radiation, the PLHC-1 cells can be effectively used as a screening tool for assessing the combined effects of radiation with toxic chemicals.     

The effect of high UV radiation exposure environment on the novel PVC polymers

Environmental Science and Pollution Research - Although plastic induces environmental damages, almost the consumption of poly(vinyl chloride) never stops increasing. Therefore, this work abstracted...     

Phytoplankton toxicity of the antibiotic chlortetracycline and its UV light degradation products

Two common freshwater phytoplankton species Microcystis aeruginosa and Scenedesmus obliquus were employed as test organisms to investigate the toxic effects of chlortetracycline widely used in human medicine and veterinary as antibiotic. Toxicity assays were performed into two parts: antibiotic toxicity test and antibiotic degraded products toxicity test. In general, chlortetracycline had significantly toxic effect on population growth and chlorophyll-a accumulation of two phytoplankton. Although M. aeruginosa had ability to grow after exposed to chlortetracycline at 0.5 mg L⁻¹, its photosynthesis function was also disrupted. Compared with the data in two phytoplankton species, the chlorophyceae was more sensitive than the cyanophyceae. The adverse effect on S. obliquus was stronger than that on M. aeruginosa with increasing concentrations. In addition, for M. aeruginosa, regardless of the UV light degradation time, the treated chlortetracycline also had adverse effect on population growth and chlorophyll-a accumulated. The degraded chlortetracycline under any treatment time was more toxic for S. obliquus than chlortetracycline itself excluding under 24 h. However, the correlation between the toxicity and degradation time was not clear and toxicity enhanced in fact did not follow the increase or decrease in degradation time. Our study showed that the antibiotic chlortetracycline and its degraded products had adverse effect on freshwater phytoplankton, the former has not been reported before and the latter has been overlooked in other research in the past.     

Photostabilization of the botanical insecticide azadirachtin in the presence of lecithin as UV protectant

Abstract

The phytochemical insecticide, azadirachtin (AZ), undergoes UV‐induced photodegradation. Using the isomer AZ‐A as a standard, its photochemical stability was studied with and without adding lecithin surfactant as a UV protectant. Standard solutions of pure AZ‐A and Margosan‐O^® were prepared in methanol‐hexane with (AZ‐A:lecithin, 1:2 by weight) and without lecithin, applied separately onto glass plates and maple (Acer L.) foliage and exposed to radiant energy under controlled conditions. Noticeable photostabilization of AZ‐A was achieved in the samples containing lecithin compared to AZ‐A samples without the lecithin additive. First‐order kinetic evaluation of the data showed that the DTy₅₀ (half‐life) and C (rate constant) values for AZ‐A with and without lecithin on glass plates were 5.68 d and 0.122, and 5.42 d and 0.128, respectively. The corresponding values for the Margosan‐0 formulation were 7.37 d and 0.094, and 6.24 d and 0.111. The DT₅₀ and C values for the pure AZ‐A on maple foliage with and without lecithin were 8.77 d and 0.079, and 6.54 d and 0.106, respectively. The corresponding values for the Margosan‐0 formulation on foliage were 8.35 d and 0.083, and 7.45 d and 0.093. The kinetic data gave quantitative information regarding the photostabilization of AZ‐A in the presence of lecithin. Good UV protection can only be achieved if the additive has the matching X_max of AZ‐A. The mechanism of photostabilization of AZ‐A in the presence of lecithin was due to either energy transfer from the excited AZ‐A to lecithin and/or competitive absorption of UV photons by the latter.     

Past changes in Arctic terrestrial ecosystems, climate and UV radiation

At the last glacial maximum, vast ice sheets covered many continental areas. The beds of some shallow seas were exposed thereby connecting previously separated landmasses. Although some areas were ice-free and supported a flora and fauna, mean annual temperatures were 10-13 degrees C colder than during the Holocene. Within a few millennia of the glacial maximum, deglaciation started, characterized by a series of climatic fluctuations between about 18,000 and 11,400 years ago. Following the general thermal maximum in the Holocene, there has been a modest overall cooling trend, superimposed upon which have been a series of millennial and centennial fluctuations in climate such as the "Little Ice Age spanning approximately the late 13th to early 19th centuries. Throughout the climatic fluctuations of the last 150,000 years, Arctic ecosystems and biota have been close to their minimum extent within the most recent 10,000 years. They suffered loss of diversity as a result of extinctions during the most recent large-magnitude rapid global warming at the end of the last glacial stage. Consequently, Arctic ecosystems and biota such as large vertebrates are already under pressure and are particularly vulnerable to current and projected future global warming. Evidence from the past indicates that the treeline will very probably advance, perhaps rapidly, into tundra areas, as it did during the early Holocene, reducing the extent of tundra and increasing the risk of species extinction. Species will very probably extend their ranges northwards, displacing Arctic species as in the past. However, unlike the early Holocene, when lower relative sea level allowed a belt of tundra to persist around at least some parts of the Arctic basin when treelines advanced to the present coast, sea level is very likely to rise in future, further restricting the area of tundra and other treeless Arctic ecosystems. The negative response of current Arctic ecosystems to global climatic conditions that are apparently without precedent during the Pleistocene is likely to be considerable, particularly as their exposure to co-occurring environmental changes (such as enhanced levels of UV-B, deposition of nitrogen compounds from the atmosphere, heavy metal and acidic pollution, radioactive contamination, increased habitat fragmentation) is also without precedent.     

Processes influencing secondary aerosol formation in the San Joaquin Valley during winter

Air quality data collected in the California Regional PM10/ PM(2.5) Air Quality Study (CRPAQS) are analyzed to qualitatively assess the processes affecting secondary aerosol formation in the San Joaquin Valley (SJV). This region experiences some of the highest fine particulate matter (PM(2.5)) mass concentrations in California (< or = 188 microg/m3 24-hr average), and secondary aerosol components (as a group) frequently constitute over half of the fine aerosol mass in winter. The analyses are based on 15 days of high-frequency filter and canister measurements and several months of wintertime continuous gas and aerosol measurements. The phase-partitioning of nitrogen oxide (NO(x))-related nitrogen species and carbonaceous species shows that concentrations of gaseous precursor species are far more abundant than measured secondary aerosol nitrate or estimated secondary organic aerosols. Comparisons of ammonia and nitric acid concentrations indicate that ammonium nitrate formation is limited by the availability of nitric acid rather than ammonia. Time-resolved aerosol nitrate data collected at the surface and on a 90-m tower suggest that both the daytime and nighttime nitric acid formation pathways are active, and entrainment of aerosol nitrate formed aloft at night may explain the spatial homogeneity of nitrate in the SJV. NO(x) and volatile organic compound (VOC) emissions plus background O3 levels are expected to determine NO(x) oxidation and nitric acid production rates, which currently control the ammonium nitrate levels in the SJV. Secondary organic aerosol formation is significant in winter, especially in the Fresno urban area. Formation of secondary organic aerosol is more likely limited by the rate of VOC oxidation than the availability of VOC precursors in winter.