The rise of low-cost sensing for managing air pollution in cities
01 Feb 2015-
TL;DR: In this article, the authors illustrate the drivers behind current rises in the use of low-cost sensors for air pollution management in cities, whilst addressing the major challenges for their effective implementation.
Abstract: Ever growing populations in cities are associated with a major increase in road vehicles and air pollution. The overall high levels of urban air pollution have been shown to be of a significant risk to city dwellers. However, the impacts of very high but temporally and spatially restricted pollution, and thus exposure, are still poorly understood. Conventional approaches to air quality monitoring are based on networks of static and sparse measurement stations. However, these are prohibitively expensive to capture tempo-spatial heterogeneity and identify pollution hotspots, which is required for the development of robust real-time strategies for exposure control. Current progress in developing low-cost micro-scale sensing technology is radically changing the conventional approach to allow real-time information in a capillary form. But the question remains whether there is value in the less accurate data they generate. This article illustrates the drivers behind current rises in the use of low-cost sensors for air pollution management in cities, whilst addressing the major challenges for their effective implementation.
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Queensland University of Technology1, Norwegian Institute for Air Research2, United States Environmental Protection Agency3, University of Surrey4, Hong Kong University of Science and Technology5, Hong Kong Environmental Protection Department6, City University of Hong Kong7, Curtin University8, Southern Cross University9
TL;DR: In this article, the authors conducted a comprehensive literature search including both the scientific and grey literature, and concluded that there is no clear answer to the question, due to a lack of: sensor/monitor manufacturers' quantitative specifications of performance, consensus regarding recommended end-use and associated minimal performance targets of these technologies, and the ability of the prospective users to formulate the requirements for their applications, or conditions of the intended use.
Abstract: Over the past decade, a range of sensor technologies became available on the market, enabling a revolutionary shift in air pollution monitoring and assessment. With their cost of up to three orders of magnitude lower than standard/reference instruments, many avenues for applications have opened up. In particular, broader participation in air quality discussion and utilisation of information on air pollution by communities has become possible. However, many questions have been also asked about the actual benefits of these technologies. To address this issue, we conducted a comprehensive literature search including both the scientific and grey literature. We focused upon two questions: (1) Are these technologies fit for the various purposes envisaged? and (2) How far have these technologies and their applications progressed to provide answers and solutions? Regarding the former, we concluded that there is no clear answer to the question, due to a lack of: sensor/monitor manufacturers' quantitative specifications of performance, consensus regarding recommended end-use and associated minimal performance targets of these technologies, and the ability of the prospective users to formulate the requirements for their applications, or conditions of the intended use. Numerous studies have assessed and reported sensor/monitor performance under a range of specific conditions, and in many cases the performance was concluded to be satisfactory. The specific use cases for sensors/monitors included outdoor in a stationary mode, outdoor in a mobile mode, indoor environments and personal monitoring. Under certain conditions of application, project goals, and monitoring environments, some sensors/monitors were fit for a specific purpose. Based on analysis of 17 large projects, which reached applied outcome stage, and typically conducted by consortia of organizations, we observed that a sizable fraction of them (~ 30%) were commercial and/or crowd-funded. This fact by itself signals a paradigm change in air quality monitoring, which previously had been primarily implemented by government organizations. An additional paradigm-shift indicator is the growing use of machine learning or other advanced data processing approaches to improve sensor/monitor agreement with reference monitors. There is still some way to go in enhancing application of the technologies for source apportionment, which is of particular necessity and urgency in developing countries. Also, there has been somewhat less progress in wide-scale monitoring of personal exposures. However, it can be argued that with a significant future expansion of monitoring networks, including indoor environments, there may be less need for wearable or portable sensors/monitors to assess personal exposure. Traditional personal monitoring would still be valuable where spatial variability of pollutants of interest is at a finer resolution than the monitoring network can resolve.
138 citations
Journal Article•
TL;DR: Forouzanfar et al. as discussed by the authors provide a review of the new air pollution sensing methods to determine indoor air quality and discuss how real-time sensing could bring a paradigm shift in controlling the concentration of key air pollutants in billions of urban houses worldwide.
Abstract: Household air pollution is ranked the 9th largest Global Burden of Disease risk (Forouzanfar et al., The Lancet 2015). People, particularly urban dwellers, typically spend over 90% of their daily time indoors, where levels of air pollution often surpass those of outdoor environments. Indoor air quality (IAQ) standards and approaches for assessment and control of indoor air require measurements of pollutant concentrations and thermal comfort using conventional instruments. However, the outcomes of such measurements are usually averages over long integrated time periods, which become available after the exposure has already occurred. Moreover, conventional monitoring is generally incapable of addressing temporal and spatial heterogeneity of indoor air pollution, or providing information on peak exposures that occur when specific indoor sources are in operation. This article provides a review of the new air pollution sensing methods to determine IAQ and discusses how real-time sensing could bring a paradigm shift in controlling the concentration of key air pollutants in billions of urban houses worldwide. However, we also show that besides the opportunities, challenges still remain in terms of maturing technologies, or data mining and their interpretation. Moreover, we discuss further research and essential development needed to close gaps between what is available today and needed tomorrow. In particular, we demonstrate that awareness of IAQ risks and availability of appropriate regulation are lagging behind the technologies.
68 citations
TL;DR: This article summarizes the existing studies on the state-of-the-art of LCS for AQM, and conceptualizes a step by step procedure to establish a sustainable AQM setup with LCS that can produce reliable data.
Abstract: Low-cost sensors (LCS) are becoming popular for air quality monitoring (AQM). They promise high spatial and temporal resolutions at low-cost. In addition, citizen science applications such as personal exposure monitoring can be implemented effortlessly. However, the reliability of the data is questionable due to various error sources involved in the LCS measurement. Furthermore, sensor performance drift over time is another issue. Hence, the adoption of LCS by regulatory agencies is still evolving. Several studies have been conducted to improve the performance of low-cost sensors. This article summarizes the existing studies on the state-of-the-art of LCS for AQM. We conceptualize a step by step procedure to establish a sustainable AQM setup with LCS that can produce reliable data. The selection of sensors, calibration and evaluation, hardware setup, evaluation metrics and inferences, and end user-specific applications are various stages in the LCS-based AQM setup we propose. We present a critical analysis at every step of the AQM setup to obtain reliable data from the low-cost measurement. Finally, we conclude this study with future scope to improve the availability of air quality data.
33 citations
01 Jan 2014
TL;DR: In this paper, the authors reviewed some fundamental drivers of UFP emissions and dispersion, and highlighted unresolved challenges, as well as recommendations to ensure sustainable urban development whilst minimising any possible adverse health impacts.
Abstract: Ultrafine particles (UFP; diameter less than 100 nm) are ubiquitous in urban air, and an acknowledged risk to human health. Globally, the major source for urban outdoor UFP concentrations is motor traffic. Ongoing trends towards urbanisation and expansion of road traffic are anticipated to further increase population exposure to UFPs. Numerous experimental studies have characterised UFPs in individual cities, but an integrated evaluation of emissions and population exposure is still lacking. Our analysis suggest that average exposure to outdoor UFPs in Asian cities is about four-times larger than those in European cities but impacts on human health are largely unknown. This article reviews some fundamental drivers of UFP emissions and dispersion, and highlights unresolved challenges, as well as recommendations to ensure sustainable urban development whilst minimising any possible adverse health impacts.
32 citations
01 Jun 2016
TL;DR: In this paper, a taxi fleet of over 15,000 vehicles was analyzed with the aim of predicting air pollution emissions for Singapore, and the results showed that highly localized areas of elevated emissions levels were identified, with a spatio-temporal precision not possible with previously used methods for estimating emissions.
Abstract: Air pollution related to traffic emissions pose an especially significant problem in cities; this is due to its adverse impact on human health and well-being. Previous studies which have aimed to quantify emissions from the transportation sector have been limited by either simulated or coarsely resolved traffic volume data. Emissions inventories form the basis of urban pollution models, therefore in this study, Global Positioning System (GPS) trajectory data from a taxi fleet of over 15,000 vehicles were analyzed with the aim of predicting air pollution emissions for Singapore. This novel approach enabled the quantification of instantaneous drive cycle parameters in high spatio-temporal resolution, which provided the basis for a microscopic emissions model. Carbon dioxide (CO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and particulate matter (PM) emissions were thus estimated. Highly localized areas of elevated emissions levels were identified, with a spatio-temporal precision not possible with previously used methods for estimating emissions. Relatively higher emissions areas were mainly concentrated in a few districts that were the Singapore Downtown Core area, to the north of the central urban region and to the east of it. Daily emissions quantified for the total motor vehicle population of Singapore were found to be comparable to another emissions dataset. Results demonstrated that high-resolution spatio-temporal vehicle traces detected using GPS in large taxi fleets could be used to infer highly localized areas of elevated acceleration and air pollution emissions in cities, and may become a complement to traditional emission estimates, especially in emerging cities and countries where reliable fine-grained urban air quality data is not easily available. This is the first study of its kind to investigate measured microscopic vehicle movement in tandem with microscopic emissions modeling for a substantial study domain.
21 citations
References
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TL;DR: It is shown how measuring the impedance of CNT-based gas sensors at different frequencies, it is possible to evaluate sensitivity coefficient for the immediate compensation of moisture content in the air, while still preserving in the considered ranges average sensitivities.
Abstract: Solid-state gas sensors are a cost-effective and well-spread alternative to conventional gas sensing, employable in most environments, ranging from homes and offices to harsh industrial scenarios. ...
19 citations
TL;DR: In this paper, the authors used low-cost, low-maintenance portable air quality monitors, specifically the Dylos 1700, to observe potential pollution sources and urban PM 2.5 levels in Gabon, a country in the region of Central Africa where no air quality data existed prior.
Abstract: A problem in many cities in sub-Saharan Africa (SSA) is the absence of air quality monitoring due to the high costs and technical expertise often required. We circumvent these issues by using low-cost, low-maintenance, portable air quality monitors, specifically the Dylos 1700, to observe potential pollution sources and urban PM 2.5 levels in Gabon, a country in the region of Central Africa where no air quality data existed prior. Our study occurred during the dry season between June 29 and July 24, 2015 in Libreville and Port Gentil, the two largest cities in Gabon. We collaborate with local students and government employees to gather data on PM2.5 and pollution sources in a high- and low-income neighborhood and explore differences in exposure by socioeconomic status. Due to possible biases from using the Dylos 1700, we are careful to interpret the quantitative size of these effects or differences and instead focus on their qualitative implications. We find worse air quality levels in the low-income neighborhood and substantial neighborhood variation in PM2.5 associated with traffic in low-income areas, which is in agreement with previous work in SSA. Finally, we provide anecdotal evidence that our monitoring approach and resulting data initiated interest and conversations around PM2.5, its sources and impacts at the local and national level. This suggests that low-cost pollution monitors could be a reasonable intermediary solution and educational tool to collecting air quality information in low- and middle-income countries in SSA where no data exist.
19 citations
TL;DR: A sensor array composed of two RTILs and two conventional films was found to improve the Wilks lambda separation for the tested gases two orders of magnitude compared to theWilks lambda using only a conventional films array.
Abstract: Twenty-eight quartz crystal microbalance (QCM) sensors coated with different sensing films were tested and analyzed in this work; twenty-three sensors were coated in different room temperature ionic liquids (RTILs) and five additional QCM sensors were coated with conventional films commonly used as stationary phases in gas chromatography. Four volatile organic compounds (VOCs), in gaseous phase—hexanol, butyl acetate, 2-hexanone, and hexanoic acid—were measured. Two transducer mechanisms were used; resonant frequency shift and resistance shift of a QCM Mason equivalent circuit. The sensors were characterized by their sensitivity to the VOCs and their discrimination power of the four VOCs. The highest separation among VOCs was obtained when frequency and resistance information of both RTIL and conventional films was used, a sensor array composed by two RTILs (1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide and 1-hexyl-3-methylimidazolium hexafluorophosphate) and two conventional films (tricresyl phosphate and apiezon-L) was found to improve the Wilks lambda separation for the tested gases two orders of magnitude compared to the Wilks lambda using only a conventional films array.
18 citations
TL;DR: In this article, the authors presented a crowdsourced sampling campaign and strategies for method selection for 100m scale PM 2.5 mapping in an intra-urban area of China, and three extensively employed modelling methods (ordinary kriging, OK; land use regression, LUR; and regression krigeling, RK) were adopted to evaluate the performance.
Abstract: . Fine particulate matter (PM 2.5 ) is of great concern to the
public due to its significant risk to human health. Numerous methods have
been developed to estimate spatial PM 2.5 concentrations in unobserved
locations due to the sparse number of fixed monitoring stations. Due to an
increase in low-cost sensing for air pollution monitoring, crowdsourced
monitoring of exposure control has been gradually introduced into cities.
However, the optimal mapping method for conventional sparse fixed
measurements may not be suitable for this new high-density monitoring
approach. This study presents a crowdsourced sampling campaign and strategies
of method selection for 100 m scale PM 2.5 mapping in an
intra-urban area of China. During this process, PM 2.5 concentrations
were measured by laser air quality monitors through a group of volunteers
during two 5 h periods. Three extensively employed modelling methods
(ordinary kriging, OK; land use regression, LUR; and regression kriging,
RK) were adopted to evaluate the performance. An interesting finding is that
PM 2.5 concentrations in micro-environments varied in the intra-urban
area. These local PM 2.5 variations can be easily identified by
crowdsourced sampling rather than national air quality monitoring stations.
The selection of models for fine-scale PM 2.5 concentration mapping
should be adjusted according to the changing sampling and pollution
circumstances. During this project, OK interpolation performs best in
conditions with non-peak traffic situations during a lightly polluted period
(holdout validation R2 : 0.47–0.82), while the RK modelling can perform
better during the heavily polluted period (0.32–0.68) and in conditions with
peak traffic and relatively few sampling sites (fewer than ∼100 ) during the lightly polluted period (0.40–0.69). Additionally, the LUR
model demonstrates limited ability in estimating PM 2.5 concentrations on
very fine spatial and temporal scales in this study (0.04–0.55), which
challenges the traditional point about the good performance of the LUR model
for air pollution mapping. This method selection strategy provides empirical
evidence for the best method selection for PM 2.5 mapping using
crowdsourced monitoring, and this provides a promising way to reduce the
exposure risks for individuals in their daily life.
18 citations
ENEA1
TL;DR: This chapter reviews the air quality sensors distributed in urban areas for wireless node network applications at the current state of art and describes the existing worldwide-operated wireless sensor networks with emphasis to the data quality objectives.
Abstract: This chapter reviews the air quality sensors distributed in urban areas for wireless node network applications at the current state of art. The functional materials such as metal oxides, carbon nanomaterials, and hybrid composites are enabling technologies for chemical sensing. Low-cost sensors integrated in low-power sensor systems are operated in wireless sensor networks for urban air quality monitoring of toxic gases and particulate matter at outdoor level with high spatial and temporal resolution. Examples of stationary sensor networks and mobile sensing on ground vehicles and unmanned aerial vehicles (UAV) are presented in terms of smart and sustainable cities and Internet-of-Things (IoT) applications as supplement of the expensive air quality monitoring stations. The air quality sensor performance of the existing worldwide-operated wireless sensor networks is described with emphasis to the data quality objectives. The article concludes on challenging applications and promising perspectives of the air quality sensors in the rapidly emerging fields.
18 citations