Field intercomparison of throughfall measurements performed within the framework of the Pan European intensive monitoring program of EU/ICP Forest

A 6-month field intercomparison study on throughfall measurements was performed at Speulder forest near the west coast in The Netherlands. Twenty throughfall sampling systems were evaluated on accuracy, sampling strategy and performance under field conditions. Throughfall fluxes of NO3-, K+ and Kjeldahl-N generally could be determined with a larger accuracy than fluxes of SO4(2-), NH4+, Na+, Cl-, Mg2+, Ca2+, and alkalinity. Throughfall fluxes of H+ generally had the lowest accuracy. Only 20% of the sampling systems differed more than 20% from the best estimate, whereas 45% of the systems stayed within a 10% range from the best estimate. The difference from the best estimate was mainly caused by aspects related to sampling strategy, like, for example, collecting area, sampler placement. The inaccuracy induced by the sampling system appeared to be much larger than that resulting from the analysis of the samples by different laboratory as determined by ring-tests. The field intercomparison described in this article gave a good insight in the different aspects contributing to the overall accuracy of the measurements. However, performing a future field intercomparison is recommended for throughfall and stemflow in order to also take in account other aspects that might influence the performance of the different measurement systems (e.g. tree species, climate zone, summer/winter period).     

A new methodological approach: The combined use of two-stage streaker samplers and optical particle counters for the characterization of airborne particulate matter

We describe a new experimental methodology based on the contemporary use of two-stage continuous streaker samplers and optical particle counters. This is a complementary approach to size-segregated particulate matter (PM) sampling, and it is able to give information on the elemental size distribution and to assess the contribution of major PM source to size bins. PM samples in the fine and coarse fraction of PM10 have been collected by a two-stage streaker sampler and analyzed by particle-induced X-ray emission (PIXE) to obtain elemental concentration time series with hourly resolution. PM sources and profiles were singled out by positive matrix factorization (PMF). A multi-linear regression of size-segregated number of particles versus the sources, resolved by PMF, made possible the apportionment of size-segregated particles number in a fast and direct way. Results obtained in three sampling sites, located in different urban districts are discussed.     

A field experiment with variable-suction multi-compartment samplers to measure the spatio-temporal distribution of solute leaching in an agricultural soil

Solutes spread out in time and space as they move downwards from the soil surface with infiltrating water. Solute monitoring in the field is often limited to observations of resident concentrations, while flux concentrations govern the movement of solutes in soils. A recently developed multi-compartment sampler is capable of measuring fluxes at a high spatial resolution with minimal disturbance of the local pressure head field. The objective of this paper is to use this sampler to quantify the spatial and temporal variation of solute leaching below the root zone in an agricultural field under natural rainfall in winter and spring. We placed two samplers at 31 and 25 cm depth in an agricultural field, leaving the soil above undisturbed. Each sampler contained 100 separate cells of 31 × 31 mm. Water fluxes were measured every 5 min for each cell. We monitored leaching of a chloride pulse under natural rainfall by frequently extracting the collected leachate while leaving the samplers buried in situ. This experiment was followed by a dye tracer experiment. This setting yielded information that widely surpassed the information that can be provided by separate anionic and dye tracer trials, and solute transport monitoring by coring or suction cups. The detailed information provided by the samplers showed that percolation at the sampling depth started much faster (approximately 3 h after the start of rainfall) in initially wet soil (pressure head above − 65 cm) than in drier soil (more than 14 h at pressure heads below − 80 cm). At any time, 25% of the drainage passed through 5–6% of the sampled area, reflecting the effect of heterogeneity on the flow paths. The amount of solute carried by individual cells varied over four orders of magnitude. The lateral concentration differences were limited though. This suggests a convective–dispersive regime despite the short vertical travel distance. On the other hand, the dilution index indicates a slight tendency towards stochastic–convective transport at this depth. There was no evidence in the observed drainage patterns and dye stained profiles of significant disturbance of the flow field by the samplers.     

Performance evaluation of a tailor-made passive sampler for monitoring of tropospheric ozone

Introduction

This study presents the performance evaluation of a tailor-made passive sampler developed for the monitoring of tropospheric ozone.

Methods

The performance of the passive sampler was tested in the field conditions in terms of accuracy, precision, blank values, detection limit, effects of some parameters such as sampling site characteristics and sampling period on the field blanks, self-consistency, experimental and theoretical uptake rates, shelf life and comparison with commercial passive samplers.

Results

There was an agreement (R ²?=?0.84) between the responses of passive sampler and the continuous automatic analyser. The accuracy of the sampler, expressed as percent relative error, was obtained lower than 15%. Method precision in terms of coefficient of variance for three simultaneously applied passive samplers was 12%. Sampler detection limit was 2.42???g?m^?3 for an exposure period of 1?week, and the sampler can be stored safely for a period of up to 8?weeks before exposure. Satisfactory self-consistency results showed that extended periods gave the same integrated response as a series of short-term samplers run side by side. The uptake rate of ozone was found to be 10.21?mL?min^?1 in a very good agreement with the theoretical uptake rate (10.32?mL?min^?1). The results of the comparison study conducted against a commercially available diffusion tube (Gradko diffusion tube) showed a good linear relationship (R ²?=?0.93) between two passive samplers.

Conclusions

The sampler seems suitable to be used in large-scale measurements of ozone where no data are available or the number of existing automated monitors is not sufficient.     

Evaluation of the use of diffusive air samplers for determining temporal and spatial variation of volatile organic compounds in the ambient air of urban communities

The Houston-Galveston metropolitan area has a relatively high density of point and mobile sources of air toxics, and determining and understanding the relationship between emissions and ambient air concentrations of air toxics is important for evaluating potential impacts on public health and formulating effective regulatory policies to control this impact, both in this region and elsewhere. However, conventional ambient air monitoring approaches are limited with regard to expense, siting limitations, and representative sampling necessary for adequate exposure assessment. The overall goal of this multiphase study is to evaluate the use of simple passive air samplers to determine temporal and spatial variability of the ambient air concentrations of selected volatile organic compounds (VOCs) in urban areas. Phase 1 of this study, reported here, was a field evaluation of 3M organic vapor monitors (OVMs) involving limited comparisons with commonly used active sampling methods, an assessment of sampler precision, a determination of optimal sampling duration, and an investigation of the utility of a simple modification of the commercial sampler. The results indicated that a sampling duration of 72 hr exhibited generally low bias relative to automated continuous gas chromatography measurements, good overall precision, and an acceptable number of measurements above detection limits. The modified sampler showed good correlation with the commercial sampler, with higher sampling rates, although lower than expected.     

Estimating the spatial scale of herbicide and soil interactions by nested sampling, hierarchical analysis of variance and residual maximum likelihood

An unbalanced nested sampling design was used to investigate the spatial scale of soil and herbicide interactions at the field scale. A hierarchical analysis of variance based on residual maximum likelihood (REML) was used to analyse the data and provide a first estimate of the variogram. Soil samples were taken at 108 locations at a range of separating distances in a 9 ha field to explore small and medium scale spatial variation. Soil organic matter content, pH, particle size distribution, microbial biomass and the degradation and sorption of the herbicide, isoproturon, were determined for each soil sample. A large proportion of the spatial variation in isoproturon degradation and sorption occurred at sampling intervals less than 60 m, however, the sampling design did not resolve the variation present at scales greater than this. A sampling interval of 20-25 m should ensure that the main spatial structures are identified for isoproturon degradation rate and sorption without too great a loss of information in this field.     

Evaluation of the Use of Diffusive Air Samplers for Determining Temporal and Spatial Variation of Volatile Organic Compounds in the Ambient Air of Urban Communities

Abstract

The Houston-Galveston metropolitan area has a relatively high density of point and mobile sources of air toxics, and determining and understanding the relationship between emissions and ambient air concentrations of air toxics is important for evaluating potential impacts on public health and formulating effective regulatory policies to control this impact, both in this region and elsewhere. However, conventional ambient air monitoring approaches are limited with regard to expense, siting limitations, and representative sampling necessary for adequate exposure assessment. The overall goal of this multiphase study is to evaluate the use of simple passive air samplers to determine temporal and spatial variability of the ambient air concentrations of selected volatile organic compounds (VOCs) in urban areas. Phase 1 of this study, reported here, was a field evaluation of 3M organic vapor monitors (OVMs) involving limited comparisons with commonly used active sampling methods, an assessment of sampler precision, a determination of optimal sampling duration, and an investigation of the utility of a simple modification of the commercial sampler. The results indicated that a sampling duration of 72 hr exhibited generally low bias relative to automated continuous gas chromatography measurements, good overall precision, and an acceptable number of measurements above detection limits. The modified sampler showed good correlation with the commercial sampler, with higher sampling rates, although lower than expected.     

Modelling and field application of the Chemcatcher passive sampler calibration data for the monitoring of hydrophobic organic pollutants in water

Passive sampling of dissolved pollutants in water has been gaining acceptance for environmental monitoring. Previously, an integrative passive sampler consisting of a C18 Empore disk receiving phase saturated with n-octanol and fitted with low density polyethylene membrane, was developed and calibrated for the measurement of time weighted average (TWA) concentrations of hydrophobic pollutants in water. In this study, the exchange kinetics were modelled to obtain a better understanding of the mechanism of the accumulation process and to enable the measurement of TWA concentrations of hydrophobic pollutants in the field. An empirical relationship that enables the calculation of in situ sampling rates of chemicals using performance reference compounds was derived and its application was demonstrated in a field study in which TWA aqueous concentrations estimated from sampler data for target analytes were compared with TWA concentrations obtained from spot samples of water collected regularly during the sampler deployment period.     

Field validation of an active sampling cartridge as a passive sampler for long-term carbonyl monitoring

A carbonyl sampler originally designed for the active sampling method (Sep-Pak XPoSure) was used for long-term passive sampling, and its applicability as a passive sampler was examined through field experiments. The uptake rates of passive sampling were determined experimentally from collocated passive and active samplings for various sampling periods. The obtained uptake rates of formaldehyde, acetaldehyde, and acetone were 1.48, 1.23, and 1.08 mL/min, respectively. These uptake rates were consistent for a wide range of the sampling term (12 hr-2 weeks). Uptake rates of each carbonyl were proportional to the diffusion coefficients of each. Therefore, the ratios of diffusion coefficients were used to calculate the uptake rates of carbonyls for which the rates were not determined experimentally. Lower limits of determination were 2.16-17.5 microg/m3 for 2-week sampling. It was confirmed that 2-week monitoring of carbonyl concentrations up to 118-229 microg/m3 was possible. Relative standard deviations of the passive method generated from the repeatability test were 2-12.3% error for five samplings, and the recovery efficiencies were larger than 90%. Thus, the passive sampler was found to be highly suitable for long-term monitoring of carbonyl compounds.     

Direct-push geochemical profiling for assessment of inorganic chemical heterogeneity in aquifers

Discrete-depth sampling of inorganic groundwater chemistry is essential for a variety of site characterization activities. Although the mobility and rapid sampling capabilities of direct-push techniques have led to their widespread use for evaluating the distribution of organic contaminants, complementary methods for the characterization of spatial variations in geochemical conditions have not been developed. In this study, a direct-push-based approach for high-resolution inorganic chemical profiling was developed at a site where sharp chemical contrasts and iron-reducing conditions had previously been observed. Existing multilevel samplers (MLSs) that span a fining-upward alluvial sequence were used for comparison with the direct-push profiling. Chemical profiles obtained with a conventional direct-push exposed-screen sampler differed from those obtained with an adjacent MLS because of sampler reactivity and mixing with water from previous sampling levels. The sampler was modified by replacing steel sampling components with stainless-steel and heat-treated parts, and adding an adapter that prevents mixing. Profiles obtained with the modified approach were in excellent agreement with those obtained from an adjacent MLS for all constituents and parameters monitored (Cl, NO(3), Fe, Mn, DO, ORP, specific conductance and pH). Interpretations of site redox conditions based on field-measured parameters were supported by laboratory analysis of dissolved Fe. The discrete-depth capability of this approach allows inorganic chemical variations to be described at a level of detail that has rarely been possible. When combined with the mobility afforded by direct-push rigs and on-site methods of chemical analysis, the new approach is well suited for a variety of interactive site-characterization endeavors.     

Radial diffusive sampler for the determination of 8-h ambient ozone concentrations

The 8-h ozone radial diffusive sampler was evaluated according to the CEN protocol for the validation of diffusive samplers. All the parameters regarding the sampler characteristics were found to be consistent with the requirements of this protocol apart from the blank value, which must be evaluated and subtracted at each sampling. The nominal uptake rate was determined in laboratory conditions. However, the uptake rate depends on the mass uptake, temperature, humidity and on the combination of temperature and humidity. Based on laboratory experiments, an empirical model has been established which improved the agreement between the radial sampler and the reference method. This improvement was observed under several different meteorological and emission conditions of sampling. By using the model equation of uptake rate, the data quality objective of 30% for the expanded uncertainty included in the O(3) European Directive, is easily attained. Therefore, the sampler represents an appropriate indicative method.     

Calibration and field performance of membrane-enclosed sorptive coating for integrative passive sampling of persistent organic pollutants in water

Membrane-enclosed sorptive coating (MESCO) is a miniaturised monitoring device that enables integrative passive sampling of persistent, hydrophobic organic pollutants in water. The system combines the passive sampling with solventless preconcentration of organic pollutants from water and subsequent desorption of analytes on-line into a chromatographic system. Exchange kinetics of chemicals between water and MESCO was studied at different flow rates of water, in order to characterize the effect of variable environmental conditions on the sampler performance, and to identify a method for in situ correction of the laboratory-derived calibration data. It was found that the desorption of chemicals from MESCO into water is isotropic to the absorption of the analytes onto the sampler under the same exposure conditions. This allows for the in situ calibration of the uptake of pollutants using elimination kinetics of performance reference compounds and more accurate estimates of target analyte concentrations. A field study was conducted to test the sampler performance alongside spot sampling. A good agreement of contaminant patterns and water concentrations was obtained by the two sampling techniques.     

A second look at the Palmes' diffusive sampler

The Palmes' tube, the first diffusive sampler incorporating a fixed path length, has received wide usage for the sampling of a large number of gaseous pollutants. But despite numerous previous studies, questions remain regarding the accuracy of these inexpensive, simple-to-construct, open-ended samplers. Here the mass transfer resistance in a Palmes' diffusive sampler was measured using the loss of cyclohexane from a Palmes' tube containing liquid cyclohexane at its base. The average loss rates, at factorial combinations of five air incidence angles evenly spaced from 270 degrees to 90 degrees, and five air speeds from 0.5 m/sec to 2.5 m/sec ranged from 46% to 121% higher than rates calculated from the physical dimensions of the sampler, proving the need to calibrate these samplers rather than relying on a theoretical calculation. The mass transfer resistance was nearly constant when the airflow was perpendicular to the sampler and sufficiently high to avoid stagnation, a finding that may explain the widespread acceptance of the results obtained using this sampler.     

Spatial Factors Influencing Winter Primary Particle Sampling and Interpretation

ABSTRACT

Aerosol samplers collect material that is locally generated as well as that transported from upwind; knowing the extent of the area from which the sample is drawn is necessary for proper interpretation of sampler data. The U.S. Environmental Protection Agency (EPA) PM_2.5 monitoring guidelines recognize a conceptual hierarchy of sampler spatial representation, but provide no objective measures of a site’s spatial representativeness. A case study of a sampler tributary area in central California provides insights into the factors that determine a sampler’s spatial representation. Winter diurnal cycles of fine particle concentrations at places of habitation ranging from urban cores to small farm towns show a marked cycle that can be linked to local human activity. Assessment of the possible causes of the observed cycles leads to the hypothesis that local sources dominate primary particle mass in winter samples. The hypothesis was tested using a simple model to relate routine 24-hr PM₁₀ and PM_2.5 samples to a sampler’s surroundings. Model results indicate that even minor sources very close to a sampler will overwhelm any regional component in a sample. The results for the cases studied also demonstrate that, in winter, most coarse (PM_10-2.5) particles collected are less than 2 hr old, and most primary fine (PM_2.5) particles are less than 4 hr old. Even on days that are not truly “stagnant,” samplers are very strongly influenced by their immediate surroundings (distances less than 10 km), and only weakly influenced by regional emissions.

The implications for interpretation of sample analyses are as follows: 1. Typical PM sampling networks are unlikely to represent regional conditions;

2. Similarity of samples in time and space between widely separated samplers probably arises from sampling analogous local environments rather than a uniformly mixed regional air mass;

3. Even weak sources near a sampler will prevent regionally representative samples, so that “background” specification in models can be strongly skewed by misapplication of sampler data;

4. Source-receptor relationships within a single modeling grid cell can cause measured and modeled source impacts at a sampler to diverge by orders of magnitude, even for grid cells as small as 1 km; and

5. Differential deposition of coarse and fine particles will skew source apportionment by chemical tracers unless the tracers and the source emissions have the same size distribution.

     

Small-scale spatial and temporal variance in the concentration of heavy metals in aquatic sediments: a review and some new concepts.

Uncertainty associated with data derived by the analyses of heavy metals in aquatic sediment is due to variance produced in the laboratory (precision), plus 'natural', small-scale spatial variance, (or field variance) at the sampling site. Precision is easily determined and is usually reported in contaminant studies, but field variance is poorly understood and seldom documented. It is important to have an understanding of the field variance because if small-scale spatial variance in the concentration of heavy metals is excessive, regional trends may be limited value. Similarly, if temporal change is large, the results of single synoptic surveys may be questionable and the ability to demonstrate anthropogenic contributions over time will be difficult. However, it is evident from the literature that the information needed to address problems of spatial and temporal variance in the field is beyond the resources of most researchers. Analytical precision of about 5% relative standard deviation (RSD) for heavy metal analysis is typical of a well-managed laboratory. Many studies of small-scale spatial variability made during the current investigation indicate that field variance is related to ambient energy and to the type of sedimentological environment. Total variance (analytical plus field variance) is approximately 10% RSD (mean for a suite of nine trace elements) for depositional parts of estuaries and the marine environment, but increases to about 20-35% RSD for the more dynamic parts of the estuarine environment and the fluvial system. Repeated sampling over periods of up to 7 years undertaken during the present study, indicate a similar order of magnitude for temporal variability in these sedimentological environments. A proposed scheme to provide information on field variance is to undertake small-scale spatial and temporal studies in discrete sedimentological environments in the study area after sediment sampling and characterisation has been completed. The comparatively large proportion of total variance associated with small-scale spatial and temporal variability in the field questions the often excessive cost and effort made in attempting minor reductions in analytical precision in contaminant investigations.     

Estimated tropospheric ozone levels on the southeast Spanish Mediterranean coast

The objective of this study is to estimate the spatial variability of tropospheric ozone in an area using a simple model. The area in this case was applied in the western Mediterranean basin. The study period was from May to September in 2003 and 2004.A multiple linear regression between ozone concentrations, altitude and distance to the precursor sources in a fluvial basin can be used to estimate ozone values at other sites during the warmer seasons. The correlation coefficients obtained with 2-week ozone values measured at five points with a passive sampling technique were high enough to apply the model (0.77<r<0.99).To verify the model, ozone concentrations were measured with passive samplers and continuous analyzers at some selected sites, and the values were compared with the estimated concentration. The results of the validations were satisfactory, in 80% of the measurements the estimated levels differ from measured less than 20%, which is included in the bound error for the type of sampler used in this study.     

Characterization of the olfactory impact around a wastewater treatment plant: Optimization and validation of a hydrogen sulfide determination procedure based on passive diffusion sampling

A monitoring program based on an indirect method was conducted to assess the approximation of the olfactory impact in several wastewater treatment plants (in the present work, only one is shown). The method uses H₂S passive sampling using Palmes-type diffusion tubes impregnated with silver nitrate and fluorometric analysis employing fluorescein mercuric acetate. The analytical procedure was validated in the exposure chamber. Exposure periods of at least 4 days are recommended. The quantification limit of the procedure is 0.61 ppb for a 5-day sampling, which allows the H₂S immission (ground concentration) level to be measured within its low odor threshold, from 0.5 to 300 ppb. Experimental results suggest an exposure time greater than 4 days, while recovery efficiency of the procedure, 93.0 ± 1.8%, seems not to depend on the amount of H₂S collected by the samplers within their application range. The repeatability, expressed as relative standard deviation, is lower than 7%, which is within the limits normally accepted for this type of sampler. Statistical comparison showed that this procedure and the reference method provide analogous accuracy. The proposed procedure was applied in two experimental campaigns, one intensive and the other extensive, and concentrations within the H₂S low odor threshold were quantified at each sampling point. From these results, it can be concluded that the procedure shows good potential for monitoring the olfactory impact around facilities where H₂S emissions are dominant.

Implications: Passive samplers are very attractive tools to experimentally tackle a number of air pollution problems, especially those related to odor impact. Their small size and cost permit a denser sampling design and thus a more detailed spatial characterization than other techniques. On the other hand, the large inherent variability in passive sampler measures requires an uncertainty analysis of the chemical species and analytical procedures used.     

An alternative way to determine the size distribution of airborne particulate matter

We developed and tested a methodology to extract both the size-segregated source apportionment of atmospheric aerosol and the size distribution of each detected element. The experiment is based on the parallel use of a standard low-volume sampler to collect Particulate Matter (PM) and an Optical Particle Counter (OPC). The approach is complementary to size-segregated PM sampling, and it was tested versus a 12-stage cascade impactor. Samples were collected inside the urban area of Genoa (Italy) and their elemental composition was measured by Energy Dispersive-X Ray Fluorescence (ED-XRF). Positive Matrix Factorization (PMF) was applied to time series of elemental concentrations to identify major PM sources, and both PM mass concentration and size-segregated particle number concentration were apportioned. Source profiles and temporal trends extracted by PMF were analyzed together with the OPC data to obtain the size distribution for several elements. The new methodology proved to be reliable for the PM apportionment as well as in providing the elemental concentrations in PM10, PM2.5, and PM1 (PM with aerodynamic diameter, D_ae < 10, 2.5, and 1 μm, respectively). The elemental size distributions are in good agreement with those obtained by the cascade impactor for several elements but some discrepancies, in particular for traffic emissions, are stressed and discussed in the text. The new methodology has two main advantages: it only requires standard semi-automatic sampling equipment and compositional analysis and it provides size-segregated information averaged over quite long periods (typically several months). This is particularly important since campaigns with cascade impactors are generally laborious and thus limited to short periods.     

Comparison between a personal PM10 sampling head and the tapered element oscillating microbalance (TEOM) system

A new personal PM₁₀ sampling head has been developed by the Institute of Occupational Medicine (IOM), Edinburgh. The purpose of this study was to compare its performance in the field with the accepted fixed-location PM₁₀ sampler, the tapered element oscillating microbalance (TEOM). The comparisons were carried out on three separate occasions during 1997 at each of two city centre locations in the UK. On each occasion two personal IOM PM₁₀ sampling heads were located adjacent to a TEOM monitor and four successive sets of 24-h filter samples were collected. The data was compared with 24-h average TEOM concentrations, calculated as the arithmetic mean of the recorded hourly averages. There was a statistically significant linear relationship between the two types of monitor, although the concentrations from the IOM PM₁₀ samplers were consistently higher than the TEOM data. It is therefore possible to use the regression equations presented in this paper to correct ambient PM₁₀ concentrations measured by either method to equivalent values. Further research is needed to properly understand the reason for the difference between the TEOM and filter samplers.