Single-particle characterization of urban aerosol particles collected in three Korean cites using low-Z electron probe X-ray microanalysis

A recently developed single-particle analytical technique, called low-Z electron probe X-ray microanalysis (low-Z EPMA), was applied to characterize urban aerosol particles collected in three cities of Korea (Seoul, CheongJu, and ChunCheon) on single days in the winter of 1999. In this study, it is clearly demonstrated that the low-Z EPMA technique can provide detailed and quantitative information on the chemical composition of particles in the urban atmosphere. The collected aerosol particles were analyzed and classified on the basis of their chemical species. Various types of particles were identified, such as soil-derived, carbonaceous, marine-originated, and anthropogenic particles. In the sample collected in Seoul, carbonaceous, aluminosilicates, silicon dioxide, and calcium carbonate aerosol particles were abundantly encountered. In the CheongJu and ChunCheon samples, carbonaceous, aluminosilicates, reacted sea salts, and ammonium sulfate aerosol particles were often seen. However, in the CheongJu sample, ammonium sulfate particles were the most abundant in the fine fraction. Also, calcium sulfate and nitrate particles were significantly observed. In the ChunCheon sample, organic particles were the most abundant in the fine fraction. Also, sodium nitrate particles were seen at high levels. The ChunCheon sample seemed to be strongly influenced by sea-salt aerosols originating from the Yellow Sea, which is located about 115 km away from the city.     

Effects of meteorological conditions on aerosol composition and mixing state in Bakersfield,CA

Particle and meteorological instrumentation were used to characterize ambient atmospheric conditions, aerosol size distributions, aerosol mass concentrations, and single particle size and chemical composition in Bakersfield, CA for the period January 9, 1999 through January 28, 1999. The sampling period included four distinct meteorological periods of stagnation, clearing, haze, and rain. Particle number and mass concentrations were the highest during the stagnation episode when a heavy and extensive fog developed. Mass and number concentrations also approached these high levels during the haze period. Single particle size and composition data from an aerosol time-of-flight mass spectrometer (ATOFMS) are used to provide unique continuous information on the diversity in types of particles present, the effects of meteorology on particle size and composition, and the distribution of important chemical species within individual particles. Aerosol composition and mixing state are found to vary with meteorological conditions. Single particle data show that carbonaceous aerosol with secondary ammonium, nitrate, and sulfate dominate the aerosol concentration during a stagnation period with a dramatic composition shift occurring to sodium type particles during the haze period. The aerosol is internally mixed with respect to carbon, nitrate, sulfate, and ammonium during the stagnation period. The mixing state changes significantly over the haze period when much greater diversity in the associations of chemical species within individual particles occurs.     

The impact of aerosol composition on the particle to gas partitioning of reactive mercury

A laboratory system was developed to study the gas-particle partitioning of reactive mercury (RM) as a function of aerosol composition in synthetic atmospheric particulate matter. The collection of RM was achieved by filter- and sorbent-based methods. Analyses of the RM collected on the filters and sorbents were performed using thermal extraction combined with cold vapor atomic fluorescence spectroscopy (CVAFS), allowing direct measurement of the RM load on the substrates. Laboratory measurements of the gas-particle partitioning coefficients of RM to atmospheric aerosol particles revealed a strong dependence on aerosol composition, with partitioning coefficients that varied by orders of magnitude depending on the composition of the particles. Particles of sodium nitrate and the chlorides of potassium and sodium had high partitioning coefficients, shifting the RM partitioning toward the particle phase, while ammonium sulfate, levoglucosan, and adipic acid caused the RM to partition toward the gas phase and, therefore, had partitioning coefficients that were lower by orders of magnitude.     

Use of time- and chemically resolved particulate data to characterize the infiltration of outdoor PM2.5 into a residence in the San Joaquin Valley

Recent studies associate particulate air pollution with adverse health effects. The indoor exposure to particles of outdoor origin is not well-characterized, particularly for individual chemical species. In response to this, a field study in an unoccupied, single-story residence in Clovis, CA, was conducted. Real-time particle monitors were used both outdoors and indoors to quantity PM2.5 nitrate, sulfate, and carbon. The aggregate of the highly time-resolved sulfate data, as well as averages of these data, was fit using a time-averaged form of the infiltration equation, resulting in reasonable values for the penetration coefficient and deposition loss rate. In contrast, individual values of the indoor/outdoor ratio can vary significantly from that predicted by the model for time scales ranging from a few minutes to several hours. Measured indoor ammonium nitrate levels were typically significantly lower than expected solely on the basis of penetration and deposition losses. The additional reduction is due to the transformation of ammonium nitrate into ammonia and nitric acid gases indoors, which are subsequently lost by deposition and sorption to indoor surfaces. This result illustrates that exposure assessments based on total outdoor particle mass can obscure the actual causal relationships for indoor exposures to particles of outdoor origin.     

Quantitative assessment of the sulfuric acid contribution to new particle growth

The Nano Aerosol Mass Spectrometer (NAMS) was deployed to rural/coastal and urban sites to measure the composition of 20-25 nm diameter nanoparticles during new particle formation (NPF). NAMS provides a quantitative measure of the elemental composition of individual, size-selected nanoparticles. In both environments, particles analyzed during NPF were found to be enhanced in elements associated with inorganic species (nitrogen, sulfur) relative to that associated with organic species (carbon). A molecular apportionment algorithm was applied to the elemental data in order to place the elemental composition into a molecular context. These measurements show that sulfate constitutes a substantial fraction of total particle mass in both environments. The contribution of sulfuric acid to new particle growth was quantitatively determined and the gas-phase sulfuric acid concentration required to incorporate the measured sulfate fraction was calculated. The calculated values were compared to those calculated by a sulfuric acid proxy that considers solar radiation and SO(2) levels. The two values agree within experimental uncertainty. Sulfate accounts for 29-46% of the total mass growth of particles. Other species contributing to growth include ammonium, nitrate, and organics. For each location, the relative amounts of these species do not change significantly with growth rate. However, for the coastal location, sulfate contribution increases with increasing temperature whereas nitrate contribution decreases with increasing temperature.     

Sampling artifacts of acidity and ionic species in PM2.5

Although sampling artifacts of acidity, ammonium, nitrate, and chloride in airborne particulate pollutants can be reduced by the use of denuders to absorb interfering gases, artifacts due to interparticle interactions still remain. In this study, the contribution of individual artifact reactions to particle evaporation and the effects of aerosol composition on the extents of sampling artifacts in PM2.5 were investigated. Samples were collected using a Harvard honeycomb denuder/filter-pack system at an urban site and a rural site in Hong Kong. The results show that the formation of artifacts can be categorized into two regimes: ammonium rich (AR) samples with a molar ratio [NH4+]/ [SO4(2-)] greater than 1.5 and ammonium poor (AP) samples with a molar ratio [NH4+]/[SO4(2-)] less than or equal to 1.5. The urban samples were all AR samples, and they were characterized by high nitrate and low in situ free acid concentrations. In contrast, the rural samples were all AP samples and they were characterized by low nitrate and high in situ free acid concentrations. We have developed a methodology to estimate the contribution of each artifact reaction to the sampling loss of nitrate, chloride, ammonium, and acidity. In the AR samples, the evaporation of HNO3 and HCl and concomitant evaporation of NH3 were the principal reactions in determining the extent of the sampling loss of nitrate and chloride. In the AP samples, the evaporation of HNO3 and HCl alone was the principal reaction instead, especially at high sampling loss. The in situ free acid concentration, a function of aerosol composition and ambient conditions, is a more useful parameter than strong acidity in understanding the sampling loss of acidity, nitrate, and chloride from the collected particles.     

Ternary nucleation as a mechanism for the production of diesel nanoparticles: experimental analysis of the volatile and hygroscopic properties of diesel exhaust using the volatilization and humidification tandem differential mobility analyzer

The volatile and hygroscopic properties of diesel nanoparticles were simultaneously determined under a range of engine loads using the volatilization and humidification tandem differential mobility analyzer (VH-TDMA). Additionally, the VH-TDMA was used to measure changes in the hygroscopic behavior of the heterogeneously nucleated diesel nanoparticles as one or more semivolatile species were removed via thermal evaporation or decomposition. Particles produced at high loads exhibited high, dual-step volatility, while those particles produced at low loads were less volatile and exhibited continuous volatilization curves. The hygroscopic growth factor of the particles was shown to be load dependent with high-load particles exhibiting growth factors similar to that of ammonium sulfate. At 85% relative humidity, particles produced at moderate loads exhibited growth factors of approximately 1.1 while low-load particles were shown to be hydrophobic. Growth factors and volatilization temperatures measured for high-load particles clearly indicate that ternary nucleation is involved in particle formation.     

Insights into the chemistry of new particle formation and growth events in Pittsburgh based on aerosol mass spectrometry

New particle formation and growth events have been observed in several urban areas and are of concern due to their potential negative effects on human health. The main purpose of this study was to investigate the chemistry of ultrafine particles during the growth phase of the frequently observed nucleation events in Pittsburgh (approximately 100 events per year) and therefore infer the mechanisms of new particle growth in the urban troposphere. An Aerodyne aerosol mass spectrometer (AMS) and two SMPS systems were deployed at the U.S. EPA Pittsburgh Supersite during September 2002. Significant nucleation events were observed in 3 out of the 16 days of this deployment, including one of the 10 strongest nucleation events observed in Pittsburgh over a period of 15 months. These events appear to be representative of the climatology of new particle formation and growth in the Pittsburgh region. Distinctive growth of sulfate, ammonium, organics, and nitrate in the ultrafine mode (33-60 nm in a vacuum aerodynamic diameter or approximately 18-33 nm in physical diameter) was observed during each of these three events, with sulfate always being the first (and the fastest) species to increase. Ultrafine ammonium usually increased 10-40 min later than sulfate, causing the ultrafine mode particles to be more acidic during the initial stages of the nucleation events. Significant increase of ultrafine organics often happened after 11:00 a.m., when photochemistry is more intense. This observation coupled with a parallel increase of ultrafine m/z 44, a mass fragment generally representative of oxygenated organic compounds, indicates that secondary organic species contribute significantly to the growth of particles at a relatively later time of the event. Among all these four species, nitrate was always a minor component of the ultrafine particles and contributed the least to the new particle growth.     

响应面法优化辣木叶蛋白提取工艺及凝集活性研究

辣木叶中含有丰富的蛋白质,但溶解性较差,本研究采用盐析法提取新鲜辣木叶中的蛋白并对其活性进行研究.以新鲜辣木叶为原料,分析提取时间、硫酸铵饱和度、料液比3个因素对蛋白得率的影响,在单因素实验的基础上,通过响应面优化盐析法提取辣木叶蛋白的最佳工艺条件.结果表明:对蛋白得率的影响依次为提取时间>硫酸铵饱和度>料液比,确定的...     

Toluene depletion in produced oil contributes to souring control in a field subjected to nitrate injection

Souring in the Medicine Hat Glauconitic C field, which has a low bottom-hole temperature (30 °C), results from the presence of 0.8 mM sulfate in the injection water. Inclusion of 2 mM nitrate to decrease souring results in zones of nitrate-reduction, sulfate-reduction, and methanogenesis along the injection water flow path. Microbial community analysis by pyrosequencing indicated dominant community members in each of these zones. Nitrate breakthrough was observed in 2-PW, a major water- and sulfide-producing well, after 4 years of injection. Sulfide concentrations at four other production wells (PWs) also reached zero, causing the average sulfide concentration in 14 PWs to decrease significantly. Interestingly, oil produced by 2-PW was depleted of toluene, the preferred electron donor for nitrate reduction. 2-PW and other PWs with zero sulfide produced 95% water and 5% oil. At 2 mM nitrate and 5 mM toluene, respectively, this represents an excess of electron acceptor over electron donor. Hence, continuous nitrate injection can change the composition of produced oil and nitrate breakthrough is expected first in PWs with a low oil to water ratio, because oil from these wells is treated on average with more nitrate than is oil from PWs with a high oil to water ratio.     

Determination of single particle mass spectral signatures from light-duty vehicle emissions

In this study, 28 light-duty gasoline vehicles (LDV) were operated on a chassis dynamometer at the California Air Resources Board Haagen-Smit Facility in El Monte, CA. The mass spectra of individual particles emitted from these vehicles were measured using aerosol time-of-flight mass spectrometry (ATOFMS). A primary goal of this study involves determining representative size-resolved single particle mass spectral signatures that can be used in future ambient particulate matter source apportionment studies. Different cycles were used to simulate urban driving conditions including the federal testing procedure (FTP), unified cycle (UC), and the correction cycle (CC). The vehicles were selected to span a range of catalytic converter (three-way, oxidation, and no catalysts) and engine technologies (vehicles models from 1953 to 2003). Exhaust particles were sampled directly from a dilution and residence chamber system using particle sizing instruments and an ATOFMS equipped with an aerodynamic lens (UF-ATOFMS) analyzing particles between 50 and 300 nm. On the basis of chemical composition, 10 unique chemical types describe the majority of the particles with distinct size and temporal characteristics. In the ultrafine size range (between 50 and 100 nm), three elemental carbon (EC) particle types dominated, all showing distinct EC signatures combined with Ca, phosphate, sulfate, and a lower abundance of organic carbon (OC). The relative fraction of EC particle types decreased as particle size increased with OC particles becoming more prevalent above 100 nm. Depending on the vehicle and cycle, several distinct OC particle types produced distinct ion patterns, including substituted aromatic compounds and polycyclic aromatic hydrocarbons (PAH), coupled with other chemical species including ammonium, EC, nitrate, sulfate, phosphate, V, and Ca. The most likely source of the Ca and phosphate in the particles is attributed to the lubricating oil. Significant variability was observed in the chemical composition of particles emitted within the different car categories as well as for the same car operating under different driving conditions. Two-minute temporal resolution measurements provide information on the chemical classes as they evolved during the FTP cycle. The first two minutes of the cold start produced more than 5 times the number of particles than any other portion of the cycle, with one class of ultrafine particles (EC coupled with Ca, OC, and phosphate) preferentially produced. By number, the three EC with Ca classes (which also contained OC, phosphate, and sulfate) were the most abundant classes produced by the nonsmoking vehicles. The smoker category produced the highest number of particles, with the dominant classes being OC comprised of substituted monoaromatic compounds and PAHs, coupled with Ca and phosphate, thus suggesting used lubricating oil was associated with many of these particles. These studies show, by number, EC particles dominate gasoline emissions in the ultrafine size range particularlyforthe lowest emitting newer vehicles, suggesting the EC signature alone cannot be used as a unique tracer for diesels. This represents the first report of high time- and size-resolved chemical composition data showing the mixing state of nonrefractory elements in particles such as EC for vehicle emissions during dynamometer source testing.     

氧化剂对甲壳素热降解性能的影响

讨论了硝酸铵、硫酸铵和浓硫酸对自制甲壳素热降解和热氧化降解过程的影响。硝酸铵加速甲壳素热降解和热氧化降解过程,而硫酸铵和浓硫酸加速甲壳素热氧化降解但推迟热降解过程。3种添加剂均改变了甲壳素等温热处理后凝聚相产物。     

红毛菜多糖组成及结构的初步研究

对福建产红毛菜(Bangiafusco-purpurea)的热水提取物采用Sevage法脱蛋白,乙醇沉淀得粗多糖。经DEAE-32和SephadexG-200柱层析纯化,得到3种多糖PY1、PY2和PY3,其中PY3为主要的多糖。PY3紫外光谱和理化鉴定显示它不含蛋白质和核酸;化学组成分析得出该多糖半乳糖的含量为65.9%,硫酸根含量为9.53%;元素分析表明该多糖C:N:S摩尔比约为72:2:3;该多糖的水解产物经气相色谱分析,主要由半乳糖及其衍生物组成,有少量木糖存在,半乳糖和木糖的摩尔比值为11:1;红外光谱揭示它基本不含3,6-内醚一半乳糖的特征吸收,却有较强的硫酸基吸收峰;推测该多糖可能主要由6-硫酸基-半乳糖和β-D-半乳吡喃糖为重复二糖的多糖,可能是一种原琼胶。     

Estimation of primary and secondary particulate matter intake fractions for power plants in Georgia

Air pollution benefit-cost analyses depend on dispersion models to predict population exposures to pollutants, but it is difficult to determine the reasonableness of the model estimates. This is in part because validation with field measurements is not feasible for marginal concentration changes and because few models can capture the necessary spatial and temporal domains with adequate sophistication. In this study, we use the concept of an intake fraction (the fraction of a pollutant or its precursor emitted that is eventually inhaled) to provide insight about population exposures and model performance. We apply CALPUFF, a regional-scale dispersion model common in health benefits assessments, to seven power plants in northern Georgia, considering both direct emissions of fine particulate matter (PM2.5) and secondarily formed ammonium sulfate and ammonium nitrate particles over a domain within 500 km of Atlanta. We estimate emission-weighted average intake fractions of 6 x 10(-7) for primary PM2.5, 2 x 10(-7) for ammonium sulfate from SO2, and 6 x 10(-8) for ammonium nitrate from NOx, with no effect of SO2 on ammonium nitrate. To provide insight about model strengths and limitations, we compare our findings with those from a frequently applied source-receptor (S-R) matrix. Using S-R matrix over an identical domain, the corresponding intake fractions are 5 x 10(-7), 2 x 10(-7), 3 x 10(-8), and -2 x 10(-8), respectively, with the values approximately doubling if the domain is expanded to cover the continental United States. Evaluation of model assumptions and comparison of past intake fraction estimates using these two models illustrates the importance of assumptions about the relative concentrations of ammonia, sulfate, and nitrate, which significantly influences ammonium nitrate intake fractions. These findings provide a framework for improved understanding of the factors that influence population exposures to particulate matter.     

Feuchtebeständigkeit und Hydrolyseresistenz von Holz-zu-Holz-Bindungen in Spanplatten,hergestellt mit formaldehydarmen modifizierten Harnstoff-Formaldehydharzen unter Einsatz verschiedener Härtungsbeschleunigersysteme

In continuation of the work conducted in the first part of this series one-layer pine wood particleboards were made using two different low-emission UF-resins (UF 1 and UF 2) using various amounts of different catalysts (ammonium chloride, ammonium sulfate, ammonium nitrate, a mixture of ammonium sulfate and formic acid) and tested regarding their properties. From the results the following conclusions can be drawn:

1. With increasing amount of catalyst in the range between 0.8% and 2.4% ammonium chloride and 0.8% and 3.2% ammonium nitrate the physical-mechanical properties of the boards deteriorated. In contrast, the formaldehyde release decreased with increasing amount of catalyst.
2. Compared with ammonium chloride ammonium nitrate led to higher mechanical properties and lowered thickness swelling of the boards.
3. Particleboards containing UF 1 as a binder showed, compared with those boards bonded with UF 2, higher mechanical properties and lower thickness swelling in water. However, the formaldehyde release of the boards bonded with UF 1 was above that of boards bonded with UF 2.
4. Particleboards bonded with UF 1 and UF 2 as a binder and containing ammonium nitrate as a catalyst showed, in general, the highest mechanical properties, those prepared with ammonium sulfate or a mixture of ammonium sulfate and formic acid as a catalyst the lowest.

     

Feuchtebeständigkeit und Hydrolyseresistenz von Holz-zu-Holz-Bindungen in Spanplatten,hergestellt mit formaldehydarmen modifizierten Harnstoff-Formaldehydharzen unter Einsatz verschiedener Härtungsbeschleunigersysteme

Two different UF-resins (UF 1 and UF 2) with significant differences in their viscosity of their 50% solutions (UF 1: 70 mPa·s, UF 2: 46 mPa·s), but almost the same molar ratio F:U (UF 1: 1,11∶1, UF 2: 1,12∶1) and small differences in the content of free formaldehyde (UF 1: 0,07%, UF 2: 0,09%) and water tolerance (UF 1: 1∶0,90, UF 2: 1∶1,18) were modified with a melamine resin (F:M=1,6∶1), resorcinol, tannin and PMDI. The unmodified and modified resins were tested for some of their technological properties before and after curing using different catalyst systems (ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium sulfate/formic acid). The results show:

1. There are no remarkable differences between the gelation time of the unmodified resins, however, the resin with the higher content of free formaldehyde shows higher reactivity especially at high dilution.
2. The thermoanalytical data of the two resins (temperature curing maximum and reaction enthalpy) are more or less the same, when the same hardener is used.
3. The catalyst has a definite influence on the temperature of curing maximum and on the enthalpy of the curing reaction. A big difference in curing temperature was noticed between ammonium chloride, ammonium sulfate and ammonium nitrate on the one side and ammonium sulfate/formic acid on the other side.
4. The unmodified resins show big differences in the formaldehyde release after curing. UF 1 releases more formaldehyde after curing compared to UF 2, as measured by the WKI-flask-method and the Perforator method.
5. Modification of UF-resins with melamine resin, resorcinol, tannin and PMDI decreases the formaldehyde release of the cured resin significantly. The effect of melamine resin and resorcinol are extremly huge.
6. Melamine resin and resorcinol have no negative effect on the shelf life of UF-resins, however, tannin and PMDI do negatively affect the storage stability of the UF-resins.

     

响应面法优化香菇柄中多酚提取工艺

目的探究超声耦合双水相法提取香菇柄中多酚类物质的最佳工艺。方法采用超声耦合双水相法对香菇柄中多酚进行提取,探讨硫酸铵质量分数、液料比、超声时间、超声功率对多酚含量的影响,在单因素试验的基础上,设计响应面优化试验,确定最佳提取工艺。结果各因素对多酚含量的影响由大到小依次为:超声功率硫酸铵质量分数液料比超声时间。超声耦合双水相法提取香菇柄中多酚的最佳工艺为:超声功率125 W,硫酸铵质量分数40 g/100 m L,液料比30:1(m L/g),超声时间40 min。在此条件下,提取的多酚含量预测值为31.746 mg/g,试验值为(31.746±0.008)mg/g,试验值与预测值基本相符。结论超声耦合双水相法提取条件温和、操作简单,与传统乙醇浸提法相比,不仅节约提取时间,还能提高多酚含量达60%,适于香菇柄中多酚类物质的提取研究。     

Real-time, single-particle measurements of oligomers in aged ambient aerosol particles

Unique high mass negative ions in the -200 to -400 mass/charge range with repetitive spacings of 12, 14, and 16 units, representative of oligomeric species, have been detected in single ambient submicrometer aerosol particles using real-time single-particle mass spectrometry during the Study of Organic Aerosols field campaign conducted in Riverside, CA (SOAR) in August and November 2005. These oligomer-containing particles represented 33-40% of the total detected particles and contained other indicators of aging including oxidized organic carbon, amine, nitrate, and sulfate ion markers. Overall, the highest mass oligomeric patterns were observed in small acidic 140-200 nm particles in the summer. Also during the summer, increased oligomer intensities were observed when the particles were heated with a thermodenuder. We hypothesize that heat removed semivolatile species, thereby increasing particle acidity, while concentrating the oligomeric precursors and accelerating oligomer formation. Differences in oligomer behavior with respect to particle size and heating can be attributed to seasonal differences in photochemical oxidation, the relative amount of ammonium, and particle acidity.     

雅致放射毛霉产孢培养基及产孢条件研究初报

雅致放射毛霉作为一种重要的发酵真菌,广泛应用在霉豆渣发酵和腐乳酿造中,研究其产孢条件对制作直投式菌种具有重要意义。初步筛选了雅致放射毛霉产孢的6种合成培养基和8种天然培养基,同时对碳源、氮源以及碳氮比对雅致放射毛霉产孢的影响进行了研究。实验表明,MEA培养基、小麦麸皮培养基上其孢子产量较高,分别为第9天的1.664×107cfu/mL和第6天的2.04×107cfu/cm2(成活率为51.67%)。以麦芽糖、淀粉、葡萄糖和硝酸钾、硫酸铵分别为碳氮源有利于其产孢。在0.05水平上碳氮比对雅致放射毛霉产孢影响显著,碳源对其产孢影响不显著,碳源为1.92g/L,碳氮比为10:1条件下雅致放射毛霉孢子产量最高。     

N2O emissions from streams in the Neuse river watershed, North Carolina

We present N2O emission data from 11 sites in the Neuse River watershed. Emissions were measured using a static surface enclosure technique deployed on eight sites on the main river channel and three tributary sites. Ancillary data collected included dissolved oxygen, nitrate, total nitrogen, ammonium, dissolved organic carbon, total phosphorus, and temperature. Analysis using standard linear models, and classification and regression trees (CART), indicated nitrate to be the primary driving variable associated with N2O emission, although dissolved organic carbon concentration and water temperature were positively related with N2O emission as well. Relationships between nitrate concentration and N2O emission were consistent with those found in previous studies, although the data presented here represent the lower end of the range for both variables among published studies. Using our measured N2O emission rates along with literature values for the ratio of nitrogen gas to N2O produced during denitrification, we estimate N loss via denitrification in the Neuse River is approximately 17% of the annual N load delivered to the estuary.