A small change in the design of a slit bioaerosol impactor significantly improves its collection characteristics

While several methods are available for bioaerosol monitoring, impaction remains the most common one, particularly for collecting fungal spores. Earlier studies have shown that the collection efficiency of many conventional single-stage bioaerosol impactors falls below 50% for spores with an aerodynamic diameter between 1.7 and 2.5 microm because their cut-off size is 2.5 microm or greater. The cut-off size reduction is primarily done by substantially increasing the sampling flow rate or decreasing the impaction jet size, W, to a fraction of a millimetre, with both measures often impractical to implement. Some success has recently been reported on the utilization of an ultra-low jet-to-plate distance, S (S/W < 0.1), in circular impactors. This paper describes a laboratory evaluation and some field testing of two single-stage, single-nozzle, slit bioaerosol impactors, Allergenco-D and Air-O-Cell, which feature the same jet dimensions and flow rate but have some design configuration differences that were initially thought to be of low significance. The collection efficiency and the spore deposit characteristics were determined in the laboratory using real-time aerosol spectrometry and different microscopic enumeration methods as the test impactors were challenged with the non-biological polydisperse NaCl aerosol and the aerosolized fungal spores of Cladosporium cladosporioides, Aspergillus versicolor, and Penicillium melinii. The tests showed that a relatively small reduction in the jet-to-plate distance of a single-stage, single-nozzle impactor with a tapered inlet nozzle, combined with adding a straight section of sufficient length, can significantly decrease the cut-off size to the level that is sufficient to efficiently collect spores of all fungal species. Furthermore, it appears that the slit jet design may improve the application of partial spore counting methodologies with respect to those applied to circular deposits. Data from a demonstration field study, conducted with the two samplers in environments containing a variety of fungal species, supported the laboratory findings.     

Quantifying trade-offs between ecological gains,economic costs,and landowners’ preferences in boreal mire protection

Private land often encompasses biodiversity features of high conservation value, but its protection is not straightforward. Commonly, landowners’ perspectives are rightfully allowed to influence conservation actions. This unlikely comes without consequences on biodiversity or other aspects such as economic considerations, but these consequences are rarely quantitatively considered in decision-making. In the context of boreal mire protection in Finland, we report how acknowledging landowners’ resistance to protection changes the combination of mires selected to conservation compared to ignoring landowners’ opinions. Using spatial prioritization, we quantify trade-offs arising between the amount of landowners’ resistance, protected biodiversity, and financial costs in different conservation scenarios. Results show that the trade-offs cannot be fully avoided. Nevertheless, we show that the systematic examination of the trade-offs opens up options to alleviate them. This can promote the evaluation of different conservation policy outcomes, enabling better-informed conservation decisions and more effective and socially sustainable allocation of conservation resources.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-021-01530-0.     

Concentration gradient patterns of aerosol particles near interstate highways in the Greater Cincinnati airshed

The objective of this study was to determine if there is an exposure gradient in particulate matter concentrations for people living near interstate highways, and to determine how far from the highway the gradient extends. Air samples were collected in a residential area of Greater Cincinnati in the vicinity of two major highways. The measurements were conducted at different distances from the highways by using ultrafine particle counters (measurement range: 0.02-1 microm), optical particle counters (0.3-20 microm), and PM2.5 Harvard Impactors (0.02-2.5 microm). The collected PM2.5 samples were analyzed for mass concentration, for elemental and organic carbon, and for elemental concentrations. The results show that the aerosol concentration gradient was most clearly seen in the particle number concentration measured by the ultrafine particle counters. The concentration of ultrafine particles decreased to half between the sampling points located at 50 m and 150 m downwind from the highway. Additionally, elemental analysis revealed a gradient in sulfur concentrations up to 400 m from the highway in a residential area that does not have major nearby industrial sources. This gradient was qualitatively attributed to the sulfate particle emissions from diesel engine exhausts, and was supported by the concentration data on several key elements indicative of traffic sources (road dust and diesel exhaust). As different particulate components gave different profiles of the diesel exposure gradient, these results indicate that no single element or component of diesel exhaust can be used as a surrogate for diesel exposure, but more comprehensive signature analysis is needed. This characterization is crucial especially when the exposure data are to be used in epidemiological studies.     

Evaluation and optimization of an urban PM2.5 monitoring network

The objective of this study was to evaluate the PM(2.5) monitoring network established in the Greater Cincinnati and Northern Kentucky metropolitan area for measuring the 24 h integrated PM(2.5) concentration, as well as-at selected sites-hourly PM(2.5) concentration and 24 h integrated PM(2.5) speciation. The data collected during three years at 13 measurement sites were analyzed for spatial and temporal variations. It was found that both daily and hourly concentrations of PM(2.5) have low spatial variation due to a regional influence of secondary ammonium sulfate. In contrast, the trace element concentrations had high spatial variation. Seasonal variation accounted for most of the total temporal variation (60%), while yearly, monthly, weekly and daily variations were lower. The variance components and cluster analyses were applied to optimize the number of sites for measuring the 24 h PM(2.5) concentration. It was found that the 13-site network may be optimized by reducing the number of sites to 8, which would result in a relative precision reduction of 9% and a relative cost reduction of 36%. At the same time, the data suggest that the spatial resolution of speciation monitors and real-time PM(2.5) mass monitors should be increased to better represent spatial and temporal variations of the markers of local air pollution sources.     

Impact of minimum winter temperatures on the population dynamics of Dendroctonus frontalis.

Predicting population dynamics is a fundamental problem in applied ecology. Temperature is a potential driver of short-term population dynamics, and temperature data are widely available, but we generally lack validated models to predict dynamics based upon temperatures. A generalized approach involves estimating the temperatures experienced by a population, characterizing the demographic consequences of physiological responses to temperature, and testing for predicted effects on abundance. We employed this approach to test whether minimum winter temperatures are a meaningful driver of pestilence from Dendroctonus frontalis (the southern pine beetle) across the southeastern United States. A distance-weighted interpolation model provided good, spatially explicit, predictions of minimum winter air temperatures (a putative driver of beetle survival). A Newtonian heat transfer model with empirical cooling constants indicated that beetles within host trees are buffered from the lowest air temperatures by approximately 1-4 degrees C (depending on tree diameter and duration of cold bout). The life stage structure of beetles in the most northerly outbreak in recent times (New Jersey) were dominated by prepupae, which were more cold tolerant (by >3 degrees C) than other life stages. Analyses of beetle abundance data from 1987 to 2005 showed that minimum winter air temperature only explained 1.5% of the variance in interannual growth rates of beetle populations, indicating that it is but a weak driver of population dynamics in the southeastern United States as a whole. However, average population growth rate matched theoretical predictions of a process-based model of winter mortality from low temperatures; apparently our knowledge of population effects from winter temperatures is satisfactory, and may help to predict dynamics of northern populations, even while adding little to population predictions in southern forests. Recent episodes of D. frontalis outbreaks in northern forests may have been allowed by a warming trend from 1960 to 2004 of 3.3 degrees C in minimum winter air temperatures in the southeastern United States. Studies that combine climatic analyses, physiological experiments, and spatially replicated time series of population abundance can improve population predictions, contribute to a synthesis of population and physiological ecology, and aid in assessing the ecological consequences of climatic trends.