Spatial variation in concentrations of dissolved nitrogen species in an upland blanket peat catchment

The concentration of nitrogen (N), particularly as nitrate (NO3-N), in upland streams, lakes and rivers is frequently used as a diagnostic of the vulnerability of upland ecosystems to increased atmospheric nitrogen deposition and N saturation. The N content of running waters, however, is generally assessed on the basis of sampling at a limited number of points in space and time within the catchment under investigation. The current study was conducted at Trout Beck, an 11.5 km2 blanket peat-dominated catchment in the North Pennine uplands of the UK. Results from sampling at 33 sites within this catchment demonstrated that the concentrations of all dissolved N species were highly variable, even over short distances. Statistical relationships between the concentrations of NO3-N and dissolved organic nitrogen (DON) and percentage catchment cover of Calluna/Eriophorum and Eriophorum vegetation were found. However, it was also noted that in catchments containing limestone outcrops, NO3-N concentration was much higher than in catchments where runoff was sourced directly from the blanket peat surface. It is possible that NH4-N and DON leached from the blanket peat are mineralised and nitrified, providing a source for the NO3-N found in the river channels. Overall, the current study suggests that interpretations of N-saturation based on river water chemistry measurements at a single point must be treated cautiously, and that the influence of catchment-scale physical factors, such as vegetation and geology cover on the concentration of dissolved N species in upland river waters should not be ignored.     

Atmospheric NH3 and NO2 concentration and nitrogen deposition in an agricultural catchment of Eastern China

To assess the atmospheric environmental impacts of anthropogenic reactive nitrogen in the fast-developing Eastern China region, we measured atmospheric concentrations of nitrogen dioxide (NO₂) and ammonia (NH₃) as well as the wet deposition of inorganic nitrogen (NO₃⁻ and NH₄⁺) and dissolved organic nitrogen (DON) levels in a typical agricultural catchment in Jiangsu Province, China, from October 2007 to September 2008_. The annual average gaseous concentrations of NO₂ and NH₃ were 42.2 μg m⁻³ and 4.5 μg m⁻³ (0 °C, 760 mm Hg), respectively, whereas those of NO₃⁻, NH₄⁺, and DON in the rainwater within the study catchment were 1.3, 1.3, and 0.5 mg N L⁻¹, respectively. No clear difference in gaseous NO₂ concentrations and nitrogen concentrations in collected rainwater was found between the crop field and residential sites, but the average NH₃ concentration of 5.4 μg m⁻³ in residential sites was significantly higher than that in field sites (4.1 μg m⁻³). Total depositions were 40 kg N ha⁻¹ yr⁻¹ for crop field sites and 30 kg N ha⁻¹ yr⁻¹ for residential sites, in which dry depositions (NO₂ and NH₃) were 7.6 kg N ha⁻¹ yr⁻¹ for crop field sites and 1.9 kg N ha⁻¹ yr⁻¹ for residential sites. The DON in the rainwater accounted for 16% of the total wet nitrogen deposition. Oxidized N (NO₃⁻ in the precipitation and gaseous NO₂) was the dominant form of nitrogen deposition in the studied region, indicating that reactive forms of nitrogen created from urban areas contribute greatly to N deposition in the rural area evaluated in this study.     

Continuous biotransformation and removal of nitrophenols under denitrifying conditions

The effect of COD/NO(3)(-)-N ratio on the biotransformation and removal of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP) was studied in bench scale upflow anaerobic sludge blanket (UASB) reactors. Sodium acetate and sodium nitrate were used as electron donor (substrate) and electron acceptor, respectively. Nitrate nitrogen loading was increased from 0.098 to 0.6 kg/m(3)d in order to keep COD/NO(3)(-)-N ratio as 20.8, 14.3, 9.8, 5.0, 4.0 and 3.33. Throughout the study, input nitrophenolic concentration and hydraulic retention time (HRT) were kept constant as 30 mg/l and 24h, respectively. 2-Aminophenol (2-AP), 4-aminophenol (4-AP) and 2-amino,4-nitrophenol (2-A,4-NP) were found as the major intermediate metabolite of 2-NP, 4-NP and 2,4-DNP, respectively. Removal of all the three nitrophenols increased with lowering of COD/NO(3)(-)-N ratio. However, nitrophenols removal got adversely affected when COD/NO(3)(-)-N ratio was reduced below 5. Maximum removal achieved were 91.63%, 90.17% and 86.10% for 2-NP, 4-NP and 2,4-DNP, respectively at a COD/NO(3)(-)-N ratio of 5. Simultaneous denitrification and methanogenesis was observed in all the reactors throughout the study.     

Erratum to “Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities”

The status of nitrate (NO₃⁻), nitrite (NO₂⁻) and ammonium (NH₄⁺) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate δ¹⁵N and δ¹⁸O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields).The exponential increase in NO₃⁻-δ¹⁵N along with the NO₃⁻ reduction and clear δ¹⁸O/δ¹⁵N slopes of NO₃⁻ (∼ 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO₃⁻ contamination via active denitrification and reduced nitrification.Our results showed that NO₃⁻ and NH₄⁺ contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Long-term continuous monitoring of the dissolved CO2 performed by using a new device in groundwater of the Mt. Etna (southern Italy)

We present a new device for continuous monitoring of the concentration of CO₂ dissolved in water. The device consists of a tube made of a polymeric semi-permeable membrane connected to an infrared gas analyser (IRGA) and a pump. Several laboratory experiments were performed to set the best operating condition and test the accuracy of measurements. We used the device for performing 20 months of continuous monitoring of dissolved CO₂ concentration (DCC) in groundwater within a drainage gallery at Mt. Etna. The monitored groundwater intercepts the Pernicana Fault, along which degassing is observed related to volcano-tectonic activity. The acquired data were compared with continuous and discrete data obtained using existing methods. The measurements of DCC resulted in some period of the year well correlated with air temperature. We also found that long-term trends, as well as short-term variations, are probably linked to the dynamics of volcanic activity and/or perturbations in the local or regional stress fields.     

Effect of shock and mixed nitrophenolic loadings on the performance of UASB reactors

The effect of nitrophenolic shock loads on the performance of three bench-scale upflow anaerobic sludge blanket (UASB) reactors was studied using synthetic wastewater. Reactors R1, R2 and R3 were fed with 30 mg/L concentration of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), respectively, along with methanol (COD = 2000 mg/ L), sodium nitrate (NO3(-)-N=200mg/L), and other nutrients. The reactors were in continuous operation for more than 2 years before the shock loading study was performed. Five nitrophenolic shock loadings of 45, 60, 75, 90 and 120mg/L d were administrated by increasing the influent nitrophenolic concentration to 45, 60, 75, 90 and 120mg/L, respectively, while keeping hydraulic retention time as 24h. The shocks were given continuously for a period of 4 days before switching back to normal nitrophenolic loading (30mg/Ld). The reactors were allowed to recover to normal performance level before administrating the next nitrophenolic shock load. The study showed that the nitrophenolic shock load of as high as 120 mg/L d did not affect the reactors performance irreversibly. After resuming the normal nitrophenolic loading, it took almost 3-18 days for the reactors to recover from the shock effect. The study was further extended to assess the maximum possible mixed nitrophenolic loading (2NP:4NP:2,4:DNP = 1:1:1) to which 2,4-DNP acclimated granular sludge containing reactor (R3) can be exposed without hampering the reactor (R3) performance irreversibly. The reactor was able to achieve pseudo-steady-state at a mixed nitrophenolic loading of 180 mg/L d with more than 90% removal of all the three nitrophenols, but failed at a mixed nitrophenolic loading of 225 mg/Ld.     

In situ measurements of SO2, NOx, NOy, and O3 in Beijing, China during August 2008

The measurement of SO₂, O₃, NO, NO₂, and NO_y mixing ratios was conducted from Jul 28, 2008 to Sep 2, 2008 at the Institute of Atmospheric Physics, Chinese Academy of Sciences (IAP, CAS) station, which is 2 km southwest to the Beijing National Stadium (Bird's Nest/Olympic Stadium). Photochemical pollution was detected during the measurement on Aug 2, 2008, and the maximum hourly average [O₃] reached 128 ppbv, caused by both the local photochemical reactions and regional transportation of pollutants. The NO_x Ozone Production Efficiency (OPE (NO_x)) values were 6.9 and 20.2 on Aug 2 and Aug 24, 2008 respectively, which were the two days with highest O₃ pollution. The OPE (NO_x) of 6.9 on Aug 2 was within a typical range in city area, and it implied that the high O₃ could be due to local sources. While OPE (NO_x) of 20.2 on Aug 24 was larger than the typical value in the region, but lower than that of the surrounding clean area during 2008 Beijing Olympics Closing Ceremony. It indicated that the pollution was because of regional transportation of pollutants. In addition, 60% of the extent of the Smog Production Model (SPM) data was less than 0.6 and the rest was slightly larger than 0.6, with maximum of 0.78. It indicated that the sensitivity of O₃ generated was volatile organic compounds (VOCs) control during the observation period. The SPM results also implied that O₃ product in high-O₃ day is a transition state from VOCs sensitivity to NO_x sensitivity. Lastly, the analysis of the wind direction and extent of SPM showed that the photochemical pollution of this region was mostly subject to the influence of southeastern air flow in the summer.     

Status of groundwater arsenic contamination in Bangladesh: A 14-year study report

Since 1996, 52,202 water samples from hand tubewells were analyzed for arsenic (As) by flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS) from all 64 districts of Bangladesh; 27.2% and 42.1% of the tubewells had As above 50 and 10 μg/l, respectively; 7.5% contained As above 300 μg/l, the concentration predicting overt arsenical skin lesions. The groundwater of 50 districts contained As above the Bangladesh standard for As in drinking water (50 μg/l), and 59 districts had As above the WHO guideline value (10 μg/l). Water analyses from the four principal geomorphological regions of Bangladesh showed that hand tubewells of the Tableland and Hill tract regions are primarily free from As contamination, while the Flood plain and Deltaic region, including the Coastal region, are highly As-contaminated. Arsenic concentration was usually observed to decrease with increasing tubewell depth; however, 16% of tubewells deeper than 100 m, which is often considered to be a safe depth, contained As above 50 μg/l. In tubewells deeper than 350 m, As >50 μg/l has not been found. The estimated number of tubewells in 50 As-affected districts was 4.3 million. Based on the analysis of 52,202 hand tubewell water samples during the last 14 years, we estimate that around 36 million and 22 million people could be drinking As-contaminated water above 10 and 50 μg/l, respectively. However for roughly the last 5 years due to mitigation efforts by the government, non-governmental organizations and international aid agencies, many individuals living in these contaminated areas have been drinking As-safe water. From 50 contaminated districts with tubewell As concentrations >50 μg/l, 52% of sampled hand tubewells contained As <10 μg/l, and these tubewells could be utilized immediately as a source of safe water in these affected regions provided regular monitoring for temporal variation in As concentration. Even in the As-affected Flood plain, sampled tubewells from 22 thanas in 4 districts were almost entirely As-safe. In Bangladesh and West Bengal, India the crisis is not having too little water to satisfy our needs, it is the challenge of managing available water resources. The development of community-specific safe water sources coupled with local participation and education are required to slow the current effects of widespread As poisoning and to prevent this disaster from continuing to plague individuals in the future.     

Alumina nanofibers grafted with functional groups: A new design in efficient sorbents for removal of toxic contaminants from water

A new design in efficient sorbents for the removal of trace pollutants from water was proposed: grafting the external surface of γ-alumina (γ-Al₂O₃) nanofibers with functional groups that have a strong affinity to the contaminants. This new grafting strategy greatly improves the accessibility of these sorption sites to adsorbates and thus efficiency of the fibrous sorbents. The product sorbents could capture the pollutants selectively even when the concentration of the contaminants is extremely low. Two types of γ-Al₂O₃ nanofibers with different size were prepared via facile hydrothermal methods. Thiol groups were then grafted on the γ-Al₂O₃ fibers by refluxing the toluene solution of 3-mercaptopropyltrimethoxysilane (MPTMS). The thiol group modified fibers not only can efficiently remove heavy metal ions (Pb²⁺ and Cd²⁺) from water at a high flux, but also display high sorption capacity under sorption equilibrium conditions. Similar result was obtained from the nanofibers grafted with octyl groups which are employed to selectively adsorb highly diluted hydrophobic 4-nonylphenol molecules from water. This study demonstrates that grafting nanofibers is a new and effective strategy for developing efficient sorbents.     

A study on the relationship between biodegradability enhancement and oxidation of 1,4-dioxane using ozone and hydrogen peroxide

Advanced oxidation involving O₃/H₂O₂ was used to eliminate 1,4-dioxane and to enhance the biodegradability of dioxane-contaminated water. Oxidation experiments were carried out in a bubble column reactor operating in fed-batch. The rate of dioxane removal and enhancement in biodegradability was investigated at hydrogen peroxide to ozone ratios between 0 and 0.6 mol:mol and pH between 5 and 11. A theoretical model was also applied to predict the experimental data and to investigate the effects of dioxane concentration, pH, and H₂O₂ concentration. The model predictions fit the experimental data well and there was a linear correlation between dioxane oxidation and BOD enhancement. At low dioxane concentrations, the oxidation rate was first order and it gradually approached zero order with increasing dioxane concentration. Also, the biodegradability of the solution increased with pH up to about 9 and it stayed constant with further pH increase. Hydrogen peroxide initially enhanced dioxane removal and biodegradability enhancement of the solution. However, at H₂O₂:O₃ ratios greater than about 0.4-0.45 mol:mol, i.e. about 2.90 mM for H₂O₂ concentration, H₂O₂ had negative impacts and resulted in reduced dioxane removal and biodegradability increase.     

Use of stable nitrogen isotope fractionation to estimate denitrification in small constructed wetlands treating agricultural runoff

Constructed wetlands (CWs) in the agricultural landscape reduce non-point source pollution through removal of nutrients and particles. The objective of this study was to evaluate if measurements of natural abundance of (15)NO(3)(-) can be used to determine the fate of NO(3)(-) in different types of small CWs treating agricultural runoff. Nitrogen removal was studied in wetland trenches filled with different filter materials (T1--sand and gravel; T3--mixture of peat, shell sand and light-weight aggregates; T8--barley straw) and a trench formed as a shallow pond (T4). The removal was highest during summer and lowest during autumn and winter. Trench T8 had the highest N removal during summer. Measurements of the natural abundance of (15)N in NO(3)(-) showed that denitrification was not significant during autumn/winter, while it was present in all trenches during summer, but only important for nitrogen removal in trench T8. The (15)N enrichment factors of NO(3)(-) in this study ranged from -2.5 to -5.9 per thousand (T3 and T8, summer), thus smaller than enrichment factors found in laboratory tests of isotope discrimination in denitrification, but similar to factors found for denitrification in groundwater and a large CW. The low enrichment factors compared to laboratory studies was attributed to assimilation in plants/microbes as well as diffusion effect. Based on a modified version of the method presented by Lund et al. [Lund LJ, Horne AJ, Williams AE, Estimating denitrification in a large constructed wetland using stable nitrogen isotope ratios. Ecol Engineer 2000; 14: 67-76], denitrification and assimilation were estimated to account for 53 to 99 and 1 to 47%, respectively, of the total N removal during summer. This method is, however, based on a number of assumptions, and there is thus a need for a better knowledge of the effect of plant uptake, microbial assimilation as well as nitrification on N isotopic fractionation before this method can be used to evaluate the contribution of dinitrification in CWs.     

Migration of As, and H/He ages, in groundwater from West Bengal: Implications for monitoring

From 2002 to 2010 inclusive we monitored concentrations of arsenic (As) and major ions (Ca, Mg, Sr, Na, K, Fe, Mn, Cl, and SO₄) in groundwater from 14 domestic wells and three piezometer nests in a shallow aquifer (<60 m depth), and 3 wells in a deep aquifer (>70 m depth), in southern West Bengal, India. In the deep aquifer, concentrations of As did not change over time despite increases in the concentration of Fe in two wells. The shallow aquifer occurs in two sedimentological settings: palaeo-channel and palaeo-interfluve. At the top of the shallow aquifer of the palaeo-channel, decreases in all constituent concentrations with time, and an ³H/³He age of 1.4 years, proves that the aquifer is beginning to be flushed of pollutants. In As-polluted groundwater (>50 μg/L As) tapped from deeper grey sands of the shallow, palaeo-channel, aquifer, concentrations of As were mostly stable over time, but both increases and decreases occurred with time in response to downward migration of the chemically-stratified water column. In groundwater tapped from Pleistocene brown sands, the concentration of As remained either low and stable (<2 μg/L As), or increased at rates up to 34 μg/L per year. The increases were caused by the flow of As-rich groundwater either downward into brown sand at the base of palaeo-channels, or laterally into a confined, unpolluted, palaeo-interfluvial, aquifer of brown sand that lies regionally beneath a palaeosol.Under the present pumping regime, the prognosis for As-pollution in the shallow aquifer is complex. Wells in brown sand may become polluted over timescales of as little as 2 years, whilst some wells tapping As-polluted groundwater from grey sand will become fit for potable use (<50 μg/L) within a few decades. The evidence of flushing, and of declining As in some of the groundwater from palaeo-channels, which are conduits for recharge of the confined, As-free, palaeo-interfluve aquifer, and probably also the deeper aquifer, offers hopes that the spread of As-pollution will be limited.     

Frequency distributions of water quality variables : Relationships between mean and maximum values

Frequency distributions of water quality variables have been analysed by using about 950 samples from 25 meso- to hypertrophic lakes. By expressing all values as relative to their means, data from all the lakes could be pooled to datasets based on about 950 values for each variable. The distributions of COD, conductivity, pH and colour were symmetrical with very high frequencies around 100% of the mean. The variables of total-N, total-P, suspended solids and Secchi disk transparency followed more skew distributions, while turbidity, chlorophyll a and MRP were markedly skewed. The inorganic nitrogen fractions had their highest frequency at or just above zero percent of the mean.Three probability density functions (pdf) namely beta, gamma and log normal distributions were fitted to the pooled data. There were two variables, colour and conductivity, which did not fit to any of the pdf's but for the rest the null hypothesis could not be rejected at the 99.5% level. Frequency distributions for each lake demonstrated that for most variables one or two lakes showed distributions deviating from the pooled data pdf. There were no discernible trends among lakes and the number of rejections seemed to be randomly distributed. The study is inconclusive but does not reject the approach of using frequency distributions of relative values when only the mean is known. Agreement between expected maxima and those observed by other investigators indicate that the log normal distributions estimated here might be generally applicable as a rule of thumb on what the maximum will be in relation to the mean. The results of this study also indicate that the frequency distributions are similar for a large variety of water quality in many lakes. This information is of great interest for water management as good approximation of maximum values might be achieved if the means are known.     

Molecular and phylogenetic approaches for assessing sources of Cryptosporidium contamination in water

The high sequence diversity and heterogeneity observed within species or genotypes of Cryptosporidium requires phylogenetic approaches for the identification of novel sequences obtained from the environment. A long-term study on Cryptosporidium in the agriculturally-intensive South Nation River watershed in Ontario, Canada was undertaken, in which 60 sequence types were detected. Of these sequence types 33 were considered novel with no identical matches in GenBank. Detailed phylogenetic analysis identified that most sequences belonged to 17 previously described species: Cryptosporidium andersoni, Cryptosporidium baileyi, Cryptosporidium hominis, Cryptosporidium parvum, Cryptosporidium ubiquitum, Cryptosporidium meleagridis, muskrat I, muskrat II, deer mouse II, fox, vole, skunk, shrew, W12, W18, W19 and W25 genotypes. In addition, two new genotypes were identified, W27 and W28. C. andersoni and the muskrat II genotype were most frequently detected in the water samples. Species associated with livestock made up 39% of the total molecular detections, while wildlife associated species and genotypes accounted for 55% of the Cryptosporidium identified. The human pathogenic species C. hominis and C. parvum had an overall prevalence of 1.6% in the environment, indicating a small risk to humans from the Cryptosporidium present in the watershed. Phylogenetic analysis and knowledge of host-parasite relationships are fundamental in using Cryptosporidium as a source-tracking or human health risk assessment tool.     

Evaluation of a multiple regression model for the forecasting of the concentrations of NOx and PM10 in Athens and Helsinki

Forecasting models based on stepwise multiple linear regression (MLR) have been developed for Athens and Helsinki. The predictor variables were the hourly concentrations of pollutants (NO, NO₂, NO_x, CO, O₃, PM_2.5 and PM₁₀) and the meteorological variables (ambient temperature, wind speed/direction, and relative humidity) and in case of Helsinki also Monin-Obukhov length and mixing height of the present day. The variables to be forecasted are the maximum hourly concentrations of PM₁₀ and NO_x, and the daily average PM₁₀ concentrations of the next day. The meteorological pre-processing model MPP-FMI was used for computing the Monin-Obukhov length and the mixing height. The limitations of such statistical models include the persistence of both the meteorological and air quality situation; the model cannot account for rapid changes (on a temporal scale of hours or less than a day) that are commonly associated, e.g., with meteorological fronts, or episodes of a long-range transport origin. We have selected the input data for the model from one urban background and one urban traffic station both in Athens and Helsinki, in 2005. We have used various statistical evaluation parameters to analyze the performance of the models, and inter-compared the performance of the predictions for both cities. Forecasts from the MLR model were also compared to those from an Artificial Neural Network model (ANN) to investigate, if there are substantial gains that might justify the additional computational effort. The best predictor variables for both cities were the concentrations of NO_x and PM₁₀ during the evening hours as well as wind speed, and the Monin-Obukhov length. In Athens, the index of agreement (IA) for NO_x ranged from 0.77 to 0.84 and from 0.69 to 0.72, in the warm and cold periods of the year. In Helsinki, the corresponding values of IA ranged from 0.32 to 0.82 and from 0.67 to 0.86 for the warm and cold periods. In case of Helsinki the model accuracy was expectedly better on the average, when Monin-Obukhov length and mixing height were included as predictor variables. The models provide better forecasts of the daily average concentration, compared with the maximum hourly concentration for PM₁₀. The results derived by the ANN model where only slightly better than the ones derived by the MLR methodology. The results therefore suggest that the MLR methodology is a useful and fairly accurate tool for regulatory purposes.     

Air quality in Delhi: status and concerns

Data on the status of air quality are presented for two locations in Delhi, the capital city of India, for 2013. Our study revealed that the levels of oxides of nitrogen (NO_x), particulate matter of 10 or <10 μm aerodynamic diameter (PM₁₀) and benzene exceeded the maximum permissible limits laid down in the National Ambient Air Quality Standards (NAAQS). On most of the monitoring days, the concentrations of PM₁₀ also exceeded the limits for 24 h averages stipulated by the NAAQS. This study also demonstrated that the concentration of pollutants varied with the season, peaking in dry season (winter) mainly because of the relatively stable meteorological conditions and recording the lowest values in the wet season (the rainy season) because of turbulence, strong winds, and rains. The post-monsoon season showed the contribution of local sources. The strong correlation among NO_x, PM₁₀, and benzene strongly suggests that motor vehicles are the major contributor to this pollution. Intervention by regulatory agencies is essential to improve the air quality of Delhi.     

Role of Saharan dust in the relationship between particulate matter and short-term daily mortality among the elderly in Madrid (Spain)

Background

Saharan dust outbreaks are a common phenomenon in the Madrid atmosphere. The current Directive 2008/50 CE governing air quality in European cities, draws no distinction between which particulate matter (PM₁₀, PM_2.5 or PM_10-2.5) would be the best indicator on days with/without Saharan dust intrusions. This study sought to identify the role played by Saharan dust in the relationship between particulate matter (PM₁₀, PM_2.5 and PM_10-2.5) concentrations and daily mortality among the elderly in the city of Madrid.

Methods

We conducted an ecological longitudinal time-series study on daily mortality among the over-75 age group, from 2003 to 2005. Poisson regression models were constructed for days with and without Saharan dust intrusions. The following causes of daily mortality were analysed: total organic causes except accidents (International Classification of Diseases-10th revision (ICD-10): A00-R99); circulatory causes (ICD-10: I00-I99); and respiratory causes (ICD-10: J00-J99). Daily mean PM₁₀, PM_2.5 and PM_10-2.5 levels were used as independent variables. Control variables were: other ambient pollutants (chemical, biotic and acoustic); trend; seasonalities; influenza epidemics; and autocorrelations between mortality series.

Results

While daily mean PM_2.5 concentrations in Madrid displayed a significant statistical association with daily mortality for all the above causes on days without Saharan dust intrusions, this association was not in evidence for PM₁₀ or PM_10-2.5 in the multivariate models. The relative risks (RRs) obtained for an increase of 10 μg/m³ in PM_2.5 concentrations were: 1.023 (1.010-1.036) for total organic causes; 1.033 (1.031-1.035) for circulatory causes; and 1.032 (1.004-1.059) for respiratory causes. On Saharan dust days, a significant statistical association was detected between PM₁₀ (though not PM_2.5 or PM_10-2.5) and mortality for all 3 causes analysed, with RRs statistically similar to those reported for PM_2.5.

Conclusions

The best air quality indicators for evaluating the short-term health effects of particulate matter in Madrid are therefore PM₁₀ concentrations on days with, and PM_2.5 concentrations on days without Saharan dust outbreaks. This fact should be taken into account in a European Directive regulating ambient air quality in almost all countries in the Mediterranean area.     

The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008). Links were found between the dissolved organic carbon (DOC), nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy. Underlying soil type determined the leaching or accumulation of these elements. Under oak, monitored at two sites, frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of ~ 16 kg ha⁻¹extra N during defoliation. Peaks of nitrate (NO₃-N) flux between 5 and 9 kg ha⁻¹ (×5 usual winter values) were recorded in consecutive years in shallow soil waters. Synchronous rises in deep soil NO₃-N fluxes at the Grizedale sandy site indicate downward flushing, not seen at the clay site. Under three Sitka spruce stands, generation of honeydew (DOC) was attributed to two aphid species (Elatobium abietinum and Cinara pilicornis) with distinctive feeding strategies. Throughfall DOC showed mean annual fluxes (6 seasons) ~ 45-60 kg ha⁻¹ compared with rainfall values of 14-22 kg ha⁻¹. Increases of total N in throughfall and NO₃-N fluxes in shallow soil solution were detected — soil water fluxes reached  8 kg ha⁻¹ in Llyn Brianne, ~ 25 kg ha⁻¹ in Tummel, and ~ 40 kg NO₃-N ha⁻¹ in Coalburn. At Tummel, on sandy soil, NO₃-N leaching showed increased concentration at depth, attributed to microbiological activity within the soil. By contrast, at Coalburn and Llyn Brianne, sites on peaty gleys, soil water NO₃-N was retained mostly within the humus layer. Soil type is thus key to predicting N movement and retention patterns. These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems, on above and below ground processes affecting tree growth, soil condition, vegetation and water quality.     

Mechanism of phenol photodegradation in the presence of pure and modified-TiO(2): A review

In recent years, the application of heterogeneous photocatalytic water purification processes has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible-light spectrum. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its costly effectiveness, inert nature and photostability. A substantial amount of research has focused on the enhancement of TiO₂ photocatalysis by modification with metal, non-metal and ion doping.This paper aims to review and summarize the recent works on the titanium dioxide (TiO₂) photocatalytic oxidation of phenol and discusses various mechanisms of phenol photodegradation (indicating the intermediates products) and formation of OH radicals. Phenol degradation pathway in both systems, TiO₂/UV and doped-TiO₂/Vis, are described.     

Air pollution and meteorological processes in the growing dryland city of Urumqi (Xinjiang, China)

Seven years (2000-2006) of monthly PM₁₀ (particulate matter, d ≤ 10 μm), SO₂, and NO₂ concentrations are reported for Urumqi, the capital of Xinjiang in NW China. Considerably high mean annual concentrations have been observed, which ranged between 150 and 240 μg m^− 3 (PM₁₀), 31 and 50 μg m^− 3 (NO₂), and 49 and 160 μg m^− 3 (SO₂). The shapes of seasonal variation of all pollutants were remarkably similar; however, winter/summer ratios of concentrations were quite different for PM₁₀ (2-3) and NO₂ (≈ 4) compared to SO₂ (up to 30). Very high consumption rates of fossil fuels for energy generation and domestic heating are mainly responsible for high annual pollution levels, as well as the (very) high winter/summer ratios. Detailed analysis of the 2000-2006 records of Urumqi's meteorological data resulted in inter-annual and seasonal frequency distributions of (a) (surface) inversion events, (b) heights of surface inversions, (c) stability classes of Urumqi's boundary layer, and (d) the “Air Stagnation Index (ASI)”. Urumqi's boundary layer is shown to be characterized by high mean annual and seasonal frequencies of (surface) inversions and by the dominance of stable dispersion classes. A further outcome of the meteorological analysis is the proof of Urumqi's strong diurnal wind system, which might have particularly contributed to the stabilization of the nocturnal boundary layer. Annual and seasonal variations of pollutant's concentrations are discussed in the context of occurrences of inversions, boundary layer, stability classes, and ASI. The trend of Urumqi's air pollution indicates a strong increase of mean annual concentrations 2000-2003, followed by a slight increase during 2003-2006. These are in strong contrast to (a) the growth of Urumqi's fleet of motor vehicles and (b) to the growing number of stable regimes of Urumqi's boundary layer climate during same period. It is concluded that the (regional and) local administrative technical countermeasures have efficiently lowered Urumqi's air pollution levels.