On-board measurement of particle numbers and their size distribution from a light-duty diesel vehicle: Influences of VSP and altitude

In this study, the particle size-resolved distribution from a China-3 certificated light-duty diesel vehicle was measured by using a portable emission measurement system (PEMS). In order to examine the influences of vehicle specific power (VSP) and high-altitude operation, measurements were conducted at 8 constant speeds, which ranged from 10 to 80 km/hr at 10 km/hr intervals, and two different high altitudes, namely 2200 and 3200 m. The results demonstrated that the numbers of particles in all size ranges decreased significantly as VSP increased when the test vehicle was running at lower speeds (< 20 km/hr), while at a moderate speed (between 30 and 60 km/hr), the particle number was statistically insensitive to increase VSP. Under high-speed cruising conditions, the numbers of ultrafine particles and PM_2.5 were insensitive to changes in VSP, but the numbers of nanoparticles and PM₁₀ surged considerably. An increase in the operational altitude of the test vehicle resulted in increased particle number emissions at low and high driving speeds; however, particle numbers obtained at moderate speeds decreased as altitude rose. When the test vehicle was running at moderate speeds, particle numbers measured at the two altitudes were very close, except for comparatively higher number concentrations of nanoparticles measured at 2200 m.     

Adding complex trophic interactions to a size-spectral plankton model: Emergent diversity patterns and limits on predictability

A new model in the NPZ (nutrient-phytoplankton-zooplankton) style is presented, mechanistically simple but with 40 size classes each of phytoplankton (1-20 μm) and small zooplankton (2.1-460 μm), in order to resolve one level of trophic interactions in detail. General, empirical allometric relationships are used to parameterize both the optimal prey size and size selectivity for each grazer class, as is rarely done. This inclusion of complex predator-prey linkages and realistic prey preferences yields a system with an emergent pattern of phytoplankton diversity consistent with global ocean observations, i.e., a parabolic relationship between diversity (as measured by the Shannon evenness) and biomass. It also yields significant long-term time evolution, which places limits on the extent to which the community response to nutrient forcing can be predicted from forcing in a pragmatic sense. When a simple annual cycle in nutrient supply is repeated exactly for many years, transient fluctuations up to a factor of two in spring bloom magnitude persist for 10-20 years before a stable seasonal biomass cycle is achieved. When the amplitude of the nutrient-supply annual cycle is given a random interannual modulation, these long-lived transients add significant noise to a 100-year correlation between annual-mean nutrient supply and annual-mean biomass. This noise is 20% of total interannual variance in the model base case, and ranges from 0% to 40% depending on the grazer size selectivity. In general, unpredictability on the bloom timescale is damped when food-web complexity is increased by making grazers less selective, while unpredictability on the interannual scale shows the opposite pattern, increasing with increasing food-web complexity up to a high threshhold, past which community structure and biomass time evolution both suddenly simplify. These results suggests a new strategy for ensemble ecosystem forecasting and uncertainty estimation, analogous to methods common in circulation and climate modeling, in which internal variability (predator-prey interactions in the biological case; eddies and climate-system oscillations in the physical case) are resolved and quantified, rather than suppressed.     

Predicting functional response and size selectivity of juvenile Notonecta maculata foraging on Daphnia magna

A mechanistic model was developed to assess the impact of predation of juvenile Notonecta maculata on size structured Daphnia magna populations and to provide a framework for quantifying the backswimmers uptake of food. Results of experiments and model predictions clearly demonstrate selective predation of backswimmers when fed with a choice of daphnid size classes, with patterns of selectivity differing across N. maculata instars. The model describes the foraging process empirically on the base of a general predation cycle including four conditional events instead of using classic functional response curves. For model parameterisation components of predation, namely probability of encounter, attack and success as well as time spent on handling prey was directly observed by means of video tracking experiments. Since attack rate, capture success and handling time appeared to be a function of prey size differing between Notonecta instars, the model takes into account ontogenic changes in both predator and prey characteristics. Independent data of functional response and size selectivity experiments were used for model validation and proved the model outcome to be consistent with observations.     

Provisional rejection of three alternative hypotheses on the maintenance of a size dichotomy in males of Dawson’s burrowing bee,Amegilla dawsoni (Apidae,Apinae, Anthophorini)

I examine three alternative hypotheses on the male size dimorphism of Dawson’s burrowing bees (Amegilla dawsoni) in which there are large (major) and small (minor) males. One possibility is that minor males are simply the incidental byproduct of environmental conditions that prevent females from provisioning brood cells optimally. This hypothesis is not supported by the finding that males of intermediate size are consistently rare in populations sampled across years and in different regions, nor can it easily account for the absence of a size dichotomy in females. A second possibility is that minors represent a “best of a bad job” response of those females that are small or otherwise disadvantaged. However, presumptive male siblings sometimes include both majors and minors, a result not predicted from this hypothesis. A third explanation is that female brood provisioning strategy results in the production of minors and majors with equal fitness benefit to fitness cost ratios. However, although it is true that minor males weigh on average about half what a major weighs, and so represent approximately half the provisioning expense of a major, minor males on average appear to secure far fewer than half the number of matings of majors. If the estimate of mating success of minors is accurate, the net gain to females from producing a minor son is unlikely to equal that derived from a major son. Therefore the third hypothesis must also be tentatively rejected, although with caution given the uncertainties in estimating the relative costs and benefits of producing major and minor sons. Received: 12 January 1996/Accepted after revision: 27 April 1996     

Using fluorescence surrogates to track algogenic dissolved organic matter (AOM) during growth and coagulation/flocculation processes of green algae

Tracking the variation of the algogenic organic matter (AOM) released during the proliferation of green algae and subsequent treatment processes is crucial for constructing and optimizing control strategies. In this study, the potential of the spectroscopic tool was fully explored as a surrogate of AOM upon the cultivation of green algae and subsequent coagulation/flocculation (C/F) treatment processes using ZrCl₄ and Al₂(SO₄)₃. Fluorescence excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC) identified the presence of three independent fluorescent components in AOM, including protein-like (C1), fulvic-like (C2) and humic-like components (C3). Size exclusion chromatography (SEC) revealed that C1 in AOM was composed of large-sized proteins and aromatic amino acids. The individual components exhibited their unique characteristics with respect to the dynamic changes. C1 showed the highest correlation with AOM concentrations (R²?=?0.843) upon the C/F processes. C1 could also be suggested as an optical predictor for the formation of trihalomethanes upon the C/F processes. This study sheds a light for the potential application of the protein-like component (C1) as a practical surrogate to track the evolution of AOM in water treatment or wastewater reclamation systems involving Chlorella vulgaris green algae.     

Making sense of predator scents: investigating the sophistication of predator assessment abilities of fathead minnows

According to the threat-sensitive predator avoidance hypothesis, selection favors prey that accurately assess the degree of threat posed by a predator and adjust their anti-predator response to match the level of risk. Many species of animals rely on chemical cues to estimate predation risk; however, the information content conveyed in these chemical signatures is not well understood. We tested the threat-sensitive predator avoidance hypothesis by determining the specificity of the information conveyed to prey in the chemical signature of their predator. We found that fathead minnows (Pimephales promelas) could determine the degree of threat posed by northern pike (Esox lucius) based on the concentration of chemical cues used. The proportion of minnows that exhibited an anti-predator response when exposed to a predator cue increased as the concentration of the pike cue used increased. More surprisingly, the prey could also distinguish large pike from small pike based on their odor alone. The minnows responded more intensely to cues of small pike than to cues of large pike. In this predator–prey system small pike likely represent a greater threat than large pike.Communicated by A. Mathis     

Evaluation of Optically Acquired Zooplankton Size-Spectrum Data as a Potential Tool for Assessment of Condition in the Great Lakes

An optical plankton counter (OPC) potentially provides an assessment tool for zooplankton condition in ecosystems that is rapid, economical, and spatially extensive. We collected zooplankton data with an OPC in 20 near-shore regions of 4 of the Laurentian Great Lakes. The zooplankton size information was used to compute mean size, biomass density, and size-spectra parameters for each location. The resulting metrics were analyzed for their ability to discriminate among the Great Lakes. Biomass density provided discrimination among lakes, as did several parameters describing spectra shape and distribution. A proposed zooplankton indicator, mean size (determined with OPC measurements in this study), was found to provide discrimination among lakes. Size-spectra-related parameters added increased ability to discriminate in conjunction with the biomass density (or mean size) metric. A discriminant function analysis of the multiple metrics (mean size, biomass density, and distribution parameters) suggests that a multi metric size-based approach might be used to classify communities among lakes improving a mean-size metric. The feasibility OPCs and size-based metrics for zooplankton assessment was found to have potential for further development as assessment tools for the biological condition of zooplankton communities in the Great Lakes.     

Sources and characteristics of fine particles over the Yellow Sea and Bohai Sea using online single particle aerosol mass spectrometer

Marine aerosols over the East China Seas are heavily polluted by continental sources. During the Chinese Comprehensive Ocean Experiment in November 2012, size and mass spectra of individual atmospheric particles in the size range from 0.2 to 2.0 μm weremeasured onboardby a single particle aerosol mass spectrometer (SPAMS). The average hourly particle number (PN) was around 4560 ± 3240 in the South Yellow Sea (SYS), 2900 ± 3970 in the North Yellow Sea (NYS), and 1700 ± 2220 in the Bohai Sea (BS). PN in NYS and BS varied greatly over 3 orders of magnitude, while that in SYS varied slightly. The size distributions were fitted with two log-normal modes. Accumulation mode dominated in NYS and BS, especially during episodic periods. Coarse mode particles played an important role in SYS. Particles were classified using an adaptive resonance theory based neural network algorithm (ART-2a). Six particle types were identified with secondary-containing, aged sea-salt, soot-like, biomass burning, fresh sea-salt, and lead-containing particles accounting for 32%, 21%, 18%, 16%, 4%, and 3% of total PN, respectively. Aerosols in BS were relatively enriched in particles from anthropogenic sources compared to SYS, probably due to emissions from more developed upwind regions and indicating stronger influence of continental outflowonmarine environment. Variation of source types dependedmainly on origins of transported air masses. This study examined rapid changes in PN, size distribution and source types of fine particles in marine atmospheres. It also demonstrated the effectiveness of high-time-resolution source apportionment by ART-2a.     

Seasonal variations and size distributions of water-soluble ions in atmospheric aerosols in Beijing, 2012

The characteristics of water-soluble ions in airborne particulate matter in Beijing were investigated using ion chromatography. The results showed that the total concentrations of ions were 83.7 ± 48.9 μg/m³ in spring, 54.0 ± 17.0 μg/m³ in summer, 54.1 ± 42.9 μg/m³ in autumn, and 88.8 ± 47.7 μg/m³ in winter, respectively. Furthermore, out of all the ions, NO₃⁻, SO₄^2 − and NH₄⁺ accounted for 81.2% in spring, 78.5% in summer, 74.6% in autumn, and 76.3% in winter. Mg^2 + and Ca^2 + were mainly associated with coarse particles, with a peak that ranged from 5.8 to 9.0 μm. Na⁺, NH₄⁺ and Cl⁻ had a multi-mode distribution with peaks that ranged from 0.43 to 1.1 μm and 4.7 to 9.0 μm. K⁺, NO₃⁻, and SO₄^2 − were mainly associated with fine particles, with a peak that ranged from 0.65 to 2.1 μm. The concentrations of Na⁺, K⁺, Mg^2 +, Ca^2 +, NH₄⁺, Cl⁻, NO₃⁻ and SO₄^2 − were 2.69, 2.32, 1.01, 4.84, 16.9, 11.8, 42.0, and 44.1 μg/m³ in particulate matter (PM) on foggy days, respectively, which were 1.4 to 7.3 times higher than those on clear days. The concentrations of these ions were 2.40, 1.66, 0.92, 4.95, 17.5, 7.00, 32.6, and 34.7 μg/m³ in PM on hazy days, respectively, which were 1.2–5.7 times higher than those on clear days.     

兰州市室外大气细菌气溶胶浓度及粒径分布特征

在兰州市不同室外环境区域布设4个采样点,使用PSW-6型安德森（Andersen）6级筛孔撞击式空气微生物采样器采集大气细菌气溶胶,分析其浓度和粒径日变化特征。结果表明,不同季节各采样点的大气细菌气溶胶浓度上午时段为88 CFU/m3～1 335 CFU/m3,下午时段为78 CFU/m3～865 CFU/m3。除了夏季兴隆山上午时段外,其余不同季节各采样点上、下午时段的大气细菌气溶胶粒径均主要分布于Ⅰ级—Ⅳ级（＞2.10μm）,占比为 70.54%～93.94%;Ⅴ级（1.10 μm～2.10μm）和Ⅵ级（0.65 μm～1.10 μm）大气细菌粒子占比较低,仅为6.06%～29.46%。