Influence of temperature changes on ambient air NO<Subscript>x</Subscript> chemiluminescence measurements

Users of automatic air pollution monitors are largely unaware of how certain parameters, like temperature, can affect readings. The present work examines the influence of temperature changes on chemiluminescence NO(x) measurements made with a Thermo Scientific 42i analyzer, a model widely used in air monitoring networks and air pollution studies. These changes are grouped into two categories according to European Standard EN 14211: (1) changes in the air surrounding the analyzers and (2) changes in the sampled air. First, the sensitivity tests described in Standard EN 14211 were performed to determine whether the analyzer performance was adapted to the requirements of the standard. The analyzer met the performance criteria of both tests; however, some differences were detected in readings with temperature changes even though the temperature compensator was on. Sample temperature changes were studied more deeply as they were the most critical (they cannot be controlled and differences of several tens of degrees can be present in a single day). Significant differences in readings were obtained when changing sample temperature; however, maximum deviations were around 3% for temperature ranges of 15°C. If other possible uncertainty contributions are controlled and temperature variations with respect to the calibration temperature are not higher than 15°C, the effect of temperature changes could be acceptable and no data correction should have to be applied.     

Evaluation of short-term Ogawa passive, photolytic, and federal reference method sampling devices for nitrogen oxides in El Paso and Houston, Texas

Passive Sampling Devices (PSDs) have been successfully used by government and academic agencies to monitor common ambient air pollutants such as ozone and nitrogen dioxide (NO(2)). Most PSD studies have involved long-term (e.g. bi-weekly or monthly) sampling. But the Passive Ozone Network of Dallas (POND) studies of 1998 and 1999 showed that high quality 24-hour and 12-hour data using the Ogawa PSD could be collected for ambient ozone concentrations. This paper presents an evaluation of short-term passive sampling results for nitrogen oxides (NO(x)) in El Paso and Houston, Texas, using the Ogawa PSD. The Ogawa NO(x) PSDs were compared to both Federal Reference Method (FRM) monitors and a photolytic converter, with the photolytic converter designed to report closer concentrations to "true" NO(x) by more effectively limiting the interferences of other nitrogen species. Overall, good agreement was noted for all three monitor types in both cities, supporting the potential use of lower cost Ogawa PSDs for large multi-site episodic NO(x)/NO(2)/NO saturation screening studies. This evaluation was conducted during two separate six week periods of the cooler winter months so additional testing of the Ogawa PSDs during different seasons is recommended.     

CO and NO2 pollution in a long two-way traffic road tunnel: investigation of NO2/NOx ratio and modelling of NO2 concentration

The CO, NO and NO2 concentrations, visibility and air flow velocity were measured using continuous analysers in a long Norwegian road tunnel (7.5 km) with traffic in both directions in April 1994 and 1995. The traffic density was monitored at the same time. The NO2 concentration exceeded Norwegian air quality limits for road tunnels 17% of the time in 1994. The traffic through the tunnel decreased from 1994 to 1995, and the mean NO2 concentration was reduced from 0.73 to 0.22 ppm. The ventilation fan control, based on the CO concentration only, was unsatisfactory and the air flow was sometimes low for hours. Models for NO2 concentration based on CO concentration and absolute air flow velocity were developed and tested. The NO2/NOx ratio showed an increase for NOx levels above 2 ppm; a likely explanation for this phenomenon is NO oxidation by O2. Exposure to high NO2 concentrations may represent a health risk for people with respiratory and cardiac diseases. In long road tunnels with two-way traffic, this study indicates that ventilation fan control based on CO concentration should be adjusted for changes in vehicle CO emission and should be supplemented by air flow monitoring to limit the NO2 concentration.     

Evaluation of method of preparation of passive diffusion tubes for measurement of ambient nitrogen dioxide

This study was carried out in response to suggestions that the measurement of NO(2) by Palmes-type passive diffusion tubes (PDT) is affected by the method of preparation of the triethanolamine (TEA) absorbent coating on the grids. The following combinations of factors were investigated: TEA solvent (acetone or water), volume composition of TEA in solvent (50% or 20%), and grid coating method (dipping in solution prior to assembly or pipetting solution on after assembly). Duplicate PDTs prepared by each of the 8 methods were exposed in parallel, in urban air, for a total of 80 separate 1 week exposures. NO(2) concentrations derived from PDTs prepared by pipetting methods were significantly less precise than concentrations from dipping methods, with mean RSDs for duplicate measurements of 13.8% and 8.5%, respectively (n= 316 each category). Pipetting methods using solutions of 50% TEA composition were particularly imprecise (mean RSD 17.2%). Data from PDTs prepared by pipetting methods were systematically more poorly correlated with each other and with data from co-located chemiluminescence analysers, than corresponding data from PDTs prepared by dipping methods, indicating that more consistent accuracy was also obtained by the latter PDTs. The statistical evidence suggested that PDTs prepared by pipetting 50% TEA in water generally gave lower NO(2) concentrations. Although this is in agreement with a previous study, it is also possible that such an observation here may be a statistical artefact given the demonstrably poorer precision of this method. The general tendency of PDTs to show positive bias in NO(2) measurement in urban air in 1 week exposures was again evident in this study (mean biases at roadside and urban centre locations of +35% (n= 475) and +18% (n= 112), respectively) consistent with augmentation of within-tube NO(2) flux by chemical reaction between co-diffusing NO and O(3). Overall, it is recommended that the pipetting method of PDT grid preparation is avoided, or at least investigated further, because of the apparent degradation in precision and accuracy of NO(2) measurement. Potential reasons for the effect are discussed.     

Air quality and ventilation fan control based on aerosol measurement in the bi-directional undersea Bømlafjord tunnel

Aerosol, NO and CO concentration, temperature, air humidity, air flow and number of running ventilation fans were measured by continuous analysers every minute for a whole week for six different one-week periods spread over ten months in 2001 and 2002 at measuring stations in the 7860 m long tunnel. The ventilation control system was mainly based on aerosol measurements taken by optical scatter sensors. The ventilation turned out to be satisfactory according to Norwegian air quality standards for road tunnels; however, there was some uncertainty concerning the NO2 levels. The air humidity and temperature inside the tunnel were highly influenced by the outside metrological conditions. Statistical models for NO concentration were developed and tested; correlations between predicted and measured NO were 0.81 for a partial least squares regression (PLS1) model based on CO and aerosol, and 0.77 for a linear regression model based only on aerosol. Hence, the ventilation control system should not solely be based on aerosol measurements. Since NO2 is the hazardous polluter, modelling NO2 concentration rather than NO should be preferred in any further optimising of the ventilation control.     

Differences between weekend and weekday ozone levels over rural and urban sites in Southern Italy

Air quality data from a network of 11 monitoring stations in the Apulia region of southern Italy during the summer of 2005 reveal a high frequency of ozone law limit violations. Since ozone is a secondary pollutant, air quality control strategies aimed at reducing ozone concentration are not immediate. Herein, we analyse weekly changes in concentration levels of ozone (O(3)), nitrogen oxides (NO(x)), carbon monoxide (CO), and volatile organic compounds (VOCs), and evaluate how the differences in primary emissions cause changes in the production of ozone. The comparison between weekend and weekday levels of O(3) and its precursors are direct evidence for the existence of the "ozone weekend effect." This effect was observed at all stations with a considerable variation in the overall ozone magnitude, including both traffic stations and non-traffic stations. Data from VOC measurements at traffic stations primarily indicated elevated levels of benzene, toluene, and xylenes (BTX); all of these substances showed an overall decrease over the weekend. A single station indicated levels of non-methane hydrocarbon (NMHC) and PM10, both of which did not demonstrate any weekly cycle. Analysis of weekly and diurnal cycles of O(3), NO(x), CO, NMHC, and PM10 indicates that higher weekend ozone levels result from a reduction in the emission of nitrogen oxides on weekends in VOC-sensitive regimes. This indicates that a reduction in VOC and NO(x) levels would be more effective than NO(x) reduction alone. Our results underscore the need for improved and more efficient VOC measurements.     

一氧化氮标准气体中二氧化氮杂质FTIR定量方法研究及标气质量分析

一氧化氮标准气体在我国空气质量监测工作中广泛用于氮氧化物分析仪的校准,标准气体的质量对环境空气中氮氧化物的测量结果也有着显著的影响.利用傅里叶变换红外光谱仪建立了一套精确测量低浓度二氧化氮方法,并对一氧化氮标准气体产品中二氧化氮杂质进行了测量.结果显示有少部分样品中存在较高浓度的二氧化氮杂质.进一步讨论了可能导致一氧化...     

环境空气气态污染物(CO、SO2、NO)标准气体质量评估

为了解当前不同来源环境空气气态污染物（CO、SO₂、NO）标气质量状况,选择12家主流气态污染物（CO、SO₂、NO）标气制造商,分别匿名采购3种气态污染物标气,建立2家参考实验室共同测试的模式和计量溯源一致性评价方法,对标气进行测试后,采用En值法评价其定值准确性,同时评估其技术资料完整性。结果显示：12家制造商的72瓶有证标气中,有9瓶标气定值结果准确性评价为不合格,涉及5个制造商来源,其中NO作为反应性气体,不合格标气数量最多,占比达20.8%;12家制造商中8家技术资料完整。鉴于标准气体对气态污染物监测结果的准确性、可比性和可溯源性具有重要意义,建议进一步加强标气质量事中事后监管和行业评估,推动制造商不断提高标气生产水平。标气使用者则应尽量选择质量可靠的有证标气。     

The equivalence of diffusive samplers to reference methods for monitoring O3, benzene and NO2 in ambient air

A study of the equivalence to the reference methods of the Radiello samplers for ozone (O(3)) and benzene as well as the membrane-closed Palmes tube (MCPT) for nitrogen dioxide (NO(2)) is presented. These samplers benefit from new model equations capable of estimating their uptake rate. For O(3), the aim here was to demonstrate the equivalence for the reference period of 8 h and 120 microg m(-3), the target value of the 3rd European Daughter Directive. For benzene, the demonstration of equivalence to the annual limit value of 5 microg m(-3) of the 2nd European Daughter Directive was examined. In the case of NO(2), the equivalence to the annual limit value of the 1st European Daughter Directive (40 microg m(-3)) was considered. Results show that the radial sampler for O(3) fails to meet the Data Quality Objective (DQO) for continuous monitoring. However, with an expanded uncertainty of less than 30%, the O(3) diffusive sampler fulfils the DQO for indicative measurements. For benzene, the Radiello sampler exposed for 7 days gave satisfying results showing the ability of the sampler to meet the DQO of the reference method. Nevertheless, the field tests should be complemented by measurements for a wider range of benzene concentrations. In the case of NO(2), all the results of the laboratory and field experiments respected the requirements necessary for the demonstration of equivalence. Overall, these findings thus show that the Radiello sampler and the MCPT are equivalent to the reference methods only for assessment of benzene and NO(2), respectively.     

A field evaluation of a piezo-optical dosimeter for environmental monitoring of nitrogen dioxide

Measurements of 8-hour time-weighted average NO(2) concentrations are reported at 7 different locations in the region of Dunkirk over 5 consecutive days using PiezOptic monitoring badges previously calibrated for the range 0-70 ppb together with data from chemiluminescent analysers in 5 sites (4 fixed and one mobile). The latter facilities also provided data on ozone and NO concentrations and meteorological conditions. Daily averages from the two pairs of badges in different types of sampling cover in each site have been compared with data from the chemiluminescent analysers, and found largely to agree within error margins of +/-30%. Although NO(2) and ozone concentrations were low, rendering detailed discussion impossible, the general features followed expected patterns.     

Analysis of the air pollution climate at a background site in the Po valley

The Po valley in northern Italy is renowned for its high air pollutant concentrations. Measurements of air pollutants from a background site in Modena, a town of 200 thousand inhabitants within the Po valley, are analysed. These comprise hourly data for CO, NO, NO(2), NO(x), and O(3), and daily gravimetric equivalent data for PM(10) from 1998-2010. The data are analysed in terms of long-term trends, annual, weekly and diurnal cycles, and auto-correlation and cross-correlation functions. CO, NO and NO(2) exhibit a strongly traffic-related pattern, with daily peaks at morning and evening rush hour and lower concentrations over the weekend. Ozone shows an annual cycle with a peak in July due to local production; notwithstanding the diurnal cycle dominated by titration by nitrogen oxide, the decreasing long term trend in NO concentration did not affect the long term trend in O(3), whose mean concentration remained steady over the sampling period. PM(10) shows a strong seasonality with higher concentration in winter and lower concentration in summer and spring. Both PM(10) and ozone show a marked weekly cycle in summer and winter respectively. Regressions of PM(10) upon NO(x) show a consistently greater intercept in winter, representing higher secondary PM(10) in the cooler months of the year. There is a seasonal pattern in primary PM(10) to NO(x) ratios, with lower values in winter and higher values in summer, but the reasons are unclear.     

Estimation of the rate of increase in nitrogen dioxide concentrations from power plant stacks using an imaging-DOAS

The emission of nitrogen compounds from power plants accounts for a significant proportion of the total emissions of nitrogen to the atmosphere. This study seeks to understand the nature of chemical reactions in the atmosphere involving nitrogen, which is important in undertaking quantitative assessments of the contribution of such reactions to local and regional air pollution. The slant column density (SCD) of power-plant-generated NO(2) was derived using imaging differential optical absorption spectroscopy (I-DOAS) with scattered sunlight as a light source. The vertical structure of NO(2) SCD from power plant stacks was simultaneously probed using a pushbroom sensor. Measured SCDs were converted to mixing ratios in calculating the rate of NO(2) increase at the center of the plume. This study presents quantitative measurements of the rate of NO(2) increase in a rising plume. An understanding of the rate of NO(2) increase is important because SO(2) and NO(x) compete for the same oxidizing radicals, and the amount of NO(x) is related to the rates of SO(2) oxidation and sulfate formation. This study is the first to directly obtain the rate of NO(2) increase in power plant plumes using the I-DOAS technique. NO(2) increase rates of 60 and 70 ppb s(-1) were observed at distances of about 45 m from the two stacks of the Pyeongtaek Power Plant, northwest South Korea.     

Multivariate Statistical Analysis of Meteorological and Air Pollution Data in the ‘Campo De Gibraltar’ Region, Spain

A complete statistical analysis of meteorological and air pollution data was carried out in the ‘Campo de Gibraltar’ region (in the South of Spain) from 1999 to 2002. This is a heavy industrialized area where, up to date, very few air pollution studies have been made. The main objectives of the study presented here have been the characterization of the meteorological and (gaseous and particulate) air pollution conditions in the area, and the relations between them. Multivariate statistical techniques, such as Principal Component Analysis (PCA), have been applied to the data. The results show that air quality in the area is highly dependent on meteorological conditions such as wind persistence and direction, dispersion capability of the atmosphere, and humidity content. On average, sulphur dioxide and nitrogen oxide air pollution, mainly caused by fuel-oil combustion and traffic, respectively, is not very high. However, an important number of exceedences of the limits established by the EU Directive 1999 for PM10 (particulate matter with a diameter less than 10 μm) have been observed in some points of the area. A significant percentage of these exceedences (about 22% on average) are likely caused by African dust intrusions, which usually take place from May to August. From gaseous and particulate air correlations, it seems that anthropogenic activities contribute with about 19% on average.     

机场大气污染物高时间分辨率排放清单计算方法研究

通过研究机场大气污染物排放特征,结合我国相关排放政策及规范,以排放因子法为主要方法,设计了可建立机场高时间分辨率大气污染物排放清单的计算方法,以期为机场大气污染物排放实时监管提供研究基础。该方法针对飞机发动机和地面保障设备(GSE),实现了颗粒物、二氧化硫、氮氧化物等大气污染物和温室气体的半小时级别排放量计算。通过收集整理北京首都国际机场日航班计划与GSE运作情况实际数据,计算并建立了高时间分辨率的排放清单,验证了计算方法的可行性。随后,从活动水平误差和排放因子适用性两方面,对清单进行了不确定性分析,并通过计算结果对机场排放特征进行了分析,提出了减排建议。     

Effect of sample flow rate and sampling duration on the absorption of NO2 in the sodium arsenite monitoring method

The effect of the two most critical parameters, the sample flow rate and sampling duration, on the absorption efficiency of NO2 in the sodium arsenite method of nitrogen dioxide determination in ambient air was studied. Laboratory experiments showed a high sensitivity to these parameters, which were subjected to variation during actual field monitoring. The reported NO2 absorption efficiency of the method of 82% at a flow rate of 0.2 l min-1 was found to be as low as 33% at a flow rate of 1.0 l min-1 for a sampling duration of 24 h. Similarly, a considerable decrease in absorption efficiency with increasing sampling duration from 2 to 24 h was observed at a particular flow rate. Correction factors for the absorption efficiency were evolved that can be used to update the existing database, as well as future NO2 data generated using this manual monitoring method.     

Modelling of the uptake rate of the nitrogen dioxide Palmes diffusive sampler based on the effect of environmental factors

The influence of environmental parameters on the uptake rate of the nitrogen dioxide (NO(2)) Palmes diffusive sampler was investigated. The main factors affecting the uptake rate were found to be wind speed, the preponderant factor, followed by relative humidity and temperature. The NO(2) concentration and exposure time, as well as the interactions among the factors were not found to have a significant influence on the uptake rate of the Palmes sampler. As a result, a model able to predict the uptake rate of the Palmes sampler was established. In addition, by using the model-predicted uptake rate, the agreement between chemiluminescence and the Palmes sampler during the field tests was improved. The NO(2) Palmes diffusive sampler was shown to comply with the requirement on accuracy defined by the European Directive for the indicative methods of measurements.     

Mathematical models for accurate prediction of atmospheric visibility with particular reference to the seasonal and environmental patterns in Hong Kong

Atmospheric visibility impairment has gained increasing concern as it is associated with the existence of a number of aerosols as well as common air pollutants and produces unfavorable conditions for observation, dispersion, and transportation. This study analyzed the atmospheric visibility data measured in urban and suburban Hong Kong (two selected stations) with respect to time-matched mass concentrations of common air pollutants including nitrogen dioxide (NO(2)), nitrogen monoxide (NO), respirable suspended particulates (PM(10)), sulfur dioxide (SO(2)), carbon monoxide (CO), and meteorological parameters including air temperature, relative humidity, and wind speed. No significant difference in atmospheric visibility was reported between the two measurement locations (p > or = 0.6, t test); and good atmospheric visibility was observed more frequently in summer and autumn than in winter and spring (p < 0.01, t test). It was also found that atmospheric visibility increased with temperature but decreased with the concentrations of SO(2), CO, PM(10), NO, and NO(2). The results showed that atmospheric visibility was season dependent and would have significant correlations with temperature, the mass concentrations of PM(10) and NO(2), and the air pollution index API (correlation coefficients mid R: R mid R: > or = 0.7, p < or = 0.0001, t test). Mathematical expressions catering to the seasonal variations of atmospheric visibility were thus proposed. By comparison, the proposed visibility prediction models were more accurate than some existing regional models. In addition to improving visibility prediction accuracy, this study would be useful for understanding the context of low atmospheric visibility, exploring possible remedial measures, and evaluating the impact of air pollution and atmospheric visibility impairment in this region.     

Simultaneous determination of atmospheric sulfur and nitrogen oxides using a battery-operated portable filter pack sampler

We developed a method to analyze atmospheric SO(x) (particulate SO(4)(2-)+ gaseous SO(2)) and NO(x) (NO + NO(2)) simultaneously using a battery-operated portable filter pack sampler. NO(x) determination using a filter pack method is new. SO(x) and NO(x) were collected on a Na(2)CO(3) filter and PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl) + TEA (triethanolamine) filters (6 piled sheets), respectively. Aqueous solutions were then used to extract pollutants trapped by the filters and the resulting extracts were pre-cleaned (e.g. elimination of PTIO) and analyzed for sulfate and nitrite by ion chromatography. Recoveries of SO(2) and NO(x) from standard pollutant gases and consistency of the field data with those from other instrumental methods were examined to evaluate our method. SO(x) and NO(x) could be analyzed accurately with determination limits of 0.2 ppbv and 1.0 ppbv (as daily average concentrations), respectively. The sampler can determine SO(x) and NO(x) concentrations at mountainous or remote sites without needing an electric power supply.     

Harmonization problems in the implemention of the EEC directive on air quality limit values and guide values for sulphur dioxide and suspended particulates

This report deals with the implementation of Article 10 of the Directive on air quality limit values and guide values for sulphur dioxide and suspended particulates (80/779/EEC). For this purpose the Commission, in cooperation with the Member States, has prepared a ‘Common Measurement Programme’ which basically provides for:

1. examination and improvement of the reference measurement methods,
2. examination of the comparability of the measuring procedures and equipment used for monitoring purposes in the Member States,
3. the provision of guidelines and the carrying out of measurements to determine the corresponding stringency of the limit values laid down in Annexes IV and I of the Directive.

     

Laboratory and field comparison of measurements obtained using the available diffusive samplers for ozone and nitrogen dioxide in ambient air

This study presents an evaluation of the extent of differences between measurements performed by O(3) and NO(2) diffusive samplers and by the reference methods for diffusive samplers commercially available. The tests were performed in an exposure chamber under extreme conditions of controlling factors and under field conditions. For NO(2), the results of the laboratory experiments showed that most of the diffusive samplers were affected by extreme exposure conditions. The agreement between the samplers and the reference method was better for the field tests than for the laboratory ones. The estimate of the uptake rate for the exposure conditions using a model equation improved the agreement between the diffusive samplers and the reference methods. The agreement between O(3) measured by the diffusive samplers and by the reference method was satisfactory for 1-week exposure. For 8-hour exposures, the diffusive samplers with high uptake rates quantified better the O(3) concentration than the samplers with low uptake rates. As for NO(2), the results of the O(3) field tests were in better agreement with the reference method than the ones of the laboratory tests. The field tests showed that the majority of diffusive samplers fulfils the 25% uncertainty requirement of the NO(2) European Directive and the 30% uncertainty requirement of the O(3) European Directive for 1-week exposure.