Anthropogenic air pollution is arguably one of the most hazardous consequences of industrial development, posing a serious threat to both public health and the environment. According to the World Health Organisation’s (WHO) air quality model, as of 2016, 91% of the global population live in areas exceeding the ambient fine particulate matter (PM2.5) annual concentration guideline . PM2.5 (particulate matter with diameter less than 2.5 microns) pollution encompasses a range of organic and inorganic constituents and is a complex mix of materials such as sulphate, nitrates, ammonia, mineral dust, and organic and elemental carbon. Given the ubiquitous nature of PM2.5, their ability to penetrate into the lung and the vast literature demonstrating their adverse impacts on health, reducing exposure to this harmful pollutant should be a priority for individuals and governments alike.
The issue of air pollution is a “wicked problem” — complicated by incomplete knowledge, both within the scientific community and amongst various stakeholders, inclusive of industry, government, pressure groups, resulting in a variety of interests and beliefs. Given what is at stake, we simply cannot afford incremental learnings from trial and error approaches. As with many issues faced by the modern world, the basis for the degradation of global air quality is multifactorial in nature, and as a result there is no “silver bullet” solution to protect human and environmental health. Instead, a holistic approach, combining a political, technological and societal response is necessary. However, to begin improving air quality, we need not just an awareness of how we got here, but an objective, evidence-based assessment of where we are. This can be achieved by equipping ourselves with up-to-date information on pollution sources, concentrations, and impacts –and for this, air quality monitoring technologies are essential. But to what extent are such technologies the “solution to pollution?” This paper explores some of the current air pollution monitoring technologies, as well as reveals the, often overlooked (yet crucial), human, educational, and financial resources that are essential for successful air pollution monitoring. We will consider the place that personal sensors hold within the challenge of improving air quality, and in doing so, will expose some risks and unintended consequences of their use. Finally, we will argue that, while air pollution monitoring technologies are fundamental to assessing by how much air quality may change over time, the real solution to pollution is anthropogenic action: changing our habits and reforming policy, even if it makes life slightly less convenient.
Sources and Impacts of Poor Air Quality
As with its sources, the impacts of air pollution are multifactorial in nature. There are both health and environmental impacts, ranging from premature death and increased healthcare utilization, to absenteeism from work and negative impacts on crop yields and biodiversity.
The issue of air pollution is a “wicked problem” — complicated by incomplete knowledge, both within the scientific community and among various stakeholders.
When combined, these have a significant secondary impact on national and international economics. Such economic impacts are not addressed here, but should not be overlooked when considering the full negative implications of poor air quality. Anthropogenic activities leading to pollution have a direct impact on the environment and significantly contribute to the climate crisis. Such actions are seen all around the globe — from combustion of fossil fuels for energy generation or vehicle use, to channeling millions of tons of pesticide onto crops — these actions are detrimental to human health and to the planet. Collectively, enormous quantities of CO2 alongside other toxic pollutants — such as PM10, PM2.5, NO2, SO2, volatile organic compounds (VOCs), ammonia, and many more — are emitted each year, causing direct negative impact to our shared environment and negatively altering ecosystems. Additionally, in producing pollutants, we contribute to stratospheric ozone depletion, as well as conversely, its generation at ground level, acid rain, and eutrophication. Furthermore, pollutants lead to increased concentrations of toxicants in both soil and water, thus resulting in harm to humans, animals, and plants alike. Indeed, poor air quality has been shown to reduce life expectancy, increase the likelihood of suffering from a chronic disease — such as a host of respiratory diseases, e.g., COPD (for example chronic bronchitis and emphysema), asthma, lung cancer, pneumonia  — as well as increase the severity of their associated symptoms. Links have also been made between pollutant exposures with cardiovascular disease, diabetes, cancer , and dementia [4, 5]. Air pollution has been shown to cause systemic inflammation, oxidative stress, and degrade immunity even within healthy populations and there is a reported increase in evidence of adverse early life impacts on birth outcomes , lung function , and cognitive development . In 2016, poor air quality (both ambient and indoor) contributed to approximately 7 million premature deaths worldwide, making it the fifth highest mortality risk factor in the world.
It is estimated that 94% of these deaths occurred in low to middle-income countries (LMICs), reflecting the disturbing level of environmental injustice at play. LMICs experience a higher burden of poor air quality compared to developed nations, with the greatest toll in the Western Pacific and Southeast Asia regions . The reliance on solid fuels (wood and coal, for example) for relatively inefficient cooking and heating facilities, involves incomplete combustion, thereby generating indoor air pollutants. Poor air quality is also strongly associated with trade: in 2007 it was found that large fractions of the total air pollution emission in China — the world’s largest emitter of anthropogenic air pollutants — were associated with goods and services consumed in other countries. International exports in China have snowballed since the turn of the century, primarily due to Western demands to cut costs, with China offering cheaper manufacture, supported by lower pay and fewer environmental laws. Recently, China has made great strides in improving its air quality through regulation, but the conditions that drove its significant pollution problem have now shifted to other tiger economies within Asia. In more developed nations, poor ambient air quality is predominantly associated with vehicle use, industrial activity, heat and power generation, as well as poor urban planning which results in sprawl and over-dependence on private vehicle transport .
Air Quality Monitoring
Current monitoring technologies range from small, personal portable sensors, to geostationary monitors, to state-of-the-art deep learning computers combined with high resolution satellite imagery. While such technology can be used in isolation, perhaps the most effective method of long-term monitoring is through the setup of air quality monitoring networks. In London, for example, a successful air quality monitoring network exists: London Air Quality Network (LAQN), which was set up in 1993 and now provides free access to monitoring via Londonair . Such infrastructure offers all access to freely downloadable, curated and up-to-date information on air quality throughout London, which can then be used for multiple purposes. With supporting infrastructure and education, individual access to monitoring data carries the potential to act as a powerful tool, arming individuals with crucial data to better understand their surroundings and the associated health implications of pollution within their own environment. This opens the door to providing individuals with more sustainable options and opportunities, as well as the ability to make more informed choices regarding their daily lifestyle, purchases, and even their vote.
Beyond individuals simply accessing the data, we are now able to produce this data ourselves. Previously, air quality monitoring approaches were limited to expensive, complex and stationary pieces of equipment, thus limiting who can collect data, how such data is collected, and setting certain parameters for motivations behind air quality data collection . However, advancement in air quality monitoring technology in recent years has resulted in the widespread availability of lower-cost and portable air pollution monitors (or sensors, to be precise), which provide individuals an opportunity to capture the air quality data from their local surroundings in near real time. Another key feature of low-cost, low-power personal sensors is their ability to reduce transaction costs associated with monitoring data collection. For example, in the absence of a monitoring network, those wishing to collect pollution level data on a particular street could utilize personal sensors to collect this data. Multiplying this across the country could then produce a national data resource built from the local scale. However, alongside the emergence of such sensors and their potential, there are technological barriers, social hurdles and unintended consequences, all of which will be discussed below.
Connecting individually generated monitoring data with larger, more advanced monitoring network equipment is a possible way to expand and enhance the coverage of air quality data. Crucial to the success of such monitoring networks is the capacity to generate local data and knowledge needed to manage local air quality . Robust air quality management systems must include measures to address country- and area-specific objectives and trajectories, as different countries, and indeed, different areas within each country, will have a different cocktail of pollutants from different sources. Therefore, using both on-the-ground individual sensors, in combination with established monitoring networks, could in theory aid the production of widespread, yet specific, data. This data could then provide an indication of pollutant sources, the short- and long-term trends in air pollution levels, and additionally, could reveal how pollutants may be transported through space and over time. However, auxiliary factors required — often overlooked — make monitoring system set up a far more laborious and costly initiative than one may first think.
Monitoring Realities — Setting up an Air Quality Monitoring Network
Monitoring systems and networks do not just appear and cannot function without considerable human input, as well as financial resources. Therefore, in order to generate a successful and sustainable monitoring system that can provide valuable and accurate data, more than just the data collection equipment is required. Human resources are fundamental at each stage of the monitoring process, from planning, to implementation, to public communication. Experts and trained individuals, alongside technicians, are needed to ensure that the most suitable monitors are correctly installed in appropriate locations. Human resources are equally important for ongoing maintenance of monitors, such as general checks, replacing parts, changing filters, recalibration, etc. . Finally, extracted data needs to be ratified through a lengthy curation process, enabling data to be ready for public dissemination and communication. Importantly, the data generated also needs to be contextualized by both researchers and policymakers in reporting to the public. Therefore, an extensive and diverse team is essential in establishing, coordinating and sustaining an air pollution monitoring network.
Once information is in the public domain, it is critical that educational resources are accessible: there must be sufficient infrastructure in place to support the public dissemination of data, while avoiding damaging trust within public scientific communication. When information is freely accessible, individuals, communities, businesses, and governments alike must have the means of interpreting and analyzing truthful and meaningful data extracted from monitoring results. Furthermore, educational resources must be provided “as and when,” to answer public queries, debunk myths, and ultimately enhance understanding and use of monitoring data. Finally, to maintain data integrity and to support the data once within the public domain, it is crucial to determine who is accessing the data and how it is subsequently used, particularly whether this information has been subject to misinterpretation or inappropriate application.
To support both human and educational resources, financial resources are required. The purchase price of monitoring equipment is not the final price, as it is not just the capital costs of equipment purchase and infrastructure construction that are involved, but financial resources are also required for personnel costs and ongoing maintenance. However, many local councils and governments simply lack the financial capability to invest in implementing monitoring networks (let alone gold-standard monitors) throughout villages, towns, and cities, or the capacity to maintain these to the necessary high standards required for valuable data extraction. Furthermore, many developing nations may lack basic prerequisite foundations, often taken for granted in developed countries, such as consistent electricity supply and the technological capacity to analyze data. Spending, especially after a sustained period of austerity is often conservative, favoring the set up and use of inexpensive — and less sensitive — monitoring, often with recourse to unproven technologies. Inexpensive sensors tend to be less accurate, do not measure all pollutant species equally well and are often highly impacted by meteorological factors, such as humidity. Therefore, at present, these are not adequate replacements for more expensive gold standard measurement technologies. However, it is important to note that not all low-cost sensors are equal, and there is a debate to be had over the relative merits of absolute precision, versus the increased geographical coverage possible with cheaper units. This debate should not, however, be conflated with the consideration of the very cheapest, consumer focused low-cost sensors. Although often framed as a device to democratize air quality data, such sensors produce data of such questionable quality that there is a genuine risk that they do more harm than good.
The hurdle of financial resources can also be noted on a local and individual scale, with personal clean air technologies often only available to those with significant disposable income. Another example of environmental injustice is observed when considering up-and-coming car cabin air filters (purifiers that can monitor air quality and filter harmful pollutants from entering the driver/passenger sphere within the car). In certain instances, pollution levels have been reported to be up to 15 times higher inside the car cabin than outside on the road . To mitigate this, new built-in car technologies can filter and recycle air within the cabin, while monitoring for a build-up of carbon dioxide. By adjusting the ratio of recycled to outdoor air, the composition can be adjusted accordingly thus reducing pollution exposure to the driver/passengers. Car cabin filters have been shown to reduce in-cabin PM2.5 and ultrafine particle matter concentrations by 37% and 47%, respectively , indicating the effectiveness of such technologies. However, such technologies come at some expense and are only available to those who can afford them. As a result, large contributors to poor air quality (i.e., those driving cars) are able to mitigate their own exposure through financial resources alone, while continuing to pollute the air for everyone else.
Ultimately, in a world where environmental issues are often insufficiently prioritized by governments, trumped by economic challenges, or set aside as “placeholders,” the establishment and maintenance of comprehensive air quality monitoring networks is challenging and often impossible in the poorest countries. In turn, levels of environmental injustice escalate, causing more harm to the poorest of our communities.
Monitoring Realities — The Boom in Personal Sensors
The possible benefits of enhancing a monitoring network through the potential combination of personal sensors and wide-scale monitoring systems was described above. Owing to the materialization of low-cost sensors, individuals and organization have begun investigating their use to determine personal exposures and to build these potential networks. This taking “matters into our own hands” approach reflects concerns over the availability of data at a local scale — particularly at locations where vulnerable individual could be exposed, such as school, nurseries and care homes — combined with the degradation of the current regulatory networks. An increase in public awareness and interest in air quality has caused a spike in the sale of personal monitors, retailing at around £100 per device. The small monitoring devices are advertised to be clipped onto backpacks, measuring pollution levels and feeding the results into a large database, thereby enabling those who can afford to, to contribute to crucial data collection, and also to access it at a very individual scale. However, the increased interest has not only been from genuine individuals, but from companies seeking to make profit, in this as-of-yet seemingly unregulated marketplace. The generation of high public demand for such “monitors” has paved the way for many individuals to become a victim of their own moral compass, as their desire to contribute has a secondary effect of feeding and expanding a consumeristic market, which exists in the place of scientifically-backed, large-scale systems.
While the idea and intention to democratize air pollution data is noble at heart, in reality, many, if not most of these mass-produced, low-cost commodities are ineffective sensors that contribute little-to-no valuable data and are therefore unlikely to be a worthwhile investment of an individual’s (often limited) disposable income. As mentioned above, often the more inexpensive sensors offer little valuable discrimination between sites, beyond what is already available from high resolution models (which are often freely available) , or could be inferred through a little knowledge of the major sources of pollution and how they disperse from their point of origin — concentrations are higher nearer a road and busier roads are more polluted than quiet roads, for example. Moreover, the companies producing these sensors are not bound by established national or international standards, and often where data is pooled, how it is quality-assured, normalized, and ultimately used is far from transparent. As it is still relatively early days for this market, questions and concerns remain, such as: what standards must be passed for a monitoring device before it can be sold to the public? And if these devices were to be utilized to control symptoms and manage exposure for vulnerable patient groups — at what point is this a medical device, therefore falling under a completely different set of rules and regulations?
With much unclarity and uncertainty, the sudden boom of this market therefore has significant risks. Well-intended consumers could potentially misuse and misinterpret results from such sensors, posing a serious threat of undermining the current debate about air quality mitigation measures. Similarly, data could be used by developers to misrepresent pollutant levels as being “safe” and hence green light projects that might be perceived as being at risk due to their potential pollution footprint. An example of this can be seen in the use of data from NO2 diffusion tubes, which have often been used to infer traffic impacts on air quality, particularly from diesel vehicles. Relatively short periods of time (weeks to months) tend to be studied, with the interpreted data then compared against the annual WHO guideline and EU limit values, and without an understanding of the seasonal pattern of NO2 concentrations, which are higher in the winter than the summer.
While this is often done innocently, the use of such data and knowledge is also subject to abuse: a developer wanting to justify project construction might show an area to be below legal limits by performing their monitoring in the summer, in contrast to an individual wanting to show poor air quality, who might focus on the colder winter months. In this example, the data is being generated to fit an argument, rather than to inform an unbiased consideration of a complex issue. Overall, our aim is not to say that a layperson should feel unable to contribute to the vital task of data collection — quite the contrary. It is to highlight the irresponsible nature of generating an exploitative market, which can lead to situations of miseducation combined with poor tools for an important job. Monitoring, and the analysis of its data, must be carried out with the highest integrity possible. Maintaining this integrity, while combining the ability for a layperson to have fair access to collecting and interpreting a wide scope of data from wherever they may venture, would be a truly excellent achievement for science and technology, as well as a potential significant contribution to the mitigation of the climate crisis.
The Solution to Pollution: Is It Technological?
Overall, air quality monitoring (and its future potential) remains crucial to providing data for regulatory purposes and for informing the development of exposure models for human health studies, thereby informing assessments of risks and impacts. Monitoring information is also vital to understanding the impact of policy measures such as the effectiveness of Clean Air Zones, or the implementation of other national “clean air” strategies . Air pollution monitoring provides fundamental information, but if the aim is to improve air quality, and subsequently reduce individuals’ exposure, then it is worth reflecting that simply “increasing monitoring” or “improving technology” will not achieve this end. Air pollution is not a simple problem, and therefore we cannot expect a simple solution, delivered by a single technological fix. Alongside monitoring, another example of a “technological fix” to air quality issues is the use of electric vehicles (EVs), seen as the “green” option, in contrast to often vilified petrol and diesel cars.1 While electrifying the system certainly has its benefits, EVs are often still marketed as “zero-emissions vehicles”, despite the energy consumption required for electrical generation and their significant contribution to non-exhaust particulates from tyre and brake wear . Therefore, a strategy that simply replaces all petrol or diesel vehicles with hybrids and electric vehicles will not reduce urban congestion and will likely make only a small dent on ambient PM2.5 concentrations, though pollution levels directly from the tailpipe, such as NO2, will fall. In addition, when considering the full environmental impact of EVs, one cannot overlook the impacts of increased battery production and their ultimate disposal.
Given the growing evidence of the health impacts of air pollution across one’s whole life course, the solution to our poor global air quality cannot simply be left to organic and incremental improvements through improved technologies. To improve air quality, it is imperative that we target the sources of pollution at both a national and international scale. This requires engagement across multiple sectors, including public, industry, and government, in combination with stringent regulation — which should be seen as an opportunity for knowledge-lead economies to innovate, in an otherwise challenging global marketplace — and ambitious targets, neither of which should be stifled by economic concerns. Indeed, the costs of meeting these ambitious emissions reduction targets should not be seen in isolation from the potential cost savings delivered through improvements made in public health. In our challenge to tackle air pollution, there has been a tendency to adopt a “pick-and-mix” style approach, particularly within the U.K. where much of the responsibility for improving air quality has been handed down to local councils, during a period of time where their budgets are under unprecedented strain. In contrast to this poor model, going forward, it would be much more beneficial to adopt a more rigorous scientific methodology — for example, one that is analogous to that used for drug trails — where, prior to widespread actions, initial small scale studies are required to demonstrate if an action has produced the desired results without unexpected consequences. The successes, or indeed failures of these schemes, must then be rapidly, and transparently, communicated to the public. Importantly here, digital communication and education (even access to raw data) can play a key role in keeping individuals on board with future decisions based on these studies. For example, the use of well validated sensors to examine the personal exposures of vulnerable groups over interventions will be critical in demonstrating that improvements in ambient air quality produce meaningful reductions in individual exposures. However, it is important that this work is researcher-lead in partnership with the community. Essentially, it is fundamental that all clean air strategies or novel technological solutions are robustly and independently evaluated and ensured to deliver on their promises. In doing so, continued measurements of, and investments in, regional and national networks are necessary.
Without moving policy decisions away from small scale actions — often delivered to quell public concerns and to be seen to be “doing something” — we will continue to act with little more effect than applying a sticky plaster to a gaping wound. In part, increasing successful outcomes requires educating the public to overcome common misconceptions (often caused by misleading language). It also requires a compelling narrative. A full understanding of the bigger picture is needed as well. Focusing too narrowly on high pollution “hot spots,” or on a single pollutant from a particular source is unlikely to address the magnitude of the current air pollution problem and may even result in perverse unexpected outcomes.2 Finally, and importantly, increasing successful outcomes also requires changing the way in which we plan our cities: allowing for fewer unnecessary car journeys, ensuring greater provision of space for active transport, and reducing the burning of wood for space heating, recreation, etc.
Overall, there is a clear pathway to success, but ultimately, the nature and extent of any potential success will depend on political will. As policy decisions of the past have contributed to the intensity and scale of the anthropogenic emissions that are the primary cause of poor air quality today, it is the policymakers who carry the greatest prospective solution to pollution. Ultimately, real substantial change requires a significant change in our behavior — whether or not governed by policy — and at the core, this means recognizing and accepting that most harmful air pollution is caused by human action. Despite political will constituting a significant part of the final solution to pollution, we, as individuals, and as communities, can and should begin to change. This starts with an action made today, sparking social change tomorrow, and eventually revolting against the ideologies deep ingrained in our social constructs. This action to start today could simply be recognizing that through changing our human activities (for example, walking, cycling, and using public transport in place of individually owned vehicles), we can contribute to the common good, reduce our own pollution output, and improve air quality for everyone — even if life is a little less convenient.
Steph Pitt is with the Department of Electrical and Electronic Engineering, Imperial College London, U.K. Email: Steph.firstname.lastname@example.org.
Ian Mudway is with the MRC Centre for Environment and Health, Kings College London and Imperial College London, U.K
Steph Pitt was supported by Association for Information Technology Trust (AITT) grant PlatformOcean.
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