Ozone production in four major cities of China: sensitivity to ozone precursors and heterogeneous processes

Abstract. Despite a large volume of research over a number of years, our understandings of the key precursors that control tropospheric ozone production and the impacts of heterogeneous processes remain incomplete. In this study, we analyze measurements of ozone and its precursors made at rural/suburban sites downwind of four large Chinese cities – Beijing, Shanghai, Guangzhou and Lanzhou. At each site the same measurement techniques were utilized and a photochemical box model based on the Master Chemical Mechanism (v3.2) was applied, to minimize uncertainties in comparison of the results due to differences in methodology. All four cities suffered from severe ozone pollution. At the rural site of Beijing, export of the well-processed urban plumes contributed to the extremely high ozone levels (up to an hourly value of 286 ppbv), while the pollution observed at the suburban sites of Shanghai, Guangzhou and Lanzhou was characterized by intense in-situ ozone production. The major anthropogenic hydrocarbons were alkenes and aromatics in Beijing and Shanghai, aromatics in Guangzhou, and alkenes in Lanzhou. The ozone production was found to be in a VOCs-limited regime in both Shanghai and Guangzhou, and a mixed regime in Lanzhou. In Shanghai, the ozone formation was most sensitive to aromatics and alkenes, while in Guangzhou aromatics were the predominant ozone precursors. In Lanzhou, either controlling NOx or reducing emissions of olefins from the petrochemical industry would mitigate the local ozone production. The potential impacts of several heterogeneous processes on the ozone formation were assessed. The hydrolysis of dinitrogen pentoxide (N2O5), uptake of the hydroperoxyl radical (HO2) on particles, and surface reactions of NO2 forming nitrous acid (HONO) present considerable sources of uncertainty in the current studies of ozone chemistry. Further efforts are urgently required to better understand these processes and refine atmospheric models

Assessing photochemical ozone formation in the Pearl River Delta with a photochemical trajectory model

A photochemical trajectory model (PTM), coupled with the Master Chemical Mechanism (MCM) describing the degradation of 139 volatile organic compounds (VOCs) in the troposphere, was developed and used for the first time to simulate the formation of photochemical pollutants at Wangqingsha (WQS), Guangzhou during photochemical pollution episodes between 12 and 17 November, 2007. The simulated diurnal variations and mixing ratios of ozone were in good agreement with observed data (R2=0.80, P<0.05), indicating that the photochemical trajectory model - an integration of boundary layer trajectories, precursor emissions and chemical processing - provides a reasonable description of ozone formation in the Pearl River Delta (PRD) region. Calculated photochemical ozone creation potential (POCP) indices for the region indicated that alkanes and oxygenated organic compounds had relatively low reactivity, while alkenes and aromatics presented high reactivity, as seen in other airsheds in Europe. Analysis of the emission inventory found that the sum of 60 of the 139 VOC species accounted for 92% of the total POCP-weighted emission. The 60 VOC species include C2-C6 alkenes, C6-C8 aromatics, biogenic VOCs, and so on. The results indicated that regional scale ozone formation in the PRD region can be mainly attributed to a relatively small number of VOC species, namely isoprene, ethene, m-xylene, and toluene, etc. A further investigation of the relative contribution of the main emission source categories to ozone formation suggested that mobile sources were the largest contributor to regional O3 formation (40%), followed by biogenic sources (29%), VOC product-related sources (23%), industry (6%), biomass burning (1%), and power plants (1%). The findings obtained in this study would advance our knowledge of air quality in the PRD region, and provide useful information to local government on effective control of photochemical smog in the region. © 2010 Elsevier Ltd

The bullwhip effect: Progress, trends and directions

This is the final version. Available on open access from Elsevier via the DOI in this recordThe bullwhip effect refers to the phenomenon where order variability increases as the orders move upstream in the supply chain. This paper provides a review of the bullwhip literature which adopts empirical, experimental and analytical methodologies. Early econometric evidence of bullwhip is highlighted. Findings from empirical and experimental research are compared with analytical and simulation results. Assumptions and approximations for modelling the bullwhip effect in terms of demand, forecast, delay, replenishment policy, and coordination strategy are considered. We identify recent research trends and future research directions concerned with supply chain structure, product type, price, competition and sustainability

Mitigating variance amplification under stochastic lead-time: The proportional control approach

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordLogistic volatility is a significant contributor to supply chain inefficiency. In this paper we investigate the amplification of order and inventory fluctuations in a state-space supply chain model with stochastic lead-time, general auto-correlated demand and a proportional order-up-to replenishment policy. We identify the exact distribution functions of the orders and the inventory levels. We give conditions for the ability of proportional control mechanism to simultaneously reduce inventory and order variances. For AR(2) and ARMA(1,1) demand, we show that both variances can be lowered together under the proportional order-up-to policy. Simulation with real demand and lead-time data also confirms a cost benefit exists

Carbonyl sulfide, dimethyl sulfide and carbon disulfide in the Pearl River Delta of southern China: Impact of anthropogenic and biogenic sources

Reduced sulfur compounds (RSCs) such as carbonyl sulfide (OCS), dimethyl sulfide (DMS) and carbon disulfide (CS2) impact radiative forcing, ozone depletion, and acid rain. Although Asia is a large source of these compounds, until now a long-term study of their emission patterns has not been carried out. Here we analyze 16 months of RSC data measured at a polluted rural/coastal site in the greater Pearl River Delta (PRD) of southern China. A total of 188 canister air samples were collected from August 2001 to December 2002. The OCS and CS2 mixing ratios within these samples were higher in autumn/winter and lower in summer due to the influence of Asian monsoon circulations. Comparatively low DMS values observed in this coastal region suggest a relatively low biological productivity during summer months. The springtime OCS levels in the study region (574 ± 40 pptv) were 25% higher than those on other East Asia coasts such Japan, whereas the springtime CS2 and DMS mixing ratios in the PRD (47 ± 38 pptv and 22 ± 5 pptv, respectively) were 3-30 times lower than elevated values that have been measured elsewhere in East Asia (Japan and Korea) at this time of year. Poor correlations were found among the three RSCs in the whole group of 188 samples, suggesting their complex and variable sources in the region. By means of backward Lagrangian particle release simulations, air samples originating from the inner PRD, urban Hong Kong and South China Sea were identified. The mean mixing ratio of OCS in the inner PRD was significantly higher than that in Hong Kong urban air and South China Sea marine air (p < 0.001), whereas no statistical differences were found for DMS and CS2 among the three regions (p > 0.05). Using a linear regression method based on correlations with the urban tracer CO, the estimated OCS emission in inner PRD (49.6 ± 4.7 Gg yr-1) was much higher than that in Hong Kong (0.32 ± 0.05 Gg yr-1), whereas the estimated CS2 and DMS emissions in the study region accounted for a very few percentage of the total CS2 and DMS emission in China. These findings lay the foundation for better understanding sulfur chemistry in the greater PRD region of southern China. © 2010 Elsevier Ltd

Confirmatory factor analysis of the stagnation scale-a traditional chinese medicine construct operationalized for mental health practice

Background Traditional Chinese medicine stagnation ("yu") syndrome is characterized by a cluster of mind/body obstruction-like symptoms. Previous studies have operationalized the concept as a psychological construct through scale development, producing a three-factor 16-item inventory with good psychometric properties. Purpose The study aimed to further validate the Stagnation Scale by confirmatory factor analysis (CFA) and examine self-appraisal of stagnation as an illness. Method A cross-sectional questionnaire survey was conducted on a random community sample of 755 adults recruited by cluster sampling in Hong Kong. Results CFA revealed a good fit of the three-factor model (CFI=.95; RMSEA=.077; SRMR=.043). ROC analysis suggested a cutoff score at 50 on stagnation total score for predicting self-appraisal of an illness condition, with false positive and negative rates at 25.8% and 23.3%, respectively. Overall, 6.2% participants self-appraised to suffer stagnation symptoms to a degree of an illness, and for it, 1.9% participants intended to seek treatment. Stagnation showed positive correlations with physical distress, depression, and anxiety (r=.59-.76, p<.01) and negative correlation with age (r=?.22, p<.01). Conclusion The Stagnation Scale appeared to be robust in factorial and construct validity. With prevalence of illness by self-appraisal at 6.2% and intention for treatment at 1.9%, stagnation is a fairly common condition associated with treatment-seeking behaviors. © International Society of Behavioral Medicine 2011.published_or_final_versionSpringer Open Choice, 21 Feb 201

Nonvolatile organic transistor-memory devices using various thicknesses of silver nanoparticle layers

Author name used in this publication: C. W. LeungAuthor name used in this publication: P. K. L. Chan2010-2011 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe