scholarly journals Atmospheric Δ<sup>17</sup>O(NO<sub>3</sub><sup>−</sup>) reveals nocturnal chemistry dominates nitrate production in Beijing haze

2018 ◽  
Vol 18 (19) ◽  
pp. 14465-14476 ◽  
Author(s):  
Pengzhen He ◽  
Zhouqing Xie ◽  
Xiyuan Chi ◽  
Xiawei Yu ◽  
Shidong Fan ◽  
...  
Keyword(s):  
Fine Particle ◽  
Driving Force ◽  
Sampling Period ◽  
Field Observations ◽  
Relative Importance ◽  
Nitrate Production ◽  
Atmospheric Nitrate ◽  
Particle Pollution ◽  
Mass Increase ◽  
Rapid Mass

Abstract. The rapid mass increase of atmospheric nitrate is a critical driving force for the occurrence of fine-particle pollution (referred to as haze hereafter) in Beijing. However, the exact mechanisms for this rapid increase of nitrate mass have not been well constrained from field observations. Here we present the first observations of the oxygen-17 excess of atmospheric nitrate (Δ17O(NO3-)) collected in Beijing haze to reveal the relative importance of different nitrate formation pathways, and we also present the simultaneously observed δ15N(NO3-). During our sampling period, 12 h averaged mass concentrations of PM2.5 varied from 16 to 323 µg m−3 with a mean of (141±88(1SD)) µg m−3, with nitrate ranging from 0.3 to 106.7 µg m−3. The observed Δ17O(NO3-) ranged from 27.5 ‰ to 33.9 ‰ with a mean of (30.6±1.8) ‰, while δ15N(NO3-) ranged from −2.5 ‰ to 19.2 ‰ with a mean of (7.4±6.8) ‰. Δ17O(NO3-)-constrained calculations suggest nocturnal pathways (N2O5+H2O/Cl- and NO3+HC) dominated nitrate production during polluted days (PM2.5≥75 µg m−3), with a mean possible fraction of 56–97 %. Our results illustrate the potentiality of Δ17O in tracing nitrate formation pathways; future modeling work with the constraint of isotope data reported here may further improve our understanding of the nitrogen cycle during haze.

scholarly journals Atmospheric Δ<sup>17</sup>O(NO<sub>3</sub><sup>−</sup>) reveals nocturnal chemistry dominates nitrate production in Beijing haze

2018 ◽  
Author(s):  
Pengzhen He ◽  
Zhouqing Xie ◽  
Xiyuan Chi ◽  
Xiawei Yu ◽  
Shidong Fan ◽  
...  
Keyword(s):  
Fine Particle ◽  
Isotopic Exchange ◽  
Sampling Period ◽  
Relative Importance ◽  
Nitrate Production ◽  
Atmospheric Nitrate ◽  
Particle Pollution ◽  
The Mean ◽  
Mass Increase ◽  
Rapid Mass

Abstract. The rapid mass increase of atmospheric nitrate is a critical driving force for the occurrence of fine-particle pollution (referred to as haze hereafter) in Beijing. However, the exact mechanisms for this rapid increase of nitrate mass has been not well constrained from field observations. Here we present the first observations of the oxygen-17 excess of atmospheric nitrate (Δ17O(NO3−)) collected in Beijing haze to reveal the relative importance of different nitrate formation pathways, and we also present the simultaneously observed δ15N(NO3−). During our sampling period, 12 h-averaged mass concentrations of PM2.5 varied from 16 to 323 μg m−3 with a mean of (141 ± 88 (1σ)) μg m−3, with nitrate ranging from 0.3 to 106.7 μg m−3. The observed Δ17O(NO3−) ranged from 27.5 ‰ to 33.9 ‰ with a mean of (30.6 ± 1.8) ‰ while δ15N(NO3−) ranged from −2.5 ‰ to 19.2 ‰ with a mean of (7.4 ± 6.8) ‰. Δ17O(NO3−)-constrained calculations suggest nocturnal pathways (N2O5 + H2O/Cl− and NO3 + HC) dominated nitrate production during polluted days (PM2.5 ≥ 75 μg m−3) with the mean possible fraction of 56 − 97 %. For δ15N(NO3−), we found that a combined effect of variability in NOX sources and isotopic exchange between NO and NO2 is likely to be most responsible for its variations. Our results illustrate the potentiality of isotope in tracing NOX sources and nitrate formation pathways, future modelling work with the constraint of isotope data reported here may further improve our understanding of nitrogen cycle during haze.

scholarly journals Possible Implications of Chytrid Parasitism for Population Subdivision in Freshwater Cyanobacteria of the GenusPlanktothrix

2010 ◽  
Vol 77 (4) ◽  
pp. 1344-1351 ◽  
Author(s):  
Jørn Henrik Sønstebø ◽  
Thomas Rohrlack
Keyword(s):  
Phylogenetic Analysis ◽  
Genetic Analysis ◽  
Driving Force ◽  
Selective Pressure ◽  
Population Subdivision ◽  
Rrna Gene ◽  
Field Observations ◽  
Filamentous Cyanobacteria ◽  
Future Studies ◽  
Host Parasite

ABSTRACTPopulations of the cyanobacteriumPlanktothrixcomprise multiple coexisting oligopeptide chemotypes that can behave differently in nature. We tested whether this population subdivision can, in principle, be driven by parasitic chytrid fungi, which are almost neglected agents ofPlanktothrixmortality. Two chytrid strains, Chy-Lys2009 and Chy-Kol2008, were isolated fromPlanktothrix-dominated lakes in Norway. The two strains shared 98.2% and 86.2% of their 28S and internal transcribe spacer rRNA gene sequences, respectively. A phylogenetic analysis placed them in the order Rhizophydiales family Angulomycetaceae. Chy-Lys2009 and Chy-Kol2008 could completely lysePlanktothrixcultures within days, while they failed to infect other filamentous cyanobacteria. The effect onPlanktothrixwas chemotype dependent, and both chytrid strains showed distinct chemotype preferences. These findings identify chytrid fungi infectingPlanktothrixas highly potent and specialized parasites which may exert strong selective pressure on their hosts. According to established hypotheses on host-parasite coevolution, parasitism with the above properties may result in subdivision ofPlanktothrixpopulations into coexisting chemotypes and periodic shifts in the relativePlanktothrixchemotype composition. These predictions are in agreement with field observations. Moreover, a genetic analysis verified the co-occurrence of Chy-Lys2009 and Chy-Kol2008 or related chytrid strains along with distinctPlanktothrixchemotypes in at least one water body. Our findings are consistent with a scenario where chytrid parasitism is one driving force ofPlanktothrixpopulation subdivision, which in turn leads to polymorphism in parasitic chytrid fungi. Future studies should test the validity of this scenario under field conditions.

scholarly journals Actividad reproductiva y dieta de Hemidactylus frenatus (Sauria: Gekkonidae) en el norte de Colombia

2017 ◽  
Vol 57 (36) ◽  
pp. 459
Author(s):  
Jorge A. Díaz-Pérez ◽  
Alcides C. Sampedro-Marín ◽  
Martha P. Ramírez-Pinilla
Keyword(s):  
Diet Composition ◽  
Sampling Period ◽  
Reproductive Activity ◽  
Climatic Conditions ◽  
Relative Importance ◽  
Adult Males ◽  
Adult Females ◽  
Ecological Aspects ◽  
Environmental Availability ◽  
Hemidactylus Frenatus

Despite its success as an invasive species, little is known about the ecological aspects of the gekkonid lizard Hemidactylus frenatus in Colombia. In the present study the size at maturity, sexual dimorphism, reproductive activity, and diet composition of a population of this species in an urban locality of Northern Colombia were determined. We conducted eleven samplings from September 2011 to August 2012 in buildings of the municipality of Sincelejo. A total of 264 specimens H. frenatus were captured, 112 were adult females, 133 adult males and 19 juveniles. Males reach sexual maturity at a smaller size (snout-vent length) than females (males: 35.7 mm; females: 42.7 mm), also they are larger and have proportionally larger heads and mouths than females. Males were reproductive throughout the year; although testicular volume varied significantly between samples, this variation was not associated with body size and precipitation in the study area. Reproductive adult females were found during all the sampling period. Females have an invariable clutch size of two eggs and we found no differences in the diameter and weight of eggs in each oviduct. The diet of H. frenatus is varied, with Diptera, Hemiptera and Formicidae being the prey types with the greatest relative importance values. Individuals of both sexes consume a similar volume and number of prey. Thus, the studied population of H. frenatus has continuous reproductive activity and a generalist-opportunistic feeding behavior. The climatic conditions of the study area, environmental availability of prey and intrinsic features of this species appear to be responsible for their abundance and colonizing success in this and other localities.

scholarly journals Blackleg Sporacle: A Model for Predicting Onset of Pseudothecia Maturity and Seasonal Ascospore Showers in Relation to Blackleg of Canola

2003 ◽  
Vol 93 (9) ◽  
pp. 1073-1081 ◽  
Author(s):  
M. U. Salam ◽  
R. K. Khangura ◽  
A. J. Diggle ◽  
M. J. Barbetti
Keyword(s):  
Mediterranean Climate ◽  
Leptosphaeria Maculans ◽  
Daily Rainfall ◽  
Field Observations ◽  
Relative Importance ◽  
Maturation Process ◽  
Blackleg Disease ◽  
Weather Factors ◽  
Total Rainfall ◽  
Daily Total

A simple model has been developed to predict the onset of pseudothecia maturity and seasonal ascospore showers in relation to blackleg disease in canola, caused by the fungus Leptosphaeria maculans. The model considers a combination of two weather factors, daily mean temperature and daily total rainfall, to drive progress of maturity of pseudothecia on the infested canola stubble left from past crops. Each day is categorized as suitable or not suitable for progress of the maturation process. The onset of pseudothecia maturity occurs when approximately 43 suitable days have occurred. Following the onset of maturity, ascospore showers are triggered when daily rainfall exceeds a threshold. The model satisfactorily predicted the timing of the onset of pseudothecia maturity when tested with 3 years of field observations at four locations in Western Australia, which characteristically has a Mediterranean climate. The model also agreed reasonably well with the daily pattern of ascospore release observed in two locations. Sensitivity analysis was performed to show the relative importance of the parameters that describe the onset of pseudothecia maturity.

Sustainment of Fine Particle Cloud by Means of Time-Averaged Particle Driving Force in Plasmas

2008 ◽  
Author(s):  
Takuma Gohda ◽  
Satoru Iizuka ◽  
José Tito Mendonça ◽  
David P. Resendes ◽  
Padma K. Shukla
Keyword(s):  
Fine Particle ◽  
Driving Force ◽  
Particle Cloud

Analysis of the Cargo Service Dynamics in East Asian Airports

2010 ◽  
Vol 1 (2) ◽  
pp. 1-22 ◽  
Author(s):  
Joyce M.W Low ◽  
Loon Ching Tang ◽  
Xue-Ming Yuan
Keyword(s):  
Driving Force ◽  
Positive Relationship ◽  
East Asian ◽  
Scale Economies ◽  
Cost Savings ◽  
Physical Capital ◽  
Economic Factors ◽  
Relative Importance ◽  
Air Cargo ◽  
Competitive Edge

This paper examines the effects of primary production and key economic factors on air cargo traffic between 1999 and 2005 in the East Asian airport industry through econometric and clustering analyses. This paper’s findings show that while the relative importance of physical capital to human capital has dramatically risen, adequate provisions and utilizations of physical facilities for landside operations appear to be a more significant driving force for an airport’s cargo traffic performances compared to those of airside operations. Even though cost savings are found to have regained their importance in the recent years, the degree of scale economies has fallen so sharply that airports can no longer rely on size for competitive edge. Nevertheless, there is still a close positive relationship between a nation’s economic development and the volume of cargo traffic at its airport.

scholarly journals Highly time-resolved chemical characterization of atmospheric fine particles during 2010 Shanghai World Expo

2012 ◽  
Vol 12 (11) ◽  
pp. 4897-4907 ◽  
Author(s):  
X.-F. Huang ◽  
L.-Y. He ◽  
L. Xue ◽  
T.-L. Sun ◽  
L.-W. Zeng ◽  
...  
Keyword(s):  
Organic Matter ◽  
High Resolution ◽  
Fine Particle ◽  
Fine Particles ◽  
Back Trajectory ◽  
Organic Mass ◽  
World Expo ◽  
Particle Pollution ◽  
Shanghai World Expo

Abstract. Shanghai, with a population of over 20 million, is the largest mega-city in China. Rapidly increasing industrial and metropolitan emissions have deteriorated its air quality in the past decades, with fine particle pollution as one of the major issues. However, systematic characterization of atmospheric fine particles with advanced measurement techniques has been very scarce in Shanghai. During 2010 Shanghai World Expo, we deployed a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a single particle soot photometer (SP2) in urban Shanghai between 15 May and 10 June 2010 to measure fine particles with a high time resolution. The 4-min resolution PM1 mass concentration ranged from 5.5 to 155 μg m−3, with an average of 29.2 μg m−3. On average, sulfate and organic matter (OM) were the most abundant PM1 components, accounting for 33.3 and 28.7% of the total mass, respectively, while the fraction of nitrate showed an increasing trend with the increasing PM1 loading, indicating the photochemical nature of high fine particle pollution in Shanghai. Taking advantage of HR-ToF-AMS and SP2, OM was found to have an average OM/OC ratio (organic matter mass/organic carbon mass) of 1.55 and black carbon (BC) had an average number fraction of internally mixed BC of 41.2%. Positive matrix factorization (PMF) analysis on the high resolution organic mass spectral dataset identified a hydrocarbon-like (HOA), a semi-volatile oxygenated (SV-OOA), and a low-volatility oxygenated (LV-OOA) organic aerosol component, which on average accounted for 24.0, 46.8, and 29.2% of the total organic mass, respectively. The diurnal patterns of them with interesting time delay possibly implied a photochemical oxidizing process from HOA (and/or its concurrently emitted gaseous organic pollutants) to SV-OOA to LV-OOA. Back trajectory analysis indicated that the northwesterly continental air mass represented the most severe pollutant regional transport condition with the highest nitrate and SV-OOA fractions. In addition, the results in Shanghai were compared with similar measurements performed recently in other mega-cities in the world.

scholarly journals Quantifying atmospheric nitrate formation pathways based on a global model of the oxygen isotopic composition (Δ<sup>17</sup>O) of atmospheric nitrate

2009 ◽  
Vol 9 (14) ◽  
pp. 5043-5056 ◽  
Author(s):  
B. Alexander ◽  
M. G. Hastings ◽  
D. J. Allman ◽  
J. Dachs ◽  
J. A. Thornton ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Tropospheric Ozone ◽  
Oxygen Isotopic Composition ◽  
Global Model ◽  
Polar Regions ◽  
Relative Importance ◽  
Formation Pathway ◽  
Atmospheric Nitrate ◽  
Oxygen Isotopic ◽  
The Tropics

Abstract. The oxygen isotopic composition (Δ17O) of atmospheric nitrate is a function of the relative abundance of atmospheric oxidants (O3, ROx=OH+HO2+RO2) and the formation pathway of nitrate from its precursor NOx (=NO+NO2). Coupled observations and modeling of nitrate Δ17O can be used to quantify the relative importance of chemical formation pathways leading to nitrate formation and reduce uncertainties in the budget of reactive nitrogen chemistry in the atmosphere. We present the first global model of atmospheric nitrate Δ17O and compare with available observations. The largest uncertainty for calculations of nitrate Δ17O is the unconstrained variability in the Δ17O value of tropospheric ozone. The model shows the best agreement with a global compilation of observations when assuming a Δ17O value of tropospheric ozone equal to 35‰ and preferential oxidation of NOx by the terminal oxygen atoms of ozone. Calculated values of annual-mean nitrate Δ17O in the lowest model layer (0–200 m above the surface) vary from 7‰ in the tropics to 41‰ in the polar-regions. The global, annual-mean tropospheric inorganic nitrate burden is dominated by nitrate formation via NO2+OH (76%), followed by N2O5 hydrolysis (18%) and NO3+DMS/HC (4%). Calculated nitrate Δ17O is sensitive to the relative importance of each nitrate formation pathway, suggesting that observations of nitrate Δ17O can be used to quantify the importance of individual reactions (e.g. N2O5 hydrolysis) leading to nitrate formation if the Δ17O value of ozone is known.

NITROGEN TRANSFORMATIONS AND TRANSPORT OVER 17 MONTHS IN FIELD FALLOW MICROPLOTS USING 15N

1978 ◽  
Vol 58 (1) ◽  
pp. 69-76 ◽  
Author(s):  
C. G. KOWALENKO
Keyword(s):  
Background Level ◽  
Sampling Period ◽  
Early Spring ◽  
Relative Importance ◽  
Clay Loam ◽  
Nitrogen Transformations ◽  
Fertilizer N ◽  
Clay Loam Soil ◽  
Loam Soil ◽  
High Precipitation

A field experiment with an Ottawa area clay loam soil utilizing open-ended microplots and 15N-labelled fertilizer showed the relative importance of seasons on transformation and transport of nitrogen. Denitrification appeared to be appreciable during the growing season; about 39% of the fertilizer N was denitrified in 86 days (May–Sept.) and 65% was lost after 511 days but leaching losses were included in the latter period. Nitrification of fertilizer N was very rapid with extractable NH4+-N approximating background level within the first 43 days. Immobilization of fertilizer N was negligible in the first 159 days and only a small amount was immobilized during the remainder of the experiment. Mineralization of soil N averaged 0.77 and 1.10 kg N/ha/day in the first two sampling periods. Clay fixation of NH4+-N was significant in this soil with 59% of the 152 kg N/ha applied being immediately fixed. Over one-half (66%) of this recently fixed NH4+-N was released in the first 86 days of the experiment with the remainder held tightly through the sampling period. Movement of fertilizer N was greatest in the late fall and early spring, i.e. periods of high precipitation and low evaporation.

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