Provenance of Chinese Loess: Evidence from Stable Lead Isotope

Twenty-seven samples of typical loess and paleosol strata collected in nine different regions of the Chinese Loess Plateau (CLP) were fractionated into PM(1.0), PM(2.5), PM(10) and Total Suspended Particulates (TSP) (particulate matter with aerodynamic diameters less than 1.0, 2.5, 10 and 30 mu m, respectively) by a resuspension chamber at the Desert Research Institute (DRI; Reno, NV, United States). The amounts and isotope ratios of lead (Pb) were quantified in the loess samples. Our size-segregated analysis demonstrated that the Pb isotopic composition in the loess-paleosol deposits was preserved after grain-size sorting and that therefore the isotope ratio can serve as a proxy for source tracing. A similar pattern of Pb isotope ratios was observed for sediment collected from potential source regions and the loess samples suggested that the Gobi and deserts in southern Mongolia and northern China are major sources for the deposits in the CLP. No significant deviation of Pb isotope amount was found between the nine samples of loess and paleosol strata, implying the stability of loess sources during the glacial and interglacial regime.</p

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

Spatiotemporal distribution of carbonyl compounds in China

A sampling campaign was carried out at nine Chinese cities in 2010/2011. Fifteen monocarbonyls (C# &frac14; 1 e9) were quantified. Temperature is the rate-determining factor of the summertime carbonyl levels. The carbonyl emissions in winter are mainly driven by the primary anthropogenic sources like automobile. A molar ratio of propionaldehyde to nonaldehyde is a barometer of the impact of atmospheric vegetation emission which suggesting that strong vegetation emissions exist in summer and high propionaldehyde abundance is caused by fossil fuel combustion in winter. Potential health risk assessment of formaldehyde and acetaldehyde was conducted and the highest cumulative risks were observed at Chengdu in summer and Wuhan in winter. Because of the strong photochemical reaction and large amount of anthropogenic emissions, high concentrations of carbonyl compounds were observed in Chengdu. The use of ethanol-blended gasoline in Wuhan is the key reason of acetaldehyde emission and action should be taken to avoid potential health risks.</p

Biases in ketone measurements using DNPH-coated solid sorbent cartridges

Biases associated with carbonyl measurement using active air sampling through a 2,4-dinitrophenylhydrazine (DNPH)-coated solid sorbent cartridge following the U.S. EPA Method TO-11A are known but have not been fully investigated. Ketones are less reactive than aldehydes in the derivatization with DNPH, resulting in poor collection efficiency. Field studies and laboratory experiments demonstrate the uncertainties associated with two ketones (i.e., acetone and methyl ethyl ketone [MEK]). Ketone collection efficiencies are inversely related to relative humidity (RH), sample flow rate, and sample duration. Since water is a product in the bidirectional derivatization of carbonyls, the reverse reaction competes with the forward reaction as RH increases. Laboratory experiments demonstrate that similar to 35-80% of the ketones can be lost for RH &gt; 50% with a single DNPH cartridge at a temperature of 22 +/- 2 degrees C. Optimal sampling flow rates and sampling durations under high RH need to be determined in various environments to ensure tolerable collection efficiencies.</p

An Environmental Chamber Study of the Characteristics of Air Pollutants Released from Environmental Tobacco Smoke

Environment tobacco smoke (ETS) is an important source of anthropogenic pollution in indoor environments. This research reports an environmental chamber study of pollutants released from ETS generated by smoking cigarettes in the chamber. Six cigarettes samples sold in Hong Kong and China were characterized. Gaseous pollutants: carbon monoxide (CO), sulphur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), methane (CH4), non-methane hydrocarbon (NMHC), carbonyls and volatile organic compounds (VOCs); and particulate matter (PM), including organic carbon (OC), elemental carbon (EC) and total carbon (TC), were determined using online and offline analytical methods during smoking and post-smoking periods. Acetaldehyde, acetone and formaldehyde were the three most abundant carbonyls. A total of 18 aromatic and chlorinated VOCs were quantified. Among these, benzene and toluene were the two most abundant VOCs. OC was more dominant (&gt; 93% of TC) than EC. The amounts of tar and nicotine in the cigarettes could have a direct correlation with the PM emitted. Menthol, an additive in cigarettes, could also contribute to the ETS pollutants. The indoor ETS could be removed by a higher air exchange rate, which would also minimize secondary VOC formation.</p

Precautions for in-injection port thermal desorption-gas chromatography_mass spectrometry (TD-GC_MS) as applied to aerosol filter samples

In-injection port thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) allows for analysis for &gt; 130 non-polar organic compounds on small quartz-fiber filter samples without extraction chemicals. TD-GC/MS has been applied to samples from long-term U.S. networks since it is cost effective and less labor intensive. However, analysis of large numbers of samples results in sensitivity reductions over time. Instrument sensitivity and reproducibility were examined after 100, 200, and 500 sample analyses. Analyses of standards between batches of heavily loaded samples from China and Japan showed signal decreases of 28-78% for major organic classes. In the GC injection port, residues can accumulate on the gold-plated seal resulting in analyte adsorption as well as elevating signal background. Decreases in signal response were 28-43% for n-alkanes, 33-45% for hopanes and steranes, 28-56% for PAHs, and 38-78% for phthalates when the gold-plated seal was not replaced after 500 TD-GC/MS sample analyses. Limits of detection (LODs) also increased by 14-76% for the targeted non-polar organic compounds. Residues trapped in the capillary column head can cause peak broadening and overlap. The GC/MS system, including the injection port and gold seal, the column head (where the eluted sample is pre-concentrated), and the ion source should be cleaned after every batch of 50-100 samples. (C) 2010 Elsevier Ltd. All rights reserved.</p

Volatile Organic Compounds in Roadside Environment of Hong Kong

Vehicular exhaust emissions are one of major sources of anthropogenic volatile organic compounds (VOCs) in urban areas of Pearl River Delta Region (PRDR). Six types of vehicle emission (VE)-dominated samples were collected at representative locations in Hong Kong in the winter of 2003. A total of 111 VOC species were quantified in the samples collected. n-Butane (31%) was the most abundant species in liquefied petroleum gas (LPG)-fueled VE-dominated samples, followed by propane (26%) and i-butane (25%). Toluene was the most abundant species in gasoline-fueled VE-dominated samples (16%), comprising about half of the quantified aromatic content. While ethene and ethyne have the greatest abundance in all diesel-fueled VE-dominated VOCs profiles (except at Tuen Mun Bus Depot). VOCs were also quantified at three roadside locations in Hong Kong. And ethene was the most abundant VOCs at roadside locations which accounted for 9.5 to 29% of the total quantified VOCs, except at Hong Kong Polytechnic University roadside monitoring station (PUX). Moreover, several VOCs were clearly in abundances in the roadside samples, namely toluene, ethyne, propane, i-butane, n-butane and i-pentane. Generally, strong and fair correlations were determined from the marker species of fuel vapor (i.e., LPG, gasoline, and diesel), which show significant fuel evaporation from vehicles in roadside environment of Hong Kong. Maximum incremental reactivity (MIR) was also calculated to evaluate the contributions of individual VOCs to ozone (O-3) formation potential. The largest contributors to O-3 production at Mong Kok roadside station (MKX) and Lok Ma Chau roadside station (LMX) were toluene (17 and 15% of the measured VOC reactivity, respectively), ethene (14 and 17% of the measured VOC reactivity, respectively), and propene (7 and 8% of the measured VOC reactivity, respectively), indicating the important roles of alkenes and aromatics in the ambient O-3 formation.</p

Seasonal and diurnal variations of mono- and di-carbonyls in Xi'an, China

Seventeen carbonyls in urban ambient air were quantified in summer (June 2009) and winter (January 2010) in an urban site located in Xi&#39;an, China. Formaldehyde, acetaldehyde and acetone were the three most abundant carbonyls in the atmosphere with the concentrations of 6.54 +/- 2.38 ppbv, 2.08 +/- 1.07 ppbv and 2.74 +/- 1.14 ppbv in summer (from 14th to 24th June, 2009), respectively. In winter, the concentrations were 4.46 +/- 1.74 ppbv, 6.52 +/- 3.88 ppbv and 3.87 +/- 2.33 ppbv respectively from 4th January, 2010 to 10th January, 2010. Most carbonyls had higher concentrations in winter than in summer. And majority of the species had higher concentrations in daytime than in nighttime, indicating photochemical oxidation/human activities played an important role in diurnal variation. Formaldehyde/acetaldehyde ratios (F/A) in summer (2.14) was much higher than that in winter (0.47), showing significant effect of photochemical oxidation in the urban air during summer. Acetaldehyde/propionaldehyde (A/P) average ratio was 12.2 in wintertime, implying anthropogenic emission was the major source of carbonyls in Xi&#39;an. In addition, the ratio of acetone to methylglyoxal (A/M) is used to determine the impact of photochemistry in the atmosphere. The average acetone/methylglyoxal ratio (10.3 +/- 2.3) in summer was lower than that in winter (21.3 +/- 5.1) in Xi&#39;an. Strong correlations among some carbonyls imply that they came from the same pollution sources. Formaldehyde and acetaldehyde play a very important role in photochemical smog formation. Methylglyoxal and glyoxal also have significant contribution to ozone formation potential.</p

Characteristics of carbonate carbon in PM2.5 in a typical semi-arid area of Northeastern China

Daily concentrations of carbonate carbon (CC) in PM(2.5) collected in semi-arid area in Northeast China (Tongyu) were quantified by acidification that measures carbon dioxide (CO(2)) gas evolved using DRI Model 2001 Thermal Optical reflectance (TOR) Carbon Analyzer. The concentrations of CC during Asian dust storm (DS) and non-dust storm (NDS) periods during 14 April to 21 June, 2006 were determined and the transport pathways and possible sources for the CO(3)(2-) aerosols were identified. Concentrations of CC in PM(2.5) collected from 14 April to 23 June, 2006 in Tongyu are ranged from 0.1 to 7.5 mu gC m(-3) with an average of 1.3 mu gC m(-3). The average CC concentration during DS events was 2.6 +/- 1.7 mu g m(-3), which was almost 4 times the daily average concentration of 0.6 +/- 0.5 mu g m(-3) during non-dust storm (NDS) period. Carbonate carbon accounted for 10% and 4% of total carbon in Tongyu during DS and NDS period, respectively. Carbonate concentrations were also derived by calculating the difference between cations and anions (ionic balance method). And good correlation is observed for the carbonate measured to the values for carbonate calculated from the ionic balance difference (R(2) = 0.90). Higher correlations were observed between Ca with selected water-soluble ions (sulfate, nitrate or chloride) and elemental carbon in DS than in NDS periods. This is consistent with previous studies that more calcium salts (sulfate, nitrate or chloride) were formed during atmospheric transport during DS period. During the DS in spring 2006, three groups (A to C) of air mass trajectories were identified that passed over Tongyu. In general, when the air mass came from northwest, and south or southwest to Tongyu, high concentrations of carbonate were observed.</p

Seasonal variations of monocarbonyl and dicarbonyl in urban and sub-urban sites of Xi'an, China

Seventeen airborne carbonyls including monocarbonyls and dicarbonyls were determined in urban and sub-urban sites of Xi&#39;an, China in three seasons in 2010. In winter, acetone was the most abundant carbonyl in the urban site due to usage of organic solvents in constructions and laboratories and its slower atmospheric removal mechanisms by photolysis and reaction with hydroxyl radical than those of formaldehyde and acetaldehyde. In the sub-urban site, acetaldehyde was the most abundant carbonyl, followed by formaldehyde and acetone. During summer, however, formaldehyde was the most dominant carbonyl in both sites. The photooxidations of a wide range of volatile organic compounds (VOCs) yielded much more formaldehyde than other carbonyls under high solar radiation and temperature. In the urban site, the average concentrations of dicarbonyls (i.e., glyoxal and methyglyoxal) in spring and summer were higher than that in winter. Transformation of aromatic VOCs emitted from fuel evaporation leads to the formation of 1,2-dicarbonyls. A reverse trend was observed in suburban sites, as explained by the relatively low abundances and accumulations of VOC precursors in the rural atmosphere during warm seasons. Moreover, cumulative cancer risk based on measured outdoor carbonyls (formaldehyde and acetaldehyde) in Xi&#39;an Jiaotong University and Heihe was estimated (8.82x10(-5) and 4.96x10(-5), respectively). This study provides a clear map on the abundances of carbonyls and their source interpretation in the largest and the most economic city in Northwestern China.</p