A Review of Techniques Available for Estimating Short-Term NO2 concentrations

The Environmental Protection Agency is reviewing the need for a short-term NO₂ standard based on an averaging time of three hours or less. State Implementation plans and New Source Reviews will require air quality simulation techniques capable of estimating ambient NO₂ concentrations. There is a need for multi-source (urban) models and for point source models.

A review of currently available techniques for the estimation of NO₂ concentrations resulting from NO_x point sources is presented. The available methods include simple screening techniques and refined reactive plume models. The screening techniques first use a standard gaussian dispersion model to estimate the maximum 1 hr NO_x concentration caused by the source. The second step involves estimating the fraction of this NO* concentration occurring as NO₂.

Reactive plume models numerically simulate the simultaneous effects of dispersion and chemistry on NO₂ concentrations. Organic as well as inorganic reactions are incorporated. Reactive plume models should be used, where screening techniques indicate the potential for violation of the NO₂ standard.

Current generation reactive plume models neglect the effect of turbulent concentration fluctuation on NO₂ formation and use inappropriately large dispersion coefficients to estimate plume concentrations. Approaches being developed to resolve these problems are discussed.     

Performance of a thermally desorbable type-tube diffusive sampler for very low air concentrations monitoring

Perkin-Elmer tubes packed with Tenax TA have been tested for the monitoring of low concentrations of aromatic compounds and linear alkanes using diffusive sampling. The uptake rates have been investigated for different exposure doses. A particular hexane and benzene behaviour has been observed: their uptake rates decrease rapidly in the lower exposure doses and so follow an exponential curve. The uptake rates of heavier compounds adopt another tendency: a slow decrease with time following a linear profile. The relative humidity influence has been studied too, and no water perturbation has been recorded.     

Heavy metal concentrations in a soil-plant-snail food chain along a terrestrial soil pollution gradient

We investigated concentrations of Zn, Cu, Cd and Pb in the compartments of a soil-plant (Urtica dioica)-snail (Cepaea nemoralis) food chain in four polluted locations in the Biesbosch floodplains, the Netherlands, and two reference locations. Total soil metal concentrations in the polluted locations were 4-20 times higher than those in the reference locations. Positive relationships between the generally low leaf concentrations and the soil concentrations were found for Zn only (r2 = 0.20). Bioaccumulation of Zn, Cu and Cd was observed in the snail tissues. We found positive relationships between the snail and leaf concentrations for all metals (range r2 = 0.19-0.46). The relationships between soil and snail concentrations were also positive, except for Cu (range r2 = 0.15-0.33). These results suggest transfer of metals to C. nemoralis snails from U. dioica leaves and from the soil. Metal transfer from polluted leaves to C. nemoralis is more important than transfer from the soil.     

Development and validation of a photobioreactor for uniform distribution of light intensity along the optical path based on numerical simulation

Environmental Science and Pollution Research - A theoretical approach was followed to optimize the design of a cylindrical photobioreactor for wastewater treatment based on algal culture. In...     

Total vs. internal element concentrations in Scots pine needles along a sulphur and metal pollution gradient

Analysis of foliar elements is a commonly used method for studying tree nutrition and for monitoring the impacts of air pollutants on forest ecosystems. Interpretations based on the results of foliar element analysis may, however, be different in nutrition vs. monitoring studies. We studied the impacts of severe sulphur and metal (mainly Cu and Ni) pollution on the element concentrations (Al, Ca, Cu, Fe, K, Mg, Mn, Ni, P, Pb, S and Zn) in Scots pine (Pinus sylvestris L.) foliage along an airborne sulphur and metal pollution gradient. Emphasis was put on determining the contribution of air-borne particles that have accumulated on needle surfaces to the total foliage concentrations. A comparison of two soil extraction methods was carried out in order to obtain a reliable estimate of plant-available element concentrations in the soil. Element concentrations in the soil showed only a weak relationship with internal foliar concentrations. There were no clear differences between the total and internal needle S concentrations along the gradient, whereas at the plot closest to the metal smelter complex the total Cu concentrations in the youngest needles were 1.3-fold and Ni concentrations over 1.6-fold higher than the internal needle concentrations. Chloroform-extracted surface wax was found to have Ni and Cu concentrations of as high as 3000 and 600 microg/g of wax, respectively. Our results suggest that bioindicator studies (e.g. monitoring studies) may require different foliar analysis techniques from those used in studies on the nutritional status of trees.     

The prediction of maximum air pollution concentrations for tsp and co using Larsen's model and the ATDL model

A modeling methodology is introduced to predict maximum TSP concentrations. The methodology consists of using the ATDL model of Gifford and Hanna (1971) and the Larsen model (1971) to predict the distribution of air pollution concentrations from wind speed data for the upper percentiles. The data set used is total suspended particulate (TSP) data. Since the highest TSP concentrations occur at extremely low wind speeds where the use of the ATDL model is questionable, the methodology adopted here is to use the ATDL model together with wind speed data to reproduce TSP concentrations only for the range of wind speeds where the model is applicable. Assuming these TSP concentrations are lognormally distributed, Larsen's model is then used to predict the maximum TSP concentration. These results agree with the work by Daly and Steele (1976) for CO. This methodology works quite well, for time averages of 8 h or more but in its present form is questionable for shorter time averages.     

Atmospheric mercury in the marine boundary layer along a cruise path from Shanghai,China to Prydz Bay,Antarctica

The total gaseous mercury (TGM) measurements were performed using an automatic Mercury Vapor Analyze (model 2537B) aboard the Chinese research vessel (R/V) XueLong during the 24th China Antarctic Research Expedition from Shanghai, China to Prydz Bay, Antarctica in 2007. TGM ranged between 0.302 and 4.496 ng m^?3 with an average of 1.536 ± 0.785 ng m^?3 over the entire period. Geographically, TGM in the Northern Hemisphere and the Southern Hemisphere along the cruise path were 1.746 ± 0.513 and 1.471 ± 0.842 ng m^?3 in average, respectively. Higher TGM concentrations were observed in the coastal regions outside the polar region due primarily to air masses transported from the adjacent mainland reflecting the contribution from anthropogenic sources. The pronounced episode was recorded when ship passed through Sunda straits, which should be ascribed to the volcano plume and/or biomass burning contamination. In the maritime Antarctic TGM level was in agreement with the values by land-based observation, presenting a diurnal cycle with the maximum around midday and minimum at night. Atmospheric mercury destruction events dominated by the oxidation of atmospheric Hg⁰ were apparently observed in this region.     

Comparison of an open path differential optical absorption spectroscopy system and a conventional in situ monitoring system on the basis of long-term measurements of SO2, NO2, and O3

A field-based intercomparison study was conducted to evaluate the performance of a line-integrating monitoring technique (a commercial differential optical absorption spectroscopy, DOAS, system by Opsis AB, Sweden) in concert with a conventional in situ monitoring technique (MACSAM-2 (or MS2) system, Japan). In the course of our study, the mixing ratios of three trace gases including SO₂, NO₂, and O₃ were measured routinely from the Ban Po district of Seoul during a 13 month period (June 1999–August 2000). The data obtained from two different systems were used to evaluate various aspects of DOAS performance. The differences in the observed mixing ratios between two techniques, if assessed in terms of the percent difference (PD) values between different data sets, were in general rather compatible not only among different species but also as a function of varying time scale. The differences in the measured mixing ratio between the two systems were also examined statistically using linear regression analysis. Results of the regression analysis indicated the existence of significant correlations among all trace gases monitored, confirming the strong compatibility between the two systems. The effects of meteorological factors on the DOAS performance were also examined through investigation of the mixing ratio differences between two systems and the concurrently determined environmental parameters. According to our analysis, it is concluded that the level of agreement between the two systems can be affected by the variations in the spatial mixing conditions. Although some uncertainties remain to be resolved, our preliminary attempts to evaluate an open path monitoring technique clearly demonstrated that consideration of meteorological conditions may be required to properly assess the DOAS performance due to its capacity to cover spatial scale over the open path length.     

Use of passive sampling devices for monitoring and compliance checking of POP concentrations in water

Background

The state of the art of passive water sampling of (nonpolar) organic contaminants is presented. Its suitability for regulatory monitoring is discussed, with an emphasis on the information yielded by passive sampling devices (PSDs), their relevance and associated uncertainties. Almost all persistent organic pollutants (POPs) targeted by the Stockholm Convention are nonpolar or weakly polar, hydrophobic substances, making them ideal targets for sampling in water using PSDs. Widely used nonpolar PSDs include semi-permeable membrane devices, low-density polyethylene and silicone rubber.

Results and discussion

The inter-laboratory variation of equilibrium partition constants between PSD and water is mostly 0.2?C0.5 log units, depending on the exact matrix used. The sampling rate of PSDs is best determined by using performance reference compounds during field deployment. The major advantage of PSDs over alternative matrices applicable in trend monitoring (e.g. sediments or biota) is that the various sources of variance including analytical variance and natural environmental variance can be much better controlled, which in turn results in a reduction of the number of analysed samples required to obtain results with comparable statistical power.

Conclusion

Compliance checking with regulatory limits and analysis of temporal and spatial contaminant trends are two possible fields of application. In contrast to the established use of nonpolar PSDs, polar samplers are insufficiently understood, but research is in progress to develop PSDs for the quantitative assessment of polar waterborne contaminants. In summary, PSD-based monitoring is a mature technique for the measurement of aqueous concentrations of apolar POPs, with a well-defined accuracy and precision.     

Roadside particle number distributions and relationships between number concentrations, meteorology, and traffic along a northern California freeway

Particle number distributions were measured simultaneously upwind and downwind of a suburban-agricultural freeway to determine relationships with traffic and meteorological parameters. Average traffic volumes were 6330 vehicles/hr with 10% heavy-duty vehicles, and volumes were higher in July than November. Most downwind particle number distributions were bimodal, with a primary mode at approximately 10-25 nm, indicating that newly formed particles were sampled. Total downwind 6-237 nm particle number concentrations (Ntot) ranged from 9.3 x 10(3) to 2.5 x 10(5) cm(-3), with higher daily average concentrations in November compared with July. Ntot correlated with wind speed, temperature, and relative humidity. Upwind photochemically initiated nucleation likely led to elevated background nanoparticle concentrations in July, as evidenced by increasing upwind distribution modal diameter with increasing temperature and a strong correlation between upwind Ntot and solar radiation. Also in summer, Ntot showed stronger correlation with heavy-duty vehicle volumes than wind speed, temperature, and relative humidity. These results indicate the importance of measuring background particle size distributions simultaneously with roadside distributions. There may be a minimum vehicle volume from which useful real-world vehicle particle number distributions can be measured at roadside, even when collecting samples within 10 m of the traveled lanes.     

Spatial distribution and internal metal concentrations of terrestrial arthropods in a moderately contaminated lowland floodplain along the Rhine River

Soil metal concentrations, inundation characteristics and abundances of 14 arthropod taxa were investigated in a moderately contaminated lowland floodplain along the Rhine River and compared to the hinterland. Internal metal concentrations were determined for the orders of Coleoptera (beetles) and Araneida (spiders) and were related to soil concentrations. The floodplain was characterized by larger arthropod abundance than the hinterland, in spite of recurrent inundations and higher soil metal concentrations. Most arthropod taxa showed increasing abundance with decreasing distance to the river channel and increasing average inundation duration. For Cd, Cu, Pb and Zn, significant relations were found between arthropod concentrations and concentrations in soil. Significant relations were few but positive, indicating that increasing soil concentrations result in increasing body burdens in arthropods. For arthropod-eating vertebrates, these results might imply that larger prey availability in the floodplain coincides with higher metal concentrations in prey, possibly leading to increased exposure to metal contamination.     

Receptor modelling of PM10 concentrations at a United Kingdom national network monitoring site in central London

A receptor model for predicting future PM₁₀ concentrations has been developed within the framework of the UK Airborne Particles Expert Group and applied during the recently completed review of the UK National Air Quality Strategy. The model uses a combination of measured PM₁₀, oxides of nitrogen and particulate sulphate concentrations to provide daily estimates of the contributions to total particle concentrations from primary combustion, secondary and other (generally coarse) particle sources. Projections of past and future concentrations of PM₁₀ are estimated by applying appropriate reductions to the current concentrations of the three components based on an understanding of the likely impact of current policies on future levels. Projections have been derived from 1996, 1997 and 1998 monitoring data and compared with UK national air quality objectives and European Union limit values. One of the key uncertainties within the receptor modelling method is the assignment of the residual PM₁₀, remaining after the assignment of primary combustion and secondary particle contributions, to the ‘other’ particle fraction. An examination of the difference between measured PM₁₀ and PM_2.5 concentrations confirms our assignment of the bulk of this residual to coarse particles. Projections based on 1996 monitoring data are the highest and those based on 1998 monitoring data are the lowest. Whilst there is considerable difference between these projections they are consistent with measured concentrations for previous years. All three projections suggest that with current agreed policies the EU annual mean limit value will be achieved. The 24-h mean limit value is projected to be achievable when projections are derived from 1997 and 1998 data, but not from 1996 data. All three projections suggest that with current agreed policies the central London site will not achieve the provisional 1997 UK National Air Quality Strategy objective.     

Particulate Emission Rates for Unpaved Shoulders along a Paved Road

ABSTRACT

This paper reports the first empirical estimate of particle emissions from unpaved shoulders along paved roads.¹ Its objectives are to develop and demonstrate an emission rate measurement methodology that can be applied in different areas; identify the mechanisms that suspend dust from unpaved shoulders and the observables related to this suspension process; and quantify PM₁₀ mass emissions in the form of an emission rate. To achieve these objectives, fast-response observations from nephelometers and a sonic anemometer were used to characterize shortlived dust plumes generated by passing vehicles. In addition, detailed soil surface measurements determined the mechanical properties of the shoulder surfaces.

Large traffic-induced turbulence events that led to significant dust entrainment were almost exclusively caused by “large” vehicles such as trucks, semis, and vehicles pulling trailers, all traveling 50-65 mph. PM₁₀ emission rates for these large, fast-traveling vehicles were determined to be 8 ± 4 grams per vehicle kilometer traveled under dry conditions. Emissions due to smaller vehicles such as cars, vans, and sport utility vehicles were negligible for normal on-road driving. These results indicate that the majority of PM₁₀ emissions from unpaved shoulders is caused by relatively few vehicles.     

Thermoluminescence as a tool for monitoring ozone-stressed plants

The effect of ozone (6 h, various concentrations from 0 to 350 ppb) on barley (Hordeum vulgare L., cv. Bomi) and tomato (Lycopersicon esculentum L., cv. Yellow Cherry) leaves was investigated in parallel by thermoluminescence (TL) and fluorescence (FL) methods. Several significant changes were found in TL glow curves measured after excitation by one single turnover flash at +2 degree C in the temperature range from 2 to 170 degree C immediately after ozone exposure. Contrary to TL, ozone induced only negligible changes in FL parameters F0, FM and Fv/FM. Measurements done 24 h after ozone exposure showed partial recovery of ozone-induced changes. The extent of recovery was not the same in different parts of TL curves. Fluorescence parameters were not significantly changed. The results demonstrate that TL parameters are more sensitive to ozone than conventially used FL parameters F0, FM and Fv/FM. Moreover, TL measurements seem to give information not only about the PSII electron transport, but also about the extent of oxidative damage and membrane lipid peroxidation. It is concluded, that TL can be a highly informative tool for monitoring the impact of ozone on plants.     

Estimating Maximum Concentrations for Open Path Monitoring Along a Fixed Beam Path

ABSTRACT

Researchers have applied open path optical sensing techniques to a variety of workplace and environmental monitoring problems. Usually these data are reported in terms of a path-average (or path-integrated) concentration. When assessing potential human exposures along a beam path, this path-average value is not always informative, since concentrations along the path can vary substantially from the beam average. The focus of this research is to arrive at a method for estimating the upper-bound in contaminant concentrations over a fixed open beam path. The approach taken here uses a statistical model to estimate an upper-bound concentration based on a combination of the path-average and a measure of the spatial variability computed from point samples along the beam path. Results of computer simulations and experimental testing in a controlled ventilation chamber indicate that the model produced conservative estimates for the maximum concentration along the beam path. This approach may have many applications for open path monitoring in workplaces or wherever maximum concentrations are a concern.     

Screening Models for Estimating Toxic Air Pollution Near a Hazardous Waste Landfill

This paper is directed to environmental scientists concerned with assessing toxic air pollution downwind of hazardous waste landfills to determine whether potential health threats or exceedances of air quality standards exist. The purpose of this paper is to evaluate the performance of four air quality screening models.

The emission rate of vinyl chloride from the BKK co-disposal landfill in West Covina, California is estimated. Ambient vinyl chloride concentrations are estimated using a ground level point source model, two virtual point source models, arid the simple box model with meteorological and landfill input data representative of periods when ambient monitoring was conducted. The two virtual point source models are most precise and accurate in estimating 24-hour vinyl chloride concentrations. However, the results could include compensating errors in the emission rate and dispersion calculations because the emission rate estimate could not be independently evaluated.     

The silvering process of European eel (Anguilla anguilla) influences PAH metabolite concentrations in bile fluid: consequences for monitoring

The stock of the catadromous European eel (Anguilla anguilla L.) continues to decline and there is growing evidence that poor health status due to contaminants might be a key element in this decrease. Organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) belong to the major threats to yellow eel in their growth habitat and their metabolites are detectable in the bile. Starting the silvering process eels undergo physiological and morphological changes including cessation of feeding and downstream migration back to their spawning grounds. Reduced feed intake results in a diminishment of bile production and induces accumulation of e.g. PAH-metabolites in bile. Therefore, the aim of the present study was to demonstrate the impact of silvering on biliary PAH metabolite concentrations and to utilize normalization procedures to overcome silvering related accumulation effects of PAH-metabolites in eel bile. We investigated the hydroxyl-metabolites of pyrene (1-OH Pyr) and phenantrene (1-OH Phen) in the bile of different maturation stages of eels (silvering index I-V) from nine German rivers. We detected increasing absolute PAH metabolite levels in bile during the silvering process. The highest rise could be observed at the transition from pre migration stage III to the migrating stage IV, suggesting the onset of cessation of feeding at this stage. A cessation bias in PAH metabolite measurement could be diminished by normalization of absolute values against bile pigments (A₃₈₀, biliverdin). In conclusion, we demonstrated the impact of silvering on PAH metabolite concentrations in eel bile and present suitable normalization procedures to overcome silvering related accumulation effects. Thus, for a future eel monitoring we recommend (1) to regularly monitor PAH metabolites in bile, (2) to determine silvering index of eel and (3) to normalize PAH metabolite values in bile based on maturation/silvering stages. The knowledge of the silvering stage is mandatory for an unbiased evaluation of PAH contamination of European eel towards an international harmonized eel monitoring program.     

Evaluation of a method for estimating pollution concentrations downwind of influencing buildings

A simple method for estimating enhanced dispersion resulting from the overall effect of buildings is presented and evaluated. A framework for applying the method to general plume dispersion modeling problems is suggested and examples are provided. The Gaussian plume equation has been modified to incorporate building wake enhanced dispersion parameters beyond the wake cavity region, and the resulting ground-level plume centerline concentration estimates are compared to 10 sets of field measurements. The results indicate that the method can provide a good correction for the overall effect of adjacent buildings. The effect of building wake enhanced dispersion on maximum ground-level concentrations is to decrease their values for releases near ground-level and to significantly increase their values for elevated releases. For elevated releases, enhanced horizontal dispersion dilutes the plume more rapidly; enhanced vertical dispersion also rapidly dilutes the plume but it can also bring the plume to ground-level while the in-plume concentrations are still high.