Passive Flux Samplers Research Articles

Simple use of the backwards Lagrangian stochastic dispersion technique for measuring ammonia emission from small field-plots

This study evaluates some simple procedures for measuring ammonia (NH 3) emission from wind speed, NH 3 concentration and an estimate of atmospheric stability using the backward Lagrangian stochastic (bLS) dispersion technique. The bLS technique, which requires measurements from only one height may prove useful when carrying out experiments simultaneously in a small field with several small plots. Commercial software exists that facilitates easy use of the bLS technique. Our study shows the bLS to be reliable using average wind speed at one height and average NH 3 concentration derived from horizontal flux measurements of NH 3 using passive flux samplers. The bLS technique underestimated the emission by 16–24% when applied at a measurement height of 0.5–1.55 m, but the inclination of bLS estimates versus integrated horizontal flux estimates was not different from 1 ( P < 0.01). The emission of NH 3 from urea applied to dry prairie soil was 29% of the nitrogen applied, emphasising the need of developing techniques for reducing NH 3 emission from zero tillage arable soils.

Measuring ammonia emission rates from livestock buildings and manure stores?part 1: development and validation of external tracer ratio, internal tracer ratio and passive flux sampling methods

Abstract There is a need for robust methods for measuring ammonia emission rates from livestock buildings and manure stores, to guide efforts to abate emissions from livestock farming. This paper reports research to develop and validate three candidate measurement techniques: (a) An external tracer ratio method, where concentrations of ammonia and sulphur hexafluoride are measured downwind of an animal house or manure store. (b) An internal tracer ratio (ITR) method, suited to animal housings, where concentrations of ammonia and sulphur hexafluoride are measured just before air leaves the building. (c) A flux sampler method, which uses sets of passive flux sampling devices positioned so as to intersect all significant flows of air out of an animal house or manure store source. All three of the measurement techniques were validated at a building section simulating a naturally ventilated (space-boarded) cattle house, with the external tracer ratio method also being validated at a simulated slurry store. In the validation tests on the external tracer ratio method the derived ammonia emission rates from the slurry store and cattle house validation studies were 25% below and 43% above the measured release rate, respectively. These biases were shown by t-tests to be statistically highly significant, but no clear explanation could be found for the different signs and magnitudes in the two cases. For the ITR method, recovery rates of 78% and 101% of released NH3 were achieved, with low and high release rates, respectively. Validation tests conducted on the flux samplers gave an average of 66% (standard deviation 2.9%) ammonia recovery. The cause of this non-ideal level of recovery has not yet been identified. However, given the low standard deviation, it was concluded that these samplers could be used to measure ammonia emission rates from real farm buildings, provided that a correction factor for the non-ideal recovery was applied.

A study on emission of phthalate esters from plastic materials using a passive flux sampler

Abstract Phthalate esters are used as plasticizer in many plastics, and several studies have shown their toxicity. Phthalate esters are gradually emitted over time, and so it is conceivable that they pose a significant health risk. This study aims to investigate the temperature dependence of the emissions of various phthalate esters and to estimate the health risks of these emissions at various temperatures. A passive-type sampler was developed to measure the flux of phthalate esters from the surface of plastic materials. With this sampler, we examined three widely used plastic materials: synthetic leather, wallpaper and vinyl flooring. The observed maximum emissions of diethyl phthalate, dibutyl phthalate, and diethylhexyl phthalate (DEHP) from these materials at 20°C were 0.89, 0.77, and 14 μg m−2 h−1, respectively. Emissions at 80°C were 2.8, 4.5×102, and 1.5×103 μg m−2 h−1, respectively. The results showed this temperature dependence is determined primarily by the type of phthalate ester and less so by the type of material. The estimation from the results of temperature dependence indicated the concentration of DEHP in a vehicle left out in the sunshine during the day can exceed the recommended levels of Japan Ministry of Health, Labour and Welfare.

Improved Passive Flux Samplers for Measuring Ammonia Emissions from Animal Houses, Part 1: Basic Principles

At present, precise, expensive and laborious methods with a high resolution in time are needed, to determine ammonia emission rates from animal houses. The high costs for equipment, maintenance and labour limit the number of sites that can be measured. This study examines a new, simpler concept for carrying out these measurements. The basis of the concept is a passive ammonia flux sampler, which improves on Ferm's original design by having a central orifice (thus halving the number of tubes per sampler and hence halving the number of analyses needed) and also by having a greatly increased ammonia-capturing capacity. Sets of the samplers can be placed in ventilation ducts, or in openings of a naturally ventilated animal house, to give a direct and simple measure of ammonia flux and hence of overall ammonia emission rate. Calibration of any sampler design based on this new concept is quick and easy: this is important because of the huge variation in designs of systems for ventilation in animal houses. Moreover, no power source is needed to perform cheap and accurate time-integrated ammonia emission measurements. The high ammonia-capturing capacity, allowing a long-term exposure, of at least 1 week, is achieved by using a glass-fibre insert to hold a large charge of a mineral acid. First results from validation tests with the simplest possible sampler design on the farm were promising. The flux samplers proved easy to handle and deploy, and gave results which agreed closely with those from a reference method based on fan-wheel anemometers to give ventilation rate and on the continuous measurement of ammonia concentration by chemiluminescence. In a companion paper, the performance of different forms of the flux sampler as a function of angle of incidence of airflow is reported.

Improved Passive Flux Samplers for measuring Ammonia Emissions from Animal Houses, Part 2: Performance of Different Types of Sampler as a Function of Angle of Incidence of Airflow

The basic principle of the improved passive flux sampler has been reported in a companion paper. In the present paper, the performance of different types of the sampler as a function of angle of incidence of airflow was studied in a wind tunnel. The following types of sampler were examined: (a) a basic straight sampler (220 mm long); (b) straight samplers (220 mm long) with openings that had been modified in one of several different ways, all aimed at reducing turbulence around the openings and thus achieving nearer-to-perfect performance as angle of incidence changed; (c) a cranked sampler, designed to reduce the distance between the planes of the two openings to 80 mm (type useful in confined spaces); and (d) two types of sampler (dual curved and angular) for both of which the two openings are in the same plane, albeit offset transversely (useful for space-boarded buildings). The dependency on the angle of incidence of the different sampler types was compared by measuring the pressure drop across the sampler, and hence calculating a normalised air velocity through each sampler's precision central orifice for each angle of incidence. Ideal performance would yield a cosine relationship between air velocity through the sampler and angle of incidence. Any deviations from such a cosine relationship imply a potential under- or over-estimation of ammonia flux rate, the magnitude of which depends on the relative persistence of the relevant angle of incidence during the exposure period of the sampler. The closest approach to ideal performance as angle of incidence changes was achieved by the straight sampler modified by the addition of solid tear-drop shapes around both its openings. However, the overall length of the straight sampler means that it is not suitable for all sampling scenarios. For confined spaces e.g. complex geometries in the roof ridges of livestock buildings, the cranked sampler is more suitable, accepting that it does not so closely approach ideal performance as the angle of incidence changes. Likewise, the dual curved and angular samplers are more suitable for ammonia fluxes through space-boarded walls or similar: in both the above scenarios, non-ideal performance is mitigated by the fact that, with defined air pathways in the roof ridge, and with a space-boarded wall of finite thickness, respectively, the range of angles of incidence likely to be seen by the cranked, dual curved and angular samplers is generally limited to angles near to 0 or 180°.

Quantification of ammonia exchange between agricultural cropland and the atmosphere: Measurements over two complete growth cycles of oilseed rape, wheat, barley and pea

The exchange of ammonia between the atmosphere and the canopy of barley, wheat, oilseed rape and pea crops was studied over two growing seasons by use of a modified aerodynamic gradient technique in which passive horizontal flux samplers were applied with a wind profile in gradient configuration. The crop foliage was a net source of NH3 to the atmosphere, with NH3 emissions on a seasonal basis between 1 and 5 kg NH3–N ha−1. The amount of NH3 lost constituted between 1 and 4% of the applied nitrogen and between 1 and 4% of the actual amount of nitrogen present in the mature shoots. The volatile NH3 losses depended on seasonal variations in climatic conditions affecting the growth and nitrogen economy of the crops and increased under conditions with excessive N absorption by roots and a high N concentration in the foliage. The accumulated NH3 loss was positively correlated with the above-ground crop N content at anthesis, but not with that at final maturity. There were no indications that NH3 emissions were larger under conditions unfavourable for nitrogen remobilization from vegetative plant parts (low N harvest index). Nevertheless, a distinct peak in NH3 emission occurred during senescence. It is concluded that crops in many areas will represent a significant input of ammonia to the atmosphere and that NH3 losses may become large enough to significantly affect crop N budgets.

Micrometeorological measurements of net ammonia fluxes over oilseed rape during two vegetation periods

Ammonia fluxes were measured semi-continuously over oilseed rape ( Brassica napus) as part of the EXAMINE North Berwick experiment during ripening of the growing plants and following cutting prior to harvest. The first period was investigated intensively, including flux measurements by continuous wet denuders at six heights, as well as by filter packs and passive flux samplers. The aerodynamic gradient method and eddy covariance were applied to estimate friction velocity ( u ∗), sensible heat fluxes ( H) and latent heat fluxes ( λE), with best estimates provided by inter-comparisons for each. The measurements represent a major exercise in data acquisition and processing, and provide approximately 30 days of semi-continuous fluxes. The largest errors in estimating the NH 3 fluxes arise from the concentration profile measurements. Fluxes from the ripening canopy were bi-directional, varying in the range −150 to 180 ng m −2 s −1, with the largest emission fluxes during the day, and both emission and deposition occurring at night. Larger net emissions were measured following cutting of the rape (up to 620 ng m −2 s −1), with an overall mean of 57 ng m −2 s −1 compared with 16 ng m −2 s −1 prior to cutting. The patterns may be explained in relation to the expected major driving forces controlling exchange (cuticular fluxes, foliar compensation point, leaf litter emissions), the link to temperature/wetness, and the potential for overlying leaves to recapture emissions from leaf litter. The comparison with the passive estimates indicates that continuous measurements of several months duration are required to make a reliable assessment of the passive approach.

Intercalibration of a passive wind-vane flux sampler against a continuous-flow denuder for the measurements of atmospheric ammonia concentrations and surface exchange fluxes

A passive wind-vane flux sampler is a simple low-cost device used to estimate long-term vertical fluxes of ammonia in the atmospheric surface boundary layer. The passive flux sampler measures the horizontal flux of ammonia. A vertical gradient of the horizontal flux, combined with micro-meteorological measurements of wind speed and temperature, is used to estimated the vertical flux of ammonia using a modified aerodynamic gradient technique. The passive wind-vane flux sampler gradient was calibrated against a gradient measured with fast response (6 min) continuous-flow denuders. The measurements were carried out at a heathland located in an intensive farming area in the centre of the Netherlands. A field campaign took place over 70 day period in the summer of 1996, during which the sampling periods of the passive wind-vane flux sampler varied between 3 and 9 days. The comparison clearly showed that the long-term measurements with the passive wind-vane flux samplers gave accurate average ammonia deposition values for the field campaign as a whole which deviated by only 18% from the reference flux. However, there was no significant correlation between the fluxes from the passive samplers and the reference method for the individual 10 periods which were compared. Possible explanations found for the lacking correlation were (I) a high percentage number of half-hour emission events within each period resulted in a significant large relative deviation between the fluxes, and (II) uncertainties in the reference method might also explain the lacking correlation. The passive wind-vane flux samplers proved to be a stable method for long-term measurements (months to years) due to a close to 100% optimal functioning during the field campaign.

A Simple, Controllable, Non-Point Source of Gaseous Ammonia, for Use in Field Experiments

A type of controllable non-point source of gaseous NH3 has been developed, which is simpler, more reliable and more versatile in use than earlier types of source. The source is based on a suitable length of a suitable type of permeable plastic tubing, to which pure NH3 gas is supplied at a suitable pressure. Once steady state is achieved, the emission rate of NH3 from the tubing equals the permeation rate through the tubing wall: the rate is continuously monitored via the rate of weight loss from the cylinder supplying the NH3 gas, mounted on a suitable recording electronic balance. A simple apparatus is described for determining permeation rates of NH3 through samples of different types of tubing, as are two examples of applying the source in field experiments. In the first example, a two-dimensional source was constructed inside the bottom of a clean, dry above-ground cylindrical slurry store (6 m diameter) and used to test passive ammonia flux samplers as a means of measuring NH3 emission rates from such stores when containing slurry. In the second example, a two-dimensional source was constructed on the floor of a full-scale simulation of part of a cattle house (naturally-ventilated), and used to test passive ammonia flux samplers as a means of measuring NH3 emission rates from such houses when cattle are in residence.

WEEKLY MEASUREMENTS OVER ONE YEAR OF AMMONIA CONCENTRATIONS AND SURFACE EXCHANGE FLUXES AT A DANISH HEATHLAND WITH PASSIVE WIND-VANE FLUX SAMPLERS IN AN AERODYNAMIC GRADIENT CONFIGURATION

The present study aims to establish the annual NH3 deposition to an inland heathland in Denmark using a micro-meterological approach with passive wind-vane flux samplers. The integrating samplers were replaced at weekly intervals from May 1995 to May 1996. The average concentration, 2.05 μg m-3 at the heathland is at a moderate level when compared to heathlands in other parts of Europe. The average deposition velocity was 0.83 cm s-1 which is within the range of depositon velocities found for other heathlands in Europe. The average canopy resistance was found to be relatively high, 61 s -1. The measurements yielded a total NH3-N deposition of 2.4 (± 0.9) kg ha-1 yr-1 with a data coverage of 71% for 1995/1996. In 40% of this time the flux is regarded as zero because the flux is not significant different from zero. In 60% of this time the significant fluxes varied from –0.052 μg m-2 s-1 (deposition equal 16.4 kg N ha-1 yr-1) to 0.089 μg m-2 s-1 (emission equal 28.2 kg N ha-1 yr-1). The method is only able to direct measure significant fluxes down to the equivalence of 0.010 μg m-2 s-1 (approximately 3.2 kg ha-1 yr-1). Therefore the exact deposition cannot be determined by the applied method at very low deposition sites such as a coastal heathland in Denmark. In a high-deposition area as in the central Netherlands the method gave significant fluxes with a 100% data coverage for a two month period.

Summer emissions of ammonia from a slurry-based, UK, dairy cow house

Emissions from dairy cow housing are an important term in the UK inventory of ammonia emissions from agriculture: even by current estimates, they contribute, on their own, 9% of total national emissions. When constructing such inventories, it has so far always been assumed that emissions arise only over the winter when the cows are housed full time, or almost so, and that the emissions from the remainder of the year are zero. This study aimed to test that assumption by suitable experiments. A preliminary survey showed that there are wide variations in summer housing practice from dairy farm to dairy farm, and the practice of not housing the cows at all during the summer is by no means universal. Therefore, the dairy cow house chosen for measuring ammonia emissions under summer and winter conditions was one at which the summer practice (which was of a very common type) resulted in cows spending an average of 4 h in every 24 inside the house. Using ‘Ferm tube’ passive ammonia flux samplers, the average summer ammonia emission rate determined from four separate experiments on that house was not significantly different, at the 5% level of probability, from the average winter ammonia emission rate determined from four separate experiments. The main implication of the above findings is that the assumption made hitherto, in both the UK and the Netherlands, when building ammonia inventories, that summer emissions from dairy cow houses are negligible, is untenable. Further measurements on summer emission rates with other common summer housing practices are needed, but meanwhile a first (perhaps pessimistic) estimate can be made of the necessary adjustment in overall ammonia emissions, by doubling the present term in the national inventory for winter emissions. The result of so doing is to increase the UK total ammonia emissions from agriculture by 9% (i.e. by 18 kt NH 3N).

Atmospheric ammonia exchange on a heathland in Denmark

Passive flux samplers were used to determine the ammonia exchange on an inland heath in Denmark over the last 2 years. The samplers measured the horizontal ammonia flux directly. Data were sampled continuously for periods of 1–4 weeks. The micro-meteorological gradient method was used with passive flux samplers and cup anemometers at different heights above the vegetation in order to calculate the vertical fluxes of ammonia. First a fixed sampler system was used with tubes mounted in four orthogonal horizontal directions. This system has been successfully applied to measure the emission from fertilized crops. Adapting this type of sampler to measure the deposition to heathlands did not prove to be straightforward. The precision of the calculated ammonia concentrations was too poor to give an acceptable accuracy for the concentration gradient. The problems were (a) driving rain which entered the tubes, (b) too few measuring points in each concentration profile, and (c) too long sampling periods to allow for the low-concentration levels above the heath area and the detection limits. Therefore, a passive flux sampler mounted on a wind vane and fitted with a rain shelter was developed. Results from the first 5 weekly periods are very promising, yielding accurate concentration gradients. The advantages of the passive flux samplers on the wind vane are (a) the minimum measuring period can be approximately halved compared to the fixed samplers, (b) some of the directional correction terms used with the fixed passive flux samplers are dispensed with, and (c) the field and laboratory work is minimized.

A Passive Flux Sampler for Measuring Ammonia Volatilization from Manure Storage Facilities

AbstractAn integrated horizontal flux technique was tested for quantification of ammonia (NH3) emission from manure storage. The method is based on a simple and inexpensive passive flux sampler consisting of two disconnectable glass tubes, coated on the inside with oxalic acid. The flux sampler is mounted at a minimum of three heights, 20 to 100 cm above the storage, on each of four masts, placed perpendicular to each other around the storage. The samplers continuously integrate the horizontal flux of NH3 at the various heights. After analysis of the NH3 content in the tubes facing the storage (exposed tubes) and surroundings (background tubes), the vertical flux of NH3 from the storage can be obtained by application of mass balance equations (micrometeorological mass balance technique). For the measurements of NH3 volatilization from slurry tanks or lagoons the technique is useful, because it is not affected by heterogenity in wind profiles and the masts with the passive flux samplers are placed on the periphery of the slurry store. The flux samplers were able to accurately quantify NH3 volatilization from slurry tanks. From above the rim of the slurry tank the horizontal net flux decline exponential with height. This may facilitate the calculation of the vertical flux of NH3. Bypass of NH3 between exposed and background tubes may occur during periods with high wind velocities (&gt;10 m s−1) or when more than one‐fifth of the oxalate in the exposed tube has reacted. However, if bypass occurs, a good estimate of NH3 volatilization can still be obtained by addition of exposed and background tubes, because the NH3 flux from storage are usually much greater than the flux from surroundings. Bypass due to high net horizontal fluxes of NH3 can be avoided by reducing the measuring period or increasing the length of the tubes. Storm conditions with heavy rain can flood the flux samplers and spoil the measurements. Within the study NH3 volatilization from stored cattle slurry were measured eight times from October to December 1992. Daily loss rates of NH3 varied between 0.33 and 4.15 g NH3‐N m−2 d−1.

Long-term quantification of ammonia exchange between agricultural cropland and the atmosphere—I. Evaluation of a new method based on passive flux samplers in gradient configuration

A new method for quantification of ammonia exchange between agricultural cropland and the atmosphere is described. Ammonia is absorbed by passive flux samplers (glass tubes coated on the inside with oxalic acid), continuously integrating the horizontal flux of ammonia in various heights above the exchange surface. The mean horizontal fluxes are subsequently divided by the mean wind speed in the same heights, giving ammonia concentrations which are finally used for calculating an ammonia concentration gradient with respect to height and the vertical net flux of ammonia. It is shown that passive flux samplers are able to measure NH 3 net fluxes over extended periods (up to about 1 week), because NH 3 cdncentrations during periods with high wind velocities are weighted higher than NH 3 concentrations during periods with low wind velocities, thereby reducing errors due to time-averaging. Emission and deposition fluxes of ammonia down to 0.1 kg NH 3 ha −1 week −1 can be measured with a variation coefficient smaller than 20%. The method allows simultaneous measurements at many locations, thus making it possible to obtain more and better information about sources and sinks for atmospheric ammonia and about the significance of ammonia exchange fluxes for atmospheric ammonia pollution and for the nitrogen enrichment of terrestrial ecosystems.

An advanced air sampling technique for hazardous waste sites

Development and performance of a passive soil-air flux sampler as an alternative to conventional sampling systems is discussed. The passive sampler is designed to provide longterm measurements of flux rates of volatile organics at waste sites without disturbing the subsurface plume. Laboratory and field experiments conducted with the passive sampler and an active sampler (emission-isolation flux chamber) indicate that the passive sampler provides results very close to those of the active sampler and that the passive sampler is sensitive to smaller emissions. The passive sampler has added advantages over the emission-isolation flux chamber, such as easy deployment, minimum maintenance, and no power requirements.

A simple passive sampler for measuring ammonia emission in the field

A new type of passive sampler for the determination of NH3 emission from land surfaces and manure storages was tested in a micrometereological mass balance method. The sampler consists of 2 glass tubes, each with a length of 10 cm and an internal diameter of 0.7 cm. The two glass tubes are connected in series, with one end fitted with a thin stainless steel disc having a 1 mm hole in the center. The inner surface of each glass tube is coated with oxalic acid. The results show that the passive flux sampler can be used to give accurate determinations of NH3 emission. The passive flux sampler makes gas washing bottles, pumps, flow meters, anemometers, and electricity unnecessary and ammonia loss can be determined easily and cheaply without the requirement of a large labor force.