Low NOx Levels Research Articles

Dual Mode NOx Sensor: Measuring Both the Accumulated Amount and Instantaneous Level at Low Concentrations

The accumulating-type (or integrating-type) NOx sensor principle offers two operation modes to measure low levels of NOx: The direct signal gives the total amount dosed over a time interval and its derivative the instantaneous concentration. With a linear sensor response, no baseline drift, and both response times and recovery times in the range of the gas exchange time of the test bench (5 to 7 s), the integrating sensor is well suited to reliably detect low levels of NOx. Experimental results are presented demonstrating the sensor’s integrating properties for the total amount detection and its sensitivity to both NO and to NO2. We also show the correlation between the derivative of the sensor signal and the known gas concentration. The long-term detection of NOx in the sub-ppm range (e.g., for air quality measurements) is discussed. Additionally, a self-adaption of the measurement range taking advantage of the temperature dependency of the sensitivity is addressed.

Photochemical analyses of ozone and related compounds under various environmental conditions

The photochemical characteristics of ozone (O3) and its main precursors (e.g. NOx and VOCs) were investigated in relation to the photochemical O3 budget and O3eNOxeVOC sensitivity, based on a modeling approach using data sets observed during intensive field campaigns conducted under various environmental conditions (i.e. urban (Seoul), rural (Yang Pyeong), landfill (Dae Gu), coastal (Gwang Yang), and remote sites (Jeju Island). The production of O3 under most environmental conditions (especially, spring season at the urban site) was found to be more strongly sensitive to VOCs than NOx .A t the landfill site and during summer at the rural and coastal sites, the production of O3 was partially sensitive to NOx. On the other hand, despite the remote air on Jeju Island, the production of O3 was mainly VOC-sensitive (high NOx levels), but in part NOx-sensitive (low NOx levels), due to the transport processes from different environmental regions (e.g. heavily and less polluted locations).

The epistasis between vascular homeostasis genes is apparent in essential hypertension

Objective The epistasis influence of vascular homeostasis genes is vital to multigenetic diseases. This study was designed to perceive the possible role of epistasis in the etiology of essential hypertension. Methods We investigated seven polymorphisms of ACE, CYP11B2 and NOS3 epistatically, and SBP, DBP, MAP, ACE activity, plasma aldosterone concentration (PAC) and NOx level in 860 age- and ethnicity-matched unrelated north-Indian subjects. Results The hypertension risk in individuals with interacted-genotypes (IwIw + IwIc) + (4aa), (IcIc) + (4bb + 4ba) and IcIc + 4aa of the CYP11B2 and NOS3 was significantly higher with odds ratio 5.5 (95% CI = 2.9–10.6, P < 0.0001), 2.4 (95% CI = 1.4–4.1, P < 0.0008) and 7.5 (95% CI = 1.6–34.8, P = 0.010), respectively. The odds ratio for hypertension with interacted-haplotypes (−344T/Ic) + (−922A/−786T/4a/894G) and (−344T/Ic) + (−922G/−786C/4a/894G) of CYP11B2 and NOS3 was 5.3 (95% CI = 2.0–14.2, P = 0.005) and 3.9 (95% CI = 1.4–10.4, P = 0.04), respectively; whereas for the protective interacted-haplotypes (−344T/Iw) + (−922A/−786T/4b/894G), the odds ratio was 0.7 (95% CI = 0.5–0.9, P = 0.03). While the interacted-genotypes, IcIc + 4aa correlated with higher SBP and MAP ( P = 0.006; P = 0.04), the interacted-haplotypes, (−344T/Ic) + (−922A/−786T/4a/894G) and (−344T/Ic) + (−922G/−786C/4a/894G) correlated with higher MAP and lower NOx level ( P = 0.02 and P = 0.03, respectively), and the protective interacted-haplotypes (−344T/Iw) + (−922A/−786T/4b/894G) correlated with lower PAC and MAP ( P = 0.024 and P = 0.018, respectively). Conclusions The epistasis between CYP11B2 and NOS3 and its correlation with varied clinical and biochemical parameters signify its possible contribution in the complex etiology of hypertension.

Dual Fuel Performance Studies of a Small Diesel Engine Using Green Fuels

The objective of this work is to review state of art practices and potential in diesel engines using greener fuels. Biogas with jatropha bio-diesel as ignition source was tested in a compression ignition diesel engine at six different loads under dual fuel mode. With a simple modification, the base engine was qualified to a dual fuel operation. For all the loads evaluated, dual fuel mode achieved a possible bio-diesel substitution of about 65%. In addition, it consumed lesser friction power as compared to the diesel mode during the operation. There were reductions in thermal efficiency, cylinder peak pressure and combustion noise under the dual fuel operation than the diesel mode due to lower burning velocity of biogas together with a longer pilot delay. However, this operation registered extremely lower NOx levels at all loads along-with reduced CO emissions at medium and higher loads. While significant increases in hydrocarbon emissions were observed.

Investigation into Light Duty Dieseline Fuelled Partially-Premixed Compression Ignition Engine

Conventional diesel fuelled Partially-Premixed Compression Ignition (PPCI) engines have been investigated by many researchers previously. However, the ease of ignition and difficulty of vaporization of diesel fuel make it imperfect for PPCI combustion. In this study, Dieseline (blending of diesel and gasoline) was looked into as the Partially-Premixed Compression Ignition fuel for its combination of two fuel properties, ignition-delay-increasing characteristics and higher volatility, which make it more suitable for PPCI combustion compared to neat diesel. A series of tests were carried out on a Euro IV light-duty common-rail diesel engine, and different engine modes, from low speed/load to middle speed/load were all tested, under which fuel blend ratios, EGR rates, injection timings and quantities were varied. The emissions, fuel consumption and combustion stability of this dieseline-fuelled PPCI combustion were all investigated. The results showed that dieseline had great advantages as a PPCI combustion fuel in terms of emission reduction. This was particularly significant at high-speed engine mode. It was also found that with a blend of 50% gasoline in diesel, the particle numbers total concentration could be reduced by 90% while low NOx level and high brake fuel conversion efficiency (around 30%) were maintained at all the loads tested. © 2011 SAE International.

The short-term consumption of a moderately high-fat diet alters nitric oxide bioavailability in lean female Zucker rats

To determine whether short-term consumption of a moderately high-fat diet (MHFD) affects nitric oxide (NO) production, the concentration of stable NO metabolites (NOx) in urine and plasma of rats fed a MHFD (15.6%g fat) or control diet (4.5%g fat) was measured weekly for 4weeks. Plasma and urine NOx levels were significantly depressed in the MHFD group by week 1 and remained so for the duration of the study. Decreased NO bioavailability may result from a decrease in NO production or the scavenging of NO by reactive oxygen species (ROS). Because endothelial NOS (eNOS) is the major contributor to NO production and circulating levels of NOx, eNOS expression was measured in several tissues. At week 1, there was a MHFD-associated decrease in eNOS expression in the liver. Subsequently, eNOS expression declined in the heart and kidney medulla of MHFD-fed rats at weeks 3 and 4, respectively. The expression of eNOS in the kidney cortex and adipose tissue did not change. These results suggest that a MHFD alters eNOS expression in a time-dependent and tissue-specific manner. In the liver, NOS activity and tissue levels of NOx and nitrotyrosine were measured. Nitrotyrosine levels were used as an indirect measure of the NO scavenged by ROS. There was a decrease in NOS activity, suggesting that the low levels of hepatic NOx were due, in part, to a decrease in NO production. In addition, there was a dramatic increase in nitrotyrosine formation, suggesting that the decline in hepatic NOx was also due to an increased interaction of NO with ROS. Tyrosine nitration commonly has detrimental effects on proteins. The decrease in NO and increase in protein nitration could potentially have adverse effects on tissue function.

Impacts of mechanistic changes on HO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; formation and recycling in the oxidation of isoprene

Abstract. Recently reported model-measurement discrepancies for the concentrations of the HOx radical species (OH and HO2) in locations characterized by high emission rates of isoprene have indicated possible deficiencies in the representation of OH recycling and formation in isoprene mechanisms currently employed in numerical models; particularly at low levels of NOx. Using version 3.1 of the Master Chemical Mechanism (MCM v3.1) as a base mechanism, the sensitivity of the system to a number of detailed mechanistic changes is examined for a wide range of NOx levels, using a simple box model. The studies consider sensitivity tests in relation to three general areas for which experimental and/or theoretical evidence has been reported in the peer-reviewed literature, as follows: (1) implementation of propagating channels for the reactions of HO2 with acyl and β-oxo peroxy radicals with HO2, with support from a number of studies; (2) implementation of the OH-catalysed conversion of isoprene-derived hydroperoxides to isomeric epoxydiols, as characterised by Paulot et al.~(2009a); and (3) implementation of a mechanism involving respective 1,5 and 1,6 H atom shift isomerisation reactions of the β-hydroxyalkenyl and cis-δ-hydroxyalkenyl peroxy radical isomers, formed from the sequential addition of OH and O2 to isoprene, based on the theoretical study of Peeters et al. (2009). All the considered mechanistic changes lead to simulated increases in the concentrations of OH, with (1) and (2) resulting in respective increases of up to about 7% and 16%, depending on the level of NOx. (3) is found to have potentially much greater impacts, with enhancements in OH concentrations of up to a factor of about 3.3, depending on the level of NOx, provided the (crucial) rapid photolysis of the hydroperoxy-methyl-butenal products of the cis-δ-hydroxyalkenyl peroxy radical isomerisation reactions is represented, as also postulated by Peeters et al.~(2009). Additional tests suggest that the mechanism with the reported parameters cannot be fully reconciled with atmospheric observations and existing laboratory data without some degree of parameter refinement and optimisation which would probably include a reduction in the peroxy radical isomerisation rates and a consequent reduction in the OH enhancement propensity. However, an order of magntitude reduction in the isomerisation rates is still found to yield notable enhancements in OH concentrations of up to a factor of about 2, with the maximum impact at the low end of the considered NOx range. A parameterized representation of the mechanistic changes is optimized and implemented into a reduced variant of the Common Representative Intermediates mechanism (CRI v2-R5), for use in the STOCHEM global chemistry-transport model. The impacts of the modified chemistry in the global model are shown to be consistent with those observed in the box model sensitivity studies, and the results are illustrated and discussed with a particular focus on the tropical forested regions of the Amazon and Borneo where unexpectedly elevated concentrations of OH have recently been reported.

Remarkable improvement of NOx–PM trade-off in a diesel engine by means of bioethanol and EGR

In order to realize a premixed compression ignition (PCI) engine, the effects of bioethanol–gas oil blends and exhaust gas recirculation (EGR) on PM–NOx trade-off have been investigated focusing on ignition delay, premixed combustion, diffusion combustion, smoke, NOx and thermal efficiency. The present experiment was done by increasing the ethanol blend ratio and ethanol and by increasing the EGR ratio in a single cylinder direct injection diesel engine. It is found that a remarkable improvement in PM–NOx trade-off can be achieved by promoting the premixing based on the ethanol blend fuel having low evaporation temperature, large latent heat and low cetane number as well, in addition, based on a marked elongation of ignition delay due to the low cetane number fuel and the low oxygen intake charge. As a result, very low levels of NOx and PM, which satisfies the 2009 emission standards imposed on heavy duty diesel engines in Japan, were achieved without deterioration of brake thermal efficiency in the PCI engine fuelled with the 50% ethanol blend diesel fuel and the high EGR ratio. It is noticed that smoke can be reduced even by increasing the EGR ratio under the highly premixed condition.

Year‐round measurements of nitrogen oxides and ozone in the tropical North Atlantic marine boundary layer

A highly sensitive chemiluminescence instrument has been deployed to measure nitric oxide (NO) and nitrogen dioxide (NO2) at the Cape Verde Atmospheric Observatory in the remote tropical North Atlantic marine boundary layer (MBL). Using two different methods, the instrument was assessed to have a detection limit of around 1.8 parts per trillion by volume (pptv) for NO and 5.5 pptv for NO2 for hour‐long integration periods. The overall accuracy was estimated at ∼18% for NO and 30% for NO2. Measurements of NO, NO2, and ozone (O3) over a period of 12 months in 2007 show very low levels of NOx (typically &lt;30 pptv) and net daytime ozone destruction on most days of the measurement period. Air originating over Africa exhibited the highest levels of NOx (∼35 pptv) and reduced daily O3 destruction, with O3 production observed on a few days. Air that had not originated over Africa showed lower NOx levels (∼25 pptv), with greater observed O3 destruction. A dependence of the observed O3 destruction on NO mixing ratios, averaged over all air masses, was observed and reproduced using a simple box model. The model results imply that the presence of between 17 and 34 pptv of NO (depending on the month) would be required to turn the tropical North Atlantic from an O3 destroying to an O3 producing regime.

An isoprene mechanism intercomparison

Abstract The chemical mechanisms describing the photo-oxidation of isoprene in current Chemistry Transport Models (CTMs) have been intercompared in a series of box model experiments. The mechanisms ranged in size and complexity from ∼600 reactions to ∼25 reactions. The box model experiments covered two isoprene emission strengths over a broad range of NO emissions to assess the performances of the mechanisms over the spectrum of atmospherically relevant conditions. There was some variability in the simulated oxidation rates of isoprene and formation rates of ozone. The variability in performance is a consequence of the details of the underlying chemistry as represented in the mechanisms, and of the different assumptions and approximations made in mechanism reduction. These differences are illustrated and discussed for a series of species involved in the degradation of isoprene and the ozone formation mechanism, namely: HOx radicals; organic peroxy radicals (RO2); hydroperoxides; oxidised organic nitrogen compounds; and major carbonyl products. The results also confirm that all the considered isoprene mechanisms are unable to generate/recycle HOx at the rates needed to match recently reported observations at locations characterized by low levels of NOx.

Design Procedure of a Novel Microturbine Low NOx Conical Wire-Mesh Duct Burner

Abstract Nowadays, air pollution and climate change have become a global environmental problem. As a result, government regulations worldwide are becoming increasingly stringent. This has led to an urgent need to develop new designs and methods for improving combustion systems to minimize the production of toxic emissions, such as nitrogen oxides. Microturbine based cogeneration units are one of the interesting alternatives for combined electrical power and heat generation (CHP). Microturbine CHP technology still needs to be developed to increase efficiency and heat-to-power ratio and to improve operating flexibility. This can all be obtained by adding a duct burner to the CHP unit. This paper documents the design process for a novel low NOx conical wire-mesh duct burner for the development of a more efficient microcogeneration unit. This burner provides the thermal energy necessary to raise the microturbine exhaust gas temperature to increase the heat recovery capability. The duct burner implements both lean premixed and surface combustion techniques to achieve low NOx and CO emission levels. The design process includes a set of preliminary design procedures relating the use of empirical and semiempirical models. The preliminary design procedures were verified and validated for key components, such as the duct burner premixer, using the laser sheet illumination (LSI) technique. The LSI was used to study the mixing process inside the premixer fitted with different swirlers. The designed duct burner successfully operated in a blue flame mode over a wide range of conditions with NOx emissions of less than 5 ppmv and CO emissions of less than 10 ppmv (corrected to 15% O2).

Hazardous air pollutants emission from coal and oil‐fired power plants

AbstractHazardous air pollutants (HAPs) emission characteristics from coal (anthracite, bituminous) and oil‐fired power plants were studied in order to control pollutants by formulating US maximum achievable control technology (MACT)‐like regulation in Korea. Sampling and analysis were carried out according to either Korean standard test method or US EPA method. Relatively lower levels of NOx and SOx were emitted from plants burning bituminous than the anthracite coal. Less dust was emitted from oil‐fired power plants. Mercury, lead, and chromium were dominant in coal‐fired power plants, following which, nickel and chromium were emitted from oil‐fired power plants. The major volatile organic compounds (VOCs) emitted from coal‐fired plants were 1,2‐dichloroethane, benzene, carbon tetrachloride, chloroform, trichloro‐ethylene. The emission of mercury and other heavy metals in flue gas was attributed to fuel types, operating conditions, residence time in the control devices and air pollution control devices configuration. After emission tests in the field and on analysis of the continuous emission monitoring data collected from facilities under operation and consideration of other various factors, management guidelines will be suggested with special reference to US MACT‐like regulation. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Effects of CPAP on oxidative stress and nitrate efficiency in sleep apnoea: a randomised trial

Previous studies have presented contradictory data concerning obstructive sleep apnoea syndrome (OSAS), lipid oxidation and nitric oxide (NO) bioavailability. This study was undertaken to (1) compare the concentration of 8-isoprostane and total nitrate and nitrite (NOx) in plasma of middle-aged men with OSAS and no other known co-morbidity and healthy controls of the same age, gender and body mass index; and (2) test the hypothesis that nasal continuous positive airway pressure (CPAP) therapy attenuates oxidative stress and nitrate deficiency. A prospective, randomised, placebo controlled, double-blind, crossover study was performed in 31 consecutive middle-aged men with newly diagnosed OSAS and 15 healthy control subjects. Patients with OSAS were randomised to receive sham CPAP or effective CPAP for 12 weeks. Blood pressure, urinary catecholamine levels and plasma 8-isoprostane and NOx concentrations were obtained before and after both treatment modalities. Patients with OSAS had significantly higher 8-isoprostane levels (median (IQR) 42.5 (29.2-78.2) vs 20.0 (12.5-52.5) pg/ml, p = 0.041, Mann-Whitney test) and lower NOx levels (264 (165-650) vs 590 (251-1465) micromol/l, p = 0.022) than healthy subjects. Body mass index, blood pressure and urinary catecholamines were unchanged by CPAP therapy, but 8-isoprostane concentrations decreased (38.5 (24.2-58.7) pg/ml at baseline vs 22.5 (16.2-35.3) pg/ml on CPAP, p = 0.0001) and NOx levels increased (280 (177-707) vs 1373 (981-1517) micromol/l, p = 0.0001) after CPAP. OSAS is associated with an increase in oxidative stress and a decrease in NOx that is normalised by CPAP therapy.

Impact of climate change on tropospheric ozone and its global budgets

Abstract. We present the chemistry-climate model UMCAM in which a relatively detailed tropospheric chemical module has been incorporated into the UK Met Office's Unified Model version 4.5. We obtain good agreements between the modelled ozone/nitrogen species and a range of observations including surface ozone measurements, ozone sonde data, and some aircraft campaigns. Four 2100 calculations assess model responses to projected changes of anthropogenic emissions (SRES A2), climate change (due to doubling CO2), and idealised climate change-associated changes in biogenic emissions (i.e. 50% increase of isoprene emission and doubling emissions of soil-NOx). The global tropospheric ozone burden increases significantly for all the 2100 A2 simulations, with the largest response caused by the increase of anthropogenic emissions. Climate change has diverse impacts on O3 and its budgets through changes in circulation and meteorological variables. Increased water vapour causes a substantial ozone reduction especially in the tropical lower troposphere (&gt;10 ppbv reduction over the tropical ocean). On the other hand, an enhanced stratosphere-troposphere exchange of ozone, which increases by 80% due to doubling CO2, contributes to ozone increases in the extratropical free troposphere which subsequently propagate to the surface. Projected higher temperatures favour ozone chemical production and PAN decomposition which lead to high surface ozone levels in certain regions. Enhanced convection transports ozone precursors more rapidly out of the boundary layer resulting in an increase of ozone production in the free troposphere. Lightning-produced NOx increases by about 22% in the doubled CO2 climate and contributes to ozone production. The response to the increase of isoprene emissions shows that the change of ozone is largely determined by background NOx levels: high NOx environment increases ozone production; isoprene emitting regions with low NOx levels see local ozone decreases, and increase of ozone levels in the remote region due to the influence of PAN chemistry. The calculated ozone changes in response to a 50% increase of isoprene emissions are in the range of between −8 ppbv to 6 ppbv. Doubling soil-NOx emissions will increase tropospheric ozone considerably, with up to 5 ppbv in source regions.

Nitric Oxide Metabolites Are Associated with Survival in Older Patients

To assess the efficacy of various vascular endocrinological substances, such as plasma nitric oxide metabolites (NOx), as surrogate markers of survival in older patients. Prospective cohort, observational. Nagoya University Hospital and related hospitals, Japan. One hundred fifty patients aged 70 and older, recruited consecutively from the outpatient clinics of Nagoya University Hospital and related hospitals. Serum biochemical analyses such as albumin and total cholesterol, various prognostic markers, such as tumor necrosis factor (TNF)-alpha, NOx, activities of daily living (ADLs), and instrumental ADLs (IADLs) were evaluated on enrollment. ADLs, IADLs, and comorbidities, especially depression and impaired cognition, were evaluated on enrollment. The main outcome was survival rate over 2.75 years. Forty-nine patients died during the follow-up period. Mann-Whitney U-test showed that hemoglobin, total protein, serum albumin, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, high sensitive c-reactive protein, NOx, B-type natriuretic peptide, interleukin-6, and TNF-alpha levels; ADLs; cognitive impairment; and depressive status were significantly different for subjects who survived and those who died. Of the dependent variables in the Cox proportional hazards regression analyses, only ADLs, NOx, and albumin were significantly different. In the Kaplan-Meier analyses of mortality, the prognosis of patients in the third and fourth quartiles of NOx was significantly worse than that of patients in the first or second quartile. The prognosis of patients with impaired ADLs was worse than that of other patients for the overall period. Lower levels of NOx may be associated with survival in older patients. It may be an effective marker, like ADLs, which is a well-known marker.

Serum levels of soluble Fas, nitric oxide and cytokines in acute decompensated cirrhotic patients

To evaluate plasma levels of nitrite/nitrate (NOx), soluble Fas (sFas) antigen, tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) in patients with compensated and acute decompensated cirrhosis and to evaluate mediators causing acute decompensation in liver cirrhosis. This prospective study was conducted in the medical intensive care unit of an academic tertiary center. Fifty-five patients with acute decompensation (gastrointestinal hemorrhage, encephalopathy, hydropic decompensation) and twenty-five patients with compensated liver cirrhosis were included. Blood samples were taken for analyses of sFas, Nox, IL-6, TNF-alpha. Liver enzymes and kidney functions were also tested. In patients with acute decompensation, plasma sFas levels were higher than in non-decompensated patients (15305 +/- 4646 vs 12458 +/- 4322 pg/mL, P < 0.05). This was also true for the subgroup of patients with alcoholic liver cirrhosis (P < 0.05). The other mediators were not different and none of the parameters predicted survival, except for ALT (alanine-aminotransferase). In patients with portal-hypertension-induced acute hemorrhage, NOx levels were significantly lower than in patients with other forms of decompensation (70.8 +/- 48.3 vs 112.9 +/- 74.9 pg/mL, P < 0.05). When NOx levels were normalized to creatinine levels, the difference disappeared. IL-6, TNF-alpha and sFas were not different between bleeders and non-bleeders. In decompensated patients sFas, IL-6 and NOx levels correlated positively with creatinine levels, while IL-6 levels were dependent on Child class. In acute decompensated cirrhotic patients sFas is increased, suggesting a role of apoptosis in this process and patients with acute bleeding have lower NOx levels. However, in this acute complex clinical situation, kidney function seems to have a predominant influence on mediator levels.

FUNDAMENTAL STUDIES OF A PARTIAL PREMIXED COUNTER-FLOW COMBUSTION SYSTEM AND ITS EFFECT ON NOx EMISSIONS

The use of air staging as a technique for reducing NOX emissions from process industry burners has been employed for many years but lower levels of NOX and high thermal efficiencies can be achieved using a partial premixed combustion mode. The development of partial premixed burners has only gradually increased because of the increased risk of flash back and the difficulties of control. The current study presents both an experimental and a numerical investigation on a laboratory-scale counter-flow combustion system of the partial premixed mode. The system aims to duplicate the mixing process observed within an industrial burner, which produces a double flame structure. Results have shown that the nozzle configuration has a direct influence on NOX emissions.

Flexible fuel engine based on multi-combustion control technologies

A combustion control strategy is proposed for diesel engine to reduce PM and NOx emissions significantly, which adopts some technologies including internal exhaust gas recirculation (EGR), split spray, adjustable fuel delivery advance angle and the application of alternative fuels. Based on this strategy, a flexible fuel engine has been developed. The experimental results show that this engine can be fueled with diesel fuel, alcohol, dimethyl carbonate (DMC), etc. It works with extremely low levels of particulate matter (PM) and NOx, 2–3% higher effective thermal efficiency on moderate and high loads when alternative fuels are used. This engine not only has lower exhaust emissions, but also can be fueled with those alternative fuels, which are difficult to be ignited by compression.

Increased Release of Cervical Nitric Oxide in Spontaneous Abortion before Clinical Symptoms: A Possible Mechanism for Preabortal Cervical Ripening

Nitric oxide (NO) affects cervical ripening. We studied cervical NO release in women with nonviable pregnancy before signs of abortion. Women with missed abortion (n = 56), blighted ovum (n = 36), or tubal pregnancy (n = 7) were selected by means of vaginal ultrasonographic examination from a population seeking early pregnancy termination; 140 women with amenorrhea-matched normal gestation were studied as controls. Cervical fluid samples were assessed for NO metabolites (Nox) by means of Griess reaction. Cervical fluid Nox was more often detectable in women with missed abortion (90%) and blighted ovum (87%) than in the control women (55%; P = 0.01), and Nox levels in women with missed abortion [median, 59.4 mumol/liter; 95% confidence interval (CI), 30.3-81.8] and blighted ovum (25.6 mumol/liter; 95% CI, 14.1-53.0) were 14 and 6 times higher (P < 0.001 and P = 0.002, respectively) than in the control group (4.3 mumol/liter; 95% CI, <3.8 to 6.4). Nox levels in women with tubal pregnancy were normal. In women with nonviable pregnancy, the lower the level of progesterone, expressed as a percentage of that in the control women, the higher (r = -0.69; P < 0.001) the level of cervical fluid Nox, and those with low pretreatment Nox levels failed to abort completely after mifepristone-misoprostol or expectant management more often (P = 0.04) than women with high Nox levels (28% vs. 4%); no such relationship was seen in the control group. Increased preabortal cervical NO release may contribute to cervical ripening and the onset of clinical abortion.

Ambient Vehicular Pollutants in the Urban Area of Taipei: Comparing Normal with Anomalous Vehicle Emissions

Continuous ambient monitoring data of major air pollutants such as CO, NOx and NMHC (non-methane hydrocarbons) for the 1994–2001 period were analysed to establish the relationship between patterns of vehicular emitting species and vehicular emissions in the urban area of Taipei. These characteristics are consistent with measurements in London and Athens, indicating that vehicular emissions are a major contributing factor to air pollution in Taipei. Sensitivity studies relating ambient air pollution to vehicular emissions in the urban area of Taipei were performed and further examined by analysing some special events where the city’s overall vehicle usage were at their extremes. Analysis of ambient measurements during the passing of Typhoon Nari shows very low levels of CO (0.3–0.4 ppmv), NOx (5–10 ppbv) and NMHC (0.01–0.05 ppmv), with no well-defined daily patterns. The measurements during Typhoon Nari were compared with measurements during the Chinese New Year and during Typhoon Herb. All analyses show distinctive low pollution periods surrounded by elevated trace gas concentrations, initiated by normal working practices. This revealed the severe impact of vehicle exhaust emissions on air pollution levels in Taipei City. Further impacts from vehicles were examined by comparing the post-Nari measurements with those before the arrival of the typhoon and comparing these data with a photochemical modelling system. It was found that as high as 15 ppmv of CO, 250 ppbv of NOx and 2.5 ppmv of NMHC were measured during the day time, with about a 50% increase in ambient vehicular pollutants in the first 2 days after the passing of Typhoon Nari. Implications for pollution related impacts on human health within Taipei are noted.