PCDD/F and dioxin-like PCB in Hong Kong air in relation to their regional transport in the Pearl River Delta region

PCDD/F and dioxin-like PCB were measured in 142 air samples of Hong Kong. The annual average PCDD/F and dioxin-like PCB concentrations obtained for Hong Kong air at Tap Mun (PCDD/F: 1724+/-1984; dioxin-like PCB: 1572+/-1170 fg m(-3)), Yuen Long (PCDD/F: 2927+/-2695; dioxin-like PCB: 4331+/-1962 fg m(-3)) and Tsuen Wan (PCDD/F: 1875+/-1502; dioxin-like PCB: 2972+/-1510 fg m(-3)) from January 2004 to March 2005 were comparable to other urban centers around the world and were within the Japanese and USA ambient air quality guidelines. A clear seasonal pattern was observed for PCDD/F, generally with a 50-60 times higher air concentration in winter when background northerly wind was weaker and land-sea breeze prevailed, resulting in regional transport; and a lower concentration in summer, due to the inflow of clean oceanic southeasterly wind from the South China Sea. A higher WHO-TEQ value of dioxin-like PCB (mainly attributed to the relatively higher WHO-TEQ value of PCB 126) in Yuen Long during winter, compared with other months, could also be related to the regional transport by the winter monsoon wind and the low mixing height in winter. Spatially, air concentrations of PCDD/F and dioxin-like PCB demonstrated a west-to-east gradient (with Yuen Long>Tsuen Wan>Tap Mun). It is suggested that PCDD/F and dioxin-like PCB were transported into the western airshed of Hong Kong from the Pearl River Delta by land-sea breeze circulation and confined to the northwestern part, due to the blocking effect of the northwestern airshed in Hong Kong.     

Use of high-resolution MM5/CALMET/CALPUFF system: SO2 apportionment to air quality in Hong Kong

Recent research has highlighted the substantial health-related costs of air pollution in the Hong Kong Special Administrative Region (HKSAR) and the potential threat from air pollution to HKSARs economic competitiveness. In order to address the air pollution problems, this paper seeks to analyse the individual contributions of major sulphur dioxide (SO₂) sources in the Pearl River Delta Region (PRDR) (Pearl River Delta + HKSAR) on the air quality in the HKSAR. This study employed the coupling of the MM5/CALMET system with the CALPUFF, the multi-layer, non-steady-state puff dispersion model, where major power plants, marine vessels and vehicles, all in the PRDR, are taken into account. The observation data and simulation results at 11 Hong Kong Environmental Protection Department (HKEPD) general (non-road-side) stations are analyzed. Urban (in-zone) and Rural (out-zone) stations are defined in order to examine the SO₂ contribution of different emission sources in different regions of the HKSAR. The model results show that the contribution of the HKSAR marine sources is significant both in summer and in winter, especially for the locations around the in-zone stations (in general 60%, and 55% in summer and winter respectively). In addition, the contribution of the HKSAR power plants is slightly higher than that of the PRD power plants in early summer, with a contribution difference of up to 20% when the prevailing wind is from the south. However, in late summer, this situation reverses. In winter, the contribution of the PRD power plants is two to three times greater than that of the HKSAR power plants. Moreover, Yantian port affects the northern part of the HKSAR when a northeasterly wind dominates the HKSAR. In order to solve these air pollution problems, the main implication of these results suggests that the HKSAR government, in close co-operation with the Guangdong government, needs to take immediate action.     

Use of stationary and mobile measurements to study power plant emissions

This paper presents a technique to study air pollution by combining high spatial resolution data obtained by a mobile platform and those measured by conventional stationary stations. Conventional stations provide time-series point data but cannot yield information that is distant from the sites. This can be complemented or supplemented by mobile measurements in the vicinity of the conventional sites. Together, the combined dataset yields a clearer and more precise picture of the dispersion and the transformation of pollutants in the atmosphere in a fixed time frame. Several experiments were conducted in the years 2002-2003 to track the impact of power plant plumes on ground receptors in the immediate vicinity (within a radius of 30 km) of the plants, using a combined mobile and stationary dataset. The mobile data allowed the identification of emissions from coal-fired and gas-fired power plants. Coal-fired power plants were the major source of sulfur dioxide (SO2), whereas nitrogen oxides (NOx) emitted from the gas-fired power plant played an important role in the formation of ozone (O3) at ground level. The mobile data showed that two particle size distribution regimes were detected: one had a dominant accumulation mode at 0.40-0.65 microm and the other at 0.65-1 microm. The existence of particles characterized by their mode at 0.65-1 microm and formed by in-cloud processes suggests that vehicular emissions were not the important source. Other local sources, such as power plants (elevated emission), were the likely sources, because Hong Kong does not have much manufacturing industry.     

Carbon content of common airborne fungal species and fungal contribution to aerosol organic carbon in a subtropical city

Interest in the role and contribution of fungi to atmospheric aerosols and processes grows in the past decade. Substantial data or information such as fungal mass or carbon loading to ambient aerosols is however still lacking. This study aimed to quantify the specific organic carbon content (OC per spore) of eleven fungal species commonly found airborne in the subtropics, and estimated their contribution to organic carbon in aerosols. The specific OC contents showed a size-dependent relationship (r = 0.64, p < 0.05) and ranged from 3.6 to 201.0 pg carbon per spore or yeast cell, giving an average of 6.0 pg carbon per spore (RSD 51%) for spore or cell size less than 10 μm. In accounting for natural variations in the composition and abundance of fungal population, weighted-average carbon content for field samples was adopted using the laboratory determined specific OC values. An average of 5.97 pg carbon per spore (RSD 3.8%) was enumerated from 28 field samples collected at the university campus. The mean fungal OC concentration was 3.7, 6.0 and 9.7 ng m^?3 in PM_2.5, PM_2.5–10 and PM₁₀, respectively. These corresponded to 0.1%, 1.2% and 0.2% of the total OC in PM_2.5, PM_2.5–10 and PM₁₀, respectively. In the study period, rain provided periods with low total OC but high fungal prevalence and fungi contributed 7–32% OC in PM_2.5–10 or 2.4–7.1% OC in PM₁₀. More extensive studies are deserved to better understand the spatial-, temporal- and episodic dependency on the fungal OC contribution to the atmospheric aerosols.     

Degradation Kinetics of Biofilter Media Treating Reduced Sulfur Odors and VOCs

ABSTRACT

A lab-scale study was conducted to determine the rate and extent of decomposition of three biofilter media materials—compost, hog fuel, and a mixture of the two in 1:1 ratio—used in biofiltration applied to removal of reduced sulfur odorous compounds from pulp mill air emissions. The rate of carbon mineralization, as a measure of biofilter media degradation, was determined by monitoring respiratory CO₂ evolution and measuring the changes in carbon and nitrogen fractions of the biofilter materials over a period of 127 days. Both ambient air and air containing reduced sulfur (RS) compounds were used, and the results were compared. After 127 days of incubation with ambient air, about 17% of the media carbon was evolved as CO₂ from compost as compared to 6 and 12% from hog fuel and the mixture, respectively. The decomposition showed sequential breakdown of carbon moieties, and three distinct stages were observed for each of the biofilter media. First-order rate kinetics were used to describe the decomposition stages. Decomposition rates in the initial stages were at least twice those of the following stages. Carbon mineralization showed close dependence on the C/N ratio of the biofilter material. Media decomposition was enhanced in the presence of RS gases as a result of increased bioactivity by sulfur-oxidizing bacteria and other microorganisms, thus reducing the media half-life by more than 50%. At higher concentrations of RS gases, the CO₂ evolution rates were proportionally lower than those at the low concentrations because of the limited acid buffering capacity of the biofilter materials.     

Preventive control of odor emissions through manipulation of operational parameters during the active phase of composting

Better understanding of the effects of key operational parameters or environmental factors on odor emission is of critical importance for minimizing the generation of composting odors. A series of laboratory experiments was conducted to examine the effects of various operating conditions on odor emissions. The results revealed that airflow rates that were too high or too low could result in higher total odor emissions. An optimal flowrate for odor control would be approximately 0.6 L/min.kg dry matter with intermittent aeration and a duty cycle of 33%. Temperature setpoint at 60°C appeared to be a turning point for odor emission. Below this point, odor emissions increased with increasing temperature setpoint; conversely, odor emissions decreased with increasing temperature setpoint above this point. With regard to the composting material properties, odor emissions were greatly affected by the initial moisture content of feedstock. Both peak odor concentration and emission rate generally increased with higher initial moisture content. Odor emission was significant only at moisture levels higher than 65%. An initial moisture level below 45% is not recommended due to concern with the resulting lower degree of biodegradation. Biodegradable volatile solids content (BVS) of feedstock had pronounced effect on odor emissions. Peak odor concentration and emission rate increased dramatically as BVS increased from 45% to 65%, thus, total odor emission increased exponentially with BVS.     

Health risk assessment for polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, and polychlorinated naphthalenes in seafood from Guangzhou and Zhoushan, China

This study determined the concentrations of organochlorine contaminants in common seafood in two Chinese coastal cities (Guangzhou and Zhoushan), and assessed the health risk due to the daily consumption of contaminated seafood. Twenty-six pooled samples, belonging to five food categories (fish, bivalves, shrimp, crab, and cephalopods), were purchased from local markets in Guangzhou and Zhoushan in 2003 and 2004. These samples were analyzed for total polychlorinated biphenyls (PCBs), non- and mono-ortho-PCBs (coplanar PCBs), polychlorinated naphthalenes (PCNs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/DFs). The concentrations of total PCBs and coplanar PCBs in fish samples were higher in Guangzhou than in Zhoushan, while the levels of PCNs and PCDDs/DFs were comparable between the two cities. The total daily intake values of dioxin-like compounds were 1.05 and 0.86pg WHO-TEQ/kg body weight in Guangzhou and Zhoushan, respectively. Hazard ratios of non-cancer risk in the two cities were all less than unity.     

Embryonic and fetal globins are expressed in adult erythroid progenitor cells and in erythroid cell cultures

The understanding of human hemoglobin ontogeny during development is of biological and clinical importance. Molecular and immunocytological techniques were used to study the expression of embryonic zeta (ζ), epsilon (ε), and fetal gamma (γ) globin genes in newborn cord blood, peripheral blood from men, pregnant and non-pregnant women, and in vitro mononuclear cell cultures. We have shown that embryonic and fetal globin mRNA and peptides are expressed in cultured erythroid cells and in circulating blood cells from newborns, adult non-pregnant women and from men. The findings suggest that during erythroid cell differentiation in newborns and adults, there is a transient recapitulation of sequential globin chain expression as found during embryonic and fetal development. Furthermore, these findings underscore the need for caution in using embryonic and fetal globin chains as markers to identify erythroid cells of fetal origin in maternal circulation for prenatal diagnosis. Copyright © 2001 John Wiley & Sons, Ltd.