BTX measurements with diffusive samplers in the vicinity of a cokery: comparison between ORSA-type samplers and pumped sampling

In the framework of new European directives in the field of ambient air quality assessment specific requirements for measurement methods for benzene will be defined and have to be met in the future. In a residential area in the vicinity of a cokery a comprehensive monitoring programme for BTX compounds (benzene, toluene, xylenes) was carried out with diffusive samplers. Measurement results from 20 sites show a distinct spatial distribution of benzene concentrations which is caused by the emissions of the plant. Comparisons with two pumped measurement methods reveal excellent agreement in the case of benzene. An assessment of measurement uncertainty for the diffusive method is presented in terms of standard deviations from parallel measurements (precision) and by comparison with a reference method according to national and international standards. Data quality objectives required by an upcoming European directive for benzene can be met by diffusive sampling.     

宁波市环境空气中VOCs污染状况及变化趋势分析

基于近7年来的连续监测数据,对宁波市环境空气中挥发性有机物(VOCs)的污染状况及变化趋势进行了初步分析。研究表明:在宁波市环境空气中检测出94种VOCs,其主要成分是饱和烷烃、芳烃、烯烃、卤代烃、卤代芳烃、含氧有机物等,有37种属有毒有害物质,其中苯系物含量最高;宁波市环境空气中苯系物的污染程度与国内外城市基本处于同一水平,近年来的污染状况变化不大,没有明显恶化;空间分布特征显示一类保护区VOCs的排放以天然源为主,二类各功能区VOCs的排放由天然源和局部人为污染源共同形成,三类区以工业污染源排放为主;时间变化趋势显示VOCs在冬季和春季的平均浓度比其他季节高,VOCs的日变化基本呈现2个主浓度峰值特征,跟城市交通流量变化具有很好相关性。     

扬州地区酸雨现状及成因分析

根据2006年1月—2010年12月的酸雨监测数据,对扬州地区酸雨的变化规律和趋势进行了统计分析。结果表明:扬州地区酸雨主要集中在扬州市区与仪征城区,"十一五"期间,扬州市区酸雨呈逐年减少趋势,仪征城区大气污染严重,降水pH年均值均小于5.6,经评价扬州市区属于非酸雨区-较重酸雨区,仪征城区属于轻酸雨区-重酸雨区。高邮、江都、宝应城区从2007年起无酸雨出现。仪征城区酸雨主要是由燃煤型和燃油型混合空气污染造成的,近年来随着机动车拥有量的迅速增加,各种机动车排放的尾气已成为形成酸雨的重要原因,应引起重视。     

Temporal and spatial variations of the quality of ambient air in the Kingdom of Bahrain during 2007

The main objective of the present investigation is to study the temporal and spatial variations of the quality of ambient air in the Kingdom of Bahrain. The non-parametric Kruskal-Wallis (KW) test showed significant spatial variations and interactions of spatial-temporal among five mobile monitoring stations for 11 air pollutants. The Mann Whitney (MW) test demonstrated the seasonality of spring over winter for the PM(10), PM(2.5), NO(2), CO and p-xylene, the seasonality of winter over spring for O(3), and no significant seasonal variation for NH(3), benzene, SO(2), toluene and H(2)S. It is concluded that emissions from automobile exhaust, industrial and developmental projects are responsible for the spatial air pollution, and that air temperature is the controlling factor for the seasonal variations.     

Monitoring of ambient BTX at Monterotondo (Rome) and indoor-outdoor evaluation in school and domestic sites

Results from a five month monitoring campaign of BTX (benzene, toluene and the sum of ethyl benzene, o-xylene, m-xylene and p-xylene), performed at Monterotondo, a little town 23 km NE of Rome, and correlation of the measured concentrations with meteorological and natural radioactivity data are presented and discussed. This campaign allowed us to extrapolate a pattern of the annual distribution of benzene in the town. A map, showing the average distribution of pollutants, is presented, as a useful tool to manage an appropriate policy of air pollution. A contemporary indoor-outdoor investigation has been performed at five homes and two classrooms of Monterotondo and at thirteen homes and thirteen classrooms in the outskirts of Rome. Non-smoking people and low polluted sites were chosen for this campaign, in order to highlight if commonly used domestic materials could act as internal sources. Data, obtained by employing long-term diffusive samplers, are compared with a parallel experiment showing the day-night indoor-outdoor trend. The obtained results, confirmed through statistical analysis of data, let us conclude that there is evidence of internal sources at homes whilst, in the schools, depletion phenomena prevail, probably due to the walls adsorption.     

Diffusive Sampling of VOCs as an Aid to Monitoring Urban Air Quality

Diffusive sampling of Volatile Organic Compounds (VOCs) onto thermal desorption tubes, followed by gas chromatography, is an established technique for area or personal monitoring of typical workplace concentrations and there has been increasing interest in extending the application to environmental levels, particularly for benzene, toluene and xylene (BTX). Diffusive sampling rates for BTX on Chromosorb 106 and Carbograph-1 (a graphitised carbon) were measured over periods of 1-4 weeks in field validation experiments using ambient air and parallel pumped sampling (the reference method) at the HSL site in central Sheffield. The reference method was also used to investigate the possible bias of an open-path spectrophotometer (OPSIS) used by Sheffield City Council. A bias for BTX was suspected from results of a two-week initial exercise in which several diffusive samplers were placed close to the light path. In the full field validation of the diffusive samplers carried out subsequently, the significant bias of BTX concentrations reported by OPSIS were confirmed when compared with concurrent results from the reference method. OPSIS gave benzene and toluene values up to eight times higher than expected from the GC measurements. Xylene discrepancies were smaller, but in one 3-day peak episode, OPSIS demonstrated a negative correlation with GC.     

基于3S技术的桂林市南溪河污染现状调查

城区小流域常是水污染较重的区域,又是污染源密集的地方,其非点源污染的监测与评估,需要实用方法。本调查基于3S技术,开展流域的监测与评价,包括空间定位的精度控制、非点源的遥感分类解译、采用排污系数对非点源污染评估、对污染源及污水管网做GIS空间分析。结合水质监测进行污径比和水环境容量的评价。重点讨论了城区人口解译方法和污染源评估方法,探讨典型城区非点源污染监测的思路。     

Spatial analysis and land use regression of VOCs and NO2 in Dallas, Texas during two seasons

Passive air sampling for nitrogen dioxide (NO(2)) and select volatile organic compounds (VOCs) was conducted at 24 fire stations and a compliance monitoring site in Dallas, Texas, USA during summer 2006 and winter 2008. This ambient air monitoring network was established to assess intra-urban gradients of air pollutants to evaluate the impact of traffic and urban emissions on air quality. Ambient air monitoring and GIS data from spatially representative fire station sites were collected to assess spatial variability. Pairwise comparisons were conducted on the ambient data from the selected sites based on city section. These weeklong samples yielded NO(2) and benzene levels that were generally higher during the winter than the summer. With respect to the location within the city, the central section of Dallas was generally higher for NO(2) and benzene than north and south. Land use regression (LUR) results revealed spatial gradients in NO(2) and selected VOCs in the central and some northern areas. The process used to select spatially representative sites for air sampling and the results of analyses of coarse- and fine-scale spatial variability of air pollutants on a seasonal basis provide insights to guide future ambient air exposure studies in assessing intra-urban gradients and traffic impacts.     

A necessary distinction between spatial representativeness of an air quality monitoring station and the delimitation of exceedance areas

The European legislation on ambient air quality introduces the concepts of spatial representativeness of a monitoring station and spatial extent of an exceedance zone. Spatial representativeness is an essential macro-scale siting criterion which should be evaluated before the setting-up and during the life of a monitoring point. As for the exceedance area, it has to be defined each time an environmental objective is exceeded in an assessment zone. No specific approach is prescribed to delimit such areas. A probabilistic methodology is presented, based on a preliminary kriging estimation of atmospheric concentrations at each point of the domain. It is applied to NO₂ pollution on the urban scale. In the proposed approach, a point belongs to the area of representativeness of a station if its concentration differs from the station measurement by less than a given threshold. To take the estimation uncertainty into account, the standard deviation of the kriging error is used in a probabilistic framework. The choice of the criteria used to deal with overlapping areas is first tested on NO₂ annual mean concentration maps of France, built by combining surface monitoring observations and outputs from the CHIMERE chemistry transport model. At the local scale, data from passive sampling surveys and high -resolution auxiliary variables are used to provide a more precise estimation of the background pollution in different French cities. The traffic-related pollution can also be accounted for in the map by additional predictors such as distance to the road, and traffic-related NO_x emissions. Similarly, the proposed approach is implemented to identify the points, at a given statistical risk, where the NO₂ concentration is above the annual limit value.     

PM2.5 and volatile organic compounds (VOCs) in ambient air: a focus on the effect of meteorology

PM(2.5) and VOCs (benzene, toluene, m-p-o-xylenes) concentrations were measured in an urban and a suburban site in Athens, Greece, during the period between April and November 2004. This period, which is considered to be the warmer period in Greece, is characterized by the development of sea-breeze over the Attica Basin. Additionally strong Northern, North-eastern winds called "The Etesians", predominate during the summer months (July-August), acting positively to the dispersion of pollutants. In this campaign, 24 days with sea-breeze development were observed, 15 days with northern winds, 6 days with southern winds while the rest of the days presented no specific wind profile. Maximum concentrations of PM(2.5), VOCs and nitrogen oxides, were detected during the days with sea-breeze, while minimum concentrations during the days with northern winds. Ozone was the only pollutant that appeared to have higher concentrations in the background site and not in the city centre, where benzene presented strong negative correlation with ozone, indicating the photochemical reaction of hydrocarbons that lead to the ozone formation. The BTX ratios were similar for both sites and wind profiles, indicating common sources for those pollutants. T/B ratio ranged in low levels, between 3-5 for site A and 2-5 for site B, suggesting vehicles emissions as the main sources of volatile compounds. Finally, the strong correlations of PM(2.5) and benzene concentrations, between the two sampling sites, indicate that both the city centre and the background site, are affected by the same sources, under common meteorological conditions (sea-breeze, northern winds).