Ambient air pollution is dangerous for both human health and environmental sustainability. Air pollution is responsible for numerous cases of pulmonary diseases, lung cancer, heart diseases, respiratory infections, and strokes. Maternal exposure is linked to birth and development complications. In addition to the dangers of human health, many of the pollutants serve as atmospheric greenhouse gasses and contribute to climate change. Urban regions generate pollutants at a much higher density than rural regions, with major cities such as Beijing, Lahore, Jakarta, and Delhi being some of the most polluted cities in the world. Therefore, understanding the amount and distribution of pollution, often characterized as small particulates, ozone, nitrogen dioxide, and sulfur dioxide, would be integral to improving the quality of life for urban residents as well as reducing the impact on the surrounding ecosystem.
In order to assist city dwellers on the location, type, and amount of ambient pollution, I propose the implementation of a WiFi-enabled spectrophotometer. Spectrometry is a simple yet powerful tool to analyze the concentration of substances by the light they absorb. Each chemical substance reacts to different light wavelengths differently. For example, chlorophyll absorbs mostly all visible light except green, resulting in an absorption peak around 650nm. Sulfur dioxide, a by-product of burning sulfur and culprit of many respiratory diseases, has an absorption peak at 15000nm. Every chemical substance has an absorptivity fingerprint. According to Beer’s law, the absorbance of a specific light frequency passing through a substance is inversely proportional to that substance’s concentration. By measuring the change of light absorbance, we can infer a similar change in a substance’s concentration. In short, spectrophotometry allows us to measure the abundance of specific chemicals, particularly pollutants, by measuring the change of absorbance at different frequencies.
A spectrophotometer is a device that does just that. In a light protected container, a light source provides a range of light wavelengths that pass through the medium (air) and is finally absorbed by an optical instrument (a camera that can record infrared and ultraviolet light). Simple image processing can break down the recorded image into a recording of light intensity for each wavelength. Diffraction grating can scatter the light so that it aligns from smallest wavelength to longest to make readings easier.
To map the ambient pollution across a city with these devices, they would be distributed evenly across the city, equipped with a wifi shield to send image data online. The devices themselves should only process and send a raw image every half a second in order not to overburden the limited connection in many lower-income countries. An online server will then be able to calculate the absorbance from the received image and then compare that with other images over time. With the use of smoothing algorithms and a known base, key wavelengths can be monitored and compared in order to see the prevalence of specific pollutants.
In total, the sensor system would consist of the spectrophotometer— light source (full spectra LED light, $15, Walmart), diffraction grating (recycled CD, $0.5), an appropriate camera (web camera, $10, Walmart), and a circuit system that would include a power source (ideally a solar panel $30, Adafruit) and wifi shield($10 Adafruit)— and an online processing system ($65 per unit). Every tenth of a mile (100 total) would be an appropriate starting point to map out the pollution of a metropolitan area.
In mapping out ambient air pollution, not just by abundance, but by location, time, and type, people and companies will be able to make informed decisions on how to protect themselves. Areas to avoid and times to remain indoors are two such examples. In addition, city officials could learn where certain pollutants are coming from, and where air purification systems could work most efficiently. Overall, this simple yet, underappreciated technology could vastly improve the quality of life for urban areas across the globe.