Positive relationships between phenol oxidase activity and extractable phenolics in estuarine soils

Decomposition of recalcitrant materials such as phenolics is known to play a pivotal role in organic matter decomposition and nutrient cycling in estuaries. The specific goals of this study were to determine temporal and spatial variations of phenol oxidase and phenolics in estuarine soils, and to elucidate controlling factors for phenol oxidase activity. To achieve these goals, phenol oxidase activity and phenolic content were measured in soils developed along the side of an estuary in the Han River, Korea. Soil samples were collected in three locations with different vegetation: mud flats, Zizania-dominated soils, and Salix-dominated soils. Monthly measurements were also made in a Zizania-dominated site over a year period. Phenol oxidase activity varied between 0.00 and 0.28 diqc min^?1 g^?1, whilst phenolic content ranged from 0.0–10.5 μg g^?1. A correlation analysis revealed that phenol oxidase activity exhibited positive correlations with phenolic content in both seasonal and spatial data. The same relationship was found when the data were analysed separately for each site. Unlike peatlands or upland forest soils where negative correlations were often found between phenol oxidase activity and phenolics, substrate induction appears to account for the positive correlation in the present study.     

MM5 simulations for air quality modeling: An application to a coastal area with complex terrain

A series of modifications were implemented in MM5 simulation in order to account for wind along the Santa Clarita valley, a north–south running valley located in the north of Los Angeles. Due to high range mountains in the north and the east of the Los Angeles Air Basin, sea breeze entering Los Angeles exits into two directions. One branch moves toward the eastern part of the basin and the other to the north toward the Santa Clarita valley. However, the northward flow has not been examined thoroughly nor simulated successfully in the previous studies. In the present study, we proposed four modifications to trigger the flow separation. They were (1) increasing drag over the ocean, (2) increasing soil moisture content, (3) selective observational nudging, and (4) one-way nesting for the innermost domain. The Control run overpredicted near-surface wind speed over the ocean and sensible heat flux, in an urbanized area, which justifies the above 1st and 2nd modification. The Modified run provided an improvement in near-surface temperature, sensible heat flux and wind fields including southeasterly flow along the Santa Clarita valley. The improved MM5 wind field triggered a transport to the Santa Clarita valley generating a plume elongated from an urban center to the north, which did not exist in MM5 Control run. In all, the modified MM5 fields yielded better agreement in both CO and O₃ simulations especially in the Santa Clarita area.     

Transport and Diffusion of Ozone in the Nocturnal and Morning Planetary Boundary Layer of the Phoenix Valley

The evolution of ozone (O ₃) in the nocturnal and morning-transitional planetary boundary layer (PBL) of the Phoenix valley was measured as a part of the `Phoenix Sunrise Experiment 2001' of the U.S. Department of Energy conducted in June 2001. The goal of the field program was to study the transport, distribution and storage of ozone and its precursors in the urban boundary layer over a diurnal cycle. The ground level O <sub>3</sub> as well as mean meteorological variables and turbulence were measured over the entire period, and vertical profiling (using a tethered balloon) was made during the morning transition period. Approximately half of the observational days showed the usual diurnal cycle of high O <sub>3</sub> during the day and low O <sub>3</sub> at night, with nitrogen oxides (NO <sub>x</sub> = NO <sub>2</sub> + NO) showing an out of phase relationship with O <sub>3</sub>. The rest of the days were signified by an anomalous increase of O <sub>3</sub> in the late evening ( 2200 LST), concomitant with a sudden drop of temperature, an enhancement of wind speed and Reynolds stresses, a positive heat flux and a change of wind direction. NO <sub>x</sub> measurements indicated the simultaneous arrival of an `aged' air mass, which was corroborated by the wind predictions of a mesoscale numerical model. In all, the results indicate that the recirculation of O ₃ rich air masses is responsible for the said high-O ₃ events. Such air masses are produced during the transport of O ₃ precursors by the upslope flow toward mountainous suburbs during the day, and they return back to the city at night via downslope winds (i.e. mountain breeze). The corresponding flow patterns, and hence the high-O ₃ events, are determined by background meteorological conditions. The vertical profiling of O ₃ and flow variables during the morning transition points to a myriad of transport, mixing and chemical processes that determine the fate of tropospheric O ₃. How well such processes are incorporated and resolved in predictive O ₃ models should determine the accuracy of their predictions.     

MM5-SMOKE-CMAQ as a modeling tool for 8-h ozone regulatory enforcement: application to the state of Arizona

The Penn State/NCAR Mesoscale Meteorological Model 5 (MM5), Sparse Matrix Operator Kernal Emissions (SMOKE), and Community Multiscale Air Quality (CMAQ) modeling systems were employed to simulate ozone concentration distribution within the State of Arizona, in particular, Phoenix air basin, as supporting information to designate nonattainment areas of the U.S. Environmental Protection Agency's new 8-h ozone standard. In general, based on statistical comparisons between predictions and available (sparsely distributed) observations, the modeling system performed reasonably well for the Phoenix basin, thus proving it to be a useful tool for both regulatory as well as research applications. Detailed inspection, however, revealed a serious problem with respect to the details of the ozone distribution in that for some days the transition from downslope flow to upslope flow in the Phoenix basin was delayed in the model, causing the ozone distribution to show an unrealistic high-ozone bias toward the west valley. Implementation of a modified subgrid parameterization improved the time of transition, and hence the prediction of ozone and its precursor distributions. This study points to possible inadequacies of commonly used subgrid parameterizations in dealing with rapidly changing flow conditions such as morning (and evening) transitions.