Air-quality monitoring

Summary

Air-quality monitoring involves the systematic sampling of ambient air. This includes analysis of samples for pollutants injurious to human health or ecosystem function, and integration of the data to inform public policy decision making. Air-quality monitoring in the United States is governed by the federal Clean Air Act of 1963 and subsequent amendments and by individual state implementation plans. Data from air monitoring are used to propose and track remediation strategies that have been credited with dramatically lowering levels of some pollutants.

Definition and Basic Principles

Air-quality monitoring aims to track atmospheric levels of chemical compounds and particulate matter that are injurious to human health or cause some form of environmental degradation. The scope could be a single room up to the entire globe. Since the 1990s, there has been a tendency to shift focus away from local, exterior air pollution to air quality inside buildings, both industrial and residential. This has included regional patterns involving air-quality issues that cross international boundaries and worldwide trends including global warming and depletion of the ozone layer.

Data from air-quality monitoring are used to alert the public to hazardous conditions, track remediation efforts, and initiate legislative approaches to environmental policy. Agencies conducting local and regional exterior monitoring include national and state environmental protection agencies, the National Oceanic and Atmospheric Administration (NOAA), and the National Aeronautics and Space Administration (NASA). Industries conduct their own interior monitoring with input from state agencies and the Occupational Safety and Health Administration (OSHA). There is an increasing market for inexpensive devices homeowners can install themselves to detect household health hazards.

The Clean Air Act of 1963 and amendments of 1970 and 1990 mandate monitoring of six criteria of air pollutants—carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, particulate matter, and lead. This is done with the aim of reducing release into the environment and minimizing human exposure. With the exception of particulate matter, atmospheric concentrations of these pollutants have decreased dramatically since the late 1980s.

A key concept in implementing monitoring programs is that of probable real-time exposure, with monitoring protocols matched to real human experience. Increasingly used are compact and automated equipment that can be left permanently at a site. These can collect data at intervals over a period of weeks and months and have been a real benefit to establishing realistic tolerance levels.

Background and History

The adverse effects of air pollution from burning coal were first noticed in England in the Middle Ages and prompted a ban on coal in London in 1306. By the mid-seventeenth century, when John Evelyn wrote Fumifugium, or The Inconvenience of the Aer and the Smoake of London Dissipated (1661), the problem of air pollution in London had become acute. Various measures, including banning certain industries were proposed to combat it. Quantifying or even identifying the chemicals responsible exceeded contemporary scientific knowledge. English statistician John Graunt, nonetheless correlated deaths from lung disease recorded in the London Bills of Mortality. In tracking incidences of “great stinking fogs,” he obtained objective evidence of health risks. In addition, scientist Robert Boyle proposed using the rate of fading of strips of dyed cloth to monitor air quality.

Chemical methods for detecting nitrogen and sulfur oxides existed in the mid-eighteenth century. By the late nineteenth century, scientists in Great Britain were undertaking chemical analyses of rainwater and measuring rates of soot deposition. This was done with the aim of encouraging industries either to adopt cleaner technologies or to move to less populated areas. Early examples of environmental legislation based on scientific evidence are the Alkali Acts, the first that was enacted in 1862, requiring industry to mitigate dramatic environmental and human health effects by reducing hydrogen chloride (HCl) emissions by 95 percent.

Until the passage of the first national Clean Air Act in 1963, monitoring and abatement of air pollution in the United States was mainly a local matter. Areas where residents were financially dependent on a single polluting industry were reluctant to take any steps toward abatement. Consequently, although air quality in most large metropolitan areas improved in the first half of the twentieth century, grave health hazards remained in some industries. This discrepancy was highlighted by the 1948 tragedy in Donora, Pennsylvania when twenty people died and almost 6,000 (about half the population) became acutely ill. This occurred during a prolonged temperature inversion that trapped effluents from a zinc smelter, including highly toxic fluorides. Although autopsies and blood tests revealed a pattern of chronic and acute fluoride poisoning, no specific legislation regulating the industry followed the investigation. Blood tests and autopsies have also been used to track incidences of lead poisoning and mercury poisoning, some of it from atmospheric pollution.

How It Works

Structure of Air-Monitoring Programs. In the United States, state environmental protection agencies, overseen by the federal government, conduct the largest share of outdoor air-quality monitoring, while indoor monitoring is usually the responsibility of the owner or operator.

The Clean Air Act (1970) and its amendments require each state to file a State Implementation Plan (SIP) for air-pollution monitoring, prevention, and remediation. States are responsible for most of the costs of implementing regulations. These guidelines may be more stringent than federal regulations but cannot fall below them. Detailed thresholds specify which pollutants must be monitored, the frequency and procedures for monitoring, and acceptable equipment. The regulations change constantly in response to developing technology, shifting patterns of pollution, and political considerations. There can be a tendency to respond rapidly and excessively to new threats while grandfathering in older programs. Examples are those aimed at asbestos and lead, which address hazards that are far less acute than they once were.

The United States Environmental Protection Agency (EPA) collects and analyzes data from state monitoring stations to track national and long-term trends. The EPA makes recommendations for expanded programs, and ensures compliance. Some pollutants can be tracked using remote sensing from satellites, a function performed by NASA. The World Health Organization (WHO), a branch of the United Nations, integrates data from national programs and conducts monitoring of its own. Air pollution is an international problem, and the lack of controls in developing nations spills over into the entire biosphere.

Workplace air monitoring falls under the auspices of state occupational safety and health administrations. In addition to protecting workers against the by-products of manufacturing processes, monitoring also identifies allergens, ventilation problems, and secondhand tobacco smoke.

Monitoring Methods and Instrumentation. Methods of monitoring are specific to the pollutant. A generalized monitoring device consists of an air pump capable of collecting samples of defined volume. It will also have a means of concentrating and fixing the pollutants of interest. The device will contain either an internal sensor that registers and records the level of the pollutant or a removable collector.

An ozone monitor is an example of a continuous emission sampler based on absorption spectroscopy. A drop in beam intensity is proportional to ozone concentration in the chamber. Absorption spectrometers exist for sulfur and nitrogen oxides. This type of technology is portable and relatively inexpensive to run. It can be used under field conditions such as monitoring in-use emissions of motor vehicles. Absorption spectroscopy is also used in satellite remote sensing and has been adapted to remote sensing devices deployed on the ground to measure vehicular emissions.

There are a number of methods for measuring particulate matter, the simplest of which, are found in home smoke detectors. These involve a photoelectric cell sensitive to the amount that a light beam is obscured. More sophisticated mass monitors measure scattering of a laser light beam, with the degree of scattering proportional to particle size and density. Forcing air through a filter traps particles for further analysis. X-ray fluorescence, in which a sample is bombarded with x-rays and emitted light is measured, will detect lead, mercury, and cadmium at very low concentrations. Asbestos fibers will turn up either by X-ray fluorescence or visual inspection of filters. Pollen and mold spores, important as allergens, are detected by visual inspection. A drawback of filters is cost and the skilled labor required to process them.

A total hydrocarbon analyzer used by the auto industry uses the flame ionization detection principle to identify specific hydrocarbons in auto exhaust. Volatile organic compounds (VOCs) present a challenge because total concentration is low outside of enclosed spaces and certain industrial sites, and rapid efficient methodology is not available for distinguishing between different classes of organic compounds.

Applications and Products

Reporting and Predicting Air Quality. Media routinely report air-quality indices along with other weather data. The general public has become accustomed to using this information to plan activities such as outdoor recreation. Projections are also used to schedule unavoidable industrial-emissions release to coincide with favorable weather patterns and minimize public inconvenience. Predicting air quality is an evolving and inexact science involving predicting and tracking weather patterns but also integrating a myriad of human activities.

Vehicular Emissions. Federal law mandates that urban areas with unhealthy levels of vehicular pollution require testing of automobile emissions. Laws concerning testing vary considerably from state to state, as well as intra-state jurisdictions. Additionally, new vehicles manufactured or sold in the United States must undergo factory testing. This applies to both the model and of the individual units, to ensure the vehicle meets federal standards.

Typical vehicle-inspection protocol requires motorists to bring the vehicle to a garage where automatic equipment samples exhaust and analyzes it for CO, aggregate hydrocarbons, nitrogen and sulfur oxides, and particulate matter. Some state departments of motor vehicles operate their own inspection stations, while others license private garages. There are a number of compact units on the market that provide the required information with little operator input.

With improving air quality and a decreasing proportion of older cars that lack pollution-control equipment, some jurisdictions are withdrawing from vehicle testing.

Public-health effects of air-pollution monitoring and mitigation on public health deserve mentioning. Adverse effects on human health were the principal rationale for instituting laws curbing air pollution. The decline in certain health problems associated with atmospheric pollution is testimony to the effectiveness of this legislation.

Rates of lung cancer and chronic obstructive pulmonary disease (COPD) have declined, and ages of onset have increased substantially since the mid-twentieth century. Although the bulk of this is due to declining tobacco use, some of it is related to pollution control.

Careers and Course Work

Air-pollution monitoring is a field with solid career prospects, in both government and private industry. The majority of openings sollicit field technicians who supervise monitoring facilities. They also conduct a varying amount of chemical and physical analyses (now mostly automated), and collect and analyze data. For this type of position a bachelor’s degree in a field that includes substantial grounding in chemistry, mathematics, and data management, and training on the types of equipment used in monitoring, is usually required. A number of state colleges offer undergraduate degrees in environmental engineering that provide a solid background. Online programs offered by for-profit institutions lack the rigor and hands-on experience necessary for this demanding occupation. For research positions in government laboratories and educational institutions, an advanced degree in meteorology, environmental science, or environmental engineering is generally required.

This is a rapidly evolving field for which knowledge of the latest techniques and regulations is essential. Degree programs that offer a solid internship program, integrating students into working government or industrial laboratories, offer a tremendous advantage in a job market where actual experience is essential. In 2021, the Occupational Outlook Handbook predicted much faster-than-average job growth for environmental science and protection technicians between 2020 and 2030.

The development, sale, and servicing of monitoring equipment offers other employment options. While coursework can provide the general level of knowledge necessary to sell, adjust, and repair sophisticated automated electronic equipment, such a career objective will also require extensive on-the-job training. Some manufacturers offer factory training for service people.

Social Context and Future Prospects

The regulations and remediation efforts that monitoring informs and supports have clearly had a positive impact on the health and well-being of Americans in the nearly half-century since the passage of the Clean Air Act. Heavy-metal exposure from atmospheric sources has dropped dramatically. Mandatory pollution-control devices on new passenger vehicles have curbed emissions in states where annual vehicle emission tests are not even required. Older diesel trucks, farm vehicles, and stationary engines remain a concern in the United States.

Air pollution remains a significant problem in the developing world, especially in China, where the rapid growth of coal-fired industries has created conditions in urban areas reminiscent of Europe in the nineteenth century. Addressing these problems is a matter of international concern because air pollution does not respect national boundaries.

Low-end environmental monitoring devices for the consumer market are a growth industry. With respect to genuine hazards such as smoke and carbon monoxide, this is a positive development. There is concern, however, that overzealous salespeople and environmental-consulting firms will exaggerate risks and push for costly solutions in order to enhance their bottom line, as occurred with asbestos abatement in the 1970s and 1980s.

Although often criticized, an integrated approach to environmental policy that includes “cap and trade”—allowing industries to use credits for exceeding standards in one area to offset lagging performance in other areas, or to sell these credits to other industries so long as an industry-wide target is met—helps ease the nontrivial burdens of complying with constantly evolving environmental standards.

Much of the information-gathering and tracking system developed to address emissions of criteria pollutants is being integrated into the effort to slow global warming due to carbon dioxide(CO₂) emissions from fossil fuel burning. While elevated CO₂ does not directly affect human health, and is actually beneficial to plants, the overall projected effects of global warming are sufficiently dire that efforts to reduce CO₂ emissions deserve a high priority in environmental planning.

As the twenty-first century progressed, both air quality and a lack of monitoring controls had become global concerns. According to the World Health Organization (WHO), 99% of the entire population on Earth consumed air that was beyond air quality limits. This tended to impact lower-income countries. The United Nations Environment Programme (UNEP) concluded that the human cost was 7 million premature deaths on an annual basis. This issue was compounded because 37 countries had no legal requirement to monitor the air of their citizens. This was particularly true in Africa, Central Asia, and Latin America.

Changing global climatic conditions had also become an acute concern. A vivid example occurred in June 2023 as high summer temperatures contributed to major wildfires in Canada. These produced large quantities of smoke and particulates that drifted over wide swaths of the United States. Major population centers in the US recorded some of the worst air qualities ever in those areas. Affected areas ranged from the US eastern seaboard to its Midwest.

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