The general public will play a vital role in helping scientists better understand how air pollution affects the environment and human health, as part of a Europe-wide photonics experiment due to begin in September.
The experiment will see thousands of people across Europe transform their mobile phones into a scientific tool – through use of an attachment and a mobile app – allowing them to measure pollutant particles in locations that have not yet been monitored with existing technologies.
The iSpex-EU project was organised by two EU organisations, Light2015 and iSpex, following an initial campaign in the Netherlands in 2013, where thousands of participants monitored Dutch air pollution using a similar method. Now Europe-wide, the experiment will run from 1 September to 15 October 2015, in major cities including Athens, Barcelona, Belgrade, Berlin, Copenhagen, London, Manchester, Milan, and Rome.
The impact of atmospheric aerosols on both human health and the environment is still poorly understood, but they can contribute to heart and respiratory disease, as well as posing a danger to air traffic and forming one of the largest uncertainties in current estimates of climate change.
Ninety per cent of atmospheric aerosols are of natural origin, which can include sea salt, mineral dust or tiny sand particles, and volcanic ash. However, the remaining 10 per cent are anthropogenic, or human-made, mainly caused by traffic, industry, and biomass burning.
For the iSpex-EU project starting in September, participants will use a device called iSpex, which consists of an add-on and corresponding app for the iPhone.
The iSpex mobile app will instruct participants to take several photos of the cloud-free sky, which will allow the iSpec add-on to obtain information on both the spectrum and the degree of linear polarisation of visible light.
The corresponding mobile app will then send all of the observations to a central database, where measurements from all over the continent will be analysed. A live map showing the results obtained from across Europe will also be constructed.
The add-on (see image 1 below) is essentially a slit spectrograph that uses a transmission grating foil and a plastic lens in addition to the lens inside the smartphone camera. It also contains a combination of stretched plastic sheets and Polaroid film to modulate every spectrum by a sine curve. The relative amplitude of this sine curve directly scales with the degree of linear polarisation, and its phase is determined by the polarisation angle. As such, all the information on both the spectrum and the linear polarisation of the light entering the slit is obtained in a single shot. The iSpex app extracts the spectral information from the polarisation information.
Image 1: The iSpex add-on. Credit: iSpex
Through this method, the degree of linear polarisation (DoLP) of the cloud-free sky can be measured as a function of wavelength and, by pointing the phone at different directions in the sky, as a function of scattering angle. This DoLP as a function of both wavelength and scattering angle yields unique information on fundamental aerosol properties, including the quantity of aerosol, as well as the particle size distribution and the chemical composition (through the refractive index).
Its measurement principles are based on the Spectropolarimeter for Planetary EXploration (SPEX), an instrument currently being developed by a Dutch team of engineers to measure aerosol and cloud particles in atmospheres of planets within our solar system.
The measurements that the public will obtain using their smartphones will be crucial in assessing the impacts of atmospheric aerosols on human health, the environment and air traffic.
The experiment also represents a new kind of science investigation, whereby citizens can contribute to answering important scientific questions by delivering measurements from almost anywhere, without the need for specialised equipment or training.
Other research institutions have proposed similar methods for involving the public in measuring air quality. In 2014, Researchers from the Karlsruhe Institute of Technology (KIT) in Germany announced that they were developing optical sensors that can be connected to a smart phone to measure the levels of dust pollution in the air.
Like the iSpex add-on, the device also works in conjunction with a mobile app, allowing users to share measurements with other participants in the same city, helping to create real-time fine dust pollution maps for different locations. At the time, the researchers proposed that the invention could be ready for use by the public in 2015.
According to the researchers, the device uses the flashlight of the smartphone camera to emit light into the measurement area, which is then scattered by dust or smoke. The camera serves as a receptor and takes a picture representing the measurement result. The brightness of the pixels can then be converted into the dust concentration.
It seems as though the decrease in cost and subsequent miniaturisation of spectral technologies are enabling a new type of 'citizen-science', whereby the public are able to carry out complex, simultaneous mass-measurements, which could potentially play an important role in scientific investigations in the future.