Air Pollution Sources, Statistics, and Health Effects, Introduction
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Air pollution threatens our health, environment, and climate. The sources of air pollution are numerous anthropogenic and natural emissions; some are pollution in their own right, and some trigger the formation of secondary pollution. Detailed knowledge of the sources of pollution and the transformations of pollution in the atmosphere is the best possible basis for effective and cost-effective management strategies. While this knowledge is the basis of environmental management as regards emissions standards and best-practice pollution control systems, it is also critically important to society as it seeks to adopt policies and behaviors to reduce air pollution and its associated impacts and direct resources toward research and technological development to achieve sustainability. In fact, reducing air pollution emissions and thereby improving air quality will help us to meet a series of United Nations Sustainable Development Goals. Environmental pollution contributes to poverty, low crop yields, and disease, and the fight for resources leads to political instability. Thus, reducing air pollution helps us achieve sustainability by reducing poverty and inequality, providing jobs in the clean technology sector, and reducing and overcoming climate change. During the 2020 Corona crises, air pollution levels have decreased substantially in urban areas around the world because of reduced travel and industrial activity. These improvements in air quality have made real some of the improvements that can be obtained from, e.g., moving towards a society less dependent on fossil fuels. Improved cleaning technologies are the result of both pull and push strategies. This can be seen in the vehicle industry where strict emission standards have forced manufacturers to develop new technologies. These developments have been important for improving air quality in many parts of the world over the past two to three decades.
Our knowledge about air pollution is based on data obtained from field measurements, laboratory studies, and air pollution modeling. It is often through the combination of information from these very different types of studies and activities that new and deeper understanding is established. One example is our understanding of the pollution distribution inside urban street canyons, achieved through painstaking analyses of data from monitoring stations in busy streets, wind tunnel experiments, and models of traffic emissions, photochemistry, and air flow. Air pollution assessments are often based on combinations of measurements and model calculations. In reporting air quality levels in the scientific community, for industry and environmental agencies, it is becoming standard practice to include indicative data from air pollution modeling. Indicative measurements are sometimes also included in such reporting based, e.g., on passive samplers with coarse temporal resolution. More recently a variety of new low-cost sensor-based measurement devices have been designed and deployed. Electrochemical and metal-oxide sensors can provide high temporal and spatial resolution and may be able to substantially extend the abilities of established monitoring stations to investigate local air pollution sources and remediation strategies. It should be noted that such devices are not intended to replace high-quality monitors and measurement stations since their precision and accuracy are not sufficient for monitoring compliance with guideline values. The requirements for using such devices are that the measurement range matches the range of ambient levels, that their accuracy and precision are sufficiently high, and that proper calibration and validation are conducted.
Since the Dockery and Pope studies in the US in the 1990s, it has been known that exposure to air pollution poses not only short-term (acute) but also long-term (chronic) health effects in the population. Recent research by the Max Planck Institute of Chemistry has established that the impact of air pollution is on the scale of a global pandemic, causing the loss of 8.8 million lives annually. Despite substantial improvements in many parts of the world, globally, air pollution is still the most hazardous environmental threat. The increasing quality of exposure assessments, access to new and better statistical methods, and more complete and precise health data have led to stronger associations between air pollution exposure and health effects. More health endpoints have been added to the list in recent years and health effects are seen at lower pollutant levels that were previously known or even expected. During the 2020 Corona crises, it was even speculated, that the death risk related to Corona infection may be strongly affected by simultaneous exposure to high air pollution levels. Air pollution exposure-effect relationships have now been established for a wide variety of health outcomes, and well documented through parallel studies in many countries around the world using a variety of approaches and methodologies. Assessments of the health effects in the population are now performed on a routine basis in many countries and by many agencies, and often these also include calculation of externalities associated with the negative health effects. Again, such knowledge is essential for pushing development towards a more sustainable society.
Ground-Level Localized Air Quality
Regional and Global Air Quality and Effects
Sensors, Measurement, and Control
There are eight chapters in the section Ground-Level Localized Air Quality that focus on pollution with a variation on local spatial scales and typically with a shorter lifetime. This section is of particular interest in pollution exposure, as obviously, this is where people spend their time.
The article “Air Quality Guidelines and Standards” by McClellan details the regulatory framework used in air quality management.
There is growing recognition of the impacts of shipping and railways on emissions and air quality, and Boulter’s entry “Air Quality, Surface Transportation Impacts on” seeks to quantify the issues and place them in context.
Rezaei and Johnson’s “Airborne Nanoparticles: Control and Detection” discusses the state of the art for the control and detection of airborne nanoparticles. Unfortunately, given the increased attention they are receiving, the chemical and physical properties of nanoparticles make them a challenge to detect and control.
“Indoor Air Quality: Status and Standards” (Hasager et al.) is an essential entry in terms of air pollution exposure, as people spend nearly 90% of their time indoors.
The meteorological processes leading to the vertical mixing of pollutants after emission and their horizontal transport by the wind are described in the entry “Urban Air Quality: Meteorological Processes” by Carruthers, Di Sabatino, and Hunt. Computational models used to describe these processes are also included.
“Urban Air Quality: Sources and Concentrations” by Goodsite, Hertel, Johnson, and Jørgensen was updated to reflect the latest developments with particular attention given recent technological advances, as well as the latest research from around the world.
The complementary entry “Urban Atmospheric Composition Processes” (Bloss) describes the key chemical reactions which serve both to limit the concentrations of toxic pollutants and control concentrations of secondary pollutants such as ozone and airborne particles, important to human health and regional pollution.
Surface water links climate change and sustainability with the human environment. Poor management of urban surface water can have serious effects. The article by Sørensen, “Urban Drainage Modelling for Management of Urban Surface Water” demonstrates how combining technologies that have previously been taken separately can assist planners in the management of urban surface water, an important climate adaptation issue.
The next section, “Regional and Global Air Quality and Effects,” comprises five chapters discussing the effects of air pollution in terms of global climate.
Air pollutants comprise both gases and particles. The latter are tiny airborne liquid or solid droplets ranging from nanometers to tens or even hundreds of micrometers in size. The entry by O’Dowd “Aerosol in Global Atmosphere” details the impact of aerosol on climate. The impacts are numerous and complex, and aerosol in the global atmosphere may have both warming and cooling effects upon climate.
Johnson et al.’s entry “Air Pollution and Climate Change: Sustainability, Restoration and Ethical Implications” describes air pollution and its links to climate change, and in addition the profound philosophical and ethical quandaries created by our current dilemma.
Aviation is a significant source of pollutant emissions. Because of the altitude at which most of these emissions occur, its effects on ground-level air quality are modest. The main consequences are due to aviation’s climate impacts, arising from emissions of greenhouse gases and water vapor, described in Grassl’s entry “Aviation and Atmosphere”.
As air pollutants are advected from urban areas, they are subject to atmospheric transport leading to impacts on “Regional Air Quality” which have important human health and ecosystem effects, described in the entry of this name by von Schneidemesser and Monks.
Release of long-lived pollutants at ground-level as well as aircraft emissions lead to “Stratospheric Pollution” (entry by Chipperfield) with consequences for stratospheric ozone concentrations, penetration of UV radiation to ground-level, and global climate.
The last section is titled “Sensors, Measurement, and Control” and comprises four chapters that primarily focus on monitoring and controlling air pollution.
The entry “Air Pollution Monitoring and Sustainability” (Knox, Evans, Lee and Brook) discusses the design of monitoring networks and how monitoring data can inform urban design and air quality management policy. In addition to monitoring networks, the monitoring of emissions sources and remote sensing of the atmosphere on regional scales from space play important roles.
Frederickson et al.’s “Low Cost Sensors for Indoor and Outdoor Pollution” introduces low-cost methods for sensing indoor and outdoor pollution. Sensing pollution is the key to monitoring, mitigating and controlling it. The lower the cost, the greater the potential deployment, especially in developing markets and as a way to increase the spatial resolution of current measurement stations.
Edwards, Lawler, Disher, and Radford’s article on “Measuring Heatwaves and their Impacts” details heatwave events that are forecast to become more frequent and severe. Heatwaves contribute to air pollution.
Kwiatkowski, Polat, Yu, W, and Johnson, in their entry “Industrial Emissions Control Technologies: Introduction” explain novel and innovative technologies for controlling industrial emissions. The ‘solution to pollution’ is no longer dilution, it is clean technology, applying basic science in analogy to natural processes to industrial-scale issues.