When talking about air quality and air pollution, it is usual to refer to immission vs emission, two concepts that, sometimes, lead to error. Their mention in the normative field is quite common, but they do not mean the same and they do not even have to keep a direct relationship.
What does emission mean?
The term emission is included in different regulations and the emissions can be:
- Continuous or discontinuous (irregular).
- Direct or indirect.
- From point or diffuse sources.
- In the form of gas, liquid, solid or energy.
- With the ability to affect the atmosphere, water or soil interchangeably.
To these characteristics, it is convenient to add that their origin can be natural (unintentional forest fires, volcanic eruptions, etc.) or anthropogenic (vehicles, industries, etc.).
Also, the term emission alludes to different media or ecosystems, but in the present article, only its condition to the atmosphere is taken into account.
What is immission?
Immission refers to:
- An amount, measured in different units, of a polluting substance present at a given time.
- A value whose limit is established under scientific knowledge.
- A cap whose goal is to protect human health and preserve the environment.
The atmosphere plays a key role in the immission, since a polluting substance, when it is emitted, undergoes a series of physical and chemical transformations in the air (transport and dispersion, for example) that cause that emission and immission do not have a direct relationship.
Differences between emission and immission
The definitions and characterizations made for both concepts reveal in a clear way what their main differences are. However, the following table reflects the main distinctive aspects:
In summary, emissions are related to the output of polluting substances to the atmosphere from any source, while immission, on the other hand, constitutes what is known as “air quality”. Immission is the concentration of pollutants at ground level that can affect people, animals, vegetation or materials.
How are emissions controlled?
Different international organizations have developed reference guides and regulations that define the emission limits allowed for different types of sources. Continuous Emission Monitoring Systems (CEMS) are used to control emissions in industrial installations (cement plants, power plants, chemical plants, refineries, paper plants, etc.). The shelters are equipped with measurement instruments for the monitoring of parameters like:
- Sulfur dioxide (SO2).
- Nitrogen oxides (NO2 / NO / NOX).
- Suspended particles (PM10 and PM2.5).
- Oxygen (O2).
- Humidity (H2O).
- Volumetric flow (Nm3 / h).
ENVIRA has an extensive experience in the design, supply and installation of Continuous Emission Monitoring Systems. Their CEMS are optimized to provide high reliability with little maintenance.
Immission of air pollutants with monitoring networks
The control and monitoring of the air quality must be carried out with air quality networks, a work in which ENVIRA has a long career. Air quality networks allow:
- Knowing the evolution of the long-term temporal space of air pollution.
- The prediction of air pollution episodes.
- Providing information to the public.
An air quality network is composed of stations equipped with systems for capturing samples and automatic analyzers for measuring pollution parameters whose characteristics may vary depending on the area. The most common monitored parameters are:
- Sulfur dioxide (SO2).
- Nitrogen oxides (NO2 / NO / NOX).
- Suspended particles. (PM10 and PM2.5).
- Carbon monoxide (CO).
- Tropospheric ozone (O3).
It is also possible to monitor other pollutants such as volatile compounds, hydrogen sulfide (H2S), hydrogen fluoride (HF), metals (cadmium, lead …), Black Carbon, etc.
The immission levels of atmospheric pollutants are regulated by the current regulations establishing:
- Air quality goals.
- Limit values.
- Tolerance margin.
- Target values.
- Information thresholds.
- Alert thresholds.
In addition to having air quality networks, smart cities are betting on the installation of sensor networks such as those provided by ENVIRA, since they complement the data of the stations and the administration can have a more global vision of the state of air quality in a city.
