Long-term trends in chemical composition of precipitation at Lijiang, southeast Tibetan Plateau, southwestern China

1090 precipitation samples were collected between 1989 and 2006 from the Lijiang region, an internationally important tourist site in Yunnan province, southwestern China. All the samples were analyzed for pH, electrical conductivity, SO4 2&minus;, Cl&minus;, NO3 &minus;, Na+, Ca2+, Mg2+ and NH4 + concentrations. pH had a mean value of 6.08 and showed a slight increase as tourism developed between 1989 and 2006. SO4 2&minus; and Ca2+ were the dominant anion and cation, respectively. Most of the ions showed significantly increasing trends, especially Ca2+ and Mg2+, with the exception of NH4 + that had a clearly decreasing trend. As a result, the neutralization capacity of Ca2+ increased significantly, and the precipitation NP/AP (neutralizing potential index/ acidifying potential index) ratio increased. There was a significant correlation between the soil-derived cations Ca2+ and Mg2+, and significant correlation of SO4 2&minus; with Ca2+ and Mg2+. The sea-salt species Cl&minus; and Na+ was not well correlated. Using Na+ as a sea-salt tracer, non-sea-salt source fractions were calculated as SO4 2&minus;: 99.1%, Mg2+: 92.6% and Ca2+: 99.8%. Furthermore, about 95.4% of NO3 &minus; and 41.7% of SO4 2&minus; were contributed by anthropogenic sources, and 57.4% of SO4 2&minus; was contributed by soil/dust sources that had a remarkably strong relationship (r=0.65, pb0.01) with the number of tourists, suggesting that human activities in a tourism-oriented city increase atmospheric dust loading.</p

Chemical Composition of PM(10) and PM(2.5) Collected at Ground Level and 100 Meters during a Strong Winter-Time Pollution Episode in Xi'an, China

An intensive sampling of aerosol particles from ground level and 100 m was conducted during a strong pollution episode during the winter in Xi&#39;an, China. Concentrations of water-soluble inorganic ions, carbonaceous compounds, and trace elements were determined to compare the composition of particulate matter (PM) at the two heights. PM mass concentrations were high at both stations: PM(10) (PM with aerodynamic diameter &lt;= 10 mu m) exceeded the China National Air Quality Standard Class II value on three occasions, and PM(2.5) (PM with aerodynamic diameter &lt;= 2.5 mu m) exceeded the daily U.S. National Ambient Air Quality Standard more than 10 times. The PM(10) organic carbon (OC) and elemental carbon (EC) were slightly lower at the ground than at 100 m, both in terms of concentration and percentage of total mass, but OC and EC in PM(2.5) exhibited the opposite pattern. Major ionic species, such as sulfate and nitrate, showed vertical variations similar to the carbonaceous aerosols. High sulfate concentrations indicated that coal combustion dominated the PM mass both at the ground and 100 m. Correlations between K(+) and OC and EC at 100 m imply a strong influence from suburban biomass burning, whereas coal combustion and motor vehicle exhaust had a greater influence on the ground PM. Stable atmospheric conditions apparently led to the accumulation of PM, especially at 100 m, and these conditions contributed to the similarities in PM at the two elevations. Low coefficient of divergence (CD) values reflect the similarities in the composition of the aerosol between sites, but higher CDs for fine particles compared with coarse ones were consistent with the differences in emission sources between the ground and 100 m.</p

Seasonal variations and chemical characteristics of sub-micrometer particles (PM1) in Guangzhou, China

Daily samples of ambient sub-micrometer particles (PM1, particles with an aerodynamic diameter &le; 1.0 &mu;m) were collected from July 2009 to April 2010 at an urban site over Guangzhou in southern China. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) were determined to characterize the chemical composition of PM1. The mass concentration of PM1 ranged from 14.6 &mu;g m&minus; 3 to 143.3 &mu;g m&minus; 3, with an annual mean value of 52.4 &plusmn; 27.3 &mu;g m&minus; 3. Seasonally-averaged PM1 concentrations decreased in the order winter &gt; autumn &gt; spring &gt; summer. The annual mean concentrations of OC and EC were 6.2 &plusmn; 3.5 and 5.0 &plusmn; 2.9 &mu;g m&minus; 3, respectively. The OC and EC concentrations were measured following the IMPROVE_A thermal/optical reflectance (TOR) protocol. Total carbonaceous aerosol (the sum of organic matter and elemental carbon) accounted for 23.0 &plusmn; 4.4% of PM1 mass. Clear seasonal variations in OC and EC suggested sources of these two constituents were remarkable difference among the four seasons. Seasonally averaged OC/EC ratios were 1.2, 1.7, 1.4, and 1.5, from spring to winter respectively. Low OC/EC ratios in comparison with other cities in China revealed that vehicle emissions play an important role in carbonaceous aerosol levels in Guangzhou. SO42 &minus;, NO3&minus; and NH4+ were the three major inorganic ions in PM1, collectively contributing 30.0% &plusmn; 6.3% of the PM1 mass. SO42 &minus; and NH4+ were both the highest in autumn and the lowest in summer. In contrast, NO3&minus; was the highest in winter. Sulfur oxidation ratio was positively correlated with solar radiation and O3, but negatively correlated with SO2. Nitrogen oxidation ratio was positively correlated with NO2, NH4+ and Cl&minus;, but showed a negative correlation with temperature. By applying the IMPROVE equation, PM1 mass was reconstructed and showed that (NH4)2SO4, NH4NO3, OM and EC accounted for (30.7 &plusmn; 11.4) %, (9.7 &plusmn; 5.2) %, (22.6 &plusmn; 5.0) % and (9.7 &plusmn; 2.3) % of PM1, respectively. Finally, source apportionment by positive matrix factorization revealed that (1) secondary aerosol and biomass burning, (2) diesel emissions, (3) gasoline emissions and sea salt, and (4) coal combustion were the greatest contributors to PM1.</p

Size Differentiation of Individual Atmospheric Aerosol during Winter in Xi'an, China

Airborne particulate matter (including TSP, PM10, PM2.5, and PM1) were collected at an urban site in Xi&#39;an during winter 2010. Individual particles were analyzed using scanning electron microscopy and energy dispersive X-ray spectrometer (SEM-EDX). The morphologies, size distributions, and relative abundance of aerosol particles in each size were summarized. The monomodal particle size distribution was found in all the samples under different weather conditions, with the peaks located at less than 1.0 mu m. The majority of particles were composed of soot, mineral dust, and tar balls, with minor fly ash particles. Soot aggregates were the predominant species (in numbers), ranging from 56.6% in TSP on a sunny day to 86.3% in PM1 on a cloudy day, with an average of 73.2% in all the samples. The particle mass concentration and chemical composition, including water-soluble inorganic ions, elemental compositions, organic carbon (OC) and elemental carbon (EC) contents of 24-hr integrated PM2.5, were also subject to chemical bulk analysis. Soot was predominantly observed in the PM2.5 samples (from 74.7% to 82.7% in numbers), whereas EC accounted for only a small amount (&lt; 8%) of the PM2.5 mass. Corresponding to the mass concentrations of geological materials (29.2%, 44.5%, and 37.3% on sunny, cloudy, and hazy days), the number concentrations of mineral dust and fly ash particles on the sunny, cloudy, and hazy days were 14.6%, 7.1%, and 7.7%, respectively.</p

Day-night differences and seasonal variations of chemical species in PM10 over Xi'an, northwest China

To investigate day-night differences and seasonal variations of PM10 and its chemical composition in an urban environment in Xi&#39;an, northwest China, day- and nighttime PM10 mass and its chemical components including water-soluble ions (Na+, NH4 (+), K+, Mg2+, Ca2+, F-, Cl-, NO3 (-), and SO4 (2-)), organic carbon (OC), elemental carbon, and water-soluble organic carbon (WSOC) were measured on selected representative days from 20 December 2006 to 12 November 2007. Annual mean PM10 concentration in this city was five times of the China Ambient Air Quality Standard for annual average (70 mu g m(-3)). Carbonaceous fractions and water-soluble ions accounted for nearly one third and 12.4 %, respectively, of the annual mean PM10 mass. No dramatic day-night differences were found in the loadings of PM10 or its chemical components. Spring samples were highlighted by abundance of Ca2+, while the secondary aerosol species (SO4 (2-), NO3 (-), and NH4 (+)) and OC dominated in summer, autumn, and winter samples. Relatively low NO3 (-)/SO4 (2-) ratio suggested that stationary source emissions were more important than vehicle emissions in the source areas in this city. Strong relationships between WSOC and biomass markers (water-soluble K+, OC1, and OP) were observed in winter and autumn, indicating that WSOC was derived mainly from biomass burning in these seasons. This was also supported by analysis results on the biomass burning events. In contrast, poor correlations between WSOC and biomass markers were demonstrated in summer and spring, implying that WSOC was mainly formed as secondary organic carbon through photochemical activities.</p

Chemical profiles of urban fugitive dust over Xi'an in the south margin of the Loess Plateau, China

Urban fugitive dust samples were collected to determine the chemical profiles of fugitive dust over Xi&#39;an. Seventy eight samples were collected and divided into categories of paved road dust, construction dust, cement dust, and soil dust. Eighteen elements, including Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ba, and Pb, and eight water-soluble inorganic ions, including Na+, Mg2+, Ca2+, NH4+, F-, Cl-, NO3- and SO42-, were measured. The most abundant elements in these urban dust samples were Al, Si, Ca, and Fe. Al, Si, K, and Ti and showed strong positive correlations with each other, indicating they are typical dust trace elements. In contrast, elements of Ca, Zn, As, and Pb had negative correlations to crustal elements. Si/Al, K/Al, Ti/Al, Mn/Al, and Fe/Al ratios varied insignificantly among these four samples types; these ratios are similar to the properties of loess, desert, and Gobi soil dust reported in previous studies. A significantly higher Ca/Al ratio was dominant in the chemical profile of the cement samples. In addition, high Pb/Al and Zn/Al ratios were detected in comparison with those in the Gobi soil, desert soil, and loess soil samples, which indicated that Pb/Al and Zn/Al ratios can be considered as markers of urban dust. Total water-soluble ions occupied only a small fraction (&lt;5%) in the urban fugitive soil samples indicating that most of the materials in the fugitive dust were insoluble. Ca2+ and SO42- were the most abundant ions in all samples. Most of the Ca and K in the fugitive soil samples were in insoluble phases, which differ significantly in comparison with combustion sources. A strong correlation was observed between Ca2+ and estimated CO32- levels indicating that most of Ca2+ was in the form of CaCO3 rather than other calcium minerals in Xi&#39;an fugitive dust.</p

Primary PM2.5 and trace gas emissions from residential coal combustion: assessing semi-coke briquette for emission reduction in the Beijing-Tianjin-Hebei region, China

In response to severe haze pollution, the Chinese State Council set PM2.5 improvement targets for the Beijing-Tianjin-Hebei (BTH) region in 2013. To achieve the targets for the residential sector, semi-coke briquettes are being considered as a replacement for traditional raw coals with the help of financial subsidy, but information on the emission from them and the impacts on the air quality is limited. Laboratory experiments were conducted to determine emission factors (EFs) for a typical semi-coke briquette, its parent material (bituminous raw-coal-chunk) and three types of traditional coals (bituminous raw-coal-chunk, anthracite raw-coal-chunk and anthracite coal-briquette) extensively used in BTH. Compared with the parent material, significant lower EFs of primary PM2.5, organic carbon (OC), element carbon (EC), the sum of 16 polycyclic aromatic hydrocarbon components (PAHs), SO42−, NO3−, hazardous trace elements (HTEs) and NOx were found in semi-coke briquette. A scenario for the BTH region in 2015 in which raw coals were replaced with the semi-coke briquette showed that amounts of pollutants emitted from residential coal combustion could decrease by 91.6% for primary PM2.5, 94.0% for OC, 99.6% for EC, 99.9% for PAHs, 94.2% for NO3−, 45.6% for HTEs, 70.9% for NOx and 22.3% for SO2. However, SO42− loadings evidently would increase if raw coals were replaced with either semi-coke briquette or anthracite coal-briquette. Geographic distributions of modeled reductions were developed to identify emission-reducing hot-spots and aid in the development of clean energy policies. Replacement of traditional raw coals with the semi-coke briquette apparently could lead to significant environmental improvements in BTH and other regions in China

Long-Term Trends in Visibility and at Chengdu, China

Long-term (1973 to 2010) trends in visibility at Chengdu, China were investigated using meteorological data from the U.S. National Climatic Data Center. The visual range exhibited a declining trend before 1982, a slight increase between 1983 and 1995, a sharp decrease between 1996 and 2005, and some improvements after 2006. The trends in visibility were generally consistent with the economic development and implementation of pollution controls in China. Intensive PM2.5 measurements were conducted from 2009 to 2010 to determine the causes of visibility degradation. An analysis based on a modification of the IMPROVE approach indicated that PM2.5 ammonium bisulfate contributed 27.7% to the light extinction coefficient (bext); this was followed by organic mass (21.7%), moisture (20.6%), and ammonium nitrate (16.3%). Contributions from elemental carbon (9.4%) and soil dust (4.3%) were relatively minor. Anthropogenic aerosol components (sulfate, nitrate, and elemental carbon) and moisture at the surface also were important determinants of the aerosol optical depth (AOD) at 550 nm, and the spatial distributions of both bext and AOD were strongly affected by regional topography. A Positive Matrix Factorization receptor model suggested that coal combustion was the largest contributor to PM2.5 mass (42.3%) and the dry-air light-scattering coefficient (47.7%); this was followed by vehicular emissions (23.4% and 20.5%, respectively), industrial emissions (14.9% and 18.8%), biomass burning (12.8% and 11.9%), and fugitive dust (6.6% and 1.1%). Our observations provide a scientific basis for improving visibility in this area.</p

Characteristics of surface O-3 over Qinghai Lake area in Northeast Tibetan Plateau, China

Surface 03 was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3200 m above sea level) in Qinghai Lake area (36 58&#39;37 &#39;&#39; N, 99 degrees 53&#39;56 &#39;&#39; E) in Northeast Tibetan Plateau, China. Daily average O-3 ranged from 21.8 ppbv to 653 ppbv with an annual average of 41.0 ppbv. Seasonal average of O-3 followed a decreasing order of summer &gt; autumn &gt; spring &gt; winter. Diurnal variations of O-3 showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13-31, 2010 to investigate correlations between meteorological or chemical conditions and O-3. It was found that O-3 was poorly correlated with solar radiation due to the insufficient NOx in the ambient air, thus limiting O-3 formation under strong solar radiation. In contrast, high O-3 levels always coincided with strong winds, suggesting that stratospheric O-3 and long range transport might be the main sources of O-3 in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions.</p

Simulation and optimization of the post plasma-catalytic system for toluene degradation by a hybrid ANN and NSGA-II method

In this study, a post-non-thermal plasma (NTP)-catalytic system was developed for the removal of toluene over a series of MnCoOx/gamma-Al2O3 catalysts. The addition of the MnCoOx/gamma-Al2O3 catalysts markedly promoted the toluene removal efficiency, CO. yield, CO2 yield and energy yield (EY) compared with the plasma alone system. The 5 wt% MnCoOx/gamma-Al2O3 catalyst exhibited the best reaction performance, which could be attributed to the reducibility and surface active oxygen species of the catalyst. With artificial neural network (ANN), the effects of experimental parameters on the reaction performance of toluene degradation were modeled and analyzed; for this analysis, four parameters were considered, namely, discharge power, initial concentration of toluene, flow rate, and relative humidity. The results indicated that the predicted results fitted well with the experimental results. The discharge power was the most significant factor for the toluene removal efficiency and CO. yield, whereas the EY was the most influenced by the gas flow rate. A multi-objective optimization model was proposed to determine optimal experimental parameters, which was then solved using the non-dominating sorting genetic algorithm II (NSGA-II). The results revealed that the Pareto front obtained from the hybrid ANN and NSGA-II method provided a series of feasible and optimal process parameters for the post-NTP-catalytic system. This hybrid method also served as an effective tool to select process parameters according to application conditions and preferences