Applications of low-cost sensing technologies for air quality monitoring and exposure assessment: How far have they gone?

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, rev ...

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011.

. A fast-growing area of research is the development of low-cost sensors for
measuring air pollutants. The affordability and size of low-cost particle
sensors makes them an attractive option for use in experiments requiring a
number of instruments such as high-density spatial mapping. However, for
these low-cost sensors to be useful for these types of studies their accuracy
and precision need to be quantified. We evaluated the Alphasense OPC-N2, a
promising low-cost miniature optical particle counter, for monitoring ambient
airborne particles at typical urban background sites in the UK. The precision
of the OPC-N2 was assessed by co-locating 14 instruments at a site to
investigate the variation in measured concentrations. Comparison to two
different reference optical particle counters as well as a TEOM-FDMS enabled
the accuracy of the OPC-N2 to be evaluated. Comparison of the OPC-N2 to the
reference optical instruments shows some limitations for measuring mass
concentrations of PM 1 , PM 2.5 and PM 10 . The OPC-N2 demonstrated
a significant positive artefact in measured particle mass during times of
high ambient RH (> 85 %) and a calibration factor was
developed based upon κ -Kohler theory, using average bulk particle
aerosol hygroscopicity. Application of this RH correction factor resulted in
the OPC-N2 measurements being within 33 % of the TEOM-FDMS, comparable to
the agreement between a reference optical particle counter and the TEOM-FDMS
(20 %). Inter-unit precision for the 14 OPC-N2 sensors of
22  ±  13 % for PM 10 mass concentrations was observed. Overall,
the OPC-N2 was found to accurately measure ambient airborne particle mass
concentration provided they are (i) correctly calibrated and (ii) corrected
for ambient RH. The level of precision demonstrated between multiple
OPC-N2s suggests that they would be
suitable devices for applications
where the spatial variability in particle concentration was to be determined.

/pdf/evaluation-of-a-low-cost-optical-particle-counter-alphasense-6wv5uuxg2t.pdf

Evaluation of a low-cost optical particle counter (Alphasense OPC-N2) for ambient air monitoring

. While low-cost particle sensors are increasingly being
used in numerous applications, most of them have no heater or dryer at the
inlet to remove water from the sample before measurement. Deliquescent
growth of particles and the formation of fog droplets in the atmosphere can
lead to significant increases in particle number concentration (PNC) and
mass concentrations reported by such sensors. We carried out a detailed
study using a Plantower PMS1003 low-cost particle sensor, both in the
laboratory and under actual ambient field conditions, to investigate its
response to increasing humidity and the presence of fog in the air. We found
significant increases in particle number and mass concentrations at relative
humidity above about 75 %. During a period of fog, the total PNC increased
by 28 %, while the PNC larger than 2.5  µ m increased by over 50 %.
The PM 10 concentration reported by the PMS1003 was 46 % greater than
that on the standard monitor with a charcoal dryer at the inlet. While there
is a causal link between particle pollution and adverse health effects, the
presence of water on the particles is not harmful to humans. Therefore, air
quality standards for particles are specifically limited to solid particles
and standard particle monitoring instruments are fitted with a heater or
dryer at the inlet to remove all liquid material from the sample before the
concentrations are measured. This study shows that it is important to
understand that the results provided by low-cost particle sensors, such as
the PMS1003, cannot be used to ascertain if air quality standards are being
met.

https://amt.copernicus.org/articles/11/4883/2018/amt-11-4883-2018.pdf

The influence of humidity on the performance of a low-cost air particle mass sensor and the effect of atmospheric fog

Air pollution is a major concern for public health and urban environments Conventional air pollution monitoring systems install a few highly accurate, expensive stations at representative locations Their sparse coverage and low spatial resolution are insufficient to quantify urban air pollution and its impacts on human health and environment Advances in low-cost portable air pollution sensors have enabled air pollution monitoring deployments at scale to measure air pollution at high spatiotemporal resolution However, it is challenging to ensure the accuracy of these low-cost sensor deployments because the sensors are more error-prone than high-end sensing infrastructures and they are often deployed in harsh environments Sensor calibration has proven to be effective to improve the data quality of low-cost sensors and maintain the reliability of long-term, distributed sensor deployments In this paper, we review the state-of-the-art low-cost air pollution sensors, identify their major error sources, and comprehensively survey calibration models as well as network recalibration strategies suited for different sensor deployments We also discuss limitations of exiting methods and conclude with open issues for future sensor calibration research

/pdf/a-survey-on-sensor-calibration-in-air-pollution-monitoring-dric23xjth.pdf

A Survey on Sensor Calibration in Air Pollution Monitoring Deployments

End-user perspective of low-cost sensors for outdoor air pollution monitoring.

Increasing concern regarding health effects caused by air pollution, together with the limited spatial resolution achievable with conventional monitoring stations, have driven efforts to develop inexpensive metal oxide gas sensors for air quality measurements. The sensing mechanism is dependent on physicochemical reactions between adsorbed gas molecules and oxygen species on the oxide surface, which modify the height of the grain boundary potential barrier and, thereby, the electrical resistance of the film. The sensitivity is dependent on the grain size and the influence of film structure on the electrical conductivity. A systematic study of the influence of deposition conditions on the structure of nanocrystalline metal oxide thin films was carried out in an attempt to understand its relation to the conductivity with the aim of improving the sensitivity to common pollutant gases such as nitrogen dioxide and carbon monoxide. Tin dioxide is the most commonly used material for gas sensor applications but also has the greatest cross sensitivity. Cross sensitivity can be reduced by the use of alternative materials such as zinc oxide, tungsten oxide, titanium dioxide or mixed metal oxides. Significant improvements in sensitivity and selectivity can be achieved by doping the oxide with a noble metal such as platinum or palladium to catalyse the reactions with adsorbed gas molecules. Solid state microsensors have been constructed by combining microelectronic fabrication methods with thin film technology. Detection of carbon monoxide, nitrogen oxides and benzene at environmentally relevant concentrations has been demonstrated. Integrated with signal processing and data transmission via the telecommunications infrastructure, sensor networks can provide real time information on air pollution with high spatial resolution.

Application of nanocrystalline metal oxide gas sensors for air quality monitoring

Improved water quality monitoring techniques based on biosensor, optical, microfluidic and information technologies are leading to radical changes in our ability to perceive, understand and manage the aquatic environment. There is a need for real-time environmental monitoring systems to implement and verify compliance with health and environmental legislation. To do this it is necessary to monitor a many different chemicals and toxins with simple and cost-effective techniques. Biosensor and microfluidics based systems could potentially detect and monitor all these contaminants. Current research is leading to solutions to problems that were previously irresolvable due to their high degree of complexity.

Biosensor Networks for Monitoring Water Pollution

In-situ and Remote Sensing Networks for Environmental Monitoring and Global Assessment of Leptospirosis Outbreaks

Classical air-quality modelling has been outdated. The outcomes of the several international initiatives have returned limited achievements as one can easily confirm from the reported measurements of air pollution concentrations. New cloud applications handling big data and social media allows accurate real-time geographical representation of population exposure. This work focuses on realistic utilization of photochemical air-quality data from measurements that allows a new era for regulatory applications in several geographical scales. It eliminates inherent levels of uncertainty and allows a realistic representation of atmospheric processes. Such applications can provide real-time representation of risks and permits the health impact assessment. With such data sets we could also revisits the concept when and where the emission reductions could be effective and why the dangers of exposure from urban atmospheric pollution have been over-estimated.

http://ieeexplore.ieee.org/iel7/7489933/7495297/07495466.pdf

David G. Rickerby

Papers

End-user perspective of low-cost sensors for outdoor air pollution monitoring.

Application of nanocrystalline metal oxide gas sensors for air quality monitoring

Biosensor Networks for Monitoring Water Pollution

In-situ and Remote Sensing Networks for Environmental Monitoring and Global Assessment of Leptospirosis Outbreaks

Big data for innovative air-pollution assessments in the era of verifiable regulatory decisions