Various chemometric methods were used to analyze data sets of marine water quality for 19 parameters measured at 16 different sites of southern Hong Kong from 2000 to 2004 (18,240 observations), to determine temporal and spatial variations in marine water quality and identify pollution sources. Hierarchical cluster analysis (CA) grouped the 12 months into three periods (January-April, May-August and September-December) and the 16 sampling sites into two groups (A and 13) based on similarities in marine water-quality characteristics. Discriminant analysis (DA) was important in data reduction because it used only eight parameters (TEMP, TURB, Si, NO3--N, NH4+-N, NO2--N, DO, and Chl-a) to correctly assign about 86% of the cases, and five parameters (SD, NH4+-N, TP, 3 4 2 4 NO2- -N, and BOD5) to correctly assign > 81.15% of the cases. In addition, principal component analysis (PCA) identified four latent pollution sources for groups A and B: organic/eutrophication pollution, natural pollution, mineral pollution, and nutrient/fecal pollution. Furthermore, during the second and third periods, all sites received more organic/eutrophication pollution and natural pollution than in the first period. SM5, SM6, SM17, SM10, SM11, SM12, and SM13 (second period) were affected by organic and eutrophication pollution, whereas SM3 (third period) and SM9 (second period) were influenced by natural pollution. However, differences between mineral pollution and nutrient/fecal pollution were not significant among the three periods. SM17 and SM10 were affected by mineral pollution, whereas SM4 and SM9 were highly polluted by nitrogenous nutrient/fecal pollution. (C) 2007 Elsevier Ltd; All rights reserved.
The cloud condensation nucleus (CCN) activity of organic-sulfate particles was investigated using a steadystate environmental chamber. The organic component consisted of secondary organic aerosol (SOA) generated in the dark from 24 +/- 2 ppb alpha-pinene for conditions of 300 +/- 5 ppb ozone, 40 +/- 2% relative humidity, and 25 +/- 1 degrees C, with the organic mass loading in the chamber ranging from 23 to 37 mu g m(-3). CCN analysis was performed for 80-to 150-nm particles having variable organic-sulfate volume fractions, which were estimated from the diameter of the organic-sulfate particle relative to that of the seed as well as independently from mass spectra. Critical supersaturation, which increased for greater SOA volume fraction and smaller particle diameter, was well predicted by a Kohler model having two components, one for ammonium sulfate and another for SOA. The entire data set could be successfully modeled by a single suite of effective chemical parameters for SOA. The results suggest that the effects of limited organic solubility in mixed SOA-sulfate particles may be reliably omitted in the treatment of cloud droplet formation.
Hyperbolic discounting is not observationally equivalent to exponential discounting. It is always possible to calibrate an exponential model so that it predicts the same level of consumption as a hyperbolic model. However, the two models have radically different comparative statics.