As the world’s population grows rapidly, many major cities are starting to feel the repercussions. The cost of living is rising, real estate prices are through the roof, and more people are being packed into smaller and smaller spaces. According to the United Nations, 68% of the global population will live in these urbanized areas by 2050, up from 55% in 2018. 

In addition to higher costs and population densities, there’s a detrimental environmental impact. Emissions from motor vehicles, heat and power generation, industrial facilities, volatile organic compounds (VOCs) from landfill sites, waste incineration, agriculture, cooking, and lighting contribute to poorer air quality. 

 

The real-time air quality index of the world's air pollution

The real-time air quality index of the world’s air pollution. Screenshot used courtesy of WAQI
 

While the World Health Organisation (WHO) has acknowledged that there has been some improvement in developed nations’ major cities, low- and middle-income cities, especially those in developing countries, are encountering worsening air pollution.

Research has proven that air pollution and mortality rates are closely linked, such as a 2014 report from Public Health England (PHE) which estimated that at least 8% of London deaths could be attributed to long-term particulate pollution. Globally, 3.8 million premature deaths are attributed to ambient air pollution, 80% of which are due to heart disease and strokes, says the WHO, and a further 20% from respiratory illnesses and cancers. 

With so many issues and known pollutants, how is the air quality in cities currently monitored?

 

Current Ways of Monitoring Air Quality

Due to the hugely detrimental impact that air quality can have on human health, it’s essential to monitor and track air quality data accurately. Monitoring air quality helps assess pollution levels relative to ambient air quality standards and regulations. Robust monitoring also protects against extreme events by alerting officials and enabling swift corrective action to be taken. 

Most traditional monitoring stations are fixed installations that are wired directly into the power grid.

 

An example of an air quality measuring system

An example of an air quality measuring system. Image used courtesy of Aeroqual
 

While they’re highly accurate, they are expensive to construct and operate because they require regular calibration and maintenance. Another drawback is with how large they are. Their size makes it challenging to build new ones in places they’re needed.

The fact that they are fixed (i.e., at the side of a busy street) means that the data collected isn’t necessarily representative of the bigger picture in terms of local air quality. This limitation increases the dependence on data modeling, which takes time and hinders accuracy. 

There’s a potential alternative, however: sensors.

 

Air-quality Sensors to the Rescue

Sensors have come a long way in recent years alongside the emergence of the Internet of Things (IoT). Sensors make up the IoT backbone, involving billions that collect, process, and communicate data in real-time across every industry.

Discrete, wireless, portable battery and self-powered sensors could be a solution for real-time, accurate air quality monitoring, central to many research applications.

 

Air Sensors in Backpacks

Cambridge University, for example, has deployed what it calls “Alphasense” sensors in the backpacks of students when they are cycling and walking. By including them within backpacks, it becomes easier to “map” air pollution across the city, with results showing areas of the city with NO2 levels almost ten times higher than what was being measured by a fixed reference station. Monitoring NO2 levels is critical since it is an air pollutant emitted by cars and gas-burning stoves that have been linked to heart disease and respiratory diseases. 

 

Multi-use Sensor With AI Processing

Research is even being conducted by Renesas, which has built a multi-purpose air quality sensor solution that measures air quality indoors, outdoors, and within refrigerators. Powered by an integrated Li-Ion battery, the sensor has a dedicated MCU for AI-backed data processing, which is sent via Bluetooth 5. 

 

A schematic of Renesas' air quality sensor.

A schematic of Renesas’ air quality sensor. Image used courtesy of Renesas
 

Smartphone Turned Gas Sensor

More recently, researchers at Berkeley Lab and UC Berkeley have developed an ultrathin (“atomically thin”) two-dimensional sensor that works at room temperature and could turn a smartphone into a gas sensor.

 

Schematic for the ultra-thin air quality sensor.

Schematic for the ultra-thin air quality sensor. Image used courtesy of Azizi et al. and UC Berkeley
 

Like the Cambridge sensor, it senses NO2. However, it is constructed from a monolayer alloy of rhenium niobium disulfide and electrically responds to NO2 molecules with minimal response to other toxic gases. In addition to being ultrathin, the sensor is both flexible and transparent. This sensor could be a potential candidate for wearable monitoring applications. 


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