Advances in sensing ammonia from agricultural sources.

Reducing ammonia emissions is one of the most difficult challenges for environmental regulators around the world. About 90% of ammonia in the atmosphere comes from agricultural sources, so that improving farm practices in order to reduce these emissions is a priority. Airborne ammonia is the key precursor for particulate matter (PM2.5) that impairs human health, and ammonia can contribute to excess nitrogen that causes eutrophication in water and biodiversity loss in plant ecosystems. Reductions in excess nitrogen (N) from ammonia are needed so that farms use N resources more efficiently and avoid unnecessary costs. To support the adoption of ammonia emission mitigation practices, new sensor developments are required to identify sources, individual contributions, to evaluate the effectiveness of controls, to monitor progress towards emission-reduction targets, and to develop incentives for behavioural change. There is specifically a need for sensitive, selective, robust and user-friendly sensors to monitor ammonia from livestock production and fertiliser application. Most currently-available sensors need specialists to set up, calibrate and maintain them, which creates issues with staffing and costs when monitoring large areas or when there is a need for high frequency sampling. This paper reports advances in monitoring airborne ammonia in agricultural areas. Selecting the right method of monitoring for each agricultural activity will provide critical data to identify and implement appropriate ammonia controls. Recent developments in chemo-resistive materials allow electrochemical sensing at room temperature, and new spectroscopic methods are sensitive enough to determine low concentrations in the order of parts per billion. However, these new methods still compromise selectivity and sensitivity due to the presence of ambient dust and other interferences, and are not yet suitable to be applied in agricultural monitoring. This review considers how ammonia measurements are made and applied, including the need for sensors that are suitable for routine monitoring by non-specialists. The review evaluates how monitoring information can be used for policies and regulations to mitigate ammonia emissions. The increasing concerns about ammonia emissions and the particular needs from the agriculture sector are addressed, giving an overview of the state-of-the-art and an outlook on future developments.

Design and laboratory testing of a new flow-through directional passive air sampler for ambient particulate matter.

A new type of directional passive air sampler (DPAS) is described for collecting particulate matter (PM) in ambient air. The prototype sampler has a non-rotating circular sampling tray that is divided into covered angular channels, whose ends are open to winds from sectors covering the surrounding 360°. Wind-blown PM from different directions enters relevant wind-facing channels, and is retained there in collecting pools containing various sampling media. Information on source direction and type can be obtained by examining the distribution of PM between channels. Wind tunnel tests show that external wind velocities are at least halved over an extended area of the collecting pools, encouraging PM to settle from the air stream. Internal and external wind velocities are well-correlated over an external velocity range of 2.0-10.0 m s⁻¹, which suggests it may be possible to relate collected amounts of PM simply to ambient concentrations and wind velocities. Measurements of internal wind velocities in different channels show that velocities decrease from the upwind channel round to the downwind channel, so that the sampler effectively resolves wind directions. Computational fluid dynamics (CFD) analyses were performed on a computer-generated model of the sampler for a range of external wind velocities; the results of these analyses were consistent with those from the wind tunnel. Further wind tunnel tests were undertaken using different artificial particulates in order to assess the collection performance of the sampler in practice. These tests confirmed that the sampler can resolve the directions of sources, by collecting particulates preferentially in source-facing channels.

Further development of a new flow-through directional passive air sampler for monitoring ambient nitrogen dioxide.

We have previously introduced a new type of rotatable flow-through directional passive air sampler (DPAS) for monitoring trace air pollutants in ambient air. In wind tunnel tests, the sampler turns into the prevailing wind direction and retains NO(2) (used as a test pollutant) on an internal sampling medium ring of triethanolamine (TEA)-coated meshes to indicate the source of pollution. However, these meshes can become saturated, after exposure times of tens of hours or a few days, due to the relatively small masses of TEA which can be coated onto them. This paper outlines the saturation problem and presents a possible redesign of the DPAS sampling approach, to allow longer-term (weeks-months) deployments, where air passes over larger volumes of TEA retained in a compartmentalised carousel. Investigations varying the volume, depth and mixing of TEA in sampling compartments suggested that the limiting step of NO(2) uptake was its rate of supply from the atmosphere. In wind tunnel trials, NO(2) uptake into TEA continued linearly in response to a stable air concentration over periods of tens of days, showing no signs of saturation. Uptake was wind velocity dependent across the range of 0.50, 2.00, 5.00 and 8.00 m s(-1). Results indicate that the total sampling time and storage capacity of the TEA for NO(2) can be varied to meet deployment time requirements, indicating that long-term, cheap, directional passive air sampling is achievable.

Field testing of a new flow-through directional passive air sampler applied to monitoring ambient nitrogen dioxide.

This paper reports the first field deployment and testing of a directional passive air sampler (DPAS) which can be used to cost-effectively identify and quantify air pollutants and their sources. The sampler was used for ambient nitrogen dioxide (NO(2)) over ten weeks from twelve directional sectors in an urban setting, and tested alongside an automatic chemiluminescent monitor. The time-integrated passive directional results were compared with the directional analysis of the active monitoring results using wind data recorded at a weather station. The DPAS discriminated air pollutant signals directionally. The attempts to derive quantitative data yielded reasonable results--usually within a factor of two of those obtained by the chemiluminescent analyser. Ultimately, whether DPAS approaches are adopted will depend on their reliability, added value and cost. It is argued that added value was obtained here from the DPAS approach applied in a routine monitoring situation, by identifying source sectors. Both the capital and running costs of DPAS were <5% of those for the automatic monitor. It is envisaged that different sorbents or sampling media will enable this rotatable DPAS design to be used for other airborne pollutants. In summary, there are reasons to be optimistic that directional passive air sampling, together with careful interpretation of results, will be of added value to air quality practitioners in future.

Frost injury prediction model for Douglas-fir seedlings in the Pacific Northwest.

Because simple seed- or breeding-zone guidelines are inadequate for controlling the risk of maladaptation to environmental stresses, we are developing operational procedures to assess the risk of frost kill to genetically improved families of Douglas-fir (Pseudotsuga menziesii Mirb. Franco). We have (1) determined the time course of cold hardening and dehardening of nursery-grown Douglas-fir seedlings over four winters, by means of controlled freezing tests, (2) fitted curves to relationships between temperature sum and both fall cold hardening and spring dehardening, (3) applied the temperature sum models to daily temperature records of 80 weather stations to estimate frequency of years with significant frost kill at those stations, (4) interpolated frost kill probabilities for tree farms, using a thin plate spline procedure with elevation, latitude and longitude as variables, and (5) prepared a coarse-scale frost risk map from the resulting grid point estimates. With the exception of a few high-elevation stations, the most damaging frost at any station in any year occurred in either the fall (October and November) or late spring (mid-April to mid-May). In general, damaging spring frosts were two to three times more frequent than fall frosts, and areas in Oregon were at greater risk than areas at similar elevations and longitudes further north. The spline surface was less precise for predicting spring frost risk than fall frost risk.