The change in O3, SO2 and NO2 concentrations in Lithuania

Due to the dynamic nature of the atmosphere, substantial amounts of gaseous and particulate pollutants are transported to the areas distant from their sources. In order to determine the regional concentration levels of atmospheric pollutants in Lithuania, concentrations of gaseous O₃, SO₂, NO₂ and other pollutants have been measured at the Preila background station (55°20′ N and 21°00′ E, 5 m a.s.l.) since 1981. The long-term concentration data set enabled us to get temporal trends, both on a seasonal and longer time scale, to identify source areas of pollutants and to relate them to the emission data. Based on the data obtained, the different tendencies in the pollutant concentration changes were revealed. Positive trends for ozone (of 2.9% per year during 1983–2000) and a distinct negative trend for both sulphur dioxide (of 3.8% per year during 1981–2000) and nitrogen dioxide (of 3.8% per year during 1983–2000) were found. The air mass back-trajectory analysis was used to assess the source region of air pollutants transported to Lithuania. The pollutant concentration levels were compared with their emission changes in Europe and Lithuania. The general trends in SO₂ as well as in NO₂ concentrations observed are consistent with changes in SO₂ and NO₂ emissions in Europe and Lithuania.     

Estimation of night-time N2O5 concentrations from ambient NO2 and NO3 radical concentrations and the role of N2O5 in night-time chemistry

Dinitrogen pentoxide (N₂O₅), which is present in equilibrium with NO₃ radicals and NO₂, has been recognized for some time as an intermediate in the NO_x chemistry of night-time atmospheres. However, until the advent of long pathlength spectroscopic techniques for the measurement of atmospheric NO₃ radical concentrations, no reliable method for estimating N₂O₅ concentrations has been available. We have calculated maximum night-time N₂O₅ concentrations from the available experimentally determined concentrations of the NO₃ radical and NO₂ in the U.S. and Germany, and find that N₂O₅ concentrations as high as ~ 15 ppb can occur. We have also estimated removal rates for N₂O₅ and for NO₃ radicals during these nights. From data obtained under conditions devoid of point sources of NO_x, upper limit estimates of the homogeneous rate constant for the reaction of N₂O₅ with water vapor are obtained, leading to the conclusion that the homogeneous gas phase rate constant for this reaction is ⩽ 1 × 10⁻²¹ cm³ molecule⁻¹ s⁻¹ at 298 K, consistent with recent environmental chamber data.     

Impacts of a strong cold front on concentrations of HONO,HCHO, O3, and NO2 in the heavy traffic urban area of Beijing

Much rain and strong winds caused by a cold front occurred in Beijing during the period of Sep. 27 to Oct. 4, 2004 and led to sharp drops in maximum and mean concentrations of HONO, HCHO, O₃, and NO₂, i.e., the maximum concentrations were reduced by 5.9, 21.3, 45.6, and 44.4 ppb, respectively, and the mean concentrations were decreased by 4.0, 5.5, 30.3, and 32.3 ppb, respectively. For daily HO_x production rates HONO photolysis was the largest contributor and over 90% contributions were from photolysis of HONO and HCHO. Large number and area percentages of soot aggregate from PM10, and high correlations between concentrations of PM10 and chemical formation of HONO suggested that heterogeneous reactions of NO₂ on surfaces of soot aggregate could be a key source of HONO in the heavy traffic areas of Beijing during the night and should be considered in air quality simulations for such areas.     

A case study of biomass burning and its smoke dispersion to Buenos Aires City, Argentina

In February and March 2000, several uncontrolled forest and grassland fires occurred in the municipalities of Campana and Zarate (100 km north of Buenos Aires, Argentina). The biomass burning emitted a large amount of smoke particulates, which caused dense fog and visibility impairment in the nearby area. From 18 to 19 March, the smoke was transported towards the Buenos Aires Metropolitan Area (BAMA), resulting in a prolonged reduction of visibility. This feature was supported by a build-up of the Aerosol Optical Thickness (AOT) and deposited particulate matter mass observed in BAMA. This paper examines the prevailing meteorological situation that produced the smoke transport towards BAMA. An anticyclone, displaced easterly over the interest area by a frontal low-pressure system, produced low-level ventilation conditions that favoured the transport and the smoke persistence in BAMA. The transport of particles and the behaviour of their normalised concentrations were simulated adequately by a regional dispersion model.     

Trend analysis of urban NO2 concentrations and the importance of direct NO2 emissions versus ozone/NOx equilibrium

The annual air quality standard of NO₂ is often exceeded in urban areas near heavy traffic locations. Despite significant decrease of NO_x emissions in 1986–2005 in the industrial and harbour area near Rotterdam, NO₂ concentrations at the urban background remain at the same level since the end of the nineties. Trend analysis of monitoring data revealed that the ozone/NO_x equilibrium is a more important factor than increasing direct NO₂ emissions by traffic. The latter has recently been identified as an additional NO₂ source due to the introduction of oxy-catalytic converters in diesel vehicles and the growing number of diesel vehicles. However, in Rotterdam over the period 1986–2005 direct NO₂ emissions by road traffic only increased 3–4%. Due to the importance of the ozone/NO_x equilibrium, it is concluded that local NO_x emissions in Rotterdam need substantial reduction to achieve lower NO₂ urban background levels. This is a relatively costly abatement strategy and, therefore, a “hotspot” approach aiming at reducing NO_x emissions by local traffic measures is more effective to meet European air quality standards.     

Two-days ahead prediction of daily maximum concentrations of SO2, O3, PM10, NO2, CO in the urban area of Palermo,Italy

Artificial neural networks are functional alternative techniques in modelling the intricate vehicular exhaust emission dispersion phenomenon. Pollutant predictions are notoriously complex when using either deterministic or stochastic models, which explains why this model was developed using a neural network. Neural networks have the ability to learn about non-linear relationships between the used variables. In this paper a recurrent neural network (Elman model) based forecaster for the prediction of daily maximum concentrations of SO₂, O₃, PM10, NO₂, CO in the city of Palermo is proposed. The effectiveness of the presented forecaster was tested using a time series recorded between 1 January 2003 to 31 December 2004 in eight monitoring stations in urban area of Palermo (Italy). Experimental trials show that the developed and tuned model is appropriate, giving small values of root mean square error (RMSE) , mean absolute error (MAE) and mean square error (MSE). In addition, the related correlation coefficient ranges from 0.72 to 0.97 for each forecasted pollutant, underlying a small difference between the forecasted and the measured values. The above results make the proposed forecaster a powerful tool for pollution management systems.     

Surface ozone and NOx concentrations at a high altitude Mediterranean site,Greece

Ozone was measured in six- and NO_x in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO^′_x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO^′_x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe.     

Neural network modelling and prediction of hourly NOx and NO2 concentrations in urban air in London

Multilayer perceptron (MLP) neural networks were trained to model hourly NO_x and NO₂ pollutant concentrations in Central London from basic hourly meteorological data. Results have shown that the models perform well when compared to previous attempts to model the same pollutants using regression based models. This work also illustrates that MLP neural networks are capable of resolving complex patterns of source emissions without any explicit external guidance.     

Large eddy simulation of shading effects on NO2 and O3 concentrations within an idealised street canyon

A large eddy simulation (LES) model that accounts for chemical reactions between oxides of nitrogen and ozone has been used to investigate the effect of local shading within an idealised street canyon on pollutant concentrations. It has shown that local shading can have a substantial impact on kerbside concentrations (>6 ppb difference for some situations presented) and that this may need to be taken into account to set up numerical model runs as well as sampling sites. A sensitivity study has been performed to investigate the effect of various governing parameters. A strong influence was found for the actual reduction of the photolytic rate constant within the shaded areas. A near linear relationship appeared between the reduction and the effect on pollutant concentrations. The chemical regime above and within the street canyon (determined by background concentrations aloft and emission rates at the ground) was also shown to be of high importance. The geometrical layout of the shading within the canyon and the wind speed in the canyon was shown to affect the spatial distribution of the shading effect rather than its overall magnitude.     

臭氧定量氧化联合湿法吸收同时脱硫脱硝

采用臭氧定量氧化NO,并结合湿法吸收进行脱硫脱硝实验研究。吸收实验选取3种常见碱性吸收液,采用鼓泡法进行NOx脱除效果对比,最终选定0.05 mol·L-1的Ca（OH）2乳浊液为吸收液。考察了NO和NO2不同配比下的吸收效果,当氧化度为60%（NO2/NO物质的量比1.3）时,吸收效果最佳。臭氧氧化实验结果表明,O3/NO物质的量比为0.6时能达到最佳氧化度,碱液吸收NOx脱除效率能达到76%,SO2脱除效率达100%。当改进鼓泡方式后,最佳氧化度条件下NOx脱除效率提高到85%。碱液pH对该法脱硝效率有影响,SO2的存在对NOx的脱除有一定促进作用。     

Prediction of NO and NO2 concentrations near a street with heavy traffic in Santiago,Chile

Based on NO concentrations and meteorological variables recorded hourly at a point close to an avenue with heavy traffic in the city of Santiago, we are able to build a simple model that allows prediction of NO concentrations several hours in advance. Predicted NO concentrations in conjunction with forecasted meteorological data may be used to predict NO₂ concentrations with reasonable accuracy. We compare predictions generated using persistence, linear regressions and multi layer neural networks.     

Absorption cross-sections of atmospheric constituents: NO2, O2, and H2O

Absorption spectroscopy, which is widely used for concentration measurements of tropospheric and stratospheric compounds, requires precise values of the absorption cross-sections of the measured species. NO₂, O₂ and its collision-induced absorption spectrum, and H₂O absorption cross-sections have been measured at temperature and pressure conditions prevailing in the Earth’s atmosphere. Corrections to the generally accepted analysis procedures used to resolve the convolution problem are also proposed.     

2015年南京市SO2、NO2、CO和O3的污染特征分析

分析了2015年南京市二氧化硫（SO2）、二氧化氮（NO2）、一氧化碳（CO）和臭氧（O3）的污染特征。南京市SO2、NO2、CO和O3的年均浓度分别为19.3 μg·m-3、50.2 μg·m-3、0.972 mg·m-3和114 μg·m-3;SO2和CO污染相对较轻,NO2和O3污染相对严重。SO2、CO和O3的日变化呈"单峰型",而NO2的呈"双峰型";SO2、NO2和CO浓度在冬季最高,夏季最低,而O3相反。秸秆焚烧产物的区域输送在夏收（6月）和秋收（11月）时节对南京市CO的贡献显著。各监测点及全市的气态污染物普遍表现出"反周末效应",指示外来污染源。     

The oxidation of SO2 on carbon particles in the presence of O3, NO2 and N2O

The oxidation of SO₂ on carbon particles at 65 % relative humidity (RH) by O₃, NO₂ and N₂O was investigated gravimetrically and compared with oxidation by air. Approximately 1 mg samples of carbon black were exposed to continuously flowing mixtures of SO₂, SO₂ + O₃, SO₂ + NO₂, and SO₂ + N₂O in air (or in N₂). Both O₃ and NO₂ in the 0.07–10ppmv range with 20–40ppmv SO₂ were found to produce sorption and desorption coverages significantly higher than those for corresponding SO₂ in air exposures. N₂O was determined to be much less effective as an oxidant than O₃ or NO₂. Identical concentrations of O₃ or NO₂ were found to produce equivalent conversions of SO₂ to sulfate on carbon for equal exposure times. Wet chemical analysis of the residue following desorption indicated that sulfate generally accounted for well over half of the retained weight.Exposure at low concentrations (0.10 ppmv SO₂ + 0.02 ppmv O₃ or NO₂), however, appeared to produce little, if any, enhancement in SO₂ transformation when compared with equivalent SO₂ in air. Weight retentions for these runs were very small, however, and measurement errors of up to 25% would be anticipated.     

UV Fourier transform measurements of tropospheric O3, NO2, SO2, benzene, and toluene.

Using the differential optical absorption spectroscopy (DOAS) technique and a Fourier transform spectrometer, NO2, SO2, O3, benzene. and toluene were measured during three measurement campaigns held in Brussels in 1995, 1996, and 1997. The O3 concentrations could be explained as the results of the local photochemistry and the dynamical properties of the mixing layer. NO2 concentrations were anti-correlated to the O3 concentrations, as expected. SO2 also showed a pronounced dependence on car traffic. Average benzene and toluene concentrations were, respectively 1.7 ppb and between 4.4 and 6.6 pbb, but high values of toluene up to 98.8 ppb were observed. SO2 concentrations and to a lesser extent, those of NO2 and 03, were dependent on the wind direction. Ozone in Brussels has been found to be influenced by the meteorological conditions prevailing in central Europe. Comparisons with other measurements have shown that 03 and SO2 data are in general in good agreement, but our NO2 concentrations seem to be generally higher.     

Aircraft measurements of O3, NOx,CO, VOCs,and SO2 in the Yangtze River Delta region

In this study, air pollutants, including ozone (O₃), nitrogen oxides (NO_x = NO + NO₂), carbon monoxides (CO), sulfur dioxide (SO₂), and volatile organic compounds (VOCs) measured in the Yangtze River Delta (YRD) region during several air flights between September/30 and October/11 are analyzed. This measurement provides horizontal and vertical distributions of air pollutants in the YRD region. The analysis of the result shows that the measured O₃ concentrations range from 20 to 60 ppbv. These values are generally below the US national standard (84 ppbv), suggesting that at the present, the O₃ pollutions are modest in this region. The NO_x concentrations have strong spatial and temporal variations, ranging from 3 to 40 ppbv. The SO₂ concentrations also have large spatial and temporal variations, ranging from 1 to 35 ppbv. The high concentrations of CO are measured with small variations, ranging from 3 to 7 ppmv. The concentrations of VOCs are relatively low, with the total VOC concentrations of less than 6 ppbv. The relative small VOC concentrations and the relative large NO_x concentrations suggest that the O₃ chemical formation is under a strong VOC-limited regime in the YRD region. The measured O₃ and NO_x concentrations are strongly anti-correlated, indicating that enhancement in NO_x concentrations leads to decrease in O₃ concentrations. Moreover, the O₃ concentrations are more sensitive to NO_x concentrations in the rural region than in the city region. The ratios of Δ[O₃]/Δ[NO_x] are ?2.3 and ?0.25 in the rural and in the city region, respectively. In addition, the measured NO_x and SO₂ concentrations are strongly correlated, highlighting that the NO_x and SO₂ are probably originated from same emission sources. Because SO₂ emissions are significantly originated from coal burnings, the strong correlation between SO₂ and NO_x concentrations suggests that the NO_x emission sources are mostly from coal burned sources. As a result, the future automobile increases could lead to rapid enhancements in O₃ concentrations in the YRD region.     

Fe/Ga2O3-Al2O3催化甲烷还原NO的性能

以甲烷为还原剂的选择性催化脱硝技术(SCR-CH_4)是一种很有潜力的新的脱硝方法,但催化剂的催化活性比较低。为了提高催化剂的活性以及抗水能力,可使用Fe对Al_2O_3负载的Ga_2O_3催化剂进行改性。采用共沉淀法,制备了xFe/Ga_2O_3-Al_2O_3催化剂,在固定床反应器中测试其选择性催化CH_4还原NO的性能。使用XRD、N_2吸附脱附、XPS、H_2-TPR、Py-IR等方法进行表征。结果表明:经过Fe改性后的催化剂提高了中高温的催化活性,提高了催化剂的N_2选择性,并改善了催化剂的抗水特性;5Fe/Ga_2O_3-Al_2O_3催化剂在500℃、富氧条件下,达到76%的NO转化率和100%的N_2选择性;在5%水蒸气条件下,5Fe/Ga_2O_3-Al_2O_3在500℃仍保持60%以上的NO转化率。N_2吸附脱附结果显示,引入Fe后,催化剂保持了原有比表面积,并且大大增加了催化剂孔径,可提高催化剂抗水能力。XPS与UV-vis显示,5Fe/Ga_2O_3-Al_2O_3具有高含量的游离态Fe~(3+),可提高催化剂的中高温活性。H2-TPR结果显示,Fe的引入提高了催化剂氧化还原能力,增强了原有Ga_2O_3-Al_2O_3中高温的还原活性。Py-FT-IR结果显示,催化剂表面同时存在Lewis酸和Br?nsted酸,铁的引入增加了催化剂表面的Lewis酸量。因此,Fe修饰Ga_2O_3-Al_2O_3是提高Ga_2O_3-Al_2O_3催化剂的SCR-CH_4脱硝性能的有效方法。     

Analysis and fit of surface CO2 concentrations at a rural site

Purpose

The impact of CO₂ urban plume in a rural area was investigated by concentrations recorded near surface.

Methods

CO₂ dry concentrations at three levels near surface were recorded for about 8 months at a rural site. Daily cycles were obtained and directional analysis was made with percentiles. Several functions were used to fit background and plume concentrations and the goodness of fit was evaluated with different statistics, which were also compared.

Results

Daily cycle showed a difference of around 2 ppm during the night between the lowest (1.8 m) and the highest (8.3 m) levels. Weighting functions of the directional analysis revealed the influence of the Valladolid urban plume. Two regions were established, with local factors prevailing below 3 m?s^?1 and transport dominating above 6 m?s^?1. The best fit was achieved with a quadratic function for the background and a cubic function for the plume due to the lack of symmetry observed. Gamma and Weibull distributions were also successfully used. Some statistics, such as the root mean square error (RMSE), stood out when evaluating the goodness of fit, whilst others were discarded due to their extremely low values and the lack of sensitivity against the functions used. Finally, a comprehensive metric merging several statistics was also tested with slight differences against RMSE.