Atmospheric Environment (v.42, #21)
Editorial board (i).
Mineral and anthropogenic aerosols in Arabian Sea–atmospheric boundary layer: Sources and spatial variability by Ashwini Kumar; M.M. Sarin; A.K. Sudheer (5169-5181).
The chemical characteristics of aerosols in the Arabian Sea–atmospheric boundary layer (AABL) have been studied during the spring inter-monsoon (April and May 2006) based on the analysis of water-soluble constituents (Na+, NH4 +, K+, Mg2+, Ca2+, Cl−, NO3 −, and SO4 2−), crustal elements (Al, Fe, and Ca), and carbonaceous species (EC and OC). The total suspended particulate (TSP) abundance ranged from 8.2 to 46.9 μg m−3 (average (Av)=24.7±10.4 μg m−3) during 22 days cruise covering a latitudinal transect from 9°N to 22°N. The water-soluble species account for 35% of TSP; with dominant contribution of Ca2+ and SO4 2− followed by Na+ and minor contributions of K+, Mg2+, Cl−, and NO3 −. The abundances of Ca2+ and SO4 2− do not exhibit any noticeable latitudinal distribution pattern but the non-sea-salt (nss) component constitutes ∼85–90% of their total concentration, indicating dominant transport from continental sources. Furthermore, a significant linear positive correlation among nss-Ca2+ and nss-SO4 2−, and nss-Ca2+/nss-SO4 2− molar ratio averaging around 0.61 (range: 0.20–1.16) suggests uptake of anthropogenic SO4 2− by mineral dust (CaCO3). The chemical reaction favoring this neutralization of nss-SO4 2− is also evident from the abundance pattern of water-soluble Ca2+ nearly equal to the total Ca content measured in the aerosols. Using Al as a proxy, the mineral dust in AABL ranged from 2.7 to 23.7 μg m−3; with relatively high abundance occurring over the south Arabian Sea. On average, mineral dust accounts for 44% of the TSP and Fe/Al weight-ratio exhibit characteristic narrow range: 0.40–0.59. The impact of carbonaceous species (EC and OC) is nowhere pronounced in the AABL. The dry-deposition fluxes of Al, Fe, and bioavailable Fe to the surface Arabian Sea are estimated to be 665, 395, and 40 μg m−2 d−1, respectively.
Keywords: Atmospheric chemistry; Aerosols; Mineral dust; Deposition fluxes;
Source of nitrogen in wet deposition to a rice agroecosystem at Tai lake region by Yingxin Xie; Zhengqin Xiong; Guangxi Xing; Xiaoyuan Yan; Shulian Shi; Guoqing Sun; Zhaoliang Zhu (5182-5192).
Nitrogen (N) in wet deposition can provide significant nutrients to algae, which potentially contributes to eutrophication in waterbodies, and to nutrient surplus of rice–wheat crops in the Tai lake region, Jiangsu Province, China. Quantifying the N compounds in wet deposition and determining their sources is important to understand how to control eutrophication in lakes and to improve recommendations for fertilizer use. In this study, the concentrations of inorganic N, molar ratios of NH4 +/NO3 − and the natural 15N abundance of NH4 + (δ 15NH4 +) in wet deposition were determined for 78 precipitation events between June 2003 and July 2005. Samples were collected at two sites in Tai lake region, a watershed rice agroecosystem currently experiencing eutrophication. The average N wet deposition amounted to 27 kg N ha−1 yr−1, with 60% in the form of NH4 +. Annually, two cycles of depleted and enriched δ 15NH4 + indicate the shifting of main source of NH3 volatilization between chemical fertilizer and excreta of local residents and domestic animals, surface waters, and other organic N. The peak in NH4 +/NO3 − ratio, coupled with depleted δ 15NH4 + in mid-June, coincided with the rice-transplanting period, which is indicative of surplus fertilizer application. Enriched δ 15NH4 + values in August–October and in April–May were indicative of enhanced emissions from excreta and polluted waterbodies in the warmer seasons. Findings suggest that δ 15NH4 + could be used to indicate the sources of NH3 volatilization, and the NH4 +/NO3 − ratio to indicate the intensity of wet N deposition.
Keywords: Nitrogen isotope; Atmospheric wet deposition; Rice agriculture; Watershed ecosystem; Eutrophication;
Seasonal and spatial patterns of mercury wet deposition in the United States: Constraints on the contribution from North American anthropogenic sources by Noelle E. Selin; Daniel J. Jacob (5193-5204).
Observed wet deposition fluxes of mercury in the United States show a maximum in the Southeast, and a consistent seasonal variation (maximum in summer, minimum in winter) that increases in amplitude from north to south. We simulate these patterns successfully with a global 3-D chemical transport model (GEOS-Chem) including our best estimates of sources and processes. We attribute the high wet deposition over the Southeast in summer to scavenging of upper-altitude Hg(II) by deep convection. Seasonal variation at higher latitudes is attributed to a combination of enhanced summertime oxidation of Hg(0) and inefficient scavenging of Hg(II) by snow. Scavenging of Hg(II) from above the boundary layer contributes over half of wet deposition to the US in the model. Even within the boundary layer, we find that most of Hg(II) originates from the global mercury pool. Wet deposition in the model accounts for only 30% of total mercury deposition in the US, the remainder being from dry deposition, including 42% from Hg(0) uptake. North American anthropogenic emissions contribute 20% of total mercury deposition in the US (up to 50% in the industrial Midwest and Northeast).
Keywords: Mercury; Wet deposition; United States; Downwelling;
Design of a monitoring network over France in case of a radiological accidental release by Rachid Abida; Marc Bocquet; Nikki Vercauteren; Olivier Isnard (5205-5219).
The Institute of Radiation Protection and Nuclear Safety (France) is planning the set-up of an automatic nuclear aerosol monitoring network over the French territory. Each of the stations will be able to automatically sample the air aerosol content and provide activity concentration measurements on several radionuclides. This should help monitor the French and neighbouring countries nuclear power plants set. It would help evaluate the impact of a radiological incident occurring at one of these nuclear facilities. This paper is devoted to the spatial design of such a network. Here, any potential network is judged on its ability to extrapolate activity concentrations measured on the network stations over the whole domain. The performance of a network is quantitatively assessed through a cost function that measures the discrepancy between the extrapolation and the true concentration fields. These true fields are obtained through the computation of a database of dispersion accidents over one year of meteorology and originating from 20 French nuclear sites. A close to optimal network is then looked for using a simulated annealing optimisation. The results emphasise the importance of the cost function in the design of a network aimed at monitoring an accidental dispersion. Several choices of norm used in the cost function are studied and give way to different designs. The influence of the number of stations is discussed. A comparison with a purely geometric approach which does not involve simulations with a chemistry-transport model is performed.
Keywords: Radionuclides dispersion; Accidental release modelling; Network design; Simulated annealing; Geostatistics;
CHAID Models on boundary conditions of metal accumulation in mosses collected in Germany in 1990, 1995 and 2000 by Lukas Kleppin; Roland Pesch; Winfried Schröder (5220-5231).
The European heavy metals in mosses surveys allow mapping the metal accumulation in mosses indicating atmospheric deposition. Yet, there is still great uncertainty on how local and regional phenomena influence the atmospheric metal bioaccumulation. Therefore, the presented study aims at ranking factors that affect the spatial patterns of the metal concentrations in the mosses. Applying chi-square automatic interaction detection (CHAID) to the German moss measurements and related sampling site-specific descriptions taken from the surveys in 1990, 1995 and 2000 and supplementary land cover data, the spatial variation in metal concentrations in mosses were proved to depend mostly on different moss species, canopy drip and distance to the sea. Most of these findings could be corroborated by classification tree analyses on the same data as presented in another study. The results of both the studies should be verified by applying the same methodology using additional emission and deposition data and monitoring information from other countries participating in the UNECE moss surveys.
Keywords: CHAID; Metal bioaccumulation; Mosses; Sampling site characteristics;
Examination of discrepancies between beta-attenuation and gravimetric methods for the monitoring of particulate matter by Katsuyuki Takahashi; Hiroaki Minoura; Kazuhiko Sakamoto (5232-5240).
Continuous monitoring of the concentration of atmospheric particulate matter was carried out for 7 years by both gravimetric method and β-ray attenuation method (BAM) from a building rooftop in the Tokyo metropolitan area. The two methods showed a different tendency in each season: the data observed by BAM were higher than those by the gravimetric method in summer, and this difference was reversed in winter. The volatilization of ammonium salts accounted for only 30% of the difference between the monitoring methods in summer. Thus, we considered the differences in the water content measured by each method. The concentration difference between methods increased when relative humidity exceeded the deliquescence point of ammonium sulfate in summer, and the water content was estimated to be 30%. However, differences in relative humidity did not explain why the data obtained by the gravimetric method exceeded BAM data by 20–30% in winter. We found that the gravimetric measurements generally exceeded BAM measurements in winter if the ambient absolute humidity during particle collection was higher than the absolute humidity during sample weighing. The water content of atmospheric aerosols greatly influences their mass concentrations. Care must be taken when using mass concentration data for purposes such as evaluating health effects.
Keywords: Ammonium salt; Deliquescence point; Relative humidity; Absolute humidity;
Methyl halide emission estimates from domestic biomass burning in Africa by M.I. Mead; M.A.H. Khan; I.R. White; G. Nickless; D.E. Shallcross (5241-5250).
Keywords: Africa; Biofuel; Domestic biomass burning; Emission factor; Methyl halide;
A model to calculate consistent atmospheric emission projections and its application to Spain by Julio Lumbreras; Rafael Borge; Juan Manuel de Andrés; Encarnación Rodríguez (5251-5266).
Global warming and air quality are headline environmental issues of our time and policy must preempt negative international effects with forward-looking strategies. As part of the revision of the European National Emission Ceilings Directive, atmospheric emission projections for European Union countries are being calculated. These projections are useful to drive European air quality analyses and to support wide-scale decision-making. However, when evaluating specific policies and measures at sectoral level, a more detailed approach is needed. This paper presents an original methodology to evaluate emission projections. Emission projections are calculated for each emitting activity that has emissions under three scenarios: without measures (business as usual), with measures (baseline) and with additional measures (target). The methodology developed allows the estimation of highly disaggregated multi-pollutant, consistent emissions for a whole country or region. In order to assure consistency with past emissions included in atmospheric emission inventories and coherence among the individual activities, the consistent emission projection (CEP) model incorporates harmonization and integration criteria as well as quality assurance/quality check (QA/QC) procedures. This study includes a sensitivity analysis as a first approach to uncertainty evaluation. The aim of the model presented in this contribution is to support decision-making process through the assessment of future emission scenarios taking into account the effect of different detailed technical and non-technical measures and it may also constitute the basis for air quality modelling. The system is designed to produce the information and formats related to international reporting requirements and it allows performing a comparison of national results with lower resolution models such as RAINS/GAINS. The methodology has been successfully applied and tested to evaluate Spanish emission projections up to 2020 for 26 pollutants but the methodology could be adopted for any particular region for different purposes, especially for European countries.
Keywords: Air pollution; Model; Emission projections; Projections uncertainty; QA/QC;
Direct measurements of the ozone formation potential from dairy cattle emissions using a transportable smog chamber by Cody J. Howard; Wenli Yang; Peter G. Green; Frank Mitloehner; Irina L. Malkina; Robert G. Flocchini; Michael J. Kleeman (5267-5277).
Tropospheric ozone continues to be an air pollution problem in the United States, particularly in California, Texas, and across the eastern seaboard. The obvious sources of ozone precursors have been largely controlled over the past several decades, leading to the critical examination of secondary sources. In particular, California has new air quality rules addressing agricultural sources of ozone precursors, including dairy farms. Some recent estimates predict that dairy cattle are second only to on-road vehicles as a leading source of ozone precursor emissions in California's San Joaquin Valley. The objective of this work was to directly measure the ozone formation potential from dairy housing. A transportable “smog” chamber was constructed and validated using organic gases known to be present in dairy emissions. The ozone formation potential of emissions from eight non-lactating dairy cows and their fresh waste was then directly evaluated in the field at a completely enclosed cow corral on the campus of the University of California, Davis. The results demonstrate that the majority of the ozone formation is explained by ethanol (EtOH) in the emissions from the dairy cows, not by acetone as previously thought. Ozone formation potential is generally small, with <20 ppb of ozone produced under typical conditions when EtOH concentrations were ∼200 ppb and NO x concentrations were ∼50 ppb. The results match our current understanding of atmospheric ozone formation potential, ruling out the possibility of unknown organic compounds in dairy emissions with significant ozone formation potential. Simulations carried out with a modified form of the Caltech Atmospheric Chemistry Mechanism verify that actual ozone formation from dairy emissions is much lower than what would be predicted using the current regulatory profiles. Based on these results, the ozone formation potential of emissions from dairy cattle in California seems to be lower than previously estimated.
Keywords: Ozone formation potential; Portable smog chamber; Ethanol; Acetone;
Macro–meso two-scale model for predicting the VOC diffusion coefficients and emission characteristics of porous building materials by Jianyin Xiong; Yinping Zhang; Xinke Wang; Dongwu Chang (5278-5290).
Through the observation of the pore structure and mercury intruding porosimetry (MIP) experiments of some typical porous building materials, we found that the diffusion coefficient of the material can be expressed by that of a representative elementary volume (REV) in which the pore structure can be simplified as a connection in series of macro and meso pores. Based upon that, a macro–meso two-scale model for predicting the diffusion coefficient of porous building materials is proposed. In contrast to the traditional porous mass transfer model for determining the diffusion coefficient described in the literature [Blondeau, P., Tiffonnet, A.L., Damian, A., Amiri, O., Molina, J.L., 2003. Assessment of contaminant diffusivities in building materials from porosimetry tests. Indoor Air 13, 302–310; Seo, J., Kato, S., Ataka, Y., Zhu, Q., 2005. Evaluation of effective diffusion coefficient in various building materials and absorbents by mercury intrusion porosimetry. In Proceedings of the Indoor Air, Beijing, China, pp. 1854–1859], the proposed model relates the volatile organic compound (VOC) diffusion coefficient of building material not only to the porosity of the building material, but also to the pore size distribution and pore connection modes. To verify the model, a series of experiments of VOC emissions of three types of medium-density board were conducted. The comparison of the model and experimental results shows that the proposed model agrees much better with the experimental results than the traditional models in the literature. More validation for other building materials is needed. The proposed model is useful for predicting the VOC diffusion coefficient of porous building materials and for developing low VOC emission building materials.
Keywords: Indoor air quality (IAQ); Volatile organic compounds (VOCs); Porous media; Diffusion coefficient; Mass transfer;
Effects of vehicle type and fuel quality on real world toxic emissions from diesel vehicles by Peter F. Nelson; Anne R. Tibbett; Stuart J. Day (5291-5303).
Diesel vehicles are an important source of emissions of air pollutants, particularly oxides of nitrogen (NO x ), particulate matter (PM), and toxic compounds with potential health impacts including volatile organic compounds (VOCs) such as benzene and aldehydes, and polycyclic aromatic hydrocarbons (PAHs). Current developments in engine design and fuel quality are expected to reduce these emissions in the future, but many vehicles exceed 10 years of age and may make a major contribution to urban pollutant concentrations and related health impacts for many years. In this study, emissions of a range of toxic compounds are reported using in-service vehicles which were tested using urban driving cycles developed for Australian conditions. Twelve vehicles were chosen from six vehicle weight classes and, in addition, two of these vehicles were driven through the urban drive cycle using a range of diesel fuel formulations. The fuels ranged in sulphur content from 24 to 1700 ppm, and in total aromatics from 7.7 to 33 mass%. Effects of vehicle type and fuel composition on emissions are reported. The results show that emissions of these toxic species were broadly comparable to those observed in previous dynamometer and tunnel studies. Emissions of VOCs and smaller PAHs such as naphthalene, which are derived largely from the combustion process, appear to be related, and show relatively little variability when compared with the variability in emissions of aldehydes and larger PAHs. In particular, aldehyde emissions are highly variable and may be related to engine operating conditions. Fuels of lower sulphur and aromatic content did not have a significant influence on emissions of VOCs and aldehydes, but tended to result in lower emissions of PAHs. The toxicity of vehicle exhaust, as determined by inhalation risk and toxic equivalency factor (TEF)-weighted PAH emissions, was reduced with fuels of lower aromatic content.
Keywords: Motor vehicle emissions; Diesels; Fuel quality; Toxic air pollutants; PAHs; Aldehydes;
Measurements and estimates of leaf wetness over agricultural grassland for dry deposition modeling of trace gases by R.J. Wichink Kruit; A.F.G. Jacobs; A.A.M. Holtslag (5304-5316).
Leaf wetness is an important and frequent phenomenon for the surface–atmosphere exchange of some atmospheric trace gases that are well soluble in water, such as ammonia (NH3 and SO2), as well as for plant disease epidemiology. This study shows a comparison of two different techniques to measure leaf wetness; namely a painted flat-plate grid sensor and a system of four clip sensors. Although both techniques gave comparable results, the flat-plate grid sensor was favored, because of its stable signal and its ease of use. In this technique, the measurement height turned out to be of great importance for the leaf wetness duration (LWD); the flat-plate sensor at 1.0 m systematically underestimated LWD, while the flat-plate sensor at 0.1 m better represented the actual LWD. To obtain a representative signal, leaf wetness should be measured close to the surface. Using the available leaf wetness measurements, a comparison was made between three physical and four empirical leaf wetness models. Without any optimization, the physical model that calculates the potential condensation at the leaf surface gave the best results. However, after optimizing the humidity thresholds in the empirical leaf wetness models, the optimized model based on the difference between the actual and saturated specific humidity at the surface gave best results. For practical applications in atmospheric transport models, like for the calculation of dry deposition of well-soluble gases, the relative humidity (RH) threshold model might be easiest to implement. This study showed that different thresholds should be used for different vegetation types. In this study, an optimized RH threshold of 71% was derived for agricultural grassland.
Keywords: Leaf wetness; Leaf wetness modeling; Leaf wetness measurements; Leaf wetness sensor; Leaf wetness grid sensor;
Large eddy simulation of flow structures and pollutant dispersion in the near-wake region of the studied ground vehicle for different driving conditions by T.L. Chan; D.D. Luo; C.S. Cheung; C.K. Chan (5317-5339).
In the present study, a three-dimensional large eddy simulation (LES) of the flow structure, and pollutant dispersion and concentration field in the near-wake region of the studied ground vehicle [Dong, G., Chan, T.L., 2006. Large eddy simulation of flow structures and pollutant dispersion in the near-wake region of a light-duty diesel vehicle. Atmospheric Environment 40, 1104–1116] for different rear slant angles (i.e., α=25° and 60°), stationary (i.e., low and high idling modes) and moving (i.e., vehicle speed modes) vehicle conditions, vehicular exhaust jet exit conditions, and ambient wind conditions (i.e., wind speed and direction) within the urban road microenvironment was investigated comprehensively. Time-averaged flow and pollutant concentration fields behind the studied ground vehicle are calculated. The vehicular exhaust jet plume condition behind the studied ground vehicle dominates the flow pattern and pollutant dispersion at lower vehicle speed and low idling conditions. The vortices and turbulent mixing induced by the interaction between the vehicular exhaust jet plume, and the ambient wind flow condition behind the studied ground vehicle plays an important role in dispersing the pollutant concentration at higher vehicle speed and high idling conditions. The increasing of the studied ground vehicle speed restrains the development of the vehicular exhaust jet plume along the downstream direction and quickens the diluting rate of the pollutant concentration behind the studied ground vehicle. The oblique ambient wind flow condition enhances the dilution of pollutant concentration behind the studied ground vehicle along its vehicular exhaust jet plume in the downstream direction. However, a more evident effect of oblique ambient wind flow on dispersing the pollutant concentration behind the studied ground vehicle is found for the lower vehicle speed and low idling cases. The results provide a better understanding of the three-dimensional flow structures, and pollutant dispersion and concentrating field in the near-wake region of the studied ground vehicle for different driving conditions in urban road microenvironments.
Keywords: Large eddy simulation (LES); Pollutant concentration and dispersion; Near-wake region; Vehicular exhaust plume; Rear slant angle; Driving conditions; Ambient wind flow condition; Urban road microenvironments;
State-space model for airborne particles in multizone indoor environments by Min Li; Chun-Liang Wu; Shi-Qi Zhao; Yi Yang (5340-5349).
A state-space model is presented to predict the concentration and the fate of particulate matters (PM) in multizone indoor air. By introducing vector-matrix notation, the ordinary differential equations to describe the dynamic behavior of PM in multizone buildings are expressed as the state equation. The state equation is solved analytically and the dynamical evolution of PM is discussed quantitatively and qualitatively. The equilibrium point of the dynamic system is asymptotically stable. The minimum decay coefficient of PM concentrations is computed by the formula, which is found to directly link the minimum decay rate with the eigenvalues of the state matrix. The analytical solution based on the eigen structure shows that the evolution modes of indoor PM are mainly determined by the eigenvalues of state matrix. The detailed quantitative analysis on the diluted ventilation and interzonal transport via the central air-conditioning system indicates that the penetration efficiency of filter Pi and the integrated loss-rate coefficient kij integrating the remove mechanisms of natural ventilation, leakage and particle deposition have significant impact on dynamical behaviors of particles, such as the decay rate of concentrations and the ability of interzonal infection via HVAC system, etc.
Keywords: Airborne particles; State-space model; Aerosol dynamics; Multizone indoor environments;
An approach for the evaluation of exposure patterns of urban populations to air pollution by P. Pérez Ballesta; R.A. Field; R. Fernández-Patier; D. Galán Madruga; R. Connolly; A. Baeza Caracena; E. De Saeger (5350-5364).
Exposure concentrations of aromatic compounds were correlated with variables derived from time-microenvironment-activity (TMA) diaries to understand the relationship between exposure patterns and commuting behaviour of the population in a case study in Madrid. Approximately 200 air pollution samples were taken during a one-day campaign by means of diffusive samplers. An approach to determine the importance of selected activities and locations relative to a baseline condition, defined by a sample of approximately 100 commuters is described. A regression model is applied to determine the relative importance of identified situations, whether related directly to transport behaviour or through a labelled situation. The regression defines a baseline exposure concentration level where activities act as multiplying factors. The relationship of this baseline level and the set of activity factors, assigned to the population considered, to the ambient background is explored for its application to future studies. The calculation of exposure concentration gradients from the regression provides a means to characterise of the relative importance of different activities. A good level of agreement, in particular for benzene, was evident between the observed exposure concentrations and those calculated using the regression model.
Keywords: Air quality monitoring; Personal exposure; Exposure assessment; Diffusive samplers; Aromatic compounds; Benzene;
Factors affecting the seasonal variation of mass and ionic composition of PM2.5 at a central Mediterranean coastal site by Sotirios D. Glavas; Panayiotis Nikolakis; Demetrios Ambatzoglou; Nikos Mihalopoulos (5365-5373).
Mass and ionic composition of PM2.5 were determined for 1-year period (11/2004–10/2005) in a rural coastal Mediterranean site. The annual mean PM2.5 concentration measured was found to be 13.9 μg m−3. Smaller values were observed during the cold and rainy period compared to the warm and dry one. This may be ascribed to the scavenging of PM2.5 by rainfall during the cold period, in conjunction with the enhanced resuspension of soil dust and increased secondary aerosol formation during the warm period. Weekday/weekend variations and segregation of PM values according to wind direction, showed that local sources are not significant factors controlling the particle levels. Long-range transport is the dominant factor. Short distance to sampling site air paths traveling near ground resulted to larger PM values. Sulfate was found to be the main ionic species with annual mean concentration of 3.2 μg m−3, contributing 23.3% to the measured PM2.5 mass. It exhibited a seasonal variation with higher values in the summer months. The contributions of nitrate and chloride to the PM2.5 mass were 3.3% and 1.2%, respectively. Ammonium had an annual mean concentration of 1.6 μg m−3 and Ca2+ 0.33 μg m−3. They were the dominant cations contributing 11.2% and 2.7%, respectively, to the measured PM mass. In total the ionic species accounted for 45% of the PM2.5 mass. The calcium ions indicate that crustal materials are also important contributors to PM2.5 in this region, even though their major occurrence would be in the coarse mode. Finally Na+, K+ and Mg2+ had annual mean concentrations 0.24, 0.19 and 0.02 μg m−3, respectively. They contributed 3.1%, 0.34% and 0.18%, respectively, to the measured particulate mass. Anthropogenic contribution was calculated to account for 40% of the PM2.5 mass, crustal material (dust) for 25% and marine aerosol 4.3%.
Keywords: PM2.5; Mediterranean; Long-range transport; Major anions; Major cations;
Intra-community spatial variation of size-fractionated PM mass, OC, EC, and trace elements in the Long Beach, CA area by Margaret A. Krudysz; John R. Froines; Philip M. Fine; Constantinos Sioutas (5374-5389).
Local traffic patterns and proximity to pollution sources are important in assessing particulate matter (PM) exposure in urban communities. This study investigated the intra-community spatial variation of PM in an urban area impacted by numerous local and regional sources. Weekly size-segregated (<0.25, 0.25–2.5, and >2.5 μm) PM samples were collected in the winter of 2005. During each 1-week sampling cycle, data were collected concurrently at four sites within four miles of one another in the Long Beach, CA area. Coefficients of divergence analyses for size-fractionated PM mass, organic and elemental carbon, sulfur, and 18 other metals and trace elements suggest a wide range of spatial divergence. High spatial variability was observed in the <0.25 μm and 0.25–2.5 μm PM fractions for many elements associated with motor vehicle emissions. Relatively lower spatial divergence was observed in the coarse fraction, although road dust components were spatially diverse but highly correlated with each other. Mass and OC concentrations were homogeneously distributed over the sampling sites. Possible oil combustion sources were identified using previously documented markers such as vanadium and nickel and by distinguishing between primary sulfur and secondary sulfate contributions. This study shows that, although PM mass in different size fractions is spatially homogeneous within a community, the spatial distribution of some elemental components can be heterogeneous. This is evidence for the argument that epidemiological studies using only PM mass concentrations from central sites may not accurately assess exposure to toxicologically relevant PM components.
Keywords: Exposure assessment; Size-resolved PM; Chemical composition; Spatial variability; Intra-community; Coefficients of divergence;
Spatial and temporal changes of heavy metal concentrations in mosses and its indication to the environments in the past 40 years in the city of Shanghai, China by Tong Cao; Li An; Min Wang; Yuxia Lou; Yinghao Yu; Jiming Wu; Zhirui Zhu; Yangkung Qing; Janice Glime (5390-5402).
The mosses have been widely used as bioindicators to investigate pollution and changes of heavy metals in different countries and regions. For a better understanding of the environmental changes in the past 40 years in Shanghai, one of the largest cities in the world, we studied the spatial and temporal changes of five heavy metal depositions in two species of the moss genus Haplocladium. By means of the atomic absorption spectroscopy (AAS) method, the concentrations of Cd, Cr, Cu, Pb, and Zn in the plants of moss Haplocladium samples collected from 16 sites in Shanghai in 1965, 1974–1976, 1978–1982, and 2005 were determined and shown in the color Isogram maps made with the computer program Arcmap 9.0. The trends of the heavy metal concentrations in selected sites including Sheshan Mt., Jin Shan Petrochemical Plant, and the four representative sites of Shanghai were analyzed with two-factor analysis of variance and linear regression analysis, respectively. The results showed that the concentrations of the five heavy metals at all sample sites increased distinctly from 1965 to 2005, especially after the 1980s. The increasing rate was Cr>Cu>Cd>Pb>Zn. The heavy metal concentrations were distinctly associated with local emission point sources and changes in emission levels, and the major emission sources in Shanghai were industry and traffic.
Keywords: Moss; Haplocladium; Biomonitoring; Heavy metal pollution; Shanghai;
A procedure for inter-comparing the skill of regional-scale air quality model simulations of daily maximum 8-h ozone concentrations by John S. Irwin; Kevin Civerolo; Christian Hogrefe; Wyat Appel; Kristen Foley; Jenise Swall (5403-5412).
An operational model evaluation procedure is described to quantitatively assess the relative skill among several regional-scale air quality models simulating various percentiles of the cumulative frequency distribution of observed daily maximum 8-h ozone concentrations. Bootstrap sampling is used to characterize the variability in the observed percentile values, thereby providing a means for assessing whether the differences seen between model predictions are significant. The procedure was designed to facilitate model inter-comparisons, since all that is needed to implement the procedure is for each modeler to provide a listing of the daily maximum 8-h ozone concentration predictions for a summer season for grid cells containing ozone monitors. Available ozone modeling results for the summer of 2002 from four regional-scale air quality simulations are used here to illustrate the results that can be obtained. These simulations were conducted using the Community Multi-Scale Air Quality (CMAQ) model with somewhat different setups. The modeling domains were different, but there is a region in the central Eastern United States where ozone estimates from all four simulations are available. Our objective is to describe the inter-comparison procedure, to illustrate the results obtained, and to stimulate discussions on how similar procedures might be developed and improved in the future.
Keywords: Model evaluation; Regional-scale; Air quality;
Stable carbon and nitrogen isotopes of the moss Haplocladium microphyllum in an urban and a background area (SW China): The role of environmental conditions and atmospheric nitrogen deposition by Xue-Yan Liu; Hua-Yun Xiao; Cong-Qiang Liu; You-Yi Li; Hong-Wei Xiao (5413-5423).
The C and N concentrations and stable isotopes in new and old tissues of the moss Haplocladium microphyllum were investigated at Guiyang and Gongga Mountain in SW China, aiming at revealing responses of these parameters to different environmental conditions and N deposition, elucidating the effect of N deposition on C fixation and signal variations during senescence. Atmospheric N deposition could be quantified by N in new tissues, showing a level of 30.18 kg N ha−1 yr−1 at Guiyang and 8.46 kg N ha−1 yr−1 at Mt. Gongga, old tissues presented lower C and N concentrations than new tissues, but there was no significant difference between N of new and old tissues at background area with lower N deposition, and the positive effect of N supply on C fixation was observed only for urban mosses under higher N deposition. More negative δ 13C mainly indicated the influences of anthropogenic CO2 sources on urban mosses, and higher δ 13C of mosses at background area was also related to higher altitude and lower temperature. More negative δ 15N of mosses mainly indicated N deposition at Guiyang was dominated by NH x –N from city wastes and sewage, while δ 15N of mosses at Mt. Gongga mainly indicated little anthropogenic N pollution in background area. Besides, no significant isotopic difference was found between new and old tissues in both areas, suggesting no isotopic effect occurred during the senescence of H. microphyllum.
Keywords: Atmospheric nitrogen deposition; Biomonitoring; Stable isotope; Moss; Environment;
Mysterious diel cycles of mercury emission from soils held in the dark at constant temperature by Hong Zhang; Steve E. Lindberg; Todd Kuiken (5424-5433).
It is well known that mercury (Hg) emission from soils is largely controlled by solar radiation and soil temperature, exhibiting diel cycles that closely follow diel variations of solar radiation. To study soil Hg emission processes, we conducted experiments by measuring soil Hg emission fluxes under controlled conditions in the laboratory with a dynamic flux chamber using outside ambient air as flushing air. Unexpectedly, we observed consistent, recurring diel cycles of Hg emissions from dry soils held at constant temperature in the dark in our laboratory. The peaks of the emissions also seemed subject to some seasonal variation and to respond to local weather conditions with lower flux peaks in wintertime and on cloudy or rainy days. Finally, much lower soil Hg emission fluxes were observed in the presence of Hg-free zero air than in the presence of outside ambient air. It is hypothesized that some unidentified air-borne substance(s) in the ambient air might be responsible for the observed diel cycles of soil Hg emission. Further elaborate mechanistic investigations are clearly needed to test the initial working hypotheses and uncover the cause for this interesting, mysterious phenomenon. The present work and recent finding of enhancement of Hg emissions from soil and mineral particles by O3 seem to point to a research need to probe the possible role of near-ground atmospheric chemistry in Hg air/soil exchange.
Keywords: Air/surface exchange; Atmospheric chemistry; Global biogeochemistry; Heavy metal; Solar radiation;
Trends in ozone concentration distributions in the UK since 1990: Local, regional and global influences by Michael E. Jenkin (5434-5445).
Data from the UK automatic monitoring network have been analysed to investigate average trends in ozone concentrations, concentration distributions and exceedences of the public information threshold (180 μg m−3) at 13 rural sites (over the period 1990–2006) and at five urban sites (over the period 1993–2006) throughout the UK. The data indicate that the observations at a given location in the UK can be influenced by a combination of global (hemispheric)-, regional- and local-scale effects. As a result, the observed trend in the ozone metrics is determined from the net trend of these three influences, the relative contributions of which can vary both spatially and temporally. Specifically, the data reflect the following three major influences: (i) a gradual increase in the hemispheric baseline ozone concentration resulting from global-scale effects, thereby influencing the baseline levels of ozone brought into the UK from the Atlantic Ocean; (ii) substantial short-term elevations in ozone concentrations during summertime episodes, resulting from the formation of additional ozone from regional-scale photochemical processing of emitted VOC and NO x over north-west Europe, with such events tending to be more frequent and intense towards the south and east of the UK. On average, the severity of such events has progressively decreased since about 1990, as a result of EU controls of anthropogenic VOC and NO x emissions; and (iii) local-scale removal of ozone by direct reaction with emitted NO has gradually decreased, as a result of the control of NO x emissions. This has resulted in a general increasing influence on ozone concentrations since about 1990, which is most apparent at urban sites, where NO x emissions are higher, but also influences the observations at the majority of rural locations.
Keywords: Regional pollution; Local pollution; Monitoring networks; Air quality; Photochemical pollution; Ozone episode; Nitrogen oxides; Volatile organic compounds; European emissions controls;
Passive scalar flux footprint analysis over horizontally inhomogeneous plant canopy using large-eddy simulation by Shaolin Mao; Monique Y. Leclerc; Efstathios E. Michaelides (5446-5458).
The large-eddy simulation (LES) method has been used to simulate passive scalar such as carbon dioxide (CO2) flux and its footprint or source weight function over a horizontally inhomogeneous canopy, in which half of the physical domain is patched soil or clearcut upwind. A step change of aerodynamic roughness length (z 01/z 02=20) across a clearcut–canopy interface, which simulates the forest edge, is examined. In order to simulate the transport and dispersion of CO2 within and above the canopy, a constant crosswind line source (tracer) is placed at the upwind boundary. This study investigates the influence of the clearcut interface on the scalar flux and its footprint at a downwind measurement tower. The study reports the contribution of all sources to a point flux measurement. The footprint function demonstrates a large platform effect, which is due to the clearcut–forest interface. The numerical results demonstrate an influence region from 3 to 5 tree heights upwind of the interface to more than 15 tree heights downwind the interface. It is observed that the rate of adjustment for a passive scalar is much slower than that of vectors, such as momentum. Thus, a much larger fetch is required than the one demanded in otherwise homogeneous conditions for the tower flux measurements to be robust and representative of the underlying forest and not of the clearcut. The results from this study provide useful information on the examination of the measurement uncertainties associated with the net ecosystem–atmosphere exchange (NEE) of CO2 under neutral conditions. The numerical results are also compared with a set of experimental data and analytical methods such as the Lagrangian stochastic (LS) simulation. The study shows that LES as an effective tool can be used to simulate atmospheric flows over heterogeneous canopies.
Keywords: Large-eddy simulation (LES); Footprint; Inhomogeneous canopy; Clearcut; Forest edge;
Comparison of activity coefficient models for atmospheric aerosols containing mixtures of electrolytes, organics, and water by Chinghang Tong; Simon L. Clegg; John H. Seinfeld (5459-5482).
Atmospheric aerosols generally comprise a mixture of electrolytes, organic compounds, and water. Determining the gas–particle distribution of volatile compounds, including water, requires equilibrium or mass transfer calculations, at the heart of which are models for the activity coefficients of the particle-phase components. We evaluate here the performance of four recent activity coefficient models developed for electrolyte/organic/water mixtures typical of atmospheric aerosols. Two of the models, the CSB model [Clegg, S.L., Seinfeld, J.H., Brimblecombe, P., 2001. Thermodynamic modelling of aqueous aerosols containing electrolytes and dissolved organic compounds. Journal of Aerosol Science 32, 713–738] and the aerosol diameter dependent equilibrium model (ADDEM) [Topping, D.O., McFiggans, G.B., Coe, H., 2005. A curved multi-component aerosol hygroscopicity model framework: part 2—including organic compounds. Atmospheric Chemistry and Physics 5, 1223–1242] treat ion–water and organic–water interactions but do not include ion–organic interactions; these can be referred to as “decoupled” models. The other two models, reparameterized Ming and Russell model 2005 [Raatikainen, T., Laaksonen, A., 2005. Application of several activity coefficient models to water–organic–electrolyte aerosols of atmospheric interest. Atmospheric Chemistry and Physics 5, 2475–2495] and X-UNIFAC.3 [Erdakos, G.B., Change, E.I., Pandow, J.F., Seinfeld, J.H., 2006. Prediction of activity coefficients in liquid aerosol particles containing organic compounds, dissolved inorganic salts, and water—Part 3: Organic compounds, water, and ionic constituents by consideration of short-, mid-, and long-range effects using X-UNIFAC.3. Atmospheric Environment 40, 6437–6452], include ion–organic interactions; these are referred to as “coupled” models. We address the question—Does the inclusion of a treatment of ion–organic interactions substantially improve the performance of the coupled models over that of the decoupled models? Performance is judged by the extent to which each model is able to reproduce experimental water activity data for mixtures of organic acids (malonic, succinic, glutaric, citric, maleic, and malic acids) and inorganic electrolytes (NaCl and (NH4)2SO4). It is found, based on the comparisons reported here, that the decoupled models perform as well as, and in some cases better than, the coupled models. Since such activity coefficient models are likely to continue to be developed in the future and because we consider here only a limited set of organic compounds, the current study should be viewed as an interim assessment. The scarcity of experimental data for mixtures of atmospheric relevance remains a limitation for testing activity coefficient models.
Keywords: Activity coefficient; Atmospheric aerosol; Organic/electrolyte/water; Water activity;
Determining breakthrough of the soil fumigant chloropicrin from 120 mg XAD-4 sorbent tubes by D.J. Ashworth; W. Zheng; S.R. Yates (5483-5488).
The emission to the atmosphere of soil fumigants such as chloropicrin represents a potentially important human exposure pathway. Commonly, determining the air concentration of fumigants is carried out by pumping air through sorbent tubes which chemically retain the fumigant. In order to obtain an accurate measurement, it is essential that the fumigant does not break through the sorbent tubes, since this would result in an underestimation. Using a simple apparatus, we tested the potential for chloropicrin breakthrough from 120 mg XAD-4 sorbent tubes. The effects of chloropicrin loading (0.33 and 3.3 mg) and air flow rate (50 and 1000 mL min−1) on the transport of chloropicrin through six XAD-4 tubes (connected in series) were examined over time periods ranging from 1 to 360 min. The higher flow rate led to rapid and high breakthrough of the chloropicrin, especially at the longer time periods. At 360 min, all six tubes together retained only 46–54% (depending on initial loading) of the added chloropicrin. At the lower flow rate, essentially all of the added chloropicrin was always retained on the first two tubes. The effect of flow rate was greater than that of initial chloropicrin loading and sampling time. It is concluded that when 120 mg XAD-4 tubes are used in soil fumigant emission studies, it should be at low flow rates only and always with at least one back-up tube.
Keywords: Fumigant pesticides; Methyl bromide alternatives; Agriculture; Volatile organic compounds; VOCs; Ozone;
Dust storm originate from Sahara covering Western Europe: A case study by P. Vanderstraeten; Y. Lénelle; A. Meurrens; D. Carati; L. Brenig; A. Delcloo; Z.Y. Offer; E. Zaady (5489-5493).
Erosion, transport and deposition of atmospheric dust are largely determined by the nature and state of the earth's surface (the dust source) and the physical characteristics of the atmosphere. The state of the atmosphere is subject to important temporal variations related to diurnal and seasonal cycles and to synoptic conditions. The dynamic evolution of particulate concentrations measured at Brussels showed a significant peak in PM10 during 24–25 March 2007. The 4-day backward trajectories calculated for this peak attributed its cause to a dust storm that had occurred 2 days earlier in the Sahara. Chemical analysis showed a significant similarity to Saharan dust composition, primarily oxides of Si, Fe, and Al. On 29 March, another peak with a very high PM concentration and an elevated PM2.5-to-PM10 ratio was recorded in Brussels. Analysis of its PM profile showed that it was mainly caused by formation of secondary aerosols.
Keywords: Atmosphere; Trajectory; Concentration; Particle size; Chemistry;
Thoron levels in the dwellings of high background radiation area located around Kudankulam nuclear power plant by J. Malathi; S. Selvasekarapandian; G.M. Brahmanandhan; D. Khanna; V. Meenakshisundaram; S. Santhanam; S. Balasundar; B. Dhanalakshmi; T.V. Ramachandran (5494-5498).
Thoron concentration levels have been measured in the high background radiation area located around Kudankulam nuclear power plant i.e. in the Agastheeswaram, thovalai taluks (sub-district) of the Kanyakumari district using solid-state nuclear track detectors. Measurements have been carried out on quarterly cycles making four measurements at each location throughout a year. Totally 100 dwellings have been selected for the study. Thoron concentration has been found to vary between 4.6 and 143.5 Bq m−3 with the geometric mean value being 25.1 Bq m−3. Results have been analyzed for different categories of dwellings with respect to their construction type.
Keywords: Thoron; Solid-state nuclear track detector; LR-115;
Environmental inequality: Air pollution exposures in California's South Coast Air Basin by Julian D. Marshall (5499-5503).
Environmental inequality is quantified here using linear regression, based on results from a recent mobility-based exposure model for 25,064 individuals in California's South Coast Air Basin [Marshall et al., 2006. Inhalation intake of ambient air pollution in California's South Coast Air Basin. Atmospheric Environment 40, 4381–4392]. For the four primary pollutants studied (benzene, butadiene, chromium particles, and diesel particles), mean exposures are higher than average for people who are nonwhite, are from lower-income households, and live in areas with high population density. For ozone (a secondary pollutant), the reverse holds. Holding constant attributes such as population density and daily travel distance, mean exposure differences between whites and nonwhites are 16–40% among the five pollutants. These findings offer a baseline to compare against future conditions or to evaluate the impact of proposed policies.
Keywords: Environmental justice; Geographic information systems; Mobility-based spatiotemporal exposure model; Particulate matter; PM2.5; Vehicle emissions;
In-use gaseous and particulate matter emissions from a modern ocean going container vessel by Harshit Agrawal; Quentin G.J. Malloy; William A. Welch; J. Wayne Miller; David R. Cocker (5504-5510).
Ocean going vessels are one of the largest uncontrolled sources of pollutants and the emissions data from these sources are scarce. This paper provides the emission measurements of gases, particulate matter (PM), metals, ions, elemental and organic carbon, conducted from the main engine of an ocean going PanaMax class container vessel, at certification cycle and at vessel speed reduction mode, during actual operation at sea. The weighted emission factor (g kW−1 h−1) of PM and NO x were 1.64 and 18.2, respectively, for the main engine operating on a 2.05 wt% sulfur heavy fuel oil (HFO). The NO x emissions at the vessel speed reduction mode (8% of full load) are 30% higher than at 52% engine power, the normal cruise speed. The composition of PM, from main engine is dominated by sulfate and water bound with sulfate (about 80% of total PM) and organic carbon constitutes about 15% of the PM. Sulfur, vanadium and nickel are the significant elements in the exhaust from the engine running on the HFO. At the point of sampling 3.7–5.0% of the fuel sulfur was converted to sulfate.
Keywords: Ship; Emissions; Main engine; Particulate matter; Elemental carbon; Organic carbon; Sulfate; Ocean going vessel; Heavy fuel oil; Vessel speed reduction;