[The effect of trabeculectomy combined with prophylactic sclerotomy as a treatment of late stage juvenile open angle glaucoma and primary congenital glaucoma patients: a primary observational study]

Objective: To evaluate the outcomes of trabeculectomy combined with a new prophylactic sclerotomy in late stage juvenile open angle glaucoma (JOAG) and primary congenital glaucoma (PCG) patients at high risks of intraoperative and postoperative suprachoroidal hemorrhage (SCH). Method: A retrospective case series study. Thirty-three eyes of 28 JOAG patients and 15 eyes of 12 PCG patients with high risk factors for severe choroidal effusion or SCH were enrolled from November 2006 to April 2012 at Eye and ENT Hospital of Fudan University. The standard trabeculectomy accompanied by prophylactic sclerotomy was performed (video attached). Ophthalmic examinations were performed before and after the surgery. Surgical outcome was assessed in terms of intraocular pressure (IOP), best-corrected visual acuity, optic nerve head cup disc ratio, visual field, and complications. All patients were followed up for at least 1 year. Complete success was defined as an IOP ≥6 mmHg (1 mmHg=0.133 kPa) but ≤18 mmHg without medication. Qualified success was defined as an IOP ≥6 mmHg but ≤18 mmHg with local application of medications. Kaplan-Meier survival curves were drawn for the success rate calculation. Results: The mean age of all 40 patients was (13.2±9.4) years old. And among them, 22 patients were male and 18 patients were female. The mean follow-up time was (31.8±15.9) months. At the postoperative 3(rd) year, the complete success rate was 75.8%, and the qualified success rate was 90.0%. In our case series, one eye had expulsive SCH intraoperatively and two eyes had delayed SCH postoperatively. All of them were successfully saved without further surgery and with no significant damage to visual function. Conclusion: Trabeculectomy combined with prophylactic sclerotomy is a promising technique developed to control IOP in late stage JOAG and PCG patients, which provides a potential intervention to reduce severe consequences of massive choroidal effusion or SCH. (Chin J Ophthalmol, 2019, 55: 347-354).

Sources of formaldehyde and their contributions to photochemical O3 formation at an urban site in the Pearl River Delta, southern China

Two models (the Positive Matrix Factorization (PMF) model and a photochemical box model with Master Chemical Mechanism (PBM-MCM)) were applied to analyze the formaldehyde (HCHO) data collected in July 2006 at an urban site (GPEMC) in the Pearl River Delta (PRD), southern China. Three major HCHO sources (secondary formation, vehicular exhaust, and solvent usage) were identified and they were found to contribute in average 53%, 31% and 16% respectively to the total HCHO loading at GPEMC. Alkenes was the most important group contributing to the secondary formation of HCHO, followed by aromatics and alkanes. Among them, trans-2-butene had the largest contribution to secondary HCHO formation, with the average percentage of 16 ± 4%, followed by i-butene, cis-2-butene, propene, isoprene and m,p-xylene. Secondary HCHO and HCHO emitted from vehicular emissions contributed comparably to ground-based measured O₃ and HO_x radical at GPEMC, higher than that from solvent usage (1.3 ± 0.1 ppbv and (4.1 ± 0.3) × 10⁶ molecule/cm³ for O₃ and HO_x radical). Our results highlight the importance of secondary HCHO formation for both photochemical formation of ozone and the oxidative capacity of the atmosphere in this region. It is hence critical for policy makers to propose strategies for controlling VOCs from vehicular emissions in order to reduce secondary HCHO formation. Our results also have important implication for improving the understanding of the source apportionments of HCHO and their contributions to photochemical pollution in the PRD region in China.

Tropospheric volatile organic compounds in China

Photochemical smog, characterized by high concentrations of ozone (O₃) and fine particles (PM_2.5) in the atmosphere, has become one of the top environmental concerns in China. Volatile organic compounds (VOCs), one of the key precursors of O₃ and secondary organic aerosol (SOA) (an important component of PM_2.5), have a critical influence on atmospheric chemistry and subsequently affect regional and global climate. Thus, VOCs have been extensively studied in many cities and regions in China, especially in the North China Plain, the Yangtze River Delta and the Pearl River Delta regions where photochemical smog pollution has become increasingly worse over recent decades. This paper reviews the main studies conducted in China on the characteristics and sources of VOCs, their relationship with O₃ and SOA, and their removal technology. This paper also provides an integrated literature review on the formulation and implementation of effective control strategies of VOCs and photochemical smog, as well as suggestions for future directions of VOCs study in China.

Evaluation of the effectiveness of air pollution control measures in Hong Kong

From 2005 to 2013, volatile organic compounds (VOCs) and other trace gases were continuously measured at a suburban site in Hong Kong. The measurement data showed that the concentrations of most air pollutants decreased during these years. However, ozone (O₃) and total non-methane hydrocarbon levels increased with the rate of 0.23 ± 0.03 and 0.34 ± 0.02 ppbv/year, respectively, pointing to the increasing severity of photochemical pollution in Hong Kong. The Hong Kong government has ongoing programs to improve air quality in Hong Kong, including a solvent program implemented during 2007-2011, and a diesel commercial vehicle (DCV) program since 2007. From before to after the solvent program, the sum of toluene, ethylbenzene and xylene isomers decreased continuously with an average rate of -99.1 ± 6.9 pptv/year, whereas the sum of ethene and propene increased by 48.2 ± 2.0 pptv/year from before to during the DCV program. Despite this, source apportionment results showed that VOCs emitted from diesel exhaust decreased at a rate of -304.5 ± 17.7 pptv/year, while solvent related VOCs decreased at a rate of -204.7 ± 39.7 pptv/year. The gasoline and liquefied petroleum gas vehicle emissions elevated by 1086 ± 34 pptv/year, and were responsible for the increases of ethene and propene. Overall, the simulated O₃ rate of increase was lowered from 0.39 ± 0.03 to 0.16 ± 0.05 ppbv/year by the solvent and DCV programs, because O₃ produced by solvent usage and diesel exhaust related VOCs decreased (p < 0.05) by 0.16 ± 0.01 and 0.05 ± 0.01 ppbv/year between 2005 and 2013, respectively. However, enhanced VOC emissions from gasoline and LPG vehicles accounted for most of the O₃ increment (0.09 ± 0.01 out of 0.16 ± 0.05 ppbv/year) in these years. To maintain a zero O₃ increment in 2020 relative to 2010, the lowest reduction ratio of VOCs/NOx was ∼1.5 under the NOx reduction of 20-30% which was based on the emission reduction plan for Pearl River Delta region in 2020.

Spatiotemporal variation of ozone precursors and ozone formation in Hong Kong: Grid field measurement and modelling study

Grid field measurements of volatile organic compounds (VOCs) covering the entire territory of Hong Kong were simultaneously carried out twice daily on 27 September 2013 and 24 September 2014, respectively, to advance our understanding on the spatiotemporal variations of VOCs and ozone (O3) formation, the factors controlling O3 formation and the efficacy of a control measure in Hong Kong. From before to after the control measure on liquefied petroleum gas (LPG) fueled vehicles, the VOCs originated from LPG vehicle exhaust deceased from 41.3±1.2μg/m(3) (49.7±1.5%) to 32.8±1.4μg/m(3) (38.8±1.7%) (p<0.05). In contrast, the contribution to VOCs made by gasoline and diesel vehicle exhaust and solvent usage increased (p<0.05). VOCs and nitric oxide (NO) in LPG source experienced the highest reductions at the roadside sites, while the variations were not significant at the urban and new town sites (p>0.05). For O3 production, LPG vehicle exhaust generally made a negative contribution (-0.17±0.06 ppbv) at the roadside sites, however it turned to a slightly positive contribution (0.004±0.038 ppbv) after the control measure. At the urban sites, although the reductions of VOCs and NO were minor (p>0.05), O3 produced by LPG vehicle significantly reduced from 4.19±1.92 ppbv to 0.95±0.38 ppbv (p<0.05). Meanwhile, O3 produced by LPG at the new town sites remained stable. The analysis of O3-precursor relationships revealed that alkenes and aromatics were the main species limiting roadside O3 formation, while aromatics were the most predominant controlling factor at urban and new town sites. In contrast, isoprene and sometimes NOx limited the O3 formation in rural environment.

Characterization and source identification of sub-micron particles at the HKUST Supersite in Hong Kong

Particle size distribution measurements were conducted continuously at a 30-second interval using the Fast Mobility Particle Sizer (FMPS) in August, September, November and December of 2011 at a coastal background site in Hong Kong. Concurrent measurements of CO, NOx, O3, SO2 and volatile organic compounds (VOCs) were used to determine the causes of high particle number concentration (PNC) events. In all sampling months, PNC were usually higher in the evening, likely resulting from the arrival of upwind air pollutants as wind direction changed in the late afternoon. On the more polluted days, the PNC were usually higher around noon, particularly in August, similar to the diurnal trend of O3. The mode diameter at noon was smaller than in other time periods in all sampling months, further highlighting the role of secondary formation at this urban background site. A prolonged period of pollution episode occurred in late August. High PNC resulted from the arrival of pollution laden air from the PRD region or super regions. In December, new particle formation followed by subsequent growth accounted for most of the polluted days. Overall, meteorology was the most important parameter affecting particle concentrations and formation at this Hong Kong background site.

Simulation of ozone formation at different elevations in mountainous area of Hong Kong using WRF-CMAQ model

Field measurements were simultaneously conducted at a mountain (Mt.) site (Tai Mao Shan, TMS) and an urban site (Tsuen Wan, TW) at the foot of the Mt. TMS in Hong Kong. An interesting event with consecutive high-ozone (O₃) days from 08:00 on 28 Oct. to 23:00 on 03 Nov., 2010 was observed at Mt. TMS, while no such polluted event was found at the foot of the mountain. The Weather Research and Forecasting (WRF)-Community Multiscale Air Quality (CMAQ) models were used to understand this event. Model performance evaluation showed that the simulated meteorological parameters and air pollutants were well in agreement with the observations. The index of agreement (IOA) of temperature, relative humidity, wind direction and wind speed were 0.93, 0.83, 0.46 and 0.60, respectively. The multi-day high O₃ episode at Mt. TMS was also reasonably reproduced (IOA=0.68). Horizontally, the photochemical processes determined the O₃ levels in southwestern Pearl River Delta (PRD) and the Pearl River Estuary (PRE), while in eastern and northern PRD, the O₃ destruction was over the production during the event. Vertically, higher O₃ values at higher levels were found at both Mt. TMS and TW, indicating a vertical O₃ gradient over Hong Kong. With the aid of the process analysis module, we found positive contribution of vertical transport including advection and diffusion to O₃ mixing ratios at the two sites, suggesting that O₃ values at lower locations could be affected by O₃ at higher locations via vertical advection and diffusion over Hong Kong.

Establishing a conceptual model for photochemical ozone pollution in subtropical Hong Kong

Photochemical ozone (O₃) formation is related to its precursors and meteorological conditions. A conceptual model of O₃ air pollution is developed based on the analysis of data obtained at Tung Chung (TC) in Hong Kong. By comparing meteorological parameters between O₃ and non-O₃ episode days, it was found that high temperatures, strong solar radiation, low wind speeds and relative humidity, northeasterly and/or northwesterly prevailing winds were favorable for the O₃ formation, while tropical cyclones were most conducive to the occurrence of O₃ episodes. Backward trajectories simulation and graphical illustration of O₃ pollution suggested that super-regional (i.e. central and eastern China) and regional (i.e. Pearl River Delta, southern China) transport was another factor that contributed to high O₃ levels in Hong Kong. The photochemical O₃ formation, generally VOC-limited in Hong Kong, was controlled by a small number of volatile organic compounds (VOCs). Furthermore, the positive matrix factorization (PMF) simulation suggested that solvent usage and vehicular emissions are the major contributors to ambient VOCs in Hong Kong. Finally, this paper presents recommendations for further O₃ research and implementation of O₃ control strategies.

Sources of ambient volatile organic compounds and their contributions to photochemical ozone formation at a site in the Pearl River Delta, southern China

The Positive Matrix Factorization (PMF) receptor model and the Observation Based Model (OBM) were combined to analyze volatile organic compound (VOC) data collected at a suburban site (WQS) in the PRD region. The purposes are to estimate the VOC source apportionment and investigate the contributions of these sources and species of these sources to the O(3) formation in PRD. Ten VOC sources were identified. We further applied the PMF-extracted concentrations of these 10 sources into the OBM and found "solvent usage 1", "diesel vehicular emissions" and "biomass/biofuel burning" contributed most to the O(3) formation at WQS. Among these three sources, higher Relative Incremental Reactivity (RIR)-weighted values of ethene, toluene and m/p-xylene indicated that they were mainly responsible for local O(3) formation in the region. Sensitivity analysis revealed that the sources of "diesel vehicular emissions", "biomass/biofuel burning" and "solvent usage 1" had low uncertainties whereas "gasoline evaporation" showed the highest uncertainty.

Which emission sources are responsible for the volatile organic compounds in the atmosphere of Pearl River Delta?

A field measurement study of volatile organic compounds (VOCs) was simultaneously carried out in October-December 2007 at an inland Pearl River Delta (PRD) site and a Hong Kong urban site. A receptor model i.e. positive matrix factorization (PMF) was applied to the data for the apportionment of pollution sources in the region. Five and six sources were identified in Hong Kong and the inland PRD region, respectively. The major sources identified in the region were vehicular emissions, solvent use and biomass burning, whereas extra sources found in inland PRD included liquefied petroleum gas and gasoline evaporation. In Hong Kong, the vehicular emissions made the most significant contribution to ambient VOCs (48 ± 4%), followed by solvent use (43 ± 2%) and biomass burning (9 ± 2%). In inland PRD, the largest contributor to ambient VOCs was solvent use (46 ± 1%), and vehicular emissions contributed 26 ± 1% to ambient VOCs. The percentage contribution of vehicular emission in Hong Kong in 2007 is close to that obtained in 2001-2003, whereas in inland PRD the contribution of solvent use to ambient VOCs in 2007 was at the upper range of the results obtained in previous studies and twice the 2006 PRD emission inventory. The findings advance our knowledge of ozone precursors in the PRD region.

Factors associated with the decline of the Cooperative Medical System and barefoot doctors in rural China

The Cooperative Medical System (CMS) and its barefoot doctors have been in decline in rural China for nearly a decade. In order to explore the reasons for this, in 1987 we carried out a survey of villagers, barefoot doctors, and local administrators in Fengxian, Shanggoa, and Loaan counties, where incomes are good, fair, and low, respectively. The state of the CMS in these counties was contrasted and the situations which prevailed in 1978, 1982, and 1985, when the system was, respectively, at its peak, had begun to decline, and had declined markedly, were compared. A random sample of villages was selected and all the barefoot doctors and administrators as well as a random sample of households were surveyed. The results indicate that health status (as measured by infant mortality, immunization coverage, and rate of infectious diseases) has decreased in areas where the CMS has declined, while per capita incomes increased. Concomitantly, villager's expenditures on health care have increased. Barefoot doctors and their patients were, however, reasonably happy with the system, and in its absence the doctors are no longer able to obtain ongoing training. The CMS was fiscally sound, and did not decline to the same extent in all areas--it continues to thrive in Fengxian, which is relatively affluent. It is concluded that the system probably declined because many local administrators perceived that it no longer enjoyed the backing of the central government.