Search

Eight chemical transport models participate in a model intercomparison study for East Asia, MICS-Asia II. This paper analyzes calculated results for particulate matter of sulfate, nitrate and ammonium through comparisons with each other and with monthly measurements at EANET (the acid deposition monitoring network in East Asia) and daily measurements at Fukue, Japan. To the EANET measurements, model ensemble means better agree with model individual results for sulfate and total ammonium, although total nitrate is consistently and considerably underestimated. To measurements at Fukue, the models show better agreement than for the EANET measurements. This is likely because Fukue is centered in many of the model domains, whereas the EANET stations are mostly in Southeast Asia and Russia. Moreover, it would be important that Fukue is in Northeast Asia, where the emission inventory is more reliable than Southeast Asia. The model–model comparisons are made in view of the total amount in the atmosphere, vertical profile, coefficient of variation in surface concentrations, and transformation changes with distance. All the models show reasonable tendencies in vertical profiles and composition ratios. However, total amounts in the atmosphere are discrepant among the models. The consistency of the total amount in the atmosphere would influence source–receptor analysis. It seems that model results would be consistent, if the models take into account the primitive processes like emission, advection/diffusion, chemical transformation and dry/wet deposition, no matter the processes are modeled simply or comprehensively. Through the comparison study, we learned that it would be difficult to find any problems from one comparison (model-observation comparison with one data or many but at one station or in a short period). Modelers tend to examine model performances only from model-observation comparisons. However, taking budget in a certain or whole model domain would be important, before the models are applied to source–receptor analysis. [Copyright &y& Elsevier]

Precipitation was collected from May 15, 2001 to November 18, 2002, at the mountain top (620 m a.s.l.) and mountain foot (47 m a.s.l.) of the Yahiko–Kakuda Mountains area, which is located in the western part of the Niigata Plain in central Japan. Major ion constituents and nitrogen isotopic ratios of ammonium (δ15N-NH4 +) and nitrate (δ15N-NO3 −) were measured in order to investigate the sources and behavior of NH4 + and NO3 − in precipitations. The concentrations of sea salt constituents considerably increased in the cold season from November to March, and for the majority of the ion species, the concentrations at the mountain foot were higher than those at the mountain top. The precipitation weighed monthly and seasonal means of δ15N-NH4 + values in the warm season were lower than those in the cold season at both the mountain top and mountain foot. The δ15N-NH4 + values at the mountain foot were lower than those of mountain top in both seasons. This seasonal variation of 15N-NH4 + could be caused by the incorporation of ammonia gas (NH3) with lower δ15N values, emitted from agricultural activities. On the other hand, the monthly and seasonal means of δ15N-NO3 − values showed noticeable seasonal difference with higher in the cold season at both the mountain top and mountain foot; however, the elevation difference was not observed either in the warm or cold season. The obtained δ15N-NH4 + and δ15N-NO3 − values were regarded as intermediate in comparison with the reported values. No significant correlations were observed either between NH4 + concentrations and δ15N-NH4+ values or between NO3 − concentrations and δ15N-NO3 − values. These results suggest that different factors may affect the nitrogen isotopic variations and concentration variations of NH4 + and NO3 − in precipitations collected at the two sites. [ABSTRACT FROM AUTHOR]

Growth and uptake kinetics for nitrate, ammonium and phosphate by Gymnodinium catenatum isolated from Hiroshima Bay were experimentally investigated. Maximum uptake rate ( ρmax) and half saturation constant ( Ks), which were obtained by short-term uptake experiments, were 6.48 pmol/cell per h and 7.60 µM for nitrate, 3.37 pmol/cell per h and 33.6 µM for ammonium, and 1.42 pmol/cell per h and 3.40 µM for phosphate, respectively. Specific maximum growth rate ( µ′m) and minimum cell quota ( Q0), which were obtained by semicontinuous growth experiments, were 0.36/day and 31.3 pmol/cell for the N-limited conditions, respectively. The µ′m and QP0 for P-limited conditions were 0.37/day and 1.83 pmol/cell, respectively. These results indicate that G. catenatum is a poor competitor in terms of utilization of inorganic nutrients and is unlikely to form blooms in Hiroshima Bay where phosphate is chronically depleted unless the growth is supported by organic species (i.e. dissolved organic phosphorus) of the nutrients. [ABSTRACT FROM AUTHOR]