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A citizen-driven approach to tackle odour pollution

A brand-new app to help citizens monitor and identify the sources of odour pollution is being offered by the D-NOSES project. The project’s work is a welcome step forward in a field where some have argued that inaction has prevailed for too long.

Climate Change and Environment

Pollution not only has a highly negative impact on the environment, it disturbs our senses too, notably the sense of smell. The statistics speak for themselves: odour pollution is the second highest cause of environmental concern among citizens after noise – accounting for more than 30 % of relevant complaints on average. Regulations have so far failed to solve this problem, and it is not an issue that industry is focusing on either. In this context, it seems only appropriate to provide citizens with the means to take things into their own hands. The D-NOSES (Distributed Network for Odour Sensing, Empowerment and Sustainability) project has been doing just that, gathering stakeholders around the table and providing them with an app to monitor odour pollution and be able to act on the evidence provided. Rosa Arias, chemical engineer at the University of Barcelona, CEO at Science for Change and coordinator of D-NOSES, discusses the project’s work and its expected impact on the issue of odour pollution.

Odour pollution is often ignored in environmental regulations. How do you explain this?

Rosa Arias: There are three key factors at play. Odour abatement techniques are usually expensive, emitting industries will typically oppose regulatory initiatives, and odours are difficult to measure. Indeed, ambient odours are mixtures made of hundreds of volatile compounds that spark a reaction in our sense of smell. The way we perceive them is so unique and complex that so-called ‘electronic noses’ or traditional chemical analysis cannot mimic it.

Do we have any information on odours’ actual impact on citizens’ health?

Odours are not just a matter of good or bad smells! All types of odours, regardless of their character and hedonic tone (good or bad smell), may cause discomfort. We may like the smell of biscuits or coffee, but that same smell, if it is very intense and frequent, can be unbearable. Although odours do not normally present serious health problems, they can act as a warning signal for more serious environmental or health issues potentially harmful to human health. Our sense of smell is very precise and we can smell harmful substances in very low concentrations to prevent any harm. For example, hydrogen sulfide (H2S), the typical smell of ‘rotten eggs’ produced by stagnated waters or the sewage system, can be perceived in concentrations as low as 10 ppb (parts per billion). This is very convenient, as higher concentrations are lethal! Broadly speaking, we can smell ambient odours at concentrations that are not harmful for our health, but even at such low levels they can generate general discomfort, headaches, lack of sleep, lack of concentration, accentuation of respiratory problems, stress, insomnia, nausea and anxiety.

D-NOSES proposes a paradigm shift in the way odour pollution is being tackled. What does your approach consist of and what makes it innovative?

D-NOSES addresses this problem by involving public administrations, industry, research institutions and citizens in participatory sessions, following the quadruple helix model of innovation. Together, they can co-design improvements that reduce the impact of odour pollution on affected communities. Our ultimate goal is to introduce the issue to policy agendas, so we created a multilevel governance model. At the local level, we work together with environmental authorities and municipalities in 10 pilots across Europe, Chile and Uganda. At national level, we inform specific regulations on odour pollution in several countries such as Chile and Portugal, while promoting the creation of a standardisation group in Spain. This will be the first standard with the ‘citizen science’ concept in its title, which will set a precedent for the entire community and may be eventually adopted at European level. Finally at the European level, we inform about the revision of the European Industrial Emissions Directive (IED) to introduce ‘odour’ as one of the sources of pollution.

How do you overcome the existing barriers to detection?

We know that each substance has different odour thresholds. The combination of dozens or hundreds of substances in ambient air produce an odour perception that is more than the sum of each individual threshold, since chemical interactions occur and the combined odour is unique. We also have to account for the fact that the sensitivity to odours can be very different from person to person, and that further difficulties can arise due to external agents such as weather conditions making it difficult to identify the emission source. To tackle these issues, I came up with the idea of creating a citizen science app to monitor odour pollution and empower citizens to create collaborative odour maps in real time based on their perceptions. The OdourCollect app takes advantage of already known research techniques and adds an extra layer of citizen collaboration on top of them. This will help ensure that directly affected communities are not left defenceless. Users can monitor odour impact in real time, understand which type of odours they are perceiving, and correlate the observations with potential origins to identify potential improvements.

How successful has the app been so far?

We have more than 1 100 registered scientists and over 9 100 odour observations collected worldwide. In Barcelona we have developed a pilot in the Forum area where we have more than 600 odour observations with more than 50 neighbours involved. The results in terms of frequencies and types of odour perceived correspond to traditional odour studies, thus showing the validity of the proposed methodology. We are currently correlating the obtained data with industrial operations, to find the situations that cause a higher impact and act upon them. The generated data is invaluable for environmental authorities to monitor odour impact and for the emitting industries to produce odour management. Anyone can contribute to the project, as in the end the best sensor for measuring an odour is the human nose itself.

How do you plan to help improve regulations?

We have been analysing the regulatory frameworks in D-NOSES countries and will produce strategic governance roadmaps for each country. Hopefully, these will push environmental authorities and policymakers to adopt scientifically sound methodologies.

The project will soon be completed. Do you have any follow-up plans?

OdourCollect and the International Odour Observatory, together with the policy documents to be generated, will be the main legacy of the project. We are currently developing the D-NOSES Exploitation Plan to guarantee the exploitation of the project results after its end. We will also seek further opportunities in the brand-new Horizon Europe to continue the good work done in D-NOSES.

What do you hope will be the long-term impact of the project?

Citizen science practices generate new scientific knowledge, empower citizens and encourage critical thinking. This process contributes to the democratisation of science and, in the case of OdourCollect and D-NOSES, can foster social awareness of odour pollution, generate a sense of co-responsibility and contribute to mitigating effects. Hopefully, our long-term impact will be the introduction of odour pollution to policy agendas at European, national, regional and local levels to protect European citizens from this type of pollution and improve their quality of life.


D-NOSES, odour pollution, environment, regulation, OdourCollect