Emissions monitoring is the observation and analysis of the gases and particulates given off by industrial activities such as manufacturing, refining, energy production, and others. Countries worldwide have enacted policies requiring emissions monitoring because of environmental and health concerns raised over the types of emissions released into the atmosphere. In many countries, continual emissions monitoring is the basis for cap-and-trade programs.
In the course of their daily operations, most industrial facilities produce emissions of gases and particulates as a byproduct of their processes. Emissions monitoring arose as a way to control combustion; that is, when the mixture of fuel and oxygen in the combustion process is less than optimal, the mixture of gases in the emissions produced reflect that fact. Thus, emissions monitoring provided the information necessary to make the combustion process most efficient. This in turn led to a reduction in the level of pollutants emitted. Systems were built for the sole purpose of monitoring emissions.
Near the end of the 20th century, many governments worldwide began paying more attention to the issue of air pollution and the many problems it causes, from human respiratory problems to acid rain. Legislation was enacted in many cases restricting the emissions permissible, and requiring continual emissions monitoring to aid in the enforcement of the statutes.
In the beginning of the 21st century, the focus shifted somewhat to the issue of global warming, and it was determined that some of the components of emissions from combustion were contributing to the greenhouse effect. Rather than impose unrealistic limits on industries, “cap and trade” plans were developed that provided manufacturing facilities with a quota of emissions of these greenhouse gases they were allowed to produce. Those that produced less than their quota could sell "carbon credits" to those who exceeded their quota. In order to make cap and trade systems work, continual emissions monitoring of industrial facilities is required.
It's not practical, though, to monitor all sources of harmful emissions. Nearly all forms of motorized transportation, for example, produce greenhouse gases, yet the technology to monitor such emissions continually is prohibitively expensive. Nevertheless, emissions standards are imposed on vehicles powered by internal combustion engines in many nations worldwide. The emissions monitoring systems for them is fixed and intermittent. Vehicles periodically report to testing stations to have their emissions analyzed for compliance. Those vehicles found to exceed the allowable standards are required to be repaired or taken off the road.
Open fires and many landscaping machines, such as lawn mowers and weed trimmers, also are significant sources of greenhouse gases in some parts of the world. It's very difficult to monitor these sources, however, and so the efforts to control their emissions are limited to measures taken during their their manufacture.