Characterization of Particulate-Phase High Molecular Weight Mono-Carbonyls (C# > 5) and Dicarbonyls in Urban Atmosphere of Xi'an, China

An analytical method to quantify particulate-phase high molecular weight mono-carbonyls (C# &gt; 5) and di-carbonyls has been developed by adopting 2,4-dinitrophenylhydrazine (DNPH) derivatization followed by high performance liquid chromatography/ultra-violet (HPLC/UV) detection. Satisfactory reproducibility and precision of the measurements were achieved. This method was applied to measure the carbonyls in PM2.5 collected on quartz-fiber filters, sampled in Xi&#39;an, China, from 2008 to 2009. Nonanaldehyde was the most abundant compound, followed by octanaldehyde, hexanaldehyde and heptaldehyde, accounting for 40%, 20%, 12% and 11% in the total quantified carbonyls. For dicarbonyls, the concentration of methylglyoxal was much higher than that of glyoxal. The seasonal variations of the particulate-phase mono-carbonyls and dicarbonyls were similar to those in the gas-phase, namely winter &gt; autumn &gt; spring &gt; summer (except octanaldehyde). A strong correlation among those carbonyls was observed in winter, resulting from low temperature partitioning, weaker photochemical reaction, and more primary emission sources. In contrast, in summer, vehicle emissions, cooking emissions and photochemical reactions are the major pollution source in Xi&#39;an.</p

Regression Analyses between Recent Air Quality and Visibility Changes in Megacities at Four Haze Regions in China

The Chinese government has put forward a series of aggressive control measures to tackle environmental problems, such as poor visibility, since the first year of its 11th five-year plan (2006-2010). Recently recorded visibility, air quality and meteorological data in four major megacities (Beijing, Shanghai, Guangzhou and Chengdu) in different haze regions (and climatic zones) of China were analyzed with the aim of evaluating the extent to which the control actions have affected these measures. The ambient concentrations of three major air pollutants (SO2, NO2 and PM10) in these cities all decreased in the years 2005-2009. However, improved visibility was observed only in Beijing and Guangzhou; it remained steady in Shanghai, and showed a decreasing trend in Chengdu. The results highlight the fact that the correlation between air quality and visibility is complex. Optimal empirical regression models were developed, based on measured air quality and meteorological parameter data, to better isolate possible causal correlations between visibility and air quality, as well as meteorological conditions. Our results show that the improvement in visibility in both Beijing and Guangzhou was mainly due to the reduced PM10 concentration. In Guangzhou, improved atmospheric visibility was also helped by a reduction in SO2 concentration in winter. In contrast, lower wind speed, together with possible changes in fine particle concentration and composition, could explain why no improvement in visibility trend was found in Shanghai or Chengdu.</p

Effects of H2O2 generation over visible light-responsive Bi/Bi2O2-xCO3 nanosheets on their photocatalytic NOx removal performance

The photocatalytic removal of gaseous NOx is commonly accompanied by secondary pollution, which necessitates the development of highly efficient nanostructured catalysts with a decreased propensity to toxic intermediate production. Herein, we describe the synthesis of plasmonic Bi/Bi2O2-xCO3 and demonstrate the presence of surface oxygen vacancies therein, revealing that the maximal NO, removal efficiency of Bi/Bi2O2-xCO3 under visible light irradiation reached 50.5% and exceeded that of a commercial photocatalyst, while the production of toxic NO2 as a by-product was completely suppressed (the selectivity reached up to 98%). In-situ introduction of plasmonic Bi on the surface of Bi2O2-xCO3 promoted the generation of H2O2 by capturing electrons from the defect states of Bi2O2-xCO3 via the two-electron reduction of O-2 and thus inhibited NO2 production (as confirmed by scavenger experiments), additionally broadening the light absorption range of the above photocatalyst. Moreover, surface oxygen vacancies in Bi-O layers provided a channel for electron transfer between Bi and Bi2O2-xCO3, which resulted in increased charge separation efficiency (maximum photocurrent = 1.1 Mu A cm(-2), 14.5 times higher than that of pristine Bi2O2CO3). Furthermore, the toxicity assessment authenticated good biocompatibility of Bi/Bi2O2-xCO3. Thus, this study sheds light on the possible roles of H2O2 in NOx degradation and provides an efficient surface engineering strategy to prepare highly reactive and selective photocatalysts

Positive sampling artifacts of organic carbon fractions for fine particles and nanoparticles in a tunnel environment

The positive artifacts in particulate organic carbon fractions for fine particles (PM2.5) and nanoparticles (PM0.1) were characterized in a tunnel environment by using the QBQ (a quartz filter behind a quartz filter) method. The OC concentrations of the backup quartz filters ranged from 3.56 to 11.38 mu g m(-3) with the average of 6.70 mu g m(-3) for PM2.5, and from 2.62 to 7.27 mu g m(-3) With the average of 4.64 mu g m(-3) for PM0.1. The most abundant species on the backup quartz filters was OC1 for both PM2.5 and PM0.1, accounting for 56.9% and 41.1% of the measured organic carbon, respectively. Most of EC fractions (EC1-EC3) on the backup filters for PM2.5 and PM0.1 were below the minimum detection limit. Therefore, only OC contributed to positive artifacts distinctly with the average percentage of 21.7% and 48.0% for PM2.5 and PM0.1, respectively. The artifacts for four organic carbon fractions ranged from 36.1% (OC1) to 4.4% (OC4) for PM2.5 and from 68.0% (OC1) to 31.9% (OC4) for PM0.1]. The uncorrected OC/EC ratios on the front quartz filters were higher by as much as 30% and 107% for PM2.5 and PM0.1 than those corrected for positive organic artifacts, respectively. That is, much higher percentage of positive artifacts was found for PM0.1 DC fractions on the front filters. The comparison of the present and previous studies shows that OC positive artifacts vary widely among various PM fractions and sampling sites attributing to many factors that are worth investigating in the future.</p

Reconstructed Light Extinction Coefficients Using Chemical Compositions of PM2.5 in Winter in Urban Guangzhou, China

The objective of this study was to reconstruct light extinction coefficients (b(ext)) according to chemical composition components of particulate matter up to 2.5 mu m in size (PM2.5). PM2.5 samples were collected at the monitoring station of the South China of institute of Environmental Science (SCIES, Guangzhou, China) during January 2010, and the online absorbing and scattering coefficients were obtained using an aethalometer and a nephelometer. The measured values of light absorption coefficient by particle (b(ap)) and light scattering coefficient by particle (b(sp)) significantly correlated (R-2 &gt; 0.95) with values of b(ap) and b(sp) that were reconstructed using the Interagency Monitoring of Protected Visual Environments (IMPROVE) formula when RH was &lt;70%. The measured b(ext) had a good correlation (R-2 &gt; 0.83) with the calculated bext under ambient RH conditions. The result of source apportionment of bext showed that ammonium sulfate [(NH4)(2)SO4] was the largest contributor (35.0%) to b(ext), followed by ammonium nitrate (NH4NO3, 22.9%), organic matter (16.1%), elemental carbon (11.8%), sea salt (4.7%), and nitrogen dioxide (NO2, 9.6%). To improve visibility in Guangzhou, the effective control of secondary particles like sulfates, nitrates, and ammonia should be given more attention in urban environmental management.</p

Methionine oxidation in albumin by fine haze particulate matter: An in vitro and in vivo study

The potential effects of inhaled fine particulate matter (PM2.5), found in haze episodes, on the oxidation of the proteins in the lungs are not well understood. We investigated the effects of PM2.5 from haze episodes on protein oxidation. PM2.5 was collected from the air pollution in Beijing (BJ), Xian (XA), Xiamen (XM) and Hong Kong (HK) during a period of intensive haze episodes. The chemical characteristics of these samples and their effects on albumin oxidation were investigated. The levels of PM2.5 in BJ and)CA were 4-6 times higher than in XM and HK. The concentrations of the polycyclic aromatic hydrocarbons (PAHs) components of the PM2.5 from BJ and XA were 10 times higher than those found in XM and HK. The haze PM2.5 increased oxidative stress. Addition of PM2.5 samples collected from haze episodes to albumin in vitro resulted in oxidation of methionine moieties; nasal instillation of PM2.5 suspensions in mice resulted in oxidation of methionine in the albumin in the bronchoalveolar lavage fluid. The methionine moieties participate in peptide chain crosslinking, and methionine oxidation in the albumin could be attributed to the PAH compounds. Our findings may be helpful in explaining the potential respiratory effects during haze episodes.</p

Simultaneous Measurements of Surface Ozone at Two Sites over the Southern Asia: A Comparative Study

This article presents variations of simultaneous measurements of near surface ozone (O(3)) at two sites namely Anantapur [14.62 degrees N, 77.65 degrees E], a semi arid rural location in India and Xi&#39;An [34.20 degrees N, 108.98 degrees E], a semi arid urban location in China during January-July 2009. The results showed a clear diurnal cycle of O(3) with a minimum at sunrise and a maximum at noon for both the sites. The monthly average diurnal variation shows that the maximum/minimum ozone was observed in March/July whereas in Xi&#39;An maximum/minimum ozone was observed in July/February because of different climatic zones and rainfall activity. The average diurnal variation of O(3) for different seasons (summer and winter) shows higher ozone concentration at Anantapur than at Xi&#39;An. This may be due to slower titration of NO in the evening hours at Anantapur. But in Xi&#39;An, the highest ozone levels recorded in noon hours for some days in June and July months. This is mainly due to strong emissions of NO(x), VOC and high solar radiation and this implies significant negative effects on vegetation and regional air quality around Xi&#39;An. The rate of increase of ozone is almost the same at two sites but the rate of decrease of ozone is more at Xi&#39;An than at Anantapur which is due to the higher NO(x) concentration from vehicular emission and also due to the fast titration of O(3). The maximum 54% of frequency distribution of ozone lies between 20-45 ppbv at Anantapur whereas in Xi&#39;An 34% lies in the range of 0-5 ppbv, 32% of Ozone lie between 5-20 ppbv and 24% of all O(3) lie in the range of 20-45 ppbv.</p