An investigation of the formation of ambient NH4NO3 aerosol

The aerosol equilibrium formulation of Stelson and Seinfeld (1982a, b, Atmospheric Environment16, 983–992, 993–1000) is incorporated into the STEM-II transport/chemistry model and is evaluated against NH₃, HNO₃ and aerosol NH₄⁺ and NO₃⁻ measured at Nagano Prefecture, Japan on 29 and 30 July 1983. These results indicate that this modeling approach is useful in analyzing field data.     

Theoretical study of the dechlorination reaction pathways of octachlorodibenzo-p-dioxin

The dechlorination reaction pathways of 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD) by the hydrogen atom are investigated by the density-functional theory B3PW91 method. The dechlorination reactions have large exothermicity and small activation energies. The activation energies (approximately 5 kcal/mol) of the sigma-complex formation due to the hydrogen addition are lower than those (approximately 9 kcal/mol) of the direct chlorine abstraction. It is suggested that the sigma-complex plays an important role in the reactions, although it has scarcely been shown in previous studies of the dechlorination of dioxins. The sigma-complex formation is favored at low temperatures and the chlorine abstraction is favored at high temperatures. Furthermore, it is found that the lateral positions have a marginal preference over the longitudinal positions. The dechlorination of OCDD by the hydrogen atom is thus not likely to result in a dominant formation of the laterally substituted toxic congeners.     

Photocatalytic and biodegradation treatments of paracetamol: investigation of the in vivo toxicity

Environmental Science and Pollution Research - Medicines and drugs consumption by all populations of the world can be expected to result in the contamination of the environment since 30–90%...     

An investigation of the assumptions of linear chemistry and superposition in LRTAP models

Most current LRTAP models assume a linear relationship between sulphur emissions and predicted acidic concentrations, as well as the ability to superpose concentrations from different emission sources. This paper uses a non-linear chemistry model and control scenarios of 50% reductions in S, N and hydrocarbon (HC) emissions to examine the validity of these two assumptions at various downwind receptors. The model predicts that a 50% reduction in S emissions will lead to a 60–65% reduction in SO₂ concentrations and a 25–40% reduction in H₂SO₄ concentrations, depending upon whether or not NO_x and/or HC emissions are reduced by 50% at the same time. The non-linearities in the model predictions are due to complex interactions between NO_x, HC, OH and HO₂. Even when there was non-linearity in the individual S species (SO₂ and SO₄), there was little non-linearity in total airborne S. Adding the results of independent model predictions for different sources (superposition) might introduce errors due to

• 1.(1) chemical interactions between the emissions from the various sources
• 2.(2) overestimates of physical processes such as mixing in of ambient air.

The model was also used to examine trends in regional air quality in eastern North Amierica.     

An investigation of the environmental impact of an artificial thermal plume

Experimental analysis of the mean and turbulent structures of artificial thermal plumes rising in the boundary layer up into the capping stable layers is reported. Scaling parameters are used to compare the structural aspects obtained from ten experimental cases. Vertical profiles of the mean excesses (temperature and vertical velocity) and of the dissipative parameters (dissipation rate and temperature structure parameter) within the plume are given. The estimates of dissipation rate and of the horizontal width of the column are used to predict the variation of the vertical eddy diffusivity coefficient from the heat source to the top level of the plume.     

An investigation of acid precipitation in Qinghai province,China

Precipitation and surface water samples from the Tibetan Plateau in Qinghai Province, China. were collected in June 1981, in both remote and settled areas on the plateau. A pH measurement in one urban precipitation sample indicated extremely acidic precipitation, with a pH of 2.25. In the remote Amne Machin mountains, precipitation pH's did not vary significantly from a value of approximately 6, but levels of certain ions were unexpectedly high. In all samples for which major anions were measured, including the very acidic urban sample, nitrate concentrations exceeded sulfate concentrations by a wide margin, despite the dominance of coal burning in the region.     

An experimental investigation of the effects of nitrogen deposition to Narthecium ossifragum

Narthecium ossifragum (L.) Hudson was subjected to artificial deposition events in three experiments. In the first, a laboratory experiment, 1.0 m nitrate significantly decreased the growth of Narthecium, and the shoot and root nitrogen content of the plants was increased in all enhanced nitrogen treatments. In the second experiment, solutes were applied in situ to a relatively unpolluted upland ombrotrophic mire at concentrations measured in cloud water at a polluted site in England. There was no effect on Narthecium tissue nitrogen concentration due to either ammonium or nitrate applied alone but the shoot nitrogen was significantly increased when the ammonium and nitrate were applied in combination. In the third experiment, a piece of upland ombrotrophic mire from a relatively unpolluted site in North Wales was transplanted to a polluted site in northern England. After two years both the shoots and roots of Narthecium present in the mire showed a higher nitrogen concentration in the transplant compared with the control. These data show that nitrogen supply in the southern Pennines is supra-optimal for Narthecium, which implies that in such situations it (and other species with a similar ecological strategy) would be out-competed by more vigorous species. The data from the field experiment at the relatively unpolluted site imply that even there, nitrogen supply is close to supra-optimal for Narthecium.     

An investigation of the pullout behaviors of tire strips embedded in tire-derived aggregate reinforced sand

Environmental Science and Pollution Research - The recycling of scrap tires has become an important issue in the area of environmental protection in the past 20 years. In recent years, tire strips...     

Half-lives of tetra-, penta-, hexa-, hepta-, and octachlorodibenzo-p-dioxin in rats,monkeys, and humans--a critical review

The elimination half-lives (t1/2) in Sprague-Dawley rats for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2, 3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (HxCDD), 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) and 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD) were estimated in long-term studies by Schlatter, Poiger and others. Furthermore, there are some published half-lives of TCDD in adult humans. The average half-life of TCDD in adult humans is approximately 2840 days, while in Sprague-Dawley rats the average t1/2 of TCDD is 19 days. The t1/2 of TCDD in humans is about 150 times that of rats. This factor was used to calculate the t1/2 values of the other polychlorinated dibenzo-p-dioxins (PCDDs) in humans from the rat data. Furthermore, the terminal t1/2 values of PCDDs in adult humans were calculated from the regression equation: logt1/2H = 1.34 logt1/2R + 1.25 which was recently established for 50 xenobiotics (t1/2H = terminal half-lives in days for humans, t1/2R = terminal half-lives in days for rats). The following terminal half-lives in adult humans were obtained: 12.6 years for 1,2,3,7,8-PeCDD, 26-45 years for 1,2,3,4,7,8-HxCDD, 80-102 years for 1,2,3,4,6,7,8-HpCDD and ca. 112-132 years for OCDD. These half-lives of PCDDs are critically compared with measured t1/2 values of PCDDs and other persistent organic pollutants in rats, monkeys and humans.     

An investigation of aqueous activity coefficients at low concentrations

The activity of a chemical in solution determines its tendency to move into other media. At low concentrations (<0.01M) it is generally considered to be linearly related to concentration. A hypothetical model based on the structure of liquid water is discussed which could cause deviations from this linearity in the ppb region, a concentration much lower than that normally investigated thermodynamically, but one of great importance environmentally. Headspace experiments are reported with carbon tetrachloride and chloroform in water at concentrations down to ～10^?3 ppb but no such deviations were discerned.     

天然色素生产废水的生物处理研究

天然色素生产废水是一种色度大、难处理的高浓度有机废水，为了寻找该废水的有效处理方法，本文作者采用由升流式厌氧污泥床（UASB）、生物接触氧化、混凝吸附组成的废水处理工艺，对该废水进行了处理试验，结果表明，对稀释4倍的原水，当进水COD为14900mg／L左右时，UASB经过36h的水力停留时间，COD的去除率为58．2％～60．2％、出水色度为180～270倍，SS为119～126mg／L，pH值为6．5～6．8；UASB出水经过24h好氧生物接触氧化反应，COD的去除率超过90％，SS〈70mg／L；最终经过Ca（CIO）2氧化和煤渣吸附深度处理，脱色可至无色，出水COD为200mg／L以下。UASB-生物接触氧化-氧化吸附组合处理工艺处理该类天然色素生产废水是可行的。     

An investigation into the acid content of aerosols in the ambient air at the Taj Mahal, Agra

A chemical analysis of suspended particulate matter (SPM) collected near the world famous Taj Mahal monument at Agra has been carried out. SPM samples collected on glass fibre filters were analysed for water-soluble sulphate, nitrate, chloride and ammonium ions. The data were derived from over 200 samples (each of 24 h), collected continuously during the winter periods (October through to March) of 1984-1985 and 1985-1986. The SO(4)(2-) and NO(3)(-) components are acidic in nature causing corrosion and effects on visibility, and so were studied in more detail. Mean values for SO(4)(2-) and NO(3)(-) derived from two-year data are 7.2 microg m(-3) and 8.2 microg m(-3), respectively. The SO(4)(2-)/SO(2) and NO(3)(-)/NO(2) ratiosobserved indicate faster conversion of SO(2) to SO(4)(2-) than NO(2) to NO(3)(-), the maximum levels being in January. Thus, both SO(4)(2-) and NO(3)(-) results appear to offer more promising indices of air quality than do SPM data alone.     

天然色素生产废水的生物处理研究

天然色素生产废水是一种色度大、难处理的高浓度有机废水,为了寻找该废水的有效处理方法,本文作者采用由升流式厌氧污泥床(UASB)、生物接触氧化、混凝吸附组成的废水处理工艺,对该废水进行了处理试验,结果表明,对稀释4倍的原水,当进水COD为14900mg/L左右时,UASB经过36h的水力停留时间,COD的去除率为58.2%～60.2%、出水色度为180～270倍,SS为119～126mg/L,pH值为6.5～6.8;UASB出水经过24h好氧生物接触氧化反应,COD的去除率超过90%,SS<70mg/L;最终经过Ca(ClO)2氧化和煤渣吸附深度处理,脱色可至无色,出水COD为200mg/L以下。UASB生物接触氧化氧化吸附组合处理工艺处理该类天然色素生产废水是可行的。     

An experimental investigation of incremental reactivities of volatile organic compounds

California has adopted a set of VOC reactivity factors for regulatory purposes that is based on a model of the ozone formation process. These incremental reactivity factors (derived by Carter) describe the amount of ozone each exhaust VOC will form under a certain set of conditions in an urban atmosphere. The main objective of this study is to measure reactivity factors using smog chamber experiments, and to compare the measurements to the Carter factors. A new facility was constructed explicitly for this study. The facility has four identical smog chambers and a temperature-controlled enclosure for the chambers. The chambers are irradiated using a set of filtered xenon arc lamps to approximate “sunlight”. The reactivities of 14 individual VOCs representative of those found in automobile exhaust and several mixtures of VOCs have been measured. The measured and Carter-reactivity factors were highly correlated, suggesting that the chemical model used by Carter accounts for the reactivities of a wide range of compounds with dramatically different uncertainties in their mechanisms. The measured results, in general, are consistent with the Carter-reactivity factors for comparing the relative reactivities of VOCs in the atmosphere. However, additional kinetic and mechanistic studies of many VOC species including aromatic isomers are needed to improve reactivity scales.     

An investigation of the impact of afforestation on stream-water chemistry in the Loch Dee catchment, SW Scotland

The impact of conifer afforestation on stream-water chemistry was investigated in the acidified catchment of Loch Dee, SW Scotland. Long-term trends in stream-water chemistry were evaluated during a period of forest growth from age 6 to 17 years. A significant increase was observed for pH (0.2 units) and a significant decline for aluminium (0.05 mg litre(-1)), sulphate (1.2 mg litre(-1)) and nitrate (0.02 mg litre(-1)) concentrations. The long-term decrease in stream-water acidity was ascribed to the marked reductions in sulphur depositions during the 1970s and early 1980s. There was no evidence that this response had been attenuated by afforestation, the improvements in stream-water chemistry being of a similar magnitude to those recorded in nearby moorland lochs and exceeding that in an adjacent moorland-catchment stream. The lack of a clear forest acidification effect is consistent with deposition-model estimates which show the increased scavenging of occult and dry deposition by the growing forest to be small at this site (相似文献   

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.     

An investigation of distributed lag models in the context of air pollution and mortality time series analysis

In particulate air pollution mortality time series studies, the particulate air pollution exposure measure used is typically the current day's or the previous day's air pollution concentration or a multi-day moving average air pollution concentration. Distributed lag models (DLMs) that allow for differential air pollution effects that are spread over multiple days are seen as an improvement over using a single- or multi-day moving average air pollution exposure measure. However, at the current time, the statistical properties of DLMs as a measure of air pollution exposure have not been investigated. In this paper, a simulation study is used to investigate the performance of DLMs as a measure of air pollution exposure in comparison with single- and multi-day moving average air pollution exposure measures under various forms for the true effect of air pollution on mortality. The simulation study shows that DLMs offer a more robust measure of the effect of air pollution on mortality and avoid the potential for a large negative bias compared with single- or multi-day moving average air pollution exposure measures. This is important information. In many U.S. cities, particulate air pollution concentrations are observed only once every six days, meaning it is often only possible to use single-day particulate air pollution exposure measures. The results from this paper will help quantify the magnitude of the negative bias that can result from using single-day exposure measures. The implications of this work for future air pollution mortality time series studies are discussed. The data used in this paper are concurrent daily time series of mortality, weather, and particulate air pollution from Cook County, IL, for the period 1987-1994.