Daytime air pollution transport mechanisms in stable atmospheres of narrow versus wide urban valleys

Transport of air pollutants emitted from urban valleys can be strongly restricted by interactions between static and dynamic factors including topographic forcing, low-level atmospheric stability related to temperature inversions, and urban heat island-induced circulations. Interplay between these processes has a complex and dynamic nature, and is determinant for the evolution of different ventilation mechanisms and the associated impacts on air quality. Here we investigate these transport mechanisms through large eddy simulations using EULAG, an established model for multiscale flows, to simulate an idealized atmospheric environment in narrow versus wide urban valleys during critical conditions for air quality (high atmospheric stability). Our results show how the ventilation of valleys depends on a dynamic (variable during the daytime) balance between interacting and sometimes competing processes related to thermally-driven slope flows, urban heat island-induced flows, and the trapping effect of atmospheric stability; and how valley width affects this balance. Particularly important is that the time-space distribution of pollutants (a passive tracer) varies greatly between both valleys despite having the same urban area and emission rates. These variations lead to pollutants being mostly concentrated in different areas of the narrow and wide valleys. We discuss the mechanisms behind these results and their potential implications for real urban valleys. Further understanding of these mechanisms is crucial for explaining the occurrence of severe air pollution episodes and informing related decision-making processes in urban valleys.

     

Fecal contamination in irrigation water and microbial quality of vegetable primary production in urban farms of Metro Manila,Philippines

Microbial contamination of fresh produce can present a severe risk to public health. By conducting a rigorous survey of irrigation waters, the impacts of fecal contamination on the quality of produce could be assessed. In this study, surface waters were observed to be contaminated with Escherichia coli, Salmonella spp., and somatic coliphages. Culture methods show that out of 373 irrigation water, soil, and vegetable samples collected for a 1-year period, 232 (62.20%) were found positive for E. coli, 213 (57.26%) for somatic coliphages, and 2 (0.53%) for Salmonella spp. Out of 190 water samples, 167 (87.9%) were found to have E.coli, 174 (91.6%) have somatic coliphages, and 1 (0.5%) with Salmonella spp. In soil samples, 36 of 91 (39.6%) have E. coli, 31 (34.0%) have somatic coliphages, and none with Salmonella spp. Lastly, out of 92 vegetable samples, 29 (31.5%), 8 (8.7%), and 1 (1.1%) were found to have E. coli, somatic coliphages, and Salmonella spp., respectively. Molecular analysis confirmed the presence of bacterial contaminants. Seasonal weather conditions were noted to have an effect on the presence and number of these fecal indicator organisms. The observed data suggest that contaminated irrigation water may greatly affect the quality of fresh produce from these agricultural operations.     

Wildfire,climate, and perceptions in Northeast Oregon

Regional Environmental Change - Wildfire poses a rising threat in the western USA, fueled by synergies between historical fire suppression, changing land use, insects and disease, and shifts toward...     

Determination of clindamycin and its metabolite clindamycin sulfoxide in diverse sewage samples

In a research project on risk management of harmful substances in water cycles, clindamycin and 12 further antibiotics were determined in different sewage samples. In contrast to other antibiotics, an increase of the clindamycin concentration in the final effluent in comparison to the influent of the sewage treatment plant (STP) was observed. A back transformation from the main metabolite clindamycin sulfoxide to clindamycin during the denitrification process has been discussed. Therefore, the concentration of this metabolite was measured additionally. Clindamycin sulfoxide was stable in the STP and the assumption of back transformation of the metabolite to clindamycin was confuted. To explain the increasing clindamycin concentration in the STP, the ratio of clindamycin sulfoxide to clindamycin was observed. The ratio increased in dry spells with concentrated samples and with long dwell time in the sewer system. A short hydraulic retention in waste water system and diluted samples in periods of extreme rainfall lead to a lower ratio of clindamycin sulfoxide to clindamycin concentration. A plausible explanation of this behavior could be that clindamycin was adsorbed strongly to a component of the sewage during this long residence time and in the STP, clindamycin was released. In the common sample preparation in the lab, clindamycin was not released. Measurements of clindamycin and clindamycin sulfoxide in the influent and effluent of STP is advised for sewage monitoring.     

Production of biodiesel from macroalgae by supercritical CO2 extraction and thermochemical liquefaction

We compare two different techniques for the extraction of biodiesel from macroalgae: the thermochemical liquefaction and the extraction using supercritical carbon dioxide (sc-CO₂). The first allows to use wet material, while sc-CO₂ requires dry material and uses moderate temperature and pressure so that it can be useful for the extraction of thermolabile compounds which may decompose at the temperature at which thermal methos are carried out. In both cases the extracted oil was characterized quantitatively and qualitatively. The novelty of the work is that in the literature the use of macroalgae for the production of biodiesel has not so far been described, while they are used mainly as food or other purposes.     

Relationship between photosynthesis and non-photochemical quenching of chlorophyll fluorescence in two red algae with different carotenoid compositions

Algae are continuously exposed to short-term fluctuations in irradiance. We investigate how two red algae species regulate photosynthetic efficiency to cope with such changes and identify some strategies that differ from higher plants. Two red algae, Gracilaria domingensis and Kappaphycus alvarezii, with antheraxanthin and lutein as major xanthophylls, respectively, reacted to the onset of low light (below E _k) with a substantial decrease of NPQ. This is different from higher plants, but similar to previous observations in, e.g. cyanobacteria where it indicates an increase in the effective absorbance cross-section of Photosystem II (PSII) by state transition. Kinetic studies in continuous light revealed a high susceptibility of PSII to light stress ((1-q _P)/NPQ) in K. alvarezii immediately after the sudden onset of high light, followed by a decrease. This was caused by a slower onset of NPQ in K. alvarezii, followed by acclimation. In G. domingensis, susceptibility of PSII to light stress was stable with time, but absolute values of (1-q _P)/NPQ were higher than in K. alvarezii. These observations suggest that K. alvarezii may be better adapted to high light levels, but is less well prepared for large sudden changes in irradiation. In K. alvarezii, photosynthesis continued to increase with increasing irradiation when NPQ was saturated. As (1-q _P) and NPQ were still balanced in this situation, most likely, processes other than photosynthetic oxygen release are responsible for the increasing net O₂ production observed.