Although not as well known as other types of pollution, unpleasant odours are the form of pollution that generates the most complaints from the public to the authorities due to their annoying and harmful effects.
This type of odour pollution is already monitored and controlled in many countries to regulate its odour impact.
What are the substances that cause unpleasant odours?
There are a variety of volatile chemical compounds that cause bad odours, but the ones that stand out as the most annoying are those that contain sulphur, nitrogen or are contained in volatile organic compounds (VOCs). Some examples are:
- Sulphides: Sulphur compounds such as hydrogen sulphide (H2S) and methyl sulphide (CH3SH) are known to smell like rotten eggs or gas and are often found around sewage treatment plants, landfills and some chemical industries.
- Ammonia and amines: Ammonia (NH3) and amines are nitrogenous compounds with a strong and unpleasant odour, which we perceive mainly in stables, farms, fishing industry and food processing plants.
- VOCs and BTXs: Volatile organic compounds (VOCs), such as aldehydes and ketones, and aromatics, such as benzene, toluene and xylene (BTX), are compounds that evaporate very quickly and give off unpleasant odours, such as the familiar “petrol smell”.
Main sources of industrial odours
Depending on their specific processes and activities, industrial plants can generate unpleasant odour emissions. The main sources of odour pollution are considered to be:
Waste Water Treatment
Hydrogen sulphide (H2S) is the compound that causes one of the most common odours in wastewater treatment plants and, as mentioned above, usually has a rotten egg smell. Ammonia (NH3) can also be released in these industries with its characteristic odour.
In this industry we find that aromatic VOCs such as benzene, toluene and others are the main source of odours. In addition, as in waste water treatment, H2S can also be present.
The odorous compounds that pollute the environment in the chemical industry can vary according to the processes carried out, but mainly include VOCs, mercaptans or thiols – which are sulphur-containing compounds that can have an odour similar to petroleum gases – and sulphur dioxide (SO2), which has an odour similar to that of a burning match and is formed when sulphur-containing fossil fuels are burned.
In agriculture, ammonia NH3 and amines released from manure decomposition and fertiliser application are the main causes of unpleasant odours.
Odour emission limits
Odour regulations and emission limits vary from jurisdiction to jurisdiction and country to country, but generally they aim to control and mitigate the negative effects of unpleasant odours.
In Spain, there is no specific legislation dedicated exclusively to odour pollution and it is mainly focused on the regulation of air quality and the prevention of air pollution.
We must therefore look to the European level, whose most important step towards standardising olfactometry was the introduction in 2003 of the European standard EN 13725 “Air quality. Determination of odour concentration by dynamic olfactometry”, which deals with various aspects of measurement, procedures, data recording and reporting.
There is also the Integrated Pollution Prevention and Control Act (IPPC), an EU law whose main objective is the prevention and control of environmental pollution, including odours, from industrial installations.
The IPPC provides a comprehensive regulatory framework to ensure that industrial activities do not have a significant negative impact on the environment, human health and air quality.
IPPC and its associated regulations address odour emissions through mechanisms such as the Integrated Environmental Authorisation (IEA), which sets out specific requirements for the prevention and control of odour emissions from certain industrial installations.
Similarly, installations subject to IPPC must carry out regular and systematic monitoring of odour emissions in an objective manner, measuring odour intensity and concentration to ensure that they comply with the limits set.
How are odours measured? Odour measurement for odour monitoring and control
As mentioned above, continuous monitoring of odour emissions is essential to ensure compliance with environmental regulations.
In facilities where monitoring requires type approval, chemical analysis techniques based on gas chromatography coupled to mass spectrometry (GC-MS) are used, an instrumental technique that allows the identification of odorous chemical compounds in a gas sample.
This chemical characterisation in turn makes it possible to assess the conformity of the emissions with the concentration or flow limits set by the competent authorities.
If we focus on odour measurement systems, there are several examples that can be useful depending on the specific application:
The Nanoenvi EQ outdoor air quality monitor is capable of measuring parameters such as H2S and VOCs using electrochemical cells, and generating alerts when the levels of these compounds exceed established limits in order to take corrective action.
Industries with more specific requirements can incorporate instruments capable of monitoring parameters such as NH3, H2S, TRS, SO2, BTX, CH4 and other VOCs into their continuous emission and process monitoring systems (CEMS), such as Siemens or AMA Instruments chromatographs.