Atmospheric Pollution Monitoring Research Articles

Improvement in lifetime of pseudo-Schottky diode sensor: Towards selective detection of O 3 in a gaseous mixture (O 3, NO 2)

This article concerns a pseudo-Schottky diode Palladium/Indium-Phosphide (Pd–InP) gas sensor. The catalytic activity of such a palladium layer coupled with a pseudo-Schottky structure enables the measurement of very low concentrations of two highly oxidant gases: nitrogen dioxide (NO 2) and ozone (O 3). The submission of the sensor to long O 3 exposures leads to a degradation of its sensor characteristics (response time, recovery time and sensitivity) due to oxidation of the palladium metallization by O 3. Therefore, to improve sensor lifetime and reduce drift, a methodology based on cyclic regeneration of the sensor's palladium surface (carbon monoxide (CO) reduction associated with thermal treatment) has been developed. The pseudo-Schottky gas sensor associated with this methodology exhibits reproducible responses, significant resolution and real time detection in the range of 20–100 ppb for NO 2 and O 3. Moreover, a sensor exposed to 20 ppb of O 3 presented twice the response of the same sensor exposed to 100 ppb of NO 2 (10.5 nA for 6.5 nA). Selectivity towards O 3, with this methodology, is demonstrated in the case of atmospheric pollution monitoring.

Online vehicle and atmospheric pollution monitoring using GIS and wireless sensor networks

A Geographical Information System (GIS) is a computer system designed to integrate, store, edit, analyse, share and display geographically referenced data. A wireless sensor network (WSN) is a wireless network of spatially distributed autonomous devices using sensors to monitor physical or environmental conditions. This paper presents the integration of these two technologies to create a system able to detect measure and transmit information regarding the presence and quantities of internal combustion derived pollution and the geographical location in real time with the aim of creating pollution maps in urban environments.

Retrieval And Monitoring of Atmospheric Trace Gas Concentrations in Nadir and Limb Geometry Using the Space-Borne Sciamachy Instrument

The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) onboard the European Envisat spacecraft performs continuous spectral observations of reflected, scattered and transmitted sunlight in various observation geometries. A unique feature of SCIAMACHY is the capability of probing the atmosphere in three different observation geometries:The nadir, limb, and occultation measurement modes. In nadir mode, column densities of trace gases are retrieved with a spatial resolution of typically 30 x 60 km using the Differential Optical Absorption Spectroscopy (DOAS) technique (Platt and Perner, 1983). Alternating with the nadir measurement, vertical profiles of absorber concentration in the stratosphere are derived in limb and occultation. In this paper we present an overview over some applications of SCIAMACHY data in space-based monitoring of atmospheric pollution. The DOAS algorithms for the retrieval of total column amounts from nadir spectra are briefly described and case studies of pollution events are presented. We also illustrate the technique used to derive stratospheric concentration profiles from limb observations and show comparisons with other remote sensing systems. Special emphasis will be given to techniques, which take advantage of SCIAMACHY's different viewing geometries. In particular, we will discuss the potential and limits of strategies to infer tropospheric abundances of O3 and NO2.

Spatial distribution and seasonal variations of polycyclic aromatic hydrocarbons (PAHs) using semi-permeable membrane devices (SPMD) and pine needles in the Pearl River Delta, South China

Semi-permeable membrane devices (SPMDs) were deployed at 12 sites in the Pearl River Delta (PRD) during 2001–2002 to elucidate the spatial distribution and seasonal variations of polycyclic aromatic hydrocarbons (PAHs) in the subtropical region. Pine needles from the same sites were also analyzed for PAHs for a comparison with SPMDs. In Guangzhou, high volume active air sampling (HiVol) was carried out weekly through out the year-round sampling campaign. The PAHs sequestered in SPMDs (in ng SPMD −1 day −1) were found to be higher in winter than in summer. Using the HiVol data, SPMD sampling rates were calculated seasonally for some dominant gas-phase PAH compounds (Fluorene to Pyrene). These sampling rates ranged from 0.7 to 2.8 m 3 day −1, which were used to determine the atmospheric PAH concentrations at other sites. The calculated PAH concentrations, based on different temperature-dependant SPMD sampling rates, in the air were higher in summer than in winter. The PAH compounds sampled with SPMDs and pine needle were mainly associated with gaseous PAHs, while pine needles accumulated more high molecular weight (HW) PAHs. Good agreements were found in the spatial distribution of atmospheric PAHs measured by SPMDs and pine needles. The potential of using SPMDs for seasonal monitoring of atmospheric organic pollutants at a regional scale was demonstrated.

Selectivity improvement of semi-conducting gas sensors by selective filter for atmospheric pollutants detection

The monitoring of atmospheric pollution using chemical gas sensors is a challenge due to the lack of selectivity of most existing devices. However, their performances can be improved using filtering films achieving the separation or the removal of some gases. This study is focused on the detection of carbon monoxide and of oxidant pollutants (nitrogen dioxide and ozone) by sensors constituted of SnO 2, or phthalocyanine compounds. Two types of filters were investigated. Filters based on MnO 2 powder are successful to remove ozone while preserving nitrogen dioxide in a large temperature range from ambient to 400 °C, but they partially convert carbon monoxide. The second type of filter constituted of indigo powder is also efficient to remove ozone without modification of nitrogen concentration at ambient. Then, these filters were associated with sensing element. MnO 2 thick films were deposited by screen-printing on SnO 2. With resulting sensors, the interference of ozone for the detection of CO or of NO 2 is reduced, but some technological problems such as adhesion of MnO 2 layer have to be solved. For phthalocyanine devices, the indigo filter placed upstream to the sensitive layer makes the sensor selective to nitrogen dioxide.

Spectroradiometric inspection of nuclear pollution in the atmosphere based on photochemical effects

Results of theoretical and experimental investigations of remote monitoring methods based on secondary radioactivity effects including anomalous gaseous fields and their emissions in optical and microwave ranges are discussed. The feasibility of remote registration of secondary emission and absorption spectra from weakly ionized regions in the atmosphere above nuclear power engineering objects, dumps, and tailings dumps of nuclear wastes are examined. Based on the literature data on the excess concentrations of aerosol and gaseous components produced in radiation fields above their background levels, the diffusion parameters of radioactive emissions in the atmosphere are evaluated. The methods under consideration are shown to be promising for ecological monitoring of atmospheric radioactive pollution. High sensitivities of these methods enable pollutants to be detected at long distances. Simultaneous use of passive and active methods gives additional information on the parameters of radioactive pollution.

Carbon Isotope Ratio Measurement on Foxtail Seed as an Environmental Index

The carbon isotope ratios in foxtail seeds, which grow well anywhere such as a residential street, roadside, empty lot, field etc., were measured by EA/IRMS (Elemental Analyzer/ Isotope Ratio Mass Spectrometer). The samplings were carried out in two ways. One set of foxtail seeds was sampled at 11 different locations to examine the effect of the traffic frequency in Daejeon and its suburbs. The other set was collected in three separate areas to examine the distance effect from the roadside. The d13C values of foxtails were increased at a distance from the center of Daejeon City. According to the results for the other set to examine the distance effect from the roadside, the d13C values of foxtails grown close to the roads were lower than those far away from the road. It means that the roadside foxtails are highly affected by automobile exhaust gases. This effect strongly decreased as the distance from the road increased, because the pollution gases by the vehicles diluted well with the air, even at 5 m from the road. We propose that these results can be used in the monitoring of the hazardous atmospheric pollutants caused by fossil fuel in addition to the monitoring of carbon dioxide.

Ammonia monitoring at trace level using photoacoustic spectroscopy in industrial and environmental applications

An ammonia traces analyser based on photoacoustic spectroscopy is described. The system uses a CO 2 laser and a properly designed resonant photoacoustic cell to achieve ammonia detection at sub-parts-per-billion (ppb) level. The instrument features unattended automatic on-line monitoring of ammonia with a detection limit of 0.1 ppb. Interferences from atmospheric CO 2 and H 2O are efficiently suppressed by a careful selection of the laser wavelength and a compensation of the water vapour signal made with a high-precision hygrometer. The cell design enables continuous measurement at high flow rates (up to 5 l/min), which guarantees a fast response time of the system for the monitoring of ammonia, a sticky polar molecule that adheres to most surfaces. Various examples of applications of the instrument in the semiconductor industry and for atmospheric pollution monitoring are presented. They demonstrate the excellent performances of the system and its suitability for these applications.

Determination of Linke turbidity factor from solar radiation measurement in northern Tunisia

The attenuation of solar radiation through a real atmosphere versus that through a clean dry atmosphere gives an indication of the atmospheric turbidity. Study of atmospheric turbidity is important in meteorology, climatology and for monitoring of atmospheric pollution. The Linke turbidity factor refers to the whole spectrum, that is, overall spectrally integrated attenuation, which includes presence of gaseous water vapour and aerosols. In this work, a procedure for calculation of Linke turbidity factor is adopted using pyrheliometric measurements in a coastal tourist location in Tunisia (Sidi Bou Saïd), during three summer months (June, July and August 1999). Real diurnal and monthly variations of the T L turbidity factor are found in the three studied months, with a maximum in August afternoon and a minimum in July morning. The increase of T L is an indication for increasing atmospheric turbidity level (pollution). The correlation between atmospheric turbidity and the local weather conditions shows that this increase is essentially due to the heavy water vapour content of maritime air masses, carried by the north-eastern winds prevalent during the afternoon. A second pollution source is the dust content of the continental air masses carried by western and southern winds prevalent in the morning. Next to this can be added the influence of traffic at rush hours and during the afternoon of summer holidays.

Optimization of the atmospheric pollution monitoring network at Santiago de Chile

Environmental pollution is a problem affecting many cities in our planet. Santiago de Chile is one with the worst indices. Because of that, local authorities implemented a few years ago an air quality monitoring network with eight monitoring stations located across the whole city. These stations continuously collect information about the presence and level of atmospheric contaminants as well as meteorological indices. As the budget for this activity is limited, to increase the monitoring network as the city grows might be an inefficient decision. To evaluate alternative decisions multiple criteria should be consider. A statistical evaluation of some low cost modifications of the network becomes a valid research topic. This paper attempts to optimize Santiago's atmospheric monitoring network by excluding the least informative stations with respect to the variables under study: carbon monoxide (CO), airborne particulate material (PM 10), ozone (O 3) and sulfur dioxide (SO 2). To accomplish this, an index of multivariate effectiveness, based on Shannon information index, is applied to that network.

Tin dioxide gas sensor as a tool for atmospheric pollution monitoring: Problems and possibilities for improvements

The monitoring of atmospheric pollution needs network of gas sensors in order to increase the number of measuring points. For this goal, tin dioxide sensors have been evaluated. Their potentials and limitations (selectivity and stability), are presented via on-site experiments of urban pollution control. The study shows that some global information indicating mainly the traffic pollution can be obtained. The general problem of long-term stability and selectivity of SnO2 sensors is discussed. Some specific solutions are proposed, for example, a chemical treatment in the case of instability due to SO2. The problem of the dual response to oxidising and reducing gases is discussed, especially in regard to CO/NO2 detection. To solve this problem, the use of active filters is proposed. For example, a thin film of rhodium deposited above the sensing material allows to filter NO2. The use of a platinum filter has also been applied to improve the selectivity for the reducing gases. The results point out the difficulty to control this type of device in thin film technology. On the contrary, with thick films obtained by screen-printing, the possibility to separate HC from VOC (CH4 from CO and C2H5OH) is demonstrated. Some preliminary results concerning the use of a MnO2 filter are also presented in order to control the ozone reaction. The possibilities offered by signal processing are finally discussed using a multi-variable approach with 90 days aged sensors. AC measurements are exploited to improve the selectivity for the oxidizing gases NO2 and O3. The results obtained with a model built with atmospheric air as carrier gas appear promising.

Nanostructured thick-film gas sensors for atmospheric pollutant monitoring: quantitative analysis on field tests

Thick-film gas sensors were fabricated by screen-printing technology starting from different nanostructured semiconducting oxide powders both n-type and p-type; ultrafine and homogeneously sized ceramic powders were prepared using chemical methods such as sol–gel techniques and thermal decomposition of heteronuclear complexes. The temporal evolution of the conductivity changes in the various semiconducting oxide thick films were studied in comparison with the concentrations of CO, NO, NO 2 and O 3 in the atmosphere as measured by the analytical equipment. An air quality control experiment in an urban area through some arrays of nanostructured thick-film sensors without an in situ calibration is described. Through the calibration performed directly in the field, one of the monitoring units by means of the conventional equipment, it was possible to evaluate the pollutants’ concentration in various points of the city. The good results obtained with this experiment allow us to consider the feasible use of the innovative station to measure the pollution due to the automotive traffic.

New Eyes for Looking Back to the Past and Thinking of the Future

While environmental pollution and destruction of nature are expanding on a global scale, it is becoming ever more important to comprehend the influence of human activities on the global environment and to consider the future. How does acid pollution caused by human activities influence the environment? When and how has it progressed, what is the situation now and how is it likely to shift in the future? Humans are creatures destined to consume energy and resources in the biosphere. Although we know that drastic and disproportionate increases in the consumption of natural and non-renewable resources have greatly altered the biosphere, reliable data on the actual levels of pollution existing in the past are scarce or lacking. Many methods involving natural or artificial materials have been used for historical monitoring, but there is still a need for new ones, which will allow us to look at the past and think of the future. The newly proposed scientific use of tree bark pockets as pollution time capsules gives us "new eyes" for historical monitoring of atmospheric pollution and changes in the global environment.

Sol-Gel Processed TiO2-Based Nano-Sized Powders for Use in Thick-Film Gas Sensors for Atmospheric Pollutant Monitoring

Sol-gel routes were used to prepare pure and 5 at% and 10 at% Ta- or Nb-dope TiO2 nano-sized powders. The thermal decomposition behaviour of the precursors was studied using simultaneous thermogravimetric and differential thermal analysis (TG/DTA). X-ray diffraction (XRD) analysis showed that the powders heated to 400°C were crystalline in the anatase TiO2 structure. The pure TiO2 powder heated to 850°C showed the rutile structure. The addition of Ta and Nb inhibited the anatase-to-rutile phase transformation up to 950–1050°C. Ta was soluble in the titania lattice up to the concentration of 10 at%, while the solubility of Nb was 5 at%. Thick films were fabricated with these powders by screen printing technology and then fired for 1 h at different temperatures in the 650–1050°C range. Scanning electron microscopy (SEM) observations showed that the anatase-to-rutile phase transformation induces a grain growth of about one order of magnitude for pure TiO2. The addition of Ta and Nb is effective to keep the TiO2 grain size at a nanometric level even at 950°C, though grain growth was observed with increasing temperature. The gas-sensitive electrical response of the thick films were tested in laboratory, in environments with CO in dry and wet air. Conductance measurements showed a good gas response only for the nanostructured titania-based films. For field tests, the prototype sensors were placed beside a conventional station for atmospheric pollutant monitoring. The electrical response of the thick films was compared with the results of the analytical instruments. The same trend was observed for both systems, demonstrating the use of gas sensors for this aim.

Array of thick film sensors for atmospheric pollutant monitoring

Chemical routes such as sol–gel techniques and thermal decomposition of heteronuclear complexes have been used to prepare nanosized powders of n-type (SnO 2, TiO 2 and In 2O 3) and p-type (LaFeO 3) semiconducting oxides. Thick film gas sensors have been fabricated using these powders, printed on laser pre-cut 96% alumina substrates, each 2×2 mm element being provided with a heater, Au interdigitated contacts and a Pt-100 resistor for controlling the operating temperature. The films have been fired at different temperatures suitable to keep the grain size at the nanometer level. Electrical responses to some major polluting gases (CO, NO, NO 2 and O 3) obtained in the field have been compared with international standard analytical techniques.

Infrared tomographic system for monitoring the two-dimensional distribution of atmospheric pollution over limited areas

The authors analyze the feasibility and performance of a particular tomographic system for atmospheric pollution monitoring over limited areas (e.g. urban areas). Such a system exploits attenuation-based infrared measurements of the average concentration of the fundamental molecular species of pollutants along rectilinear paths. First, the paper demonstrates the feasibility of an apparatus based on semiconductor infrared laser diode transmitters and passive retroreflectors, capable of measuring the average concentration of pollutants along rectilinear paths with 2 km maximum length, by exploiting their infrared absorption properties. For each gaseous species of interest, the optimal wavelength is then singled out, with the purpose of applying the derivative method for measuring the corresponding average atmospheric concentration. The optimal wavelengths are determined based on both absorption data of atmospheric components and plausible ranges of variation of their concentration. Finally, the authors present simulations carried out to evaluate the reconstruction of spatial concentration fields of several air pollutants, obtained through a tomographic inversion algorithm exploiting simultaneous attenuation measurements made along different infrared links. Two different network topologies for such measurements are considered.

Ozone measurements along vertical transects in the Alps

To investigate the vertical profiles of air pollutants in the boundary layer, aircraft and balloon-born measurements and measurements using a cable car as an instrument platform have been performed in different parts of the Alps. This on-line monitoring of atmospheric pollutants requires expensive and sophisticated techniques. In order to control ambient air quality in remote regions, where no infrastructure like power supply is available, simple instruments are required. The objective of this study, which was coordinated and evaluated by the GSF-Forschungszentrum für Umwelt und Gesundheit was first, to investigate the vertical distribution of ozone in different parts of the Alps and secondly, in addition to continuous analyser measurements, to test monitoring by means of two types of passive samplers. The selection of these samplers - one for one week use and another one for two week application - was based on a passive sampler intercomparison done in a preliminary study one year earlier.

Nano-Sized Semiconducting Oxide Powders for Thick Film Gas Sensors: From Powder Processing to Environmental Monitoring Devices

ABSTRACTThis paper reports the study of semiconducting oxides to develop gas sensors in thick-film form for use in atmospheric pollutant monitoring devices. The investigation was achieved with the following steps: selection of the suitable oxides and of their most appropriate processing method to obtain nano-sized powders, fabrication using screen-printing technology of thick-film sensors from these powders, and electrical measurements in laboratory and in the field. Chemical routes such as sol-gel techniques and thermal decomposition of heteronuclear complexes have been used to prepare nano-sized powders of n-type (TiO2) and p-type (LaFeO3 and SmFeO3) semiconducting oxides. Thick-film gas sensors have been produced by screen-printing technology. Pastes have been prepared and printed on laser precut 96% alumina substrates, each 2×2 mm element being provided with a heater, comb-type Au contacts and a Pt-100 resistor for controlling the operating temperature. The firing of the films has been performed in conditions able to keep grain size at nanometer level. Electrical responses to some major polluting gases (CO, NO, NO2 and O3) have been tested in laboratory and in the field, and compared with results of the analytical techniques approved by the international standards.

Bricks reveal recent history of heavy metal pollution in soil around a north Indian city

Up to now, geochemical monitoring of atmospheric heavy metal pollution has been limited to the use of peat, ice deposits and aquatic sediments as sample types. These systems are open, dynamic and easily affected by climatic variations. In a recent report, Shrivastav et al. (Environ Mon Ass 1996;40:271–278) have suggested the use of bricks as a geochemical monitor of heavy metal fallout and their study has clearly demonstrated the practical feasibility of the above concept at least in some parts of the world. However, more research is required in order to understand the suitability of using bricks as a geochemical monitor of heavy metal fallout. As part of our continuing research in this direction, in this article we report on the history of heavy metal pollution in the soils of Agra since 1900, that have been traced by analysing bricks of different ages collected from the old buildings/monuments. The study indicated that the soil concentrations of lead, zinc and chromium rose initially until between 1950 and 1960 and then fell sharply especially over the last 2–3 decades, which can be explained as an outcome of socio-economic fluctuations on a local scale and climatic changes on a global or regional scale.

Powerful mid-infrared light emitting diodes forpollution monitoring

Powerful mid-infrared (1.7-4.8 /spl mu/m) light emitting diodes were manufactured by liquid phase epitaxy using GaSb-InAs compounds. Their output optical power was enhanced up to 2-3.5 mW using symmetrical double heterostructures with large band offsets. These diodes can be used as narrow bandwidth emitters for cost-reduced setups for atmospheric pollution monitoring.