Application of positive matrix factorization in estimating aerosol secondary organic carbon in Hong Kong and its relationship with secondary sulfate

International audienceSecondary organic carbon (SOC) is often a significant portion of organic carbon (OC) in ambient particulate matter (PM). The levels and seasonal patterns of SOC in Hong Kong were examined using more than 2000 PM10 measurements made over a 4.5-year period (1998?2002) in a network of ten air quality monitoring stations. The positive matrix factorization (PMF) model was used to analyze this large data set for source identification and apportioning. SOC was subsequently estimated to be the sum of OC present in the secondary sources, i.e., secondary sulfate, secondary nitrate, and secondary organic aerosol. The annual average SOC as estimated by the PMF method was 4.25 ?g C/m3 while the summer average was 1.66 ?g C/m3 and the winter average was 7.05 ?g C/m3. In comparison, the method that uses EC as a tracer for primary carbonaceous aerosol sources to derive SOC overestimated SOC by 70?212% for the summer samples and by 4?43% for the winter samples. The overestimation by the EC tracer method resulted from the inability of obtaining a single OC/EC ratio that represented a mixture of primary sources varying in time and space. We found that SOC and secondary sulfate had synchronous seasonal variation and were correlated in individual seasons, suggesting common factors that control their formation. Additionally, the presence of SOC was found to be enhanced more than that of secondary sulfate in the winter. We postulate this to be a combined result of favorable partitioning of semivolatile SOC species in the particle phase and more abundant SOC precursors in the winter

Application of positive matrix factorization in estimating aerosol secondary organic carbon in Hong Kong and insights into the formation mechanisms

International audienceSecondary organic carbon (SOC) is often a significant portion of organic carbon (OC) in ambient particulate matter (PM). The levels and seasonal patterns of SOC in Hong Kong were examined using more than 2000 PM10 measurements made over a 4.5-year period (1998?2002) in a network of ten air quality monitoring stations. The positive matrix factorization (PMF) model was used to analyze this large data set for source identification and apportioning. SOC was subsequently estimated to be the sum of OC present in the secondary sources, i.e., secondary sulfate, secondary nitrate, and secondary organic aerosol. The annual average SOC as estimated by the PMF method was 4.25 µg C/m3 while the summer average was 1.66 µg C/m3 and the winter average was 7.05 µg C/m3. In comparison, the method that uses EC as a tracer for primary carbonaceous aerosol sources to derive SOC overestimated SOC by 70?212% for the summer samples and by 4?43% for the winter samples. The overestimation by the EC tracer method resulted from the inability of obtaining a single OC/EC ratio that represented a mixture of primary sources varying in time and space. We found that SOC and secondary sulfate had synchronous seasonal variation and were correlated in individual seasons, suggesting common factors that control their formation. Considering the well-established fact that both gas phase oxidation and in-cloud processing are important formation pathways for sulfate, the synchronicity of SOC and sulfate suggests that in-cloud pathways are also important for SOC formation. Additionally, the presence of SOC was found to be enhanced more than that of secondary sulfate in the winter. We postulate this to be a combined result of favorable partitioning of semivolatile SOC species in the particle phase and more abundant SOC precursors in the winter

Domestic Value Added and Employment Generated by Chinese Exports: A Quantitative Estimation

We develop an input-output methodology to estimate how Chinese exports affect the country’s total domestic value added (DVA) and employment for 1995 and 2002. Total DVA generated by exports is obtained by subtracting all direct and indirect imported intermediate goods from the gross value of exports, and total employment is obtained by adding all direct and indirect employment generated by exports. To implement these estimations, we use hitherto unpublished Chinese government data to construct several completely new datasets, including an input-output table with separate input-output and employment-output coefficients for processing and non-processing exports. In 2002 (1995), for every US$1,000 dollar of Chinese exports, DVA and employment are estimated to be US$466 (US$545) and 0.242 (0.375) person-year, respectively.Input-output tables, Chinese exports, employment, domestic value added

Rejection of human intestinal allografts: Alone or in combination with the liver

The current results of the present series demonstrate that intestinal allografts are more vulnerable to rejection and continue to be at a significantly higher risk long after transplantation compared with isolated liver allograft recipients. Unexpectedly, a combined liver allograft does not protect small bowel from rejection. The necessarily continuous heavy immunosuppression for these unique recipients is potentially self-defeating. This is clearly demonstrated by their high susceptibility to early and late infectious complications after transplantation as reported in this issue. With the minimal graft-versus-host disease threat in this clinical trial, our revised protocol for future intestinal transplantation is to maximize the passenger leukocyte traffic with supplementary bone marrow from the same intestinal donor in an attempt to augment the development of systemic chimerism and the gradual induction of donor-specific nonreactivity

Help-seeking and antibiotic prescribing for acute cough in a Chinese primary care population: a prospective multicentre observational study

Acute cough is a common reason to prescribe antibiotics in primary care. This study aimed to explore help-seeking and antibiotic prescribing for acute cough in Chinese primary care population. This is a prospective multicentre observational study that included adults presenting with acute cough. Clinicians recorded patients’ presenting symptoms, examination findings and medication prescription. Patients completed symptom diaries for up to 28 days by charting their symptom severity and recovery. Adjusted binary logistic regression models identified factors independently associated with antibiotic prescription. Primary care clinicians (n=19) recruited 455 patients. A total of 321 patients (70.5%) returned their completed symptom diaries. Concern about illness severity (41.6%) and obtaining a prescription for symptomatic medications (45.9%), rather than obtaining a prescription for antibiotics, were the main reasons for consulting. Antibiotics were prescribed for 6.8% (n=31) of patients, of which amoxicillin was the most common antimicrobial prescribed (61.3%), as it was associated with clinicians’ perception of benefit from antibiotic treatment (odds ratio (OR): 25.9, 95% confidence interval (CI): 6.7–101.1), patients’ expectation for antibiotics (OR: 5.1, 95% CI: 1.7–11.6), anticipation (OR: 5.1, 95% CI: 1.6–15.0) and request for antibiotics (OR 15.7, 95% CI: 5.0–49.4), as well as the severity of respiratory symptoms (cough, sputum, short of breath and wheeze OR: 2.7–3.7, all P<0.05). There was a significant difference in antibiotic prescription rates between private primary care clinicians and public primary care clinicians (17.4 vs 1.6%, P=0.00). Symptomatic medication was prescribed in 98.0% of patients. Mean recovery was 9 days for cough and 10 days for all symptoms, which was not significantly associated with antibiotic treatment. Although overall antibiotic-prescribing rates were low, there was a higher rate of antibiotic prescribing among private primary care clinicians, which warrants further exploration and scope for education and intervention.published_or_final_versio

A physical modeling approach for identification of source regions of primary and secondary air pollutants

International audienceThis paper describes a simple but practical methodology to identify the contribution of primary and secondary air pollutants from the local/regional emission sources to Hong Kong, a highly urbanized city with complex terrain and coastlines. The meteorological model MM5 coupled with a three-dimensional, mutli-particle trajectory model is used to identify salient aspects of regional air pollutant transport characteristics during some typical meteorological conditions over the Pearl River Delta (PRD) region. Several weighting factors are determined for calculating the air mass/pollutant trajectory and are used to evaluate the local and regional contribution of primary pollutants over the PRD to Hong Kong pollution. The relationships between emission inventories, physical paths and chemical transformation rates of the pollutants, and observational measurements are formulated. The local and regional contributions of secondary pollutants are obtained by this conceptual module under different weather scenarios. Our results demonstrate that major pollution sources over Hong Kong come from regional transport. In calm-weather situations, 78% of the respirable suspended particulates (RSP) totals in Hong Kong are contributed by regional transport, and 49% are contributed by the power plants within the PRD. In normal-day situations, 71% of the RSP are contributed by regional transport, and 45% are contributed by the power plants

Intestinal transplantation at the University of Pittsburgh

Our experience with clinical intestinal transplantation under FK 506 immunosuppression showed that 50% of the recipients were able to be independent from TPN after transplantation, but 10% require partial TPN with functioning grafts, 10% needed total TPN after graft removal, and 30% of the recipients died postoperatively, mostly from sepsis due to severe graft rejection. For further improvement in patient survival and in the quality of life for patients after intestinal transplantation, it is mandatory to establish a new strategy for treatment and prevention of graft rejection and systemic infection