Evaluation of Global Daily Reference ET Using Oklahoma's Environmental Monitoring Network-MESONET

The objective of this study is to evaluate the potential utility of the USGS Global Data Assimilation System (GDAS) 1-degree, daily reference Evapotranspiration (ET(0)) products by comparing them with observed Oklahoma mesonet daily ET(0) over a 2 year period (2005-2006). The comparison showed a close match between the two independent ET(0) products, with bias within a range of 10% for most of the sites and the overall bias of -aEuro parts per thousand 2.80%. The temporal patterns are strongly correlated, with a correlation coefficient above 0.9 for all groups. In summary, we conclude that (1) the consistent low bias shows the original GDAS ET(0) products have high potentials to be used in land surface modeling; (2) the high temporal correlations demonstrate the capability of GDAS ET(0) to represent the major atmospheric processes that control the daily variation of surface hydrology; (3) The temporal and spatial correspondences in trend between independent datasets (GDAS and MESONET) were good. The finding in Oklahoma, a different hydro-climate region from a similar regional study conducted in California by Senay et al. (J Am Water Res Assoc 44(4):969-979, 2008), reconfirms the reliability and potential of using GDAS reference ET for regional energy balance and water resources management in many parts of the world.</p

Measurements of vertical and horizontal distributions of ozone over Beijing from 2007 to 2010

The vertical distributions of ozone (O-3) over a mega city (Beijing, China), and the horizontal O-3 distributions in the lower troposphere (2-3.6 km) over Beijing and its surrounding areas located in the North China Plain (NCP), were analyzed based on the aircraft measurements from 159 flights during 2007-2010. The results are highlighted as follows: (1) There was a peak of O-3 concentration occurring at 1 km over Beijing, and the peak values ranged between 60 and 120 ppbv. (2) There was an O-3 minimum at the surface. The minimum was largely caused by the chemical reaction of NO + O-3. This process produced about 30 ppbv of the O-3 reduction below 0.5 km in the morning (9:00-10:00). (3) There was a transition altitude (similar to 1 km), below which the ozone formation was in a VOC-limited condition, and above which the ozone formation was in a NOx-limited condition. (4) The analysis of the horizontal distribution shows that O-3 concentrations were enhanced in the downwind of the city plumes. This result suggests that there was an important regional O-3 chemical production in the NCP region.</p

Evolution of aerosol chemistry in Xi'an, inland China, during the dust storm period of 2013-Part 1: Sources, chemical forms and formation mechanisms of nitrate and sulfate

A total suspended particulate (TSP) sample was collected hourly in Xi&#39;an, an inland megacity of China near the Loess Plateau, during a dust storm event of 2013 (9 March 18: 00-12 March 10: 00 LT), along with a size-resolved aerosol sampling and an online measurement of PM2.5. The TSP and size-resolved samples were determined for elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC) and nitrogen (WSON), inorganic ions and elements to investigate chemistry evolution of dust particles. Hourly concentrations of Cl-, NO3-, SO42-, Na+ and Ca2+ in the TSP samples reached up to 34, 12, 180, 72 and 28 mu g m(-3), respectively, when dust peak arrived over Xi&#39;an. Chemical compositions of the TSP samples showed that during the whole observation period NH4+ and NO3- were linearly correlated with each other (r(2) = 0.76) with a molar ratio of 1 : 1, while SO42- and Cl- were well correlated with Na+, Ca2+, Mg2+ and K+ (r(2) &gt; 0.85). Size distributions of NH4+ and NO3- presented a same pattern, which dominated in the coarse mode (&gt;2.1 mu m) during the event and predominated in the fine mode (&lt;2.1 mu m) during the non-event. SO42- and Cl- also dominated in the coarse mode during the event hours, but both exhibited two equivalent peaks in both the fine and the coarse modes during the non-event, due to the fine-mode accumulations of secondarily produced SO42- and biomass-burning-emitted Cl- and the coarse-mode enrichments of urban soil-derived SO42- and Cl-. Linear fit regression analysis further indicated that SO42- and Cl- in the dust samples possibly exist as Na2SO4, CaSO4 and NaCl, which directly originated from Gobi desert surface soil, while NH4+ and NO3- in the dust samples exist as NH4NO3. We propose a mechanism to explain these observations in which aqueous phase of dust particle surface is formed via uptake of water vapor by hygroscopic salts such as Na2SO4 and NaCl, followed by heterogeneous formation of nitrate on the liquid phase and subsequent absorption of ammonia. Our data indicate that 54 +/- 20% and 60 +/- 23% of NH4+ and NO3- during the dust period were secondarily produced via this pathway, with the remaining derived from the Gobi desert and Loess Plateau, while SO42- in the event almost entirely originated from the desert regions. Such cases are different from those in the East Asian continental outflow region, where during Asia dust storm events SO42- is secondarily produced and concentrates in sub-micrometer particles as (NH4)(2)SO4 and/or NH4HSO4. To the best of our knowledge, the current work for the first time revealed an infant state of the East Asian dust ageing process in the regions near the source, which is helpful for researchers to understand the panorama of East Asian dust ageing process from the desert area to the downwind region.</p

Plasmonic Bi/ZnWO4 Microspheres with Improved PhotocatalyticActivity on NO Removal under Visible Light

In this work, bismuth (Bi) nanoparticle anchored ZnWO4 microspheres (Bi/ZnWO4) were prepared and used as robust and efficient photocatalysts for NO removal at parts-per-billion level under visible light irradiation. The as-synthesized composite with a proper mass ratio of Bi (50%) displayed a higher reaction rate (0.067 min&ndash;1) than its single counterparts ZnWO4 (0.004 min&ndash;1) and Bi (0.027 min&ndash;1), respectively. Due to the surface plasmon resonance (SPR) effect of Bi nanoparticles, the Bi/ZnWO4 composites showed broad light absorption in the visible spectrum. Moreover, the formation of the Bi/ZnWO4 heterointerface promoted the separation of photoexcited electron&ndash;hole pairs, which is demonstrated by the increased photocurrent density in comparison to the pristine materials. The above characteristics endowed the Bi/ZnWO4 composites with superior photocatalytic activity for NO removal. The radical scavanger tests revealed that the superoxide radical was the main active species to initiate NO oxidation, while the hydroxyl radical was not involved in the process. This study shows practical value in air pollutant abatement, because it provides an economical and feasible route to fabricate SPR-enhanced composite photocatalysts using earth abundant Bi material instead of noble metals.</p

Characterization, mixing state, and evolution of urban single particles inXi'an (China) during wintertime haze days

A Single Particle Aerosol Mass Spectrometer (SPAMS) was deployed in the urban area of Xi&#39;an to investigate size-resolved chemical composition and mixing state of single particles during the heavy haze episode occurred from January 13 to January 27 in 2013. Nine major single particle types were resolved with ART-2a algorithm including biomass burning (BB), Potassium-Secondary (KSec), elemental and organic Carbon (ECOC), sodium-potassium-rich ECOC (NaKECOC), sodium-potassium-rich-secondary (NaKSec), EC, OC, and Dust. Daily PM2.5 mass concentration was 213&nbsp;&plusmn;&nbsp;122&nbsp;&mu;g&nbsp;m&minus;&nbsp;3. ~&nbsp;96% of the ambient particles were carbonaceous and internally mixed with secondary species such as sulfate and nitrate. The major particle types were from combustion sources, including coal burning, biomass burning, and vehicle exhaust. Mixing state analysis suggests gas-to-particle conversion was an important mechanism forming organic species during the winter haze episode. The relative abundances of the aged particle types, such as KSec and NaKSec increased with the elevated RH when RH&nbsp;&lt;&nbsp;80%. The fraction of aged particles in terms of number concentration was prominent during high levels of PM2.5 under stagnant air conditions. This study gained new knowledge on atmospheric aerosol formation and evolution in urban environment heavy winter haze condition.</p

Enhanced visible-light-driven photocatalytic removal of NO: Effect onlayer distortion on g-C3N4 by H2 heating

We report a simple strategy for realizing the tunable structure distortion of graphitic carbon nitride (g-C3N4) layers by H2 post calcination to improve the intrinsic electronic structure and the photocatalytic performances of g-C3N4 samples. In comparison with the O2 or N2 post treatment, the H2-modified g-C3N4 develops new optical absorption above 460&nbsp;nm and enhances photocatalytic activity for NO removal. The combined characterization results reveal that H2 heating induced the structure distortion of g-C3N4 layers is originated from the creation of amino groups within the structure and generation of the strong hydrogen bonding interactions between layers. The distorted structure allows n&ndash;&pi;* electron transitions in g-C3N4 to increase visible-light absorption. The structure distortion also enables more electrons to be available for initiating the photocatalytic reaction and the separation of photogenerated charge carriers in g-C3N4. This work provides a simple strategy for realizing the tunable structure distortion of g-C3N4 layers to adjust its electronic structure and photocatalysis.</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

Fossil vs. non-fossil sources of fine carbonaceous aerosols in fourChinese cities during the extreme winter haze episode of 2013

During winter 2013, extremely high concentrations (i.e., 4&ndash;20 times higher than the World Health Organization guideline) of PM2.5 (particulate matter with an aerodynamic diameter &lt; 2.5 &mu;m) mass concentrations (24 h samples) were found in four major cities in China including Xi&#39;an, Beijing, Shanghai and Guangzhou. Statistical analysis of a combined data set from elemental carbon (EC), organic carbon (OC), 14C and biomass-burning marker measurements using Latin hypercube sampling allowed a quantitative source apportionment of carbonaceous aerosols. Based on 14C measurements of EC fractions (six samples each city), we found that fossil emissions from coal combustion and vehicle exhaust dominated EC with a mean contribution of 75 &plusmn; 8% across all sites. The remaining 25 &plusmn; 8% was exclusively attributed to biomass combustion, consistent with the measurements of biomass-burning markers such as anhydrosugars (levoglucosan and mannosan) and water-soluble potassium (K+). With a combination of the levoglucosan-to-mannosan and levoglucosan-to-K+ ratios, the major source of biomass burning in winter in China is suggested to be combustion of crop residues. The contribution of fossil sources to OC was highest in Beijing (58 &plusmn; 5%) and decreased from Shanghai (49 &plusmn; 2%) to Xi&#39;an (38 &plusmn; 3%) and Guangzhou (35 &plusmn; 7%). Generally, a larger fraction of fossil OC was from secondary origins than primary sources for all sites. Non-fossil sources accounted on average for 55 &plusmn; 10 and 48 &plusmn; 9% of OC and total carbon (TC), respectively, which suggests that non-fossil emissions were very important contributors of urban carbonaceous aerosols in China. The primary biomass-burning emissions accounted for 40 &plusmn; 8, 48 &plusmn; 18, 53 &plusmn; 4 and 65 &plusmn; 26% of non-fossil OC for Xi&#39;an, Beijing, Shanghai and Guangzhou, respectively. Other non-fossil sources excluding primary biomass burning were mainly attributed to formation of secondary organic carbon (SOC) from non-fossil precursors such as biomass-burning emissions. For each site, we also compared samples from moderately to heavily polluted days according to particulate matter mass. Despite a significant increase of the absolute mass concentrations of primary emissions from both fossil and non-fossil sources during the heavily polluted events, their relative contribution to TC was even decreased, whereas the portion of SOC was consistently increased at all sites. This observation indicates that SOC was an important fraction in the increment of carbonaceous aerosols during the haze episode in China.</p

Seasonal characteristics of oxalic acid and related SOA in the free troposphere of Mt. Hua, central China: Implications for sources and formation mechanisms

PM10 aerosols from the summit of Mt. Hua (2060 m a.s.l) in central China during the winter and summer of 2009 were analyzed for dicarboxylic acids, ketocarboxylic acids and alpha-dicarbonyls. Molecular composition of dicarboxylic acids (C-2-C-11) in the free tropospheric aerosols reveals that oxalic acid (C-2, 399 +/- 261 ng m(-3) in winter and 522 +/- 261 ng m(-3) in summer) is the most abundant species in both seasons, followed by malonic (C-3) and succinic (C-4) acids, being consistent with that on ground levels. Most of the diacids are more abundant in summer than in winter, but adipic (C-6) and phthalic (Ph) acids are twice lower in summer, suggesting more significant impact of anthropogenic pollution on the wintertime alpine atmosphere. Moreover, glyoxal (Gly) and methylglyoxal (mGly) are also lower in summer (12 +/- 6.1 ng m(-3)) than in winter (22 +/- 13 ng m(-3)). As both dicarbonyls are a major precursor of C-2, their seasonal variation patterns, which are opposite to those of the diacids, indicate that the mountain troposphere is more oxidative in summer. C-2 showed strong linear correlations with levoglucosan in winter and oxidation products of isoprene and monoterpane in summer. PCA analysis further suggested that the wintertime C-2 and related SOA in the Mt Hua troposphere mostly originate from photochemical oxidations of anthropogenic pollutants emitted from biofuel and coal combustion in lowland regions. On contrast, the summertime C-2 and related SOA mostly originate from further oxidation of the mountainous isoprene and monoterpene oxidation products. The AIM model calculation results showed that oxalic acid concentration well correlated with particle acidity (R-2 = 0.60) but not correlated with particle liquid water content, indicating that particle acidity favors the organic acid formation because aqueous-phase C-2 production is the primary mechanism of C-2 formation in ambient aerosols and is driven by acid-catalyzed oxidation.</p

Quantification of carbonate carbon in aerosol filter samples using a modified thermal/optical carbon analyzer (M-TOCA)

Measurement of carbon dioxide (CO2) gas evolved from acidification is a method to quantify carbonate carbon (CC) in aerosols collected on quartz fiber-filters. This paper describes the installation of an add-on device in a DRI Model 2001 Thermal Optical reflectance (TOR)/Thermal Optical Transmittance (TOT) Carbon Analyzer (M-TOCA) to facilitate a direct CC measurement. In each run, a maximum of 20 filter punches (each of 0.5 cm(2)) were acidified with 1 mL of 20% v/v phosphoric (V) acid in a vial under a 100% helium gas environment. The CO2 evolved was reduced to methane (CH4) and detected by a flame ionization detector (FID). The optimum reaction kinetics were obtained under an operational temperature of 40 degrees C and ultrasonic agitation. Method precisions were +/- 3.5% on average for carbonate standards ranging from 3.0 to 60.0 mu g and +/- 3.8% on average for ambient samples in masses ranging from 0.30 to 56.0 mu g respectively. Method accuracy was on average 91.9%, ranging from 81.4 to 102.1%. Minimum detection limit (MDL) of the M-TOCA method was 0.048 mu g cm(-2), corresponding to an ambient concentration of 0.098 mu g m(-3) for a sampled volume of air of 7.2 m(3). The MDL is &gt;22 times lower than the value obtained using the novel method with a regular TOCA. Comparison studies on standards and ambient samples have demonstrated that the two methods do not yield systematic differences in concentrations of the carbonate. The lower MDL value provided by the M-TOCA allows a simple, precise and accurate measurement for ambient samples having a low CC concentration.</p